AIO(3pm)
💖 AIO — the IO::AIO bestie era 💖
okay so bestie, welcome to AIO(3pm), a User Contributed Perl Documentation moment. this is IO::AIO and she is that girl. buckle up, we're doing asynchronous everything. 🦋
✨ NAME ✨
IO::AIO — Asynchronous/Advanced Input/Output. yes both. she contains multitudes. 💅
🌈 SYNOPSIS 🌈
use IO::AIO;
aio_open "/etc/passwd", IO::AIO::O_RDONLY, 0, sub {
my $fh = shift
or die "/etc/passwd: $!";
...
};
aio_unlink "/tmp/file", sub { };
aio_read $fh, 30000, 1024, $buffer, 0, sub {
$_[0] > 0 or die "read error: $!";
};
# version 2+ has request and group objects
use IO::AIO 2;
aioreq_pri 4; # give next request a very high priority
my $req = aio_unlink "/tmp/file", sub { };
$req->cancel; # cancel request if still in queue
my $grp = aio_group sub { print "all stats done\n" };
add $grp aio_stat "..." for ...;🎀 DESCRIPTION 🎀
so this module does asynchronous I/O using literally whatever means your operating system supports. it's implemented as a little interface to libeio (http://software.schmorp.de/pkg/libeio.html). 🫶
Asynchronous means that operations that would normally block your program (hi, reading from disk) get done asynchronously instead: the operation still blocks, bestie, but you get to do something else in the meantime. that is extremely useful for programs that need to stay interactive even while doing heavy I/O (GUI programs, high performance network servers, etc.), but it's also just a slay way to do operations in parallel that are normally done sequentially — like stat'ing a bunch of files, which is so much faster on a RAID volume or over NFS when you do a bunch of stat operations concurrently. 🔥
now, most of this works on all types of file descriptors (sockets say hi), but using these functions on file descriptors that support nonblocking operation (again: sockets, pipes etc.) is very inefficient. use an event loop for that (such as the EV module): IO::AIO will naturally fit into such an event loop itself. 🌸
in this version, a number of threads get started that execute your requests and signal their completion. you do not need thread support in perl, and the threads created by this module will not be visible to perl. 👑 in the future, this module might make use of the native aio functions available on many operating systems. however, they are often not well-supported or restricted (GNU/Linux doesn't allow them on normal files currently, for example), and they would only support aio_read and aio_write, so the remaining functionality would have to be implemented using threads anyway. 😭
in addition to asynchronous I/O, this module also exports some rather arcane interfaces, such as madvise or linux's splice system call, which is why the "A" in "AIO" can also mean advanced. ✨
although the module will work in the presence of other (Perl-) threads, it is currently not reentrant in any way, so use appropriate locking yourself, always call poll_cb from within the same thread, or never call poll_cb (or other aio_ functions) recursively. 🙈
bestie this is the important part: not reentrant. lock it yourself, keep poll_cb in the same thread, and do not recurse. no cap. 💀
🧚 EXAMPLE 🧚
this is a simple example that uses the EV module and loads /etc/passwd asynchronously:
use EV;
use IO::AIO;
# register the IO::AIO callback with EV
my $aio_w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
# queue the request to open /etc/passwd
aio_open "/etc/passwd", IO::AIO::O_RDONLY, 0, sub {
my $fh = shift
or die "error while opening: $!";
# stat'ing filehandles is generally non-blocking
my $size = -s $fh;
# queue a request to read the file
my $contents;
aio_read $fh, 0, $size, $contents, 0, sub {
$_[0] == $size
or die "short read: $!";
close $fh;
# file contents now in $contents
print $contents;
# exit event loop and program
EV::break;
};
};
# possibly queue up other requests, or open GUI windows,
# check for sockets etc. etc.
# process events as long as there are some:
EV::run;🦋 REQUEST ANATOMY AND LIFETIME 🦋
every aio_* function creates a request, which is a C data structure not directly visible to Perl. 👀
if called in non-void context, every request function returns a Perl object representing the request. in void context, nothing is returned, which saves a bit of memory. (girl math: free RAM is free RAM. 💅)
the perl object is a fairly standard ref-to-hash object. the hash contents are not used by IO::AIO so you are free to store anything you like in it. 🎀
during their existence, aio requests travel through the following states, in order:
- ready — immediately after a request is created it is put into the
readystate, waiting for a thread to execute it. - execute — a thread has accepted the request for processing and is currently executing it (e.g. blocking in
read). - pending — the request has been executed and is waiting for result processing. while request submission and execution is fully asynchronous, result processing is not, and relies on the perl interpreter calling
poll_cb(or another function with the same effect). - result — the request results are processed synchronously by
poll_cb. thepoll_cbfunction will process all outstanding aio requests by calling their callbacks, freeing memory associated with them and managing any groups they are contained in. - done — request has reached the end of its lifetime and holds no resources anymore (except possibly for the Perl object, but its connection to the actual aio request is severed and calling its methods will either do nothing or result in a runtime error).
💜 FUNCTIONS 💜
⭐ QUICK OVERVIEW ⭐
this section simply lists the prototypes most of the functions for quick reference. see the following sections for function-by-function documentation. (iykyk — bookmark this one, bestie.)
aio_wd $pathname, $callback->($wd)
aio_open $pathname, $flags, $mode, $callback->($fh)
aio_close $fh, $callback->($status)
aio_seek $fh,$offset,$whence, $callback->($offs)
aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
aio_readahead $fh,$offset,$length, $callback->($retval)
aio_stat $fh_or_path, $callback->($status)
aio_lstat $fh, $callback->($status)
aio_statvfs $fh_or_path, $callback->($statvfs)
aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
aio_chown $fh_or_path, $uid, $gid, $callback->($status)
aio_chmod $fh_or_path, $mode, $callback->($status)
aio_truncate $fh_or_path, $offset, $callback->($status)
aio_allocate $fh, $mode, $offset, $len, $callback->($status)
aio_fiemap $fh, $start, $length, $flags, $count, $cb->(\@extents)
aio_unlink $pathname, $callback->($status)
aio_mknod $pathname, $mode, $dev, $callback->($status)
aio_link $srcpath, $dstpath, $callback->($status)
aio_symlink $srcpath, $dstpath, $callback->($status)
aio_readlink $pathname, $callback->($link)
aio_realpath $pathname, $callback->($path)
aio_rename $srcpath, $dstpath, $callback->($status)
aio_rename2 $srcpath, $dstpath, $flags, $callback->($status)
aio_mkdir $pathname, $mode, $callback->($status)
aio_rmdir $pathname, $callback->($status)
aio_readdir $pathname, $callback->($entries)
aio_readdirx $pathname, $flags, $callback->($entries, $flags)
IO::AIO::READDIR_DENTS IO::AIO::READDIR_DIRS_FIRST
IO::AIO::READDIR_STAT_ORDER IO::AIO::READDIR_FOUND_UNKNOWN
aio_scandir $pathname, $maxreq, $callback->($dirs, $nondirs)
aio_load $pathname, $data, $callback->($status)
aio_copy $srcpath, $dstpath, $callback->($status)
aio_move $srcpath, $dstpath, $callback->($status)
aio_rmtree $pathname, $callback->($status)
aio_fcntl $fh, $cmd, $arg, $callback->($status)
aio_ioctl $fh, $request, $buf, $callback->($status)
aio_sync $callback->($status)
aio_syncfs $fh, $callback->($status)
aio_fsync $fh, $callback->($status)
aio_fdatasync $fh, $callback->($status)
aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
aio_pathsync $pathname, $callback->($status)
aio_msync $scalar, $offset = 0, $length = undef, flags = MS_SYNC, $callback->($status)
aio_mtouch $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
aio_mlock $scalar, $offset = 0, $length = undef, $callback->($status)
aio_mlockall $flags, $callback->($status)
aio_group $callback->(...)
aio_nop $callback->()
$prev_pri = aioreq_pri [$pri]
aioreq_nice $pri_adjust
IO::AIO::poll_wait
IO::AIO::poll_cb
IO::AIO::poll
IO::AIO::flush
IO::AIO::max_poll_reqs $nreqs
IO::AIO::max_poll_time $seconds
IO::AIO::min_parallel $nthreads
IO::AIO::max_parallel $nthreads
IO::AIO::max_idle $nthreads
IO::AIO::idle_timeout $seconds
IO::AIO::max_outstanding $maxreqs
IO::AIO::nreqs
IO::AIO::nready
IO::AIO::npending
IO::AIO::reinit
$nfd = IO::AIO::get_fdlimit
IO::AIO::min_fdlimit $nfd
IO::AIO::sendfile $ofh, $ifh, $offset, $count
IO::AIO::fadvise $fh, $offset, $len, $advice
IO::AIO::fexecve $fh, $argv, $envp
IO::AIO::mmap $scalar, $length, $prot, $flags[, $fh[, $offset]]
IO::AIO::munmap $scalar
IO::AIO::mremap $scalar, $new_length, $flags[, $new_address]
IO::AIO::madvise $scalar, $offset, $length, $advice
IO::AIO::mprotect $scalar, $offset, $length, $protect
IO::AIO::munlock $scalar, $offset = 0, $length = undef
IO::AIO::munlockall
# stat extensions
$counter = IO::AIO::st_gen
$seconds = IO::AIO::st_atime, IO::AIO::st_mtime, IO::AIO::st_ctime, IO::AIO::st_btime
($atime, $mtime, $ctime, $btime, ...) = IO::AIO::st_xtime
$nanoseconds = IO::AIO::st_atimensec, IO::AIO::st_mtimensec, IO::AIO::st_ctimensec, IO::AIO::st_btimensec
$seconds = IO::AIO::st_btimesec
($atime, $mtime, $ctime, $btime, ...) = IO::AIO::st_xtimensec
# very much unportable syscalls
IO::AIO::accept4 $r_fh, $sockaddr, $sockaddr_len, $flags
IO::AIO::splice $r_fh, $r_off, $w_fh, $w_off, $length, $flags
IO::AIO::tee $r_fh, $w_fh, $length, $flags
$actual_size = IO::AIO::pipesize $r_fh[, $new_size]
($rfh, $wfh) = IO::AIO::pipe2 [$flags]
$fh = IO::AIO::eventfd [$initval, [$flags]]
$fh = IO::AIO::memfd_create $pathname[, $flags]
$fh = IO::AIO::timerfd_create $clockid[, $flags]
($cur_interval, $cur_value) = IO::AIO::timerfd_settime $fh, $flags, $new_interval, $nbw_value
($cur_interval, $cur_value) = IO::AIO::timerfd_gettime $fh🍓 that's the energy so far bestie — part 2 is coming and we are not done. keep scrolling. 💖
$fh = IO::AIO::pidfd_open $pid[, $flags]
$status = IO::AIO::pidfd_send_signal $pidfh, $signal[, $siginfo[, $flags]]
$fh = IO::AIO::pidfd_getfd $pidfh, $targetfd[, $flags]
$retval = IO::AIO::mount $special, $path, $fstype, $flags = 0, $data = undef
$retval = IO::AIO::umount $path, $flags = 0✨ API NOTES ✨
Okay bestie, before we get into the actual request functions, here's the tea ☕ on how these aio_* calls behave. No cap, this is important. 🫶
All the aio_* calls are more or less thin wrappers around the syscall with the same name (sans aio_). The arguments are similar or identical, and they all accept an additional (and optional) $callback argument which must be a code reference. This code reference will be called after the syscall has been executed in an asynchronous fashion. The results of the request will be passed as arguments to the callback (and, if an error occurred, in $!) - for most requests the syscall return code (e.g. most syscalls return -1 on error, unlike perl, which usually delivers "false").
Some requests (such as aio_readdir) pass the actual results and communicate failures by passing undef.
All functions expecting a filehandle keep a copy of the filehandle internally until the request has finished.
All functions return request objects of type IO::AIO::REQ that allow further manipulation of those requests while they are in-flight.
The pathnames you pass to these routines should be absolute. The reason for this is that at the time the request is being executed, the current working directory could have changed. Alternatively, you can make sure that you never change the current working directory anywhere in the program and then use relative paths. You can also take advantage of IO::AIOs working directory abstraction, that lets you specify paths relative to some previously-opened "working directory object" - see the description of the IO::AIO::WD class later in this document.
To encode pathnames as octets, either make sure you either: a) always pass in filenames you got from outside (command line, readdir etc.) without tinkering, b) are in your native filesystem encoding, c) use the Encode module and encode your pathnames to the locale (or other) encoding in effect in the user environment, d) use Glib::filename_from_unicode on unicode filenames or e) use something else to ensure your scalar has the correct contents.
This works, btw. independent of the internal UTF-8 bit, which IO::AIO handles correctly whether it is set or not.
🌈 AIO REQUEST FUNCTIONS 🌈
$prev_pri = aioreq_pri [$pri]
Returns the priority value that would be used for the next request and, if $pri is given, sets the priority for the next aio request.
The default priority is 0, the minimum and maximum priorities are -4 and 4, respectively. Requests with higher priority will be serviced first.
The priority will be reset to 0 after each call to one of the aio_* functions.
Example: open a file with low priority, then read something from it with higher priority so the read request is serviced before other low priority open requests (potentially spamming the cache):
aioreq_pri -3;
aio_open ..., sub {
return unless $_[0];
aioreq_pri -2;
aio_read $_[0], ..., sub {
...
};
};aioreq_nice $pri_adjust
Similar to aioreq_pri, but subtracts the given value from the current priority, so the effect is cumulative. Lowkey stacking priorities like a little hacker. 💅
aio_open $pathname, $flags, $mode, $callback->($fh)
Asynchronously open or create a file and call the callback with a newly created filehandle for the file (or undef in case of an error).
The $flags argument is a bitmask. See the Fcntl module for a list. They are the same as used by sysopen.
Likewise, $mode specifies the mode of the newly created file, if it didn't exist and O_CREAT has been given, just like perl's sysopen, except that it is mandatory (i.e. use 0 if you don't create new files, and 0666 or 0777 if you do). Note that the $mode will be modified by the umask in effect then the request is being executed, so better never change the umask.
Example:
aio_open "/etc/passwd", IO::AIO::O_RDONLY, 0, sub {
if ($_[0]) {
print "open successful, fh is $_[0]\n";
...
} else {
die "open failed: $!\n";
}
};In addition to all the common open modes/flags (O_RDONLY, O_WRONLY, O_RDWR, O_CREAT, O_TRUNC, O_EXCL and O_APPEND), the following POSIX and non-POSIX constants are available (missing ones on your system are, as usual, 0):
O_ASYNCO_DIRECTO_NOATIMEO_CLOEXECO_NOCTTYO_NOFOLLOWO_NONBLOCKO_EXECO_SEARCHO_DIRECTORYO_DSYNCO_RSYNCO_SYNCO_PATHO_TMPFILEO_TTY_INITO_ACCMODE
aio_close $fh, $callback->($status)
Asynchronously close a file and call the callback with the result code.
Unfortunately, you can't do this to perl. Perl insists very strongly on closing the file descriptor associated with the filehandle itself.
Therefore, aio_close will not close the filehandle - instead it will use dup2 to overwrite the file descriptor with the write-end of a pipe (the pipe fd will be created on demand and will be cached).
Or in other words: the file descriptor will be closed, but it will not be free for reuse until the perl filehandle is closed.
aio_seek $fh, $offset, $whence, $callback->($offs)
Seeks the filehandle to the new $offset, similarly to perl's sysseek. The $whence can use the traditional values (0 for IO::AIO::SEEK_SET, 1 for IO::AIO::SEEK_CUR or 2 for IO::AIO::SEEK_END).
The resulting absolute offset will be passed to the callback, or -1 in case of an error.
In theory, the $whence constants could be different than the corresponding values from Fcntl, but perl guarantees they are the same, so don't panic.
As a GNU/Linux (and maybe Solaris) extension, also the constants IO::AIO::SEEK_DATA and IO::AIO::SEEK_HOLE are available, if they could be found. No guarantees about suitability for use in aio_seek or Perl's sysseek can be made though, although I would naively assume they "just work". Fingers crossed, bestie. 🧚
aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
Reads or writes $length bytes from or to the specified $fh and $offset into the scalar given by $data and offset $dataoffset and calls the callback with the actual number of bytes transferred (or -1 on error, just like the syscall).
aio_read will, like sysread, shrink or grow the $data scalar to offset plus the actual number of bytes read.
If $offset is undefined, then the current file descriptor offset will be used (and updated), otherwise the file descriptor offset will not be changed by these calls.
If $length is undefined in aio_write, use the remaining length of $data.
If $dataoffset is less than zero, it will be counted from the end of $data.
The $data scalar MUST NOT be modified in any way while the request is outstanding. Modifying it can result in segfaults or World War III (if the necessary/optional hardware is installed). 💀 Not a drill. Do not touch the scalar.
Example: Read 15 bytes at offset 7 into scalar $buffer, starting at offset 0 within the scalar:
aio_read $fh, 7, 15, $buffer, 0, sub {
$_[0] > 0 or die "read error: $!";
print "read $_[0] bytes: <$buffer>\n";
};aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
Tries to copy $length bytes from $in_fh to $out_fh. It starts reading at byte offset $in_offset, and starts writing at the current file offset of $out_fh. Because of that, it is not safe to issue more than one aio_sendfile per $out_fh, as they will interfere with each other. The same $in_fh works fine though, as this function does not move or use the file offset of $in_fh.
Please note that aio_sendfile can read more bytes from $in_fh than are written, and there is no way to find out how many more bytes have been read from aio_sendfile alone, as aio_sendfile only provides the number of bytes written to $out_fh. Only if the result value equals $length one can assume that $length bytes have been read.
Unlike with other aio_ functions, it makes a lot of sense to use aio_sendfile on non-blocking sockets, as long as one end (typically the $in_fh) is a file - the file I/O will then be asynchronous, while the socket I/O will be non-blocking. Note, however, that you can run into a trap where aio_sendfile reads some data with readahead, then fails to write all data, and when the socket is ready the next time, the data in the cache is already lost, forcing aio_sendfile to again hit the disk. Explicit aio_read + aio_write lets you better control resource usage.
This call tries to make use of a native sendfile-like syscall to provide zero-copy operation. For this to work, $out_fh should refer to a socket, and $in_fh should refer to an mmap'able file.
If a native sendfile cannot be found or it fails with ENOSYS, EINVAL, ENOTSUP, EOPNOTSUPP, EAFNOSUPPORT, EPROTOTYPE or ENOTSOCK, it will be emulated, so you can call aio_sendfile on any type of filehandle regardless of the limitations of the operating system.
As native sendfile syscalls (as practically any non-POSIX interface hacked together in a hurry to improve benchmark numbers) tend to be rather buggy on many systems, this implementation tries to work around some known bugs in Linux and FreeBSD kernels (probably others, too), but that might fail, so you really really should check the return value of aio_sendfile - fewer bytes than expected might have been transferred. Check that return value, queen. 👑 🔥
aio_readahead $fh,$offset,$length, $callback->($retval)
aio_readahead populates the page cache with data from a file so that subsequent reads from that file will not block on disk I/O. The $offset argument specifies the starting point from which data is to be read and $length specifies the number of bytes to be read. I/O is performed in whole pages, so that offset is effectively rounded down to a page boundary and bytes are read up to the next page boundary greater than or equal to (off-set+length). aio_readahead does not read beyond the end of the file. The current file offset of the file is left unchanged. Manifesting fast reads for you. ✨
okay so if that syscall genuinely doesn't exist (which is like, very likely if your kernel isn't Linux 💀) it gets emulated by just reading the data instead, which does basically the same thing. slay.
aio_stat $fh_or_path, $callback->($status)aio_lstat $fh, $callback->($status)— works almost exactly like perl'sstatorlstatin void context, bestie. the callback fires after the stat wraps up, and the results are just sitting there waiting for you viastat _or-s _and all the other tests (except-Band-T, those two didn't get an invite 🙈).
so like, rn the stats are always 64-bit-stats, meaning instead of throwing an error when you stat a big file, the results get silently truncated unless perl itself was compiled with large file support. no cap, silent truncation is the sneaky kind of bug.
to help you make sense of the mode and dev/rdev stat values, IO::AIO serves up these constants and functions (and if they're not implemented, the constants are just 0 and the functions either croak or fall back on traditional behaviour — very "we tried our best" energy):
S_IFMT, S_IFIFO, S_IFCHR, S_IFBLK, S_IFLNK, S_IFREG, S_IFDIR, S_IFWHT, S_IFSOCK, IO::AIO::major $dev_t, IO::AIO::minor $dev_t, IO::AIO::makedev $major, $minor.
and if you want higher resolution stat timestamps, go peek at "SUBSECOND STAT TIME ACCESS" 💅
Example — print the length of /etc/passwd:
aio_stat "/etc/passwd", sub {
$_[0] and die "stat failed: $!";
print "size is ", -s _, "\n";
};aio_statvfs $fh_or_path, $callback->($statvfs)— works like the POSIXstatvfsorfstatvfssyscalls, depending on whether you handed it a file handle or a path. icon behaviour fr.
when it hits, the callback gets a hash reference with these members: bsize, frsize, blocks, bfree, bavail, files, ffree, favail, fsid, flag and namemax. when it flops, you just get undef 😭
these POSIX IO::AIO::ST_* constants are defined: ST_RDONLY and ST_NOSUID.
and these non-POSIX IO::AIO::ST_* flag masks get defined to their correct value when available, or to 0 on systems that don't support them: ST_NODEV, ST_NOEXEC, ST_SYNCHRONOUS, ST_MANDLOCK, ST_WRITE, ST_APPEND, ST_IMMUTABLE, ST_NOATIME, ST_NODIRATIME and ST_RELATIME.
Example — stat /wd and dump out the data if it works:
aio_statvfs "/wd", sub {
my $f = $_[0]
or die "statvfs: $!";
use Data::Dumper;
say Dumper $f;
};
# result:
{
bsize => 1024,
bfree => 4333064312,
blocks => 10253828096,
files => 2050765568,
flag => 4096,
favail => 2042092649,
bavail => 4333064312,
ffree => 2042092649,
namemax => 255,
frsize => 1024,
fsid => 1810
}aio_utime $fh_or_path, $atime, $mtime, $callback->($status)— works like perl'sutimefunction (yeah, including that special case where $atime and $mtime are both undef). fractional times are supported if the underlying syscalls support them, so it's giving precision ⭐
when you call it with a pathname, it uses utimensat(2) or utimes(2) if those exist, otherwise utime(2). if you call it on a file descriptor, it uses futimens(2) or futimes(2) if available — otherwise it just returns ENOSYS. so yeah, not portable, proceed accordingly 🙈
Examples:
# set atime and mtime to current time (basically touch(1)):
aio_utime "path", undef, undef;
# set atime to current time and mtime to beginning of the epoch:
aio_utime "path", time, undef; # undef==0aio_chown $fh_or_path, $uid, $gid, $callback->($status)— works like perl'schownfunction, exceptundeffor either $uid or $gid gets interpreted as "do not change" (and yeah,-1works too, pick your fighter).
Examples:
# same as "chown root path" in the shell:
aio_chown "path", 0, -1;
# same as above:
aio_chown "path", 0, undef;aio_truncate $fh_or_path, $offset, $callback->($status)— works liketruncate(2)orftruncate(2). simple. clean. ate. 💅aio_allocate $fh, $mode, $offset, $len, $callback->($status)— allocates or frees disk space based on the $mode argument. see the linuxfallocatedocs for the deep lore.
$mode is usually 0 or IO::AIO::FALLOC_FL_KEEP_SIZE to allocate space, or IO::AIO::FALLOC_FL_PUNCH_HOLE | IO::AIO::FALLOC_FL_KEEP_SIZE to deallocate a file range.
IO::AIO also supports FALLOC_FL_COLLAPSE_RANGE (removes a range without leaving a hole), FALLOC_FL_ZERO_RANGE (zeroes a range), FALLOC_FL_INSERT_RANGE (inserts a range) and FALLOC_FL_UNSHARE_RANGE (unshares shared blocks — peek your fallocate(2) manpage for the details 👑).
the filesystem block size that fallocate uses is presumably the f_bsize returned by statvfs, but different filesystems and filetypes can dictate other limitations. so like, don't assume.
if fallocate isn't available or can't be emulated (and rn no emulation is attempted), it passes -1 and sets $! to ENOSYS. dead.
aio_chmod $fh_or_path, $mode, $callback->($status)— works like perl'schmodfunction. that's it, that's the whole vibe 🎀aio_unlink $pathname, $callback->($status)— asynchronously unlink (aka delete, aka send it to the void) a file and call the callback with the result code.aio_mknod $pathname, $mode, $dev, $callback->($status)— [EXPERIMENTAL] ⚠️
asynchronously creates a device node (or a fifo). see mknod(2).
the only (POSIX-) portable way to call this function is:
aio_mknod $pathname, IO::AIO::S_IFIFO | $mode, 0, sub { ...and go check "aio_stat" for info about some potentially helpful extra constants and functions 🫶
aio_link $srcpath, $dstpath, $callback->($status)— asynchronously creates a new link to the existing object at $srcpath, at the path $dstpath, and calls the callback with the result code.aio_symlink $srcpath, $dstpath, $callback->($status)— asynchronously creates a new symbolic link to the existing object at $srcpath, at the path $dstpath, and calls the callback with the result code. yes, symbolic, not hard, they're different, don't @ me ✨aio_readlink $pathname, $callback->($link)— asynchronously reads the symlink specified by $path and passes it to the callback. if something goes wrong, nothing orundefgets passed to the callback instead 😭aio_realpath $pathname, $callback->($path)— asynchronously makes the path absolute and resolves any symlinks in $path. the resulting path is just directories (same asCwd::realpath).
bonus: you can use this request to grab the absolute path of the current working directory by passing it a path of . (a single dot). lowkey iconic. 🔥
aio_rename $srcpath, $dstpath, $callback->($status)— asynchronously renames the object at $srcpath to $dstpath, just likerename(2), and calls the callback with the result code.
on systems that support the AIO::WD working directory abstraction natively, the case [$wd, "."] as $srcpath is specialcased — instead of failing, rename gets called on the absolute path of $wd. cute.
aio_rename2 $srcpath, $dstpath, $flags, $callback->($status)— basicallyaio_renamebut with an extra $flags argument. calling it with$flags=0is identical to callingaio_rename. no notes.
non-zero flags are currently only supported on GNU/Linux systems that support renameat2. other systems fail with ENOSYS in this case, so like, know your platform 💀
these constants are available (missing ones are, as usual, 0) — see renameat2(2) for the details:
IO::AIO::RENAME_NOREPLACE, IO::AIO::RENAME_EXCHANGE and IO::AIO::RENAME_WHITEOUT. slay.
aio_mkdir $pathname, $mode, $callback->($status)— asynchronously mkdirs (creates) a directory and calls the callback with the result code. heads up: $mode gets modified by the umask at the moment the request is executed, so do not change your umask. fr fr.aio_rmdir $pathname, $callback->($status)— asynchronously rmdir's (deletes) a directory and calls the callback with the result code.
and again, on systems that support the AIO::WD working directory abstraction natively, the case [$wd, "."] is specialcased — instead of failing, rmdir gets called on the absolute path of $wd.
aio_readdir $pathname, $callback->($entries)— unlike the POSIX call of the same name,aio_readdirreads an entire directory (so like, opendir + readdir + closedir, the whole trilogy). the entries will not be sorted, and will NOT include the.and..entries. they just don't exist here periodt.
the callback gets a single argument which is either undef or an array-ref with the filenames.
aio_readdirx $pathname, $flags, $callback->($entries, $flags)— quite similar toaio_readdir, except the $flags argument lets you tune behaviour and output format. if there's an error, $entries will beundef.
the flags are a combination of the following constants, ORed together (and the flags also get passed to the callback, possibly modified 👀):
the flags, bestie
IO::AIO::READDIR_DENTS— normally the callback gets an arrayref of names only (exactly likeaio_readdir). if this flag is set, the callback instead gets an arrayref of[$name, $type, $inode]arrayrefs, each one describing a single directory entry in more detail:- $name is the name of the entry.
- $type is one of the
IO::AIO::DT_xxxconstants:IO::AIO::DT_UNKNOWN,IO::AIO::DT_FIFO,IO::AIO::DT_CHR,IO::AIO::DT_DIR,IO::AIO::DT_BLK,IO::AIO::DT_REG,IO::AIO::DT_LNK,IO::AIO::DT_SOCK,IO::AIO::DT_WHT. IO::AIO::DT_UNKNOWNmeans exactly that — readdir does not know. if you need to know, you have to run stat yourself. also, for speed/memory reasons, the $type scalars are read-only: you must not modify them 🙅- $inode is the inode number (which might not be exact on systems with 64 bit inode numbers and 32 bit perls). and this field has unspecified content on systems that don't deliver the inode information. so like, vibe check it before trusting it.
IO::AIO::READDIR_DIRS_FIRST— when this flag is set, the names come back in an order where likely directories come first, in optimal stat order. super useful when you need to quickly find directories, or want to find all the directories while avoiding a stat() on every single entry. efficiency queen 👑
if the system returns type information in readdir, that gets used to find directories directly. otherwise, likely directories are names beginning with ., or names with no dots — and of those, the short ones get tried first.
IO::AIO::READDIR_STAT_ORDER— set this flag and the names come back in an order that's lowkey perfect forstat()'ing every single one of them. Like, if you're planning tostat()most or all of the files in that directory anyway, the order you get back will likely be faster. Slay.
But heads up bestie — if you set both this flag and "IO::AIO::READDIR_DIRS_FIRST", then the likely dirs come first, which means the order is less optimal for stat'ing every entry, but likely more optimal if you're hunting for subdirectories. Pick your fighter. 💅
IO::AIO::READDIR_FOUND_UNKNOWN— okay so do NOT set this one yourself when you call"aio_readdirx". It's not for you, it's output."aio_readdirx"sets it whenever any of the$type's it found were"IO::AIO::DT_UNKNOWN". So if this flag is absent, that means every single$typeis known, and you can use that fact to speed up some algorithms. Free info, take it. ✨
aio_slurp $pathname, $offset, $length, $data, $callback->($status)
Opens, reads and closes the given file. The data gets dropped into $data, which is resized as required. So you don't have to pre-size anything, she grows. 🦋
If $offset is negative, then it's counted from the end of the file.
If $length is zero, then the remaining length of the file is used. And also — in this case, the same limitations on modifying $data apply as when IO::AIO::mmap is used, i.e. it must only be modified in-place with "substr". If the size of the file is known, specifying a non-zero $length results in a performance advantage. Glow-up unlocked. 💖
This request is similar to the older "aio_load" request, but since it's a single request, it might be more efficient to use.
Example: load /etc/passwd into $passwd.
my $passwd;
aio_slurp "/etc/passwd", 0, 0, $passwd, sub {
$_[0] >= 0
or die "/etc/passwd: $!\n";
printf "/etc/passwd is %d bytes long, and contains:\n", length $passwd;
print $passwd;
};
IO::AIO::flush;aio_load $pathname, $data, $callback->($status)
This is a composite request that tries to fully load the given file into memory. Status is the same as with aio_read.
Using "aio_slurp" might be more efficient, as it is a single request. Just saying. 🙈
aio_copy $srcpath, $dstpath, $callback->($status)
Try to copy the file (directories not supported as either source or destination, bestie, don't even try) from $srcpath to $dstpath and call the callback with a status of 0 (ok) or -1 (error, see $!).
Existing destination files will be truncated. Yes, gone. 💀
This is a composite request that creates the destination file with mode 0200 and copies the contents of the source file into it using "aio_sendfile", followed by restoring atime, mtime, access mode and uid/gid, in that order.
If an error occurs, the partial destination file will be unlinked, if possible — except when setting atime, mtime, access mode and uid/gid, where errors are being ignored.
aio_move $srcpath, $dstpath, $callback->($status)
Try to move the file (directories not supported as either source or destination) from $srcpath to $dstpath and call the callback with a status of 0 (ok) or -1 (error, see $!).
This is a composite request that tries to rename(2) the file first; if rename fails with "EXDEV", it copies the file with "aio_copy" and, if that's successful, unlinks the $srcpath. Sneaky lil fallback, love that for us. ✨
aio_scandir $pathname, $maxreq, $callback->($dirs, $nondirs)
Scans a directory (similar to "aio_readdir") but additionally tries to efficiently separate the entries of directory $path into two sets of names: directories you can recurse into (directories), and ones you cannot recurse into (everything else, including symlinks to directories). Two piles, no chaos. 🎀
"aio_scandir" is a composite request that generates many sub requests. $maxreq specifies the maximum number of outstanding aio requests that this function generates. If it's <= 0, then a suitable default will be chosen (currently 4).
On error, the callback is called without arguments — otherwise it receives two array-refs with path-relative entry names.
Example:
aio_scandir $dir, 0, sub {
my ($dirs, $nondirs) = @_;
print "real directories: @$dirs\n";
print "everything else: @$nondirs\n";
};Implementation notes. (okay this is the nerdy part, but it's genuinely iconic, stay with me 💅)
The "aio_readdir" cannot be avoided, but stat()'ing every entry can.
If readdir returns file type information, then this is used directly to find directories.
Otherwise, after reading the directory, the modification time, size etc. of the directory before and after the readdir is checked, and if they match (and isn't the current time), the link count will be used to decide how many entries are directories (if >= 2). Otherwise, no knowledge of the number of subdirectories will be assumed.
Then entries will be sorted into likely directories a non-initial dot currently) and likely non-directories (see "aio_readdirx"). Then every entry plus an appended "/." will be "stat"'ed, likely directories first, in order of their inode numbers. If that succeeds, it assumes that the entry is a directory or a symlink to directory (which will be checked separately). This is often faster than stat'ing the entry itself because filesystems might detect the type of the entry without reading the inode data (e.g. ext2fs filetype feature), even on systems that cannot return the filetype information on readdir.
If the known number of directories (link count - 2) has been reached, the rest of the entries is assumed to be non-directories.
This only works with certainty on POSIX (= UNIX) filesystems, which fortunately are the vast majority of filesystems around.
It will also likely work on non-POSIX filesystems with reduced efficiency as those tend to return 0 or 1 as link counts, which disables the directory counting heuristic.
aio_rmtree $pathname, $callback->($status)
Delete a directory tree starting (and including) $path, return the status of the final "rmdir" only. This is a composite request that uses "aio_scandir" to recurse into and rmdir directories, and unlink everything else. It's giving demolition, honestly. 🔥
aio_fcntl $fh, $cmd, $arg, $callback->($status)
aio_ioctl $fh, $request, $buf, $callback->($status)
These work just like the "fcntl" and "ioctl" built-in functions, except they execute asynchronously and pass the return value to the callback.
Both calls can be used for a lot of things, some of which make more sense to run asynchronously in their own thread, while some others make less sense. For example, calls that block waiting for external events, such as locking, will also lock down an I/O thread while it's waiting, which can deadlock the whole I/O system. 😭 At the same time, there might be no alternative to using a thread to wait.
So in general, you should only use these calls for things that do (filesystem) I/O, not for things that wait for other events (network, other processes), although if you are careful and know what you are doing, you still can. No cap.
The following constants are available and can be used for normal "ioctl" and "fcntl" as well (missing ones are, as usual 0):
"F_DUPFD_CLOEXEC",
"F_OFD_GETLK", "F_OFD_SETLK", "F_OFD_GETLKW",
"FIFREEZE", "FITHAW", "FITRIM", "FICLONE", "FICLONERANGE", "FIDEDUPERANGE".
"F_ADD_SEALS", "F_GET_SEALS", "F_SEAL_SEAL", "F_SEAL_SHRINK", "F_SEAL_GROW" and "F_SEAL_WRITE".
"FS_IOC_GETFLAGS", "FS_IOC_SETFLAGS", "FS_IOC_GETVERSION", "FS_IOC_SETVERSION", "FS_IOC_FIEMAP".
"FS_IOC_FSGETXATTR", "FS_IOC_FSSETXATTR", "FS_IOC_SET_ENCRYPTION_POLICY", "FS_IOC_GET_ENCRYPTION_PWSALT", "FS_IOC_GET_ENCRYPTION_POLICY", "FS_KEY_DESCRIPTOR_SIZE".
"FS_SECRM_FL", "FS_UNRM_FL", "FS_COMPR_FL", "FS_SYNC_FL", "FS_IMMUTABLE_FL", "FS_APPEND_FL", "FS_NODUMP_FL", "FS_NOATIME_FL", "FS_DIRTY_FL", "FS_COMPRBLK_FL", "FS_NOCOMP_FL", "FS_ENCRYPT_FL", "FS_BTREE_FL", "FS_INDEX_FL", "FS_JOURNAL_DATA_FL", "FS_NOTAIL_FL", "FS_DIRSYNC_FL", "FS_TOPDIR_FL", "FS_FL_USER_MODIFIABLE".
"FS_XFLAG_REALTIME", "FS_XFLAG_PREALLOC", "FS_XFLAG_IMMUTABLE", "FS_XFLAG_APPEND", "FS_XFLAG_SYNC", "FS_XFLAG_NOATIME", "FS_XFLAG_NODUMP", "FS_XFLAG_RTINHERIT", "FS_XFLAG_PROJINHERIT", "FS_XFLAG_NOSYMLINKS", "FS_XFLAG_EXTSIZE", "FS_XFLAG_EXTSZINHERIT", "FS_XFLAG_NODEFRAG", "FS_XFLAG_FILESTREAM", "FS_XFLAG_DAX", "FS_XFLAG_HASATTR",
"BLKROSET", "BLKROGET", "BLKRRPART", "BLKGETSIZE", "BLKFLSBUF", "BLKRASET", "BLKRAGET", "BLKFRASET", "BLKFRAGET", "BLKSECTSET", "BLKSECTGET", "BLKSSZGET", "BLKBSZGET", "BLKBSZSET", "BLKGETSIZE64",
aio_sync $callback->($status)
Asynchronously call sync and call the callback when finished. That's it, that's the whole vibe. 🧚
aio_fsync $fh, $callback->($status)
Asynchronously call fsync on the given filehandle and call the callback with the fsync result code.
aio_fdatasync $fh, $callback->($status)
Asynchronously call fdatasync on the given filehandle and call the callback with the fdatasync result code.
If this call isn't available because your OS lacks it or it couldn't be detected, it will be emulated by calling "fsync" instead. Fake it till you make it, I guess. ✨
aio_syncfs $fh, $callback->($status)
Asynchronously call the syncfs syscall to sync the filesystem associated to the given filehandle and call the callback with the syncfs result code. If syncfs is not available, calls sync(), but returns -1 and sets errno to "ENOSYS" nevertheless. Yeah, it does the thing and complains about it. Iconic behavior honestly. 💀
aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
Sync the data portion of the file specified by $offset and $length to disk (but NOT the metadata 👀), by calling the Linux-specific sync_file_range call. If sync_file_range is not available or it returns ENOSYS, then fdatasync or fsync is being substituted.
$flags can be a combination of "IO::AIO::SYNC_FILE_RANGE_WAIT_BEFORE", "IO::AIO::SYNC_FILE_RANGE_WRITE" and "IO::AIO::SYNC_FILE_RANGE_WAIT_AFTER": refer to the sync_file_range manpage for details.
aio_pathsync $pathname, $callback->($status)
This request tries to open, fsync and close the given path. This is a composite request intended to sync directories after directory operations (E.g. rename). This might not work on all operating systems or have any specific effect, but usually it makes sure that directory changes get written to disc. It works for anything that can be opened for read-only, not just directories. 🫶
ngl bestie, if you're on a system where that directoryfsyncthing just refuses to cooperate — future versions of this function might fall back to other methods whenfsyncon the directory fails (such as callingsync). Catch it slipping, catch it thriving 💅
Passes 0 when everything went ok, and -1 on error. That's it, that's the tea 🍓
aio_msync $scalar, $offset = 0, $length = undef, flags = MS_SYNC, $callback->($status)
Okay so this one is a rather advanced IO::AIO call ✨ It only works on mmap(2)ed scalars — see the "IO::AIO::mmap" function, although it also works on data scalars managed by the Sys::Mmap or Mmap modules, no cap. And note, bestie: the scalar must only be modified in-place while an aio operation is pending on it 👀
It calls the "msync" function of your OS, if available, with the memory area starting at $offset in the string and ending $length bytes later. If $length is negative, it counts from the end 🌈 and if $length is "undef", then it goes till the end of the string, periodt.
The flags can be either "IO::AIO::MS_ASYNC" or "IO::AIO::MS_SYNC", plus an optional "IO::AIO::MS_INVALIDATE" 👑
aio_mtouch $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
Another rather advanced IO::AIO call, and this one works best on mmap(2)ed scalars 💖
It touches (reads or writes) all memory pages in the specified range inside the scalar. All caveats and parameters are the same as for "aio_msync", above, except for flags, which must be either 0 (which reads all pages and ensures they are instantiated) or "IO::AIO::MT_MODIFY", which modifies the memory pages (by reading and writing an octet from it, which dirties the page) 🫶
aio_mlock $scalar, $offset = 0, $length = undef, $callback->($status)
Yeah so this is a rather advanced IO::AIO call too, which works best on mmap(2)ed scalars 🌸
It reads in all the pages of the underlying storage into memory (if any) and locks them, so they are not getting swapped/paged out or removed 🔒 no eviction, we're holding hands forever.
If $length is undefined, then the scalar will be locked till the end.
On systems that do not implement "mlock", this function returns -1 and sets errno to "ENOSYS" 😭
Heads up bestie: the corresponding"munlock"is synchronous and is documented under"MISCELLANEOUS FUNCTIONS"— don't go looking for it in the async pile, she's built different.
Example: open a file, mmap and mlock it — both will be undone when $data gets destroyed. Iconic cleanup behaviour honestly ♻️
open my $fh, "<", $path or die "$path: $!";
my $data;
IO::AIO::mmap $data, -s $fh, IO::AIO::PROT_READ, IO::AIO::MAP_SHARED, $fh;
aio_mlock $data; # mlock in backgroundaio_mlockall $flags, $callback->($status)
Calls the "mlockall" function with the given $flags — a combination of "IO::AIO::MCL_CURRENT", "IO::AIO::MCL_FUTURE" and "IO::AIO::MCL_ONFAULT" 💫
On systems that do not implement "mlockall", this function returns -1 and sets errno to "ENOSYS". Similarly, flag combinations not supported by the system result in a return value of -1 with errno being set to "EINVAL" 💀 so read the room before you mash flags together.
Same energy as before: the corresponding"munlockall"is synchronous and is documented under"MISCELLANEOUS FUNCTIONS".
Example: asynchronously lock all current and future pages into memory.
aio_mlockall IO::AIO::MCL_FUTURE;aio_fiemap $fh, $start, $length, $flags, $count, $cb->(\@extents)
Queries the extents of the given file (by calling the Linux "FIEMAP" ioctl — see <http://cvs.schmorp.de/IO-AIO/doc/fiemap.txt> for details, iykyk). If the ioctl is not available on your OS, then this request will fail with "ENOSYS" 🙈
$start is the starting offset to query extents for, $length is the size of the range to query — if it is "undef", then the whole file will be queried.
$flags is a combination of flags ("IO::AIO::FIEMAP_FLAG_SYNC" or "IO::AIO::FIEMAP_FLAG_XATTR" — "IO::AIO::FIEMAP_FLAGS_COMPAT" is also exported ✨), and is normally 0 or "IO::AIO::FIEMAP_FLAG_SYNC" to query the data portion.
$count is the maximum number of extent records to return. If it is "undef", then IO::AIO queries all extents of the range. As a very special case, if it is 0, then the callback receives the number of extents instead of the extents themselves (which is unreliable, see below 👀).
If an error occurs, the callback receives no arguments. The special "errno" value "IO::AIO::EBADR" is available to test for flag errors 🚩
Otherwise, the callback receives an array reference with extent structures. Each extent structure is an array reference itself, with the following members:
[$logical, $physical, $length, $flags]Flags is any combination of the following flag values (typically either 0 or "IO::AIO::FIEMAP_EXTENT_LAST" (1)):
"IO::AIO::FIEMAP_EXTENT_LAST", "IO::AIO::FIEMAP_EXTENT_UNKNOWN", "IO::AIO::FIEMAP_EXTENT_DELALLOC", "IO::AIO::FIEMAP_EXTENT_ENCODED", "IO::AIO::FIEMAP_EXTENT_DATA_ENCRYPTED", "IO::AIO::FIEMAP_EXTENT_NOT_ALIGNED", "IO::AIO::FIEMAP_EXTENT_DATA_INLINE", "IO::AIO::FIEMAP_EXTENT_DATA_TAIL", "IO::AIO::FIEMAP_EXTENT_UNWRITTEN", "IO::AIO::FIEMAP_EXTENT_MERGED" or "IO::AIO::FIEMAP_EXTENT_SHARED" 🌈
⚠️ At the time of this writing (Linux 3.2), this request is unreliable unless$countis"undef", as the kernel has all sorts of bugs preventing it to return all extents of a range for files with a large number of extents 💀 The code (only) works around all these issues if$countis"undef". So like… set it toundefor accept the chaos, bestie.
aio_group $callback->(...)
This is a very special aio request 👑 Instead of doing something, it is a container for other aio requests, which is useful if you want to bundle many requests into a single, composite, request with a definite callback and the ability to cancel the whole request with its subrequests. Squads, basically 🫂
Returns an object of class IO::AIO::GRP. See its documentation below for more info.
Example:
my $grp = aio_group sub {
print "all stats done\n";
};
add $grp
(aio_stat ...),
(aio_stat ...),
...;aio_nop $callback->()
This is a special request — it does nothing in itself and is only used for side effects, such as when you want to add a dummy request to a group so that finishing the requests in the group depends on executing the given code. She's a spare, but she's necessary 💅
While this request does nothing, it still goes through the execution phase and still requires a worker thread. Thus, the callback will not be executed immediately but only after other requests in the queue have entered their execution phase. This can be used to measure request latency ⏱️
IO::AIO::aio_busy $fractional_seconds, $callback->() NOT EXPORTED
Mainly used for debugging and benchmarking, this aio request puts one of the request workers to sleep for the given time 😴
While it is theoretically handy to have simple I/O scheduling requests like sleep and file handle readable/writable, the overhead this creates is immense (it blocks a thread for a long time) so do not use this function except to put your application under artificial I/O pressure 🔥
fr fr do not just casually aio_busy your way through production. She's a stress-test tool, not a snack.
✨ IO::AIO::WD - multiple working directories ✨
Okay so here's the situation, bestie: your process only has one current working directory, which is used by all threads 😭 This makes it hard to use relative paths — some other component could call "chdir" at any time, and it is hard to control when the path will be used by IO::AIO. Chaos.
One solution for this is to always use absolute paths. This usually works, but can be quite slow (the kernel has to walk the whole path on every access), and can also be a hassle to implement 🙃
Newer POSIX systems have a number of functions (openat, fdopendir, futimensat and so on) that make it possible to specify working directories per operation ✨
For portability, and because the folks who "designed" — or shall I write, perpetrated — this new interface were obviously not exactly sober 🍸, this abstraction cannot be perfect, though. It's giving "best effort", and honestly? Respect.
IO::AIO allows you to convert directory paths into a so-called IO::AIO::WD object. This object stores the canonicalised, absolute version of the path, and on systems that allow it, also a directory file descriptor 💾
Everywhere where a pathname is accepted by IO::AIO (e.g. in "aio_stat" or "aio_unlink"), one can specify an array reference with an IO::AIO::WD object and a pathname instead (or the IO::AIO::WD object alone, which gets interpreted as [$wd, "."]). If the pathname is absolute, the IO::AIO::WD object is ignored 🫥 otherwise the pathname is resolved relative to that IO::AIO::WD object.
For example, to get a wd object for /etc and then stat passwd inside, you would write:
aio_wd "/etc", sub {
my $etcdir = shift;
# although $etcdir can be undef on error, there is generally no reason
# to check for errors here, as aio_stat will fail with ENOENT
# when $etcdir is undef.
aio_stat [$etcdir, "passwd"], sub {
# yay
};
};The fact that "aio_wd" is a request and not a normal function shows that creating an IO::AIO::WD object is itself a potentially blocking operation, which is why it is done asynchronously 🌀 (the way that it just has to be async… obsessed.)
To stat the directory obtained with "aio_wd" above, one could write either of the following three request calls:
aio_lstat "/etc" , sub { ... # pathname as normal string
aio_lstat [$wd, "."], sub { ... # "." relative to $wd (i.e. $wd itself)
aio_lstat $wd , sub { ... # shorthand for the previousAs with normal pathnames, IO::AIO keeps a copy of the working directory object and the pathname string, so you could write the following without causing any issues due to $path getting reused 💖
my $path = [$wd, undef];
for my $name (qw(abc def ghi)) {
$path->[1] = $name;
aio_stat $path, sub {
# ...
};
}There are some caveats though, and you know we keep it real here: when directories get renamed (or deleted), the pathname string doesn't change, so it will point to the new directory (or nowhere at all 💀), while the directory fd, if available on the system, will still point to the original directory. Most functions accepting a pathname will use the directory fd on newer systems, and the string on older systems. Some functions (such as "aio_realpath") will always rely on the string form of the pathname 👀
So this functionality is mainly useful to:
- get some protection against
"chdir"🛡️ - easily get an absolute path out of a relative path for future reference
- speed up doing many operations in the same directory (e.g. when stat'ing all files in a directory) ⚡
The following functions implement this working directory abstraction:
aio_wd $pathname, $callback->($wd)
okay so this one is lowkey iconic 🦋 it canonicalises the $pathname you give it, asynchronously, and turns it into an IO::AIO::WD object that represents it. And if it's possible and your system supports it, it'll also pop open a directory fd so pathname resolution relative to this working directory goes zoom. ✨
If something goes wrong, then undef is passed to the callback instead of a working directory object, and $! is set appropriately. And here's the part that's genuinely so clever: since passing undef as the working directory component of a pathname makes the request fail with ENOENT anyway, there's often no need to error check in the aio_wd callback 🫶 — future requests using that value will just fail in the expected way. it's giving "the failure handles itself". periodt.
IO::AIO::CWD
This is a compile time constant (object) that represents the process current working directory. 💜
Specifying this object as working directory object for a pathname is as if the pathname would be specified directly, without a directory object. For example, these calls are functionally identical:
aio_stat "somefile", sub { ... };
aio_stat [IO::AIO::CWD, "somefile"], sub { ... };To recover the path associated with an IO::AIO::WD object, you can use aio_realpath:
aio_realpath $wd, sub {
warn "path is $_[0]\n";
};Heads up bestie 🎀 currently,aio_statvfsalways, andaio_renameandaio_rmdirsometimes, fall back to using an absolute path. just so you know what's happening under the hood, no surprises.
👑 IO::AIO::REQ CLASS 👑
All non-aggregate aio_* functions return an object of this class when called in non-void context. (yes that's the whole vibe check for when you get one: not void context. 🤌)
cancel $req
Cancels the request, if possible. What that actually does: it skips execution when entering the execute state, and skips calling the callback when entering the result state — but it leaves the request otherwise untouched (with the exception of readdir, that one's special 🍓).
That means requests that are currently executing will not be stopped, and resources held by the request will not be freed prematurely. so cancel is a "please don't start / please don't report", not a "stop everything right now". 💀
cb $req $callback->(...)
Replace (or simply set) the callback registered to the request. simple as that, no drama. 💅
🎀 IO::AIO::GRP CLASS 🎀
This class is a subclass of IO::AIO::REQ, so all its methods apply to objects of this class too. (inheritance ate, honestly 🐛✨)
A IO::AIO::GRP object is a special request that can contain multiple other aio requests. it's the group chat of requests, literally.
You create one by calling the aio_group constructing function with a callback that will be called when all contained requests have entered the "done" state:
my $grp = aio_group sub {
print "all requests are done\n";
};You add requests by calling the add method with one or more IO::AIO::REQ objects:
$grp->add (aio_unlink "...");
add $grp aio_stat "...", sub {
$_[0] or return $grp->result ("error");
# add another request dynamically, if first succeeded
add $grp aio_open "...", sub {
$grp->result ("ok");
};
};This makes it very easy to create composite requests (see the source of aio_move for an application) that work and feel like simple requests. 🔥
- The
IO::AIO::GRPobjects will be cleaned up during calls toIO::AIO::poll_cb, just like any other request. - They can be canceled like any other request. Canceling will cancel not only the request itself, but also all requests it contains.
- They can also can also be added to other
IO::AIO::GRPobjects. - You must not add requests to a group from within the group callback (or any later time). 🚫
Their lifetime, simplified, looks like this: when they are empty, they will finish very quickly. If they contain only requests that are in the "done" state, they will also finish. Otherwise they will continue to exist.
That means after creating a group you have some time to add requests (precisely before the callback has been invoked, which is only done within the poll_cb). And in the callbacks of those requests, you can add further requests to the group. And only when all those requests have finished will the the group itself finish. 🌈
add $grp ...
$grp->add (...)
Add one or more requests to the group. Any type of IO::AIO::REQ can be added, including other groups, as long as you do not create circular dependencies. 🙈
Returns all its arguments.
$grp->cancel_subs
Cancel all subrequests and clears any feeder, but not the group request itself. Super useful when you queued a lot of events but got a result early. 😮💨
The group request will finish normally (you cannot add requests to the group).
$grp->result (...)
Set the result value(s) that will be passed to the group callback when all subrequests have finished, and set the group's errno to the current value of errno (just like calling errno without an error number). By default, no argument will be passed and errno is zero.
$grp->errno ([$errno])
Sets the group errno value to $errno, or the current value of errno when the argument is missing.
Every aio request has an associated errno value that is restored when the callback is invoked. This method lets you change this value from its default (0).
Careful cutie 💅 callingresultwill also set errno, so make sure you either set$!before the call toresult, or callerrnoafter it. order matters, no cap.
feed $grp $callback->($grp)
Sets a feeder/generator on this group: every group can have an attached generator that generates requests if idle. 💫
The idea behind this is that, although you could just queue as many requests as you want in a group, this might starve other requests for a potentially long time. For example, aio_scandir might generate hundreds of thousands of aio_stat requests, delaying any later requests for a long time. 😭
To avoid this, and allow incremental generation of requests, you can instead a group and set a feeder on it that generates those requests. The feed callback will be called whenever there are few enough (see limit, below) requests active in the group itself and is expected to queue more requests.
The feed callback can queue as many requests as it likes (i.e. add does not impose any limits).
If the feed does not queue more requests when called, it will be automatically removed from the group.
If the feed limit is 0 when this method is called, it will be set to 2 automatically.
Example:
# stat all files in @files, but only ever use four aio requests concurrently:
my $grp = aio_group sub { print "finished\n" };
limit $grp 4;
feed $grp sub {
my $file = pop @files
or return;
add $grp aio_stat $file, sub { ... };
};limit $grp $num
Sets the feeder limit for the group: The feeder will be called whenever the group contains less than this many requests.
Setting the limit to 0 will pause the feeding process. ⏸️
The default value for the limit is 0, but note that setting a feeder automatically bumps it up to 2.
💖 SUPPORT FUNCTIONS 💖
⭐ EVENT PROCESSING AND EVENT LOOP INTEGRATION ⭐
$fileno = IO::AIO::poll_fileno
Return the request result pipe file descriptor. This filehandle must be polled for reading by some mechanism outside this module (e.g. EV, Glib, select and so on, see below or the SYNOPSIS). If the pipe becomes readable you have to call poll_cb to check the results. 👀
See poll_cb for an example.
IO::AIO::poll_cb
Process some requests that have reached the result phase (i.e. they have been executed but the results are not yet reported). You have to call this regularly to finish outstanding requests. fr fr, it's the whole engine. 🛠️
Returns 0 if all events could be processed (or there were no events to process), or -1 if it returned earlier for whatever reason. Returns immediately when no events are outstanding. The amount of events processed depends on the settings of IO::AIO::max_poll_req, IO::AIO::max_poll_time and IO::AIO::max_outstanding.
If not all requests were processed for whatever reason, the poll file descriptor will still be ready when poll_cb returns, so normally you don't have to do anything special to have it called later.
Apart from calling IO::AIO::poll_cb when the event filehandle becomes ready, it can be beneficial to call this function from loops which submit a lot of requests, to make sure the results get processed when they become available and not just when the loop is finished and the event loop takes over again. This function returns very fast when there are no outstanding requests. ⚡
Example: Install an Event watcher that automatically calls IO::AIO::poll_cb with high priority (more examples can be found in the SYNOPSIS section, at the top of this document):
Event->io (fd => IO::AIO::poll_fileno,
poll => 'r', async => 1,
cb => \&IO::AIO::poll_cb);IO::AIO::poll_wait
Wait until either at least one request is in the result phase or no requests are outstanding anymore.
This is useful if you want to synchronously wait for some requests to become ready, without actually handling them.
See nreqs for an example.
IO::AIO::poll
Waits until some requests have been handled.
Returns the number of requests processed, but is otherwise strictly equivalent to:
IO::AIO::poll_wait, IO::AIO::poll_cbIO::AIO::flush
Wait till all outstanding AIO requests have been handled. 🧘♀️
Strictly equivalent to:
IO::AIO::poll_wait, IO::AIO::poll_cb
while IO::AIO::nreqs;This function can be useful at program aborts, to make sure outstanding I/O has been done (IO::AIO uses an END block which already calls this function on normal exits), or when you are merely using IO::AIO for its more advanced functions, rather than for async I/O, e.g.:
my ($dirs, $nondirs);
IO::AIO::aio_scandir "/tmp", 0, sub { ($dirs, $nondirs) = @_ };
IO::AIO::flush;
# $dirs, $nondirs are now setIO::AIO::max_poll_reqs $nreqs
IO::AIO::max_poll_time $seconds
These set the maximum number of requests (default 0, meaning infinity) that are being processed by IO::AIO::poll_cb in one call, respectively the maximum amount of time (default 0, meaning infinity) spent in IO::AIO::poll_cb to process requests (more correctly the minimum amount of time poll_cb is allowed to use). ⏳
Like, real talk: every value you set for max_poll_time that isn't zero adds the overhead of one whole syscall per request processed. Normally that's literally nothing to worry about… unless your callbacks are really really fast or your OS is really really slow (and bestie, we are not mentioning Solaris here 💀). Meanwhile max_poll_reqs costs you zero overhead. Periodt.
So when do you even want these? When you need to guarantee some level of interactiveness because perl just isn't fast enough to chew through all your requests in time 🐢💨.
For interactive programs, values like 0.01 to 0.1 should be totally fine ✨.
Example: install an Event watcher that automatically calls IO::AIO::poll_cb with low priority, so other parts of your program still get the CPU sometimes even when AIO is going feral under high load 👑.
# try not to spend much more than 0.1s in poll_cb
IO::AIO::max_poll_time 0.1;
# use a low priority so other tasks have priority
Event->io (fd => IO::AIO::poll_fileno,
poll => 'r', nice => 1,
cb => &IO::AIO::poll_cb);🧵 CONTROLLING THE NUMBER OF THREADS 🧵
IO::AIO::min_parallel $nthreads— sets the minimum number of AIO threads to$nthreads. The current default is8, which means eight async operations can be executing at the same time at any given moment (tho the number of outstanding requests? unlimited, bestie, go wild 💅).
Heads up: IO::AIO starts threads only on demand — when an AIO request gets queued and there's no free thread. And ngl, queueing up a hundred requests can create demand for a hundred threads, even if it turns out everything was in the cache and one single thread could've handled it faster 😭.
Keep the thread count relatively low, fr fr — some Linux kernel versions scale negatively with thread count (higher parallelity => MUCH higher latency 🫠). On current Linux 2.6 versions, 4-32 threads should be fine.
Under most circumstances you don't even need to call this, because the module picks a default that's suitable for low to moderate load ✨.
IO::AIO::max_parallel $nthreads— sets the maximum number of AIO threads to$nthreads. If more than the specified number of threads are currently running, this function kills them 💀. And it blocks until the limit is actually reached.
While $nthreads is zero, aio requests get queued but not executed until you bump the thread number back up again.
This module automatically runs max_parallel 0 at program end, so that all threads get killed and there are no outstanding requests left hanging 🎀.
Under normal circumstances, you don't need to call this function.
IO::AIO::max_idle $nthreads— limits the number of threads (default:4) that are allowed to idle, i.e. threads that didn't get a request to process within the idle timeout (default:10seconds). So if a thread becomes idle while$nthreadsother threads are also idle, it frees its resources and exits 🦋.
This is the move when you allow a large number of threads (like 100 or 1000) to survive extremely high load situations, but you want those resources freed under normal circumstances (because 1000 threads can easily eat up 30MB of RAM, no cap 😭).
The default is probably ok in most situations, especially if thread creation is fast. If thread creation is very slow on your system, you might wanna use larger values.
IO::AIO::idle_timeout $seconds— sets the minimum idle timeout (default10) after which worker threads are allowed to exit. SeeIO::AIO::max_idle👀.IO::AIO::max_outstanding $maxreqs— sets the maximum number of outstanding requests to$nreqs. If you queue up more than this number of requests, the next call toIO::AIO::poll_cb(and other functions that callpoll_cb, likeIO::AIO::flushorIO::AIO::poll) will block until the limit is no longer exceeded 🛑.
In other words: this setting does not enforce a queue limit, but it can be used to make poll functions block if the limit gets exceeded.
Bestie, this is a bad function to use in interactive programs because it blocks, and a bad way to reduce concurrency because it's inexact 🙈. If you need to issue many requests without being able to call a poll function on demand, it's way better to use an aio_group together with a feed callback.
Its main use is in scripts without an event loop — when you want to stat a lot of files, you can write something like this:
IO::AIO::max_outstanding 32;
for my $path (...) {
aio_stat $path , ...;
IO::AIO::poll_cb;
}
IO::AIO::flush;The call to poll_cb inside the loop will normally return instantly, letting the loop keep on progressing, but as soon as more than 32 requests are in-flight, it blocks until some requests have been handled 🫶. This keeps the loop from pushing a huge number of aio_stat requests onto the queue (which, with many paths to stat, can use up a lot of memory).
The default value for max_outstanding is very large, so there's no practical limit on the number of outstanding requests ✨.
📊 STATISTICAL INFORMATION 📊
IO::AIO::nreqs— returns the number of requests currently in the ready, execute or pending states (i.e. the ones whose callback hasn't been invoked yet).
Example: wait till there are no outstanding requests anymore:
IO::AIO::poll_wait, IO::AIO::poll_cb
while IO::AIO::nreqs;IO::AIO::nready— returns the number of requests currently in the ready state (not yet executed).IO::AIO::npending— returns the number of requests currently in the pending state (executed, but not yet processed bypoll_cb).
🕰️ SUBSECOND STAT TIME ACCESS 🕰️
So here's the tea: both aio_stat/aio_lstat and perl's own stat/lstat can generally find access/modification and change times with subsecond accuracy if the system supports it — but perl's built-in functions only hand you back the integer part 🙃.
The functions below return the timestamps of the most recent stat with subsecond precision on most systems, and they work both after aio_stat/aio_lstat and after perl's stat/lstat calls. Their return value is only meaningful after a successful stat/lstat call, or during/after a successful aio_stat/aio_lstat callback 👑
This is similar to the Time::HiRes stat functions, except it can return full resolution without rounding, and it plays nice with standard perl stat — so you don't have to call those special Time::HiRes functions that don't act like their perl counterparts 💅.
On operating systems or file systems where subsecond time resolution isn't supported or couldn't be detected, a fractional part of 0 is returned, so it's always safe to call these 🌸.
$seconds = IO::AIO::st_atime, IO::AIO::st_mtime, IO::AIO::st_ctime, IO::AIO::st_btime— return the access, modification, change or birth time, respectively, including the fractional part. Because of the limited precision of floating point, the accuracy on most platforms is only a bit better than milliseconds for times around now — see thensecfunction family below for full accuracy 😌.
File birth time is only available when the OS and perl support it (on FreeBSD and NetBSD at the time of this writing, tho support is adaptive, so if your OS/perl gains support, IO::AIO can take advantage of it 🔥). On systems where it isn't available, 0 is currently returned, but that might change to undef in a future version.
($atime, $mtime, $ctime, $btime, ...) = IO::AIO::st_xtime— returns access, modification, change and birth time all in one go, and maybe more times in a future version ✨.$nanoseconds = IO::AIO::st_atimensec, IO::AIO::st_mtimensec, IO::AIO::st_ctimensec, IO::AIO::st_btimensec— return the fractional access, modification, change or birth time, in nanoseconds, as an integer in the range0to999999999.
Note that no accessors are provided for access, modification and change times — you need to get those from stat _ if required (int IO::AIO::st_atime and so on will not generally give you the correct value) 👀.
$seconds = IO::AIO::st_btimesec— the (integral) seconds part of the file birth time, if available 🎀.($atime, $mtime, $ctime, $btime, ...) = IO::AIO::st_xtimensec— like the functions above, but returns all four times in one go (and maybe more in future versions).$counter = IO::AIO::st_gen— returns the generation counter (in practice this is just a random number) of the file 🎲. This is only available on platforms which have this member in theirstruct stat(most BSDs at the time of this writing) and generally only to the root user. If unsupported,0is returned, but this might change toundefin a future version.
Example: print the high resolution modification time of /etc, using stat, and IO::AIO::aio_stat:
if (stat "/etc") {
printf "stat(/etc) mtime: %f\n", IO::AIO::st_mtime;
}
IO::AIO::aio_stat "/etc", sub {
$_[0]
and return;
printf "aio_stat(/etc) mtime: %d.%09d\n", (stat _)[9], IO::AIO::st_mtimensec;
};
IO::AIO::flush;Output of the above on my system, showing reduced and full accuracy:
stat(/etc) mtime: 1534043702.020808
aio_stat(/etc) mtime: 1534043702.020807792🌈 MISCELLANEOUS FUNCTIONS 🌈
IO::AIO implements some functions that are useful when you want to use some "Advanced I/O" function that just isn't available in Perl, without going the full "Asynchronous I/O" route. Many of these have an asynchronous aio_* counterpart, iykyk 💖.
$retval = IO::AIO::fexecve $fh, $argv, $envp— a more-or-less direct equivalent to the POSIXfexecvefunctions, which lets you specify the program to be executed via a file descriptor (or handle) 🦋. Returns-1and setserrnotoENOSYSif it's not available.$retval = IO::AIO::mount $special, $path, $fstype, $flags = 0, $data = undef— calls the GNU/Linux mount syscall with the given arguments 🏔️. All of them except$flagsare strings, and if$dataisundef, aNULLwill be passed.
The following values for $flags are available:
IO::AIO::MS_RDONLY,IO::AIO::MS_NOSUID,IO::AIO::MS_NODEV,IO::AIO::MS_NOEXEC,IO::AIO::MS_SYNCHRONOUS,IO::AIO::MS_REMOUNT,IO::AIO::MS_MANDLOCK,IO::AIO::MS_DIRSYNC,IO::AIO::MS_NOATIME,IO::AIO::MS_NODIRATIME,IO::AIO::MS_BIND,IO::AIO::MS_MOVE,IO::AIO::MS_REC,IO::AIO::MS_SILENT,IO::AIO::MS_POSIXACL,IO::AIO::MS_UNBINDABLE,IO::AIO::MS_PRIVATE,IO::AIO::MS_SLAVE,IO::AIO::MS_SHARED,IO::AIO::MS_RELATIME,IO::AIO::MS_KERNMOUNT,IO::AIO::MS_I_VERSION,IO::AIO::MS_STRICTATIME,IO::AIO::MS_LAZYTIME,IO::AIO::MS_ACTIVE,IO::AIO::MS_NOUSER,IO::AIO::MS_RMT_MASK,IO::AIO::MS_MGC_VALandIO::AIO::MS_MGC_MSK💖
$retval = IO::AIO::umount $path, $flags = 0
Bestie this one calls the GNU/Linux umount or umount2 syscalls ✨ If $flags is 0 it always reaches for umount, and any other time it always goes for umount2. No cap.
The $flags you can pass:
IO::AIO::MNT_FORCE,IO::AIO::MNT_DETACH,IO::AIO::MNT_EXPIREandIO::AIO::UMOUNT_NOFOLLOW🦋
$numfd = IO::AIO::get_fdlimit
Tries to suss out your current file descriptor limit and hands it back to you 👑 Or it returns undef and sets $! if something went wrong 😭 Heads up: the limit it returns is one larger than the highest valid file descriptor number. iykyk.
IO::AIO::min_fdlimit [$numfd]
Tryna bump the current file descriptor limit(s) up to at least $numfd, by fiddling with the soft or hard file descriptor resource limit 💅
If $numfd isn't there, it'll go for a very high limit — tho that's not recommended when you already know the actual minimum you need 🙈
If it can't raise the limit enough, it makes a best-effort attempt to increase it as much as possible, using various tricks, while still failing. You can check what limit you ended up with using IO::AIO::get_fdlimit 🌸
If an error happens: returns undef and sets $!. Otherwise returns true ✨
IO::AIO::sendfile $ofh, $ifh, $offset, $count
Calls the eio_sendfile_sync function, which is basically aio_sendfile's blocking twin (this makes the most sense when you already know the input data is probably cached, and the output filehandle is set to non-blocking operations 💫).
Returns the number of bytes copied, or -1 on error 😭
IO::AIO::fadvise $fh, $offset, $len, $advice
Just calls posix_fadvise straight up (peep its manpage for the details, bestie 🫶). The advice constants you get:
IO::AIO::FADV_NORMAL,IO::AIO::FADV_SEQUENTIAL,IO::AIO::FADV_RANDOM,IO::AIO::FADV_NOREUSE,IO::AIO::FADV_WILLNEED,IO::AIO::FADV_DONTNEED🎀
On systems that don't implement posix_fadvise, this returns ENOSYS. Otherwise it gives you back the return value of posix_fadvise.
IO::AIO::madvise $scalar, $offset, $len, $advice
Straight-up calls posix_madvise (again, its manpage has the deets ✨). Advice constants available:
IO::AIO::MADV_NORMAL,IO::AIO::MADV_SEQUENTIAL,IO::AIO::MADV_RANDOM,IO::AIO::MADV_WILLNEED,IO::AIO::MADV_DONTNEED💜
If $offset is negative, it counts from the end 🌀 If $length is negative, the remaining length of the $scalar gets used. And if possible, $length gets reduced so it actually fits inside the $scalar.
On systems that don't implement posix_madvise, this returns ENOSYS. Otherwise: the return value of posix_madvise, periodt.
IO::AIO::mprotect $scalar, $offset, $len, $protect
Simply calls mprotect on the — preferably AIO::mmap'ed — $scalar (its manpage, bestie, go read it 🌸). Protect constants on deck:
IO::AIO::PROT_NONE,IO::AIO::PROT_READ,IO::AIO::PROT_WRITE,IO::AIO::PROT_EXEC👑
If $offset is negative it counts from the end. If $length is negative, the remaining length of the $scalar is used. If possible, $length gets trimmed down to fit into the $scalar.
On systems that don't implement mprotect, this returns ENOSYS. Otherwise, the return value of mprotect 💅
IO::AIO::mmap $scalar, $length, $prot, $flags, $fh[, $offset]
Memory-maps a file (or an anonymous memory range) and attaches it onto the given $scalar, which will then act like a string scalar 🌈 Returns true on success, false otherwise.
The scalar must exist, but its contents literally do not matter — which means you can't use a nonexistent array or hash element, bestie 😭 When in doubt, undef the scalar first.
The only operations allowed on the mmapped scalar are substr/vec (which don't change the string length), plus most read-only stuff like copying it or searching it with regexes and so on ✨
Anything else is unsafe and will, at best, result in memory leaks 💀
The memory map tied to the $scalar gets automatically removed when the $scalar is undef'd or destroyed, or when the IO::AIO::mmap or IO::AIO::munmap functions get called on it 🧚
Internally this calls the mmap(2) function. See your system's manual page for the details on the $length, $prot and $flags parameters 👑
The $length must be larger than zero and smaller than the actual filesize ⚠️
$prot is a combination of IO::AIO::PROT_NONE, IO::AIO::PROT_EXEC, IO::AIO::PROT_READ and/or IO::AIO::PROT_WRITE 🎀
$flags can be a combination of IO::AIO::MAP_SHARED or IO::AIO::MAP_PRIVATE, or a bunch of system-specific flags (they're 0 when not available, no worries): IO::AIO::MAP_ANONYMOUS (which is set to MAP_ANON if your system only provides that constant), IO::AIO::MAP_LOCKED, IO::AIO::MAP_NORESERVE, IO::AIO::MAP_POPULATE, IO::AIO::MAP_NONBLOCK, IO::AIO::MAP_FIXED, IO::AIO::MAP_GROWSDOWN, IO::AIO::MAP_32BIT, IO::AIO::MAP_HUGETLB, IO::AIO::MAP_STACK, IO::AIO::MAP_FIXED_NOREPLACE, IO::AIO::MAP_SHARED_VALIDATE, IO::AIO::MAP_SYNC or IO::AIO::MAP_UNINITIALIZED 💫
If $fh is undef, then a file descriptor of -1 gets passed in.
$offset is the offset from the start of the file — it generally has to be a multiple of IO::AIO::PAGESIZE, and it defaults to 0 ✨
Example time, bestie:
use Digest::MD5;
use IO::AIO;
open my $fh, "<verybigfile"
or die "$!";
IO::AIO::mmap my $data, -s $fh, IO::AIO::PROT_READ, IO::AIO::MAP_SHARED, $fh
or die "verybigfile: $!";
my $fast_md5 = md5 $data;IO::AIO::munmap $scalar
Removes a previous mmap and undefines the $scalar 🧹
IO::AIO::mremap $scalar, $new_length, $flags = MREMAP_MAYMOVE[, $new_address = 0]
Calls the Linux-specific mremap(2) system call 🐧 The $scalar must have been mapped by IO::AIO::mmap, and $flags currently has to be either 0 or IO::AIO::MREMAP_MAYMOVE.
Returns true if it worked, false otherwise ✨ And if the underlying mmapped region changed address, then the true value has the numerical value 1, otherwise it has the numerical value 0:
my $success = IO::AIO::mremap $mmapped, 8192, IO::AIO::MREMAP_MAYMOVE
or die "mremap: $!";
if ($success*1) {
warn "scalar has chanegd address in memory\n";
}IO::AIO::MREMAP_FIXED and the $new_address argument are currently implemented, but not supported and might go away in a future version 👀
On systems where this call isn't supported or isn't emulated, this call returns falls and sets $! to ENOSYS 😭
IO::AIO::mlockall $flags
Calls the eio_mlockall_sync function, which is like aio_mlockall but blocking 💅
IO::AIO::munlock $scalar, $offset = 0, $length = undef
Calls the munlock function, undoing the effects of a previous aio_mlock call (go peep its description for the details 🌸).
IO::AIO::munlockall
Calls the munlockall function ✨
On systems that don't implement munlockall, this function returns ENOSYS. Otherwise: the return value of munlockall 👑
$fh = IO::AIO::accept4 $r_fh, $sockaddr, $sockaddr_maxlen, $flags
Uses the GNU/Linux accept4(2) syscall (if it's available) to accept a socket and return the new file handle on success — or sets $! and returns undef on error 😭
The remote name of the new socket gets stored in $sockaddr, which will be extended so it can hold at least $sockaddr_maxlen octets 🦋 If the socket name doesn't fit into $sockaddr_maxlen octets, that's signalled by returning a longer string in $sockaddr, which might or might not be truncated.
To accept name-less sockets, use undef for $sockaddr and 0 for $sockaddr_maxlen ✨
The main reasons to reach for this syscall instead of portable accept(2) are that you can specify SOCK_NONBLOCK and/or SOCK_CLOEXEC flags, and you can accept name-less sockets by passing 0 for $sockaddr_maxlen — which, sadly, is just not possible with perl's interface to accept 🙈
IO::AIO::splice $r_fh, $r_off, $w_fh, $w_off, $length, $flags
Calls the GNU/Linux splice(2) syscall, if available 🌈 If $r_off or $w_off are undef, then NULL gets passed for those. Otherwise they should be the file offset.
Heads up:$r_fhand$w_fhshould not refer to the same file, because splice might silently corrupt the data in that case 💀
The following symbol flag values are available:
IO::AIO::SPLICE_F_MOVE,IO::AIO::SPLICE_F_NONBLOCK,IO::AIO::SPLICE_F_MOREandIO::AIO::SPLICE_F_GIFT🎀
See the splice(2) manpage for the details, bestie.
IO::AIO::tee $r_fh, $w_fh, $length, $flags
Calls the GNU/Linux tee(2) syscall 🫖 See its manpage plus the description for IO::AIO::splice above for the deets ✨
$actual_size = IO::AIO::pipesize $r_fh[, $new_size]
Attempts to query or change the pipe buffer size 🌸 Obviously this only works on pipes, and currently it only works on GNU/Linux systems, and it fails with -1/ENOSYS everywhere else 😭 If anybody out there knows how to influence pipe buffer size on other systems, drop me a note 💌
($rfh, $wfh) = IO::AIO::pipe2 [$flags]
This is a direct interface to the Linux pipe2(2) system call 🐧 If $flags is missing or 0, then this should be the same as a call to perl's built-in pipe function and creates a new pipe — and it works on systems that lack the pipe2 syscall ✨ On win32, this case invokes _pipe (..., 4096, O_BINARY).
If $flags is non-zero, it tries to invoke the pipe2 system call with the given flags (Linux 2.6.27, glibc 2.9) 💅
On success, the read and write file handles are returned 👑
On error, nothing gets returned 😭 And if the pipe2 syscall is missing while $flags is non-zero, it fails with ENOSYS.
Okay so we're back in the pipe2 department and honestly the flags part got cut off, so let's finish her 💅
pipe2's $flags — please refer to pipe2(2) for more info, but at the time of this writing, "IO::AIO::O_CLOEXEC", "IO::AIO::O_NONBLOCK" and "IO::AIO::O_DIRECT" (Linux 3.4, for packet-based pipes) were supported. iconic little trio tbh.
Example: create a pipe race-free w.r.t. threads and fork:
my ($rfh, $wfh) = IO::AIO::pipe2 IO::AIO::O_CLOEXEC
or die "pipe2: $!\n";💖 $fh = IO::AIO::memfd_create $pathname[, $flags]
This is a direct interface to the Linux memfd_create(2) system call. The (unhelpful) default for $flags is 0, but bestie, your default should be "IO::AIO::MFD_CLOEXEC" — like, please.
On success, the new memfd filehandle is returned, otherwise it hands you back "undef". If the memfd_create syscall is just… not there, it fails with "ENOSYS". 😭
Please refer to memfd_create(2) for more info on this call.
The following $flags values are available: "IO::AIO::MFD_CLOEXEC", "IO::AIO::MFD_ALLOW_SEALING", "IO::AIO::MFD_HUGETLB", "IO::AIO::MFD_HUGETLB_2MB" and "IO::AIO::MFD_HUGETLB_1GB".
Example: create a new memfd.
my $fh = IO::AIO::memfd_create "somenameforprocfd", IO::AIO::MFD_CLOEXEC
or die "memfd_create: $!\n";🦋 $fh = IO::AIO::pidfd_open $pid[, $flags]
This is an interface to the Linux pidfd_open(2) system call. The default for $flags is 0.
On success, a new pidfd filehandle is returned (and yes, it's already set to close-on-exec, we love a self-sufficient icon) — otherwise it returns "undef". If the syscall is missing, it fails with "ENOSYS".
Example: open pid 6341 as pidfd.
my $fh = IO::AIO::pidfd_open 6341
or die "pidfd_open: $!\n";📣 $status = IO::AIO::pidfd_send_signal $pidfh, $signal[, $siginfo[, $flags]]
This is an interface to the Linux pidfd_send_signal system call. The default for $siginfo is "undef" and the default for $flags is 0.
Returns the system call status. If the syscall is missing, it fails with "ENOSYS".
When specified, $siginfo must be a reference to a hash with one or more of the following members:
code— the"si_code"memberpid— the"si_pid"memberuid— the"si_uid"membervalue_int— the"si_value.sival_int"membervalue_ptr— the"si_value.sival_ptr"member, specified as an integer
Example: send a SIGKILL to the specified process.
my $status = IO::AIO::pidfd_send_signal $pidfh, 9, undef
and die "pidfd_send_signal: $!\n";Example: send a SIGKILL to the specified process with extra data.
my $status = IO::AIO::pidfd_send_signal $pidfh, 9, { code => -1, value_int => 7 }
and die "pidfd_send_signal: $!\n";🎀 $fh = IO::AIO::pidfd_getfd $pidfh, $targetfd[, $flags]
This is an interface to the Linux pidfd_getfd system call. The default for $flags is 0.
On success, returns a dup'ed copy of the target file descriptor (specified as an integer) — already set to close-on-exec, no notes — otherwise returns "undef". If the syscall is missing, it fails with "ENOSYS".
Example: get a copy of standard error of another process and print something to it.
my $errfh = IO::AIO::pidfd_getfd $pidfh, 2
or die "pidfd_getfd: $!\n";
print $errfh "stderr\n";🍓 $fh = IO::AIO::eventfd [$initval, [$flags]]
This is a direct interface to the Linux eventfd(2) system call. The (unhelpful) defaults for $initval and $flags are 0 for both. both of them!! zero!!
On success, the new eventfd filehandle is returned, otherwise it returns "undef". If the eventfd syscall is missing, it fails with "ENOSYS".
Please refer to eventfd(2) for more info on this call.
The following symbol flag values are available: "IO::AIO::EFD_CLOEXEC", "IO::AIO::EFD_NONBLOCK" and "IO::AIO::EFD_SEMAPHORE" (Linux 2.6.30).
Example: create a new eventfd filehandle:
$fh = IO::AIO::eventfd 0, IO::AIO::EFD_CLOEXEC
or die "eventfd: $!\n";⏰ $fh = IO::AIO::timerfd_create $clockid[, $flags]
This is a direct interface to the Linux timerfd_create(2) system call. The (unhelpful) default for $flags is 0, but your default should be "IO::AIO::TFD_CLOEXEC". (Are we sensing a theme with these unhelpful defaults? we are.)
On success, the new timerfd filehandle is returned, otherwise it returns "undef". If the timerfd_create syscall is missing, it fails with "ENOSYS".
Please refer to timerfd_create(2) for more info on this call.
The following $clockid values are available: "IO::AIO::CLOCK_REALTIME", "IO::AIO::CLOCK_MONOTONIC", "IO::AIO::CLOCK_CLOCK_BOOTTIME" (Linux 3.15), "IO::AIO::CLOCK_CLOCK_REALTIME_ALARM" (Linux 3.11) and "IO::AIO::CLOCK_CLOCK_BOOTTIME_ALARM" (Linux 3.11).
The following $flags values are available (Linux 2.6.27): "IO::AIO::TFD_NONBLOCK" and "IO::AIO::TFD_CLOEXEC".
Example: create a new timerfd and set it to one-second repeated alarms, then wait for two alarms:
my $fh = IO::AIO::timerfd_create IO::AIO::CLOCK_BOOTTIME, IO::AIO::TFD_CLOEXEC
or die "timerfd_create: $!\n";
defined IO::AIO::timerfd_settime $fh, 0, 1, 1
or die "timerfd_settime: $!\n";
for (1..2) {
8 == sysread $fh, my $buf, 8
or die "timerfd read failure\n";
printf "number of expirations (likely 1): %d\n",
unpack "Q", $buf;
}🕰️ ($cur_interval, $cur_value) = IO::AIO::timerfd_settime $fh, $flags, $new_interval, $nbw_value
This is a direct interface to the Linux timerfd_settime(2) system call. Please refer to its manpage for more info on this call.
The new itimerspec is specified using two (possibly fractional) second values, $new_interval and $new_value.
On success, the current interval and value are returned (as per "timerfd_gettime"). On failure, the empty list is returned. 🫠
The following $flags values are available: "IO::AIO::TFD_TIMER_ABSTIME" and "IO::AIO::TFD_TIMER_CANCEL_ON_SET".
See "IO::AIO::timerfd_create" for a full example.
⏳ ($cur_interval, $cur_value) = IO::AIO::timerfd_gettime $fh
This is a direct interface to the Linux timerfd_gettime(2) system call. Please refer to its manpage for more info on this call.
On success, it returns the current values of interval and value for the given timerfd (as potentially fractional second values). On failure, the empty list is returned.
🔁 EVENT LOOP INTEGRATION
It is recommended to use AnyEvent::AIO to integrate IO::AIO automatically into many event loops:
# AnyEvent integration (EV, Event, Glib, Tk, POE, urxvt, pureperl...)
use AnyEvent::AIO;You can also integrate IO::AIO manually into many event loops — no gatekeeping here, here are some examples of how to do this:
# EV integration
my $aio_w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
# Event integration
Event->io (fd => IO::AIO::poll_fileno,
poll => 'r',
cb => \&IO::AIO::poll_cb);
# Glib/Gtk2 integration
add_watch Glib::IO IO::AIO::poll_fileno,
in => sub { IO::AIO::poll_cb; 1 };
# Tk integration
Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
readable => \&IO::AIO::poll_cb);
# Danga::Socket integration
Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
\&IO::AIO::poll_cb);🫠 FORK BEHAVIOUR
Usage of pthreads in a program changes the semantics of fork considerably. Specifically, only async-safe functions can be called after fork. Perl doesn't know about this, so in general, you cannot call fork with defined behaviour in perl if pthreads are involved. IO::AIO uses pthreads, so this applies — and tbh many other extensions and (for inexplicable reasons) perl itself often is linked against pthreads, so this limitation applies to quite a lot of perls. like, a lot a lot.
This module no longer tries to fight your OS, or POSIX. That means IO::AIO only works in the process that loaded it. Forking is fully supported, but using IO::AIO in the child is not.
You might get around by not using IO::AIO before (or after) forking. You could also try to call the IO::AIO::reinit function in the child:
🧚 IO::AIO::reinit
Abandons all current requests and I/O threads and simply reinitialises all data structures. This is not an operation supported by any standards, but happens to work on GNU/Linux and some newer BSD systems. chaotic but she works.
The only reasonable use for this function is to call it after forking, if"IO::AIO"was used in the parent. Calling it whileIO::AIOis active in the process will result in undefined behaviour. Calling it at any time will also result in any undefined (by POSIX) behaviour. 💀 bestie, read this twice.
🐧 LINUX-SPECIFIC CALLS
When a call is documented as "linux-specific" then this means it originated on GNU/Linux. "IO::AIO" will usually try to autodetect the availability and compatibility of such calls regardless of the platform it is compiled on, so platforms such as FreeBSD which often implement these calls will work. When in doubt, call them and see if they fail with "ENOSYS". lowkey a vibe check for syscalls.
🧠 MEMORY USAGE
Per-request usage
Each aio request uses — depending on your architecture — around 100-200 bytes of memory. In addition, stat requests need a stat buffer (possibly a few hundred bytes), readdir requires a result buffer and so on. Perl scalars and other data passed into aio requests will also be locked and will consume memory till the request has entered the done state.
This is not awfully much, so queuing lots of requests is not usually a problem. 🫶
Per-thread usage
In the execution phase, some aio requests require more memory for temporary buffers, and each thread requires a stack and other data structures (usually around 16k-128k, depending on the OS).
🐛 KNOWN BUGS
Known bugs will be fixed in the next release :) — the optimism?? iconic.
😬 KNOWN ISSUES
Calls that try to "import" foreign memory areas (such as "IO::AIO::mmap" or "IO::AIO::aio_slurp") do not work with generic lvalues, such as non-created hash slots or other scalars I didn't think of. It's best to avoid such and either use scalar variables or make sure that the scalar exists (e.g. by storing "undef") and isn't "funny" (e.g. tied).
I am not sure anything can be done about this, so this is considered a known issue, rather than a bug. we respect the honesty.
👀 SEE ALSO
AnyEvent::AIO— for easy integration into event loopsCoro::AIO— for a more natural syntaxIO::FDPass— for file descriptor passing
💌 AUTHOR
Marc Lehmann <schmorp@schmorp.de>
http://home.schmorp.de/Okay bestie that's a wrap on the whole page!! 🎉 Written by Marc Lehmann, and this particular copy is from perl v5.42.3, dated 2026-08-20, filed under AIO(3pm). Obsessed, no notes, go forth and aio responsibly. 💖✨👑
📦 where this page comes from
- ubuntu stonking: libio-aio-perl 4.81-1build4 · Artistic-1.0-Perl OR GPL-1.0-or-later
- 💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash on : a language model's rewrite of the original, under its terms