MCE::Stream(3)

🌸 NAME

MCE::Stream — a parallel stream model for chaining multiple maps and greps. It's giving pipeline energy, bestie. 💅

✨ VERSION

This document describes MCE::Stream version 1.902.

---

🎀 SYNOPSIS

Okay so first things first, it exports mce_stream, mce_stream_f, and mce_stream_s:

## Exports mce_stream, mce_stream_f, mce_stream_s
use MCE::Stream;

my (@m1, @m2, @m3);

## Default mode is map and processed from right-to-left
@m1 = mce_stream sub { $_ * 3 }, sub { $_ * 2 }, 1..10000;
mce_stream \@m2, sub { $_ * 3 }, sub { $_ * 2 }, 1..10000;

## Native Perl
@m3 = map { $_ * $_ } grep { $_ % 5 == 0 } 1..10000;

## Streaming grep and map in parallel
mce_stream \@m3,
   { mode => 'map',  code => sub { $_ * $_ } },
   { mode => 'grep', code => sub { $_ % 5 == 0 } }, 1..10000;

## Array or array_ref
my @a = mce_stream sub { $_ * $_ }, 1..10000;
my @b = mce_stream sub { $_ * $_ }, \@list;

## Important; pass an array_ref for deeply input data
my @c = mce_stream sub { $_->[1] *= 2; $_ }, [ [ 0, 1 ], [ 0, 2 ], ... ];
my @d = mce_stream sub { $_->[1] *= 2; $_ }, \@deeply_list;

## File path, glob ref, IO::All::{ File, Pipe, STDIO } obj, or scalar ref
## Workers read directly and not involve the manager process
my @e = mce_stream_f sub { chomp; $_ }, "/path/to/file"; # efficient

## Involves the manager process, therefore slower
my @f = mce_stream_f sub { chomp; $_ }, $file_handle;
my @g = mce_stream_f sub { chomp; $_ }, $io;
my @h = mce_stream_f sub { chomp; $_ }, \$scalar;

## Sequence of numbers (begin, end [, step, format])
my @i = mce_stream_s sub { $_ * $_ }, 1, 10000, 5;
my @j = mce_stream_s sub { $_ * $_ }, [ 1, 10000, 5 ];

my @k = mce_stream_s sub { $_ * $_ }, {
   begin => 1, end => 10000, step => 5, format => undef
};

---

💜 DESCRIPTION

So basically this module lets you stream multiple map and/or grep operations in parallel. The code blocks run simultaneously from right-to-left. And the results get appended immediately when you hand it a reference to an array. Periodt. 👑

## Appends are serialized, even out-of-order ok, but immediately.
## Out-of-order chunks are held temporarily until ordered chunks
## arrive.

mce_stream \@a, sub { $_ }, sub { $_ }, sub { $_ }, 1..10000;

##                                                    input
##                                        chunk1      input
##                            chunk3      chunk2      input
##                chunk2      chunk2      chunk3      input
##   append1      chunk3      chunk1      chunk4      input
##   append2      chunk1      chunk5      chunk5      input
##   append3      chunk5      chunk4      chunk6      ...
##   append4      chunk4      chunk6      ...
##   append5      chunk6      ...
##   append6      ...
##   ...
##

ngl, MCE does incur a small overhead because of the whole passing-data-around thing. A fast code block will legit run faster natively when you're chaining multiple map functions together. But here's the tea: that overhead will likely diminish as the complexity increases for the code. 🫶

## 0.334 secs -- baseline using the native map function
my @m1 = map { $_ * 4 } map { $_ * 3 } map { $_ * 2 } 1..1000000;

## 0.427 secs -- this is quite amazing considering data passing
my @m2 = mce_stream
      sub { $_ * 4 }, sub { $_ * 3 }, sub { $_ * 2 }, 1..1000000;

## 0.355 secs -- appends to @m3 immediately, not after running
my @m3; mce_stream \@m3,
      sub { $_ * 4 }, sub { $_ * 3 }, sub { $_ * 2 }, 1..1000000;

Even faster?? mce_stream_s. Obsessed. It's useful when your input data is a range of numbers. The workers generate sequences mathematically among themselves, with zero interaction from the manager process. Main character behavior fr fr. 💅

Two arguments are required for mce_stream_s (begin, end). Step defaults to 1 if begin is smaller than end, otherwise -1.

## 0.278 secs -- numbers are generated mathematically via sequence
my @m4; mce_stream_s \@m4,
      sub { $_ * 4 }, sub { $_ * 3 }, sub { $_ * 2 }, 1, 1000000;

---

🌈 OVERRIDING DEFAULTS

Here's the list of options you can override when loading the module. Heads up bestie: the fast option is obsolete in 1.867 onwards; it gets ignored if you specify it. 💀

use Sereal qw( encode_sereal decode_sereal );
use CBOR::XS qw( encode_cbor decode_cbor );
use JSON::XS qw( encode_json decode_json );

use MCE::Stream
    max_workers => 8,                # Default 'auto'
    chunk_size => 500,               # Default 'auto'
    tmp_dir => "/path/to/app/tmp",   # $MCE::Signal::tmp_dir
    freeze => \&encode_sereal,       # \&Storable::freeze
    thaw => \&decode_sereal,         # \&Storable::thaw
    init_relay => 0,                 # Default undef; MCE 1.882+
    use_threads => 0,                # Default undef; MCE 1.882+
    default_mode => 'grep',          # Default 'map'
;

From MCE 1.8 onwards, Sereal 3.015+ is loaded automatically if available. Specify "Sereal => 0" to use Storable instead:

use MCE::Stream Sereal => 0;

---

🦋 CUSTOMIZING MCE

MCE::Stream->init ( options )

MCE::Stream::init { options }

The init function accepts a hash of MCE options. The gather and bounds_only options, if specified, are ignored — that's because they're used internally by the module (so they're not shown below). 🙈

In scalar context (API available since 1.897), it'll call MCE::Stream->finish automatically upon leaving the scope or program. So convenient, honestly.

use MCE::Stream;

my $guard = MCE::Stream->init(
   chunk_size => 1, max_workers => 4,

   user_begin => sub {
      print "## ", MCE->wid, " started\n";
   },

   user_end => sub {
      print "## ", MCE->wid, " completed\n";
   }
);

my @a = mce_stream sub { $_ * $_ }, 1..100;

print "\n", "@a", "\n";

-- Output

## 1 started
## 2 started
## 3 started
## 4 started
## 3 completed
## 1 completed
## 2 completed
## 4 completed

1 4 9 16 25 36 49 64 81 100 121 144 169 196 225 256 289 324 361
400 441 484 529 576 625 676 729 784 841 900 961 1024 1089 1156
1225 1296 1369 1444 1521 1600 1681 1764 1849 1936 2025 2116 2209
2304 2401 2500 2601 2704 2809 2916 3025 3136 3249 3364 3481 3600
3721 3844 3969 4096 4225 4356 4489 4624 4761 4900 5041 5184 5329
5476 5625 5776 5929 6084 6241 6400 6561 6724 6889 7056 7225 7396
7569 7744 7921 8100 8281 8464 8649 8836 9025 9216 9409 9604 9801
10000

Like with MCE::Stream->init above, MCE options may be specified using an anonymous hash for the first argument. And look — notice how both max_workers and task_name can take an anonymous array for setting values uniquely per each code block. Cute, right? 🎀

Remember: MCE::Stream processes from right-to-left when setting the individual values. Don't forget it or you'll be like 😭.

use MCE::Stream;

my @a = mce_stream {
   task_name   => [ 'c', 'b', 'a' ],
   max_workers => [  2,   4,   3, ],

   user_end => sub {
      my ($mce, $task_id, $task_name) = @_;
      print "$task_id - $task_name completed\n";
   },

   task_end => sub {
      my ($mce, $task_id, $task_name) = @_;
      MCE->print("$task_id - $task_name ended\n");
   }
},
sub { $_ * 4 },             ## 2 workers, named c
sub { $_ * 3 },             ## 4 workers, named b
sub { $_ * 2 }, 1..10000;   ## 3 workers, named a

-- Output

0 - a completed
0 - a completed
0 - a completed
0 - a ended
1 - b completed
1 - b completed
1 - b completed
1 - b completed
1 - b ended
2 - c completed
2 - c completed
2 - c ended

Note that the anonymous hash, for specifying options, also comes first when passing an array reference. Yes, even then. 👑

my @a; mce_stream {
   ...
}, \@a, sub { ... }, sub { ... }, 1..10000;

---

🌈 API DOCUMENTATION 🌈

Okay bestie, so writing scripts with MCE::Stream? You can go long form or short form. The long form is what you reach for when you're mixing modes, and remember — the processing happens right-to-left, always. 💅

 my @m3 = mce_stream
    { mode => 'map',  code => sub { $_ * $_ } },
    { mode => 'grep', code => sub { $_ % 5 == 0 } }, 1..10000;

 my @m4; mce_stream \@m4,
    { mode => 'map',  code => sub { $_ * $_ } },
    { mode => 'grep', code => sub { $_ % 5 == 0 } }, 1..10000;

When you've got multiple grep blocks, the short form eats. Just tell the module your default mode, okay? The two valid values for default_mode are 'grep' and 'map'. 🎀

 use MCE::Stream default_mode => 'grep';

 my @f = mce_stream_f sub { /ending$/ }, sub { /^starting/ }, $file;

The stuff below assumes 'map' for default_mode so we can show you every single possibility for handing over input data. no cap. ✨

---

💖 MCE::Stream->run ( sub { code }, list ) / mce_stream sub { code }, list

Input data can be a list or an array reference. But heads up — unlike MCE::Loop, Flow, and Step, passing a hash reference as input data is not allowed. sorry bestie, it's just not the vibe. 🙈

## Array or array_ref
my @a = mce_stream sub { $_ * 2 }, 1..1000;
my @b = mce_stream sub { $_ * 2 }, \@list;

## Important; pass an array_ref for deeply input data
my @c = mce_stream sub { $_->[1] *= 2; $_ }, [ [ 0, 1 ], [ 0, 2 ], ... ];
my @d = mce_stream sub { $_->[1] *= 2; $_ }, \@deeply_list;

## Not supported
my @z = mce_stream sub { ... }, \%hash;

💖 MCE::Stream->run_file ( sub { code }, file ) / mce_stream_f sub { code }, file

The fastest one of these is the /path/to/file, periodt. The workers sort out the next offset position among themselves with zero interaction from the manager process. iconic behavior honestly. 👑

"IO::All" { File, Pipe, STDIO } is supported since MCE 1.845.

my @c = mce_stream_f sub { chomp; $_ . "\r\n" }, "/path/to/file";  # faster
my @d = mce_stream_f sub { chomp; $_ . "\r\n" }, $file_handle;
my @e = mce_stream_f sub { chomp; $_ . "\r\n" }, $io;              # IO::All
my @f = mce_stream_f sub { chomp; $_ . "\r\n" }, \$scalar;

💖 MCE::Stream->run_seq ( sub { code }, $beg, $end [, $step, $fmt ] ) / mce_stream_s sub { code }, $beg, $end [, $step, $fmt ]

A sequence can be a list, an array reference, or a hash reference. These functions need both begin and end values to run — step and format are optional, they're just the little accessories. 💅 The format gets passed to sprintf (and yeah, the % may be omitted below).

my ($beg, $end, $step, $fmt) = (10, 20, 0.1, "%4.1f");

my @f = mce_stream_s sub { $_ }, $beg, $end, $step, $fmt;
my @g = mce_stream_s sub { $_ }, [ $beg, $end, $step, $fmt ];

my @h = mce_stream_s sub { $_ }, {
   begin => $beg, end => $end, step => $step, format => $fmt
};

💖 MCE::Stream->run ( { input_data => iterator }, sub { code } ) / mce_stream { input_data => iterator }, sub { code }

You can hand over an iterator reference for input_data. The only other way to do it is to set input_data through MCE::Stream->init — and the reason matters, bestie: that's what stops MCE::Stream from configuring the iterator reference as another user task, which will not work. 😭

Iterators are described under section "SYNTAX for INPUT_DATA" at MCE::Core.

 MCE::Stream->init(
    input_data => iterator
 );

 my @a = mce_stream sub { $_ * 3 }, sub { $_ * 2 };

---

🛑 MANUAL SHUTDOWN 🛑

MCE::Stream->finish
MCE::Stream::finish

Workers stay persistent as much as possible after running, and shutdown happens automatically when the script terminates. So call finish when you don't need the workers anymore — it's the polite lil goodbye. 🫶

 use MCE::Stream;

 MCE::Stream->init(
    chunk_size => 20, max_workers => 'auto'
 );

 my @a = mce_stream { ... } 1..100;

 MCE::Stream->finish;

---

📚 INDEX 📚

MCE, MCE::Core

---

👑 AUTHOR 👑

Mario E. Roy, <marioeroy AT gmail DOT com>

---

and that's the whole page, bestie — no crumbs left. 🦋 This was perl v5.42.0, dated 2025-09-10, and yes, it's MCE::Stream(3). go forth and stream responsibly. 💖✨🌸