recorder_dump(3)

📦 version 1.2.3, in fedora 43, fedora 44

Hiii bestie 💖 you've stumbled onto the manual page for recorder_dump(3), and yes, it lives in the Recorder Library (which is, lowkey, the main character of this whole thing). This is the page where you learn how to yeet every single recorded event onto your screen, and honestly? It's giving observability. Let's get into it 🦋

✨ NAME ✨

  • recorder_dump — Dump all recorder entries
  • recorder_dump_for — Dump selected recorders
  • recorder_sort — Fine-controlled recorder dump
  • recorder_dump_on_signal — Dump the recorder when receiving a signal
  • recorder_dump_on_common_signals — Dump the recorder for standard signals

🌸 SYNOPSIS 🌸

#include <recorder/recorder.h>

typedef unsigned (*recorder_show_fn) (const char *text,
                                      size_tlen,
                                      void *output);
typedef void (*recorder_format_fn)(recorder_show_fn show,
                                   void *output,
                                   const char * label,
                                   const char *location,
                                   uintptr_torder,
                                   uintptr_ttimestamp,
                                   const char *message);
typedef size_t (*recorder_type_fn)(intptr_t trace,
                                   const char *format,
                                   char *buffer,
                                   size_tlength,
                                   uintptr_tdata);

unsigned recorder_dump(void);
unsigned recorder_dump_for(const char *pattern);
unsigned recorder_sort(const char *pattern,
                       recorder_format_fn format,
                       recorder_show_fn show,
                       void * show_arg);
void recorder_dump_on_signal(int signal);
void recorder_dump_on_common_signals(unsigned add,
                                     unsigned remove);

💅 DESCRIPTION 💅

Okay so, the tea ☕:

recorder_dump() dumps the content of all the event recorders, in the exact order in which they were recorded. No shuffling, no vibe-based reordering — chronological, periodt.

recorder_dump_for() is the picky one: it only dumps the recorders that get selected by the regular expression pattern. Very "I only want these ones" of it 💁♀️

recorder_sort() is the fully customizable icon: it dumps the recorders selected by the regular expression pattern, using format to format an event record, show to show it, and passing show_arg to the function show. You're literally the director of this production 🎬

And here's the cute shortcut: calls to recorder_dump() and recorder_dump_for() are equivalents to calls to recorder_sort where format, show and arg take their standard default values. Those defaults are changeable, bestie — use recorder_configure_format(3), recorder_configure_show(3) and recorder_configure_output(3) respectively. 🫶

recorder_dump_on_signal() makes sure that recorder_dump() gets called if the program receives the given signal. So when things go sideways, you still get your receipts 📜

recorder_dump_on_common_signals() makes a recorder dump happen if the program receives any of a common set of signals — namely SIGQUIT, SIGILL, SIGABRT, SIGBUS, SIGSEGV, SIGSYS, SIGXCPU, SIGXFSZ, SIGINFO, SIGUSR1, SIGUSR2, SIGSTKFLT and SIGPWR, insofar as they are defined for the operating system (so if your OS doesn't have one, no drama, it just doesn't apply).

The add and remove arguments are bit masks that you can use to add or remove other signals compared to the default list. Customize your chaos ✨

🔥 RETURN VALUE 🔥

recorder_dump(), recorder_dump_for() and recorder_sort() return the number of event records that were dumped. That's your little receipt number, bestie 🧾

🌈 ENVIRONMENT VARIABLES 🌈

recorder_dump_on_common_signals() also reads these environment variables, and ngl they're kinda powerful:

  • RECORDER_TRACES — A trace description, in the format expected by recorder_trace_set(3).
  • RECORDER_TWEAKS — Like RECORDER_TRACES, but normally used for tweaking configuration values as opposed to tracing.
  • RECORDER_DUMP — Activates a background thread to dump the given pattern at regular intervals. It's giving automation 💅

🎀 EXAMPLES 🎀

Okay bestie, first up: the program below records its input arguments, and crashes if you pass crash as the first command-line argument. Very "f around and find out" energy 💀

#include <recorder/recorder.h>
#include <string.h>

RECORDER(program_args, 32, "Program command-line arguments");
int main(int argc, char **argv)
{
    int a;
    recorder_dump_on_common_signals(0, 0);
    for (a = 0; a < argc; a++)
        record(program_args, "Argument %d is %+s", a, argv[a]);

    if (argc >= 2 && strcmp(argv[1], "crash") == 0)
    {
        char *ptr = NULL;
        strcpy(ptr, argv[1]);
    }
}

When a crash occurs, previously recorded events are printed out on the console. Iconic behaviour, honestly ✨

Next up: the program below is an instrumented version of the classical recursive Fibonacci computation. It uses several recorders corresponding to different types of events, and activates warnings and errors in a way that can be configured by setting an environment variable. So extra, so good 🧚

#include <recorder/recorder.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>

RECORDER(fib_main,    32, "Loops in fib function");
RECORDER(fib_loops,   32, "Loops in fib function");
RECORDER(fib_warning, 32, "Warnings in fib function");
RECORDER(fib_error,   32, "Errors in fib function");

int fib(int n)
{
    if (n <= 1) {
        if (n < 0)
            record(fib_error, "fib is undefined for negative value %d", n);
        return n;
    }
    record(fib_loops, "Computing fib(%d)", n);
    int result = fib(n-1) + fib(n-2);
    record(fib_loops, "Computed fib(%d) = %d", n, result);
    return result;
}

int main(int argc, char **argv)
{
    int a;
    recorder_dump_on_common_signals(0, 0);
    recorder_trace_set(".*_warning=35 .*_error");
    recorder_trace_set(getenv("FIB_TRACES"));
    for (a = 1; a < argc; a++) {
        int n = atoi(argv[a]);
        if (n >= RECORDER_TRACE(fib_warning))
            record(fib_warning, "Computing for %d may take a while", n);
        printf("fib(%d) = %d0, n, fib(n));
        if (n >= RECORDER_TRACE(fib_warning))
            record(fib_warning, "Computation for %d finally completed", n);
    }
}

This program will produce an output similar to the following:

% fib 1 2 3 4 10 20 30 35 10 40 -1
fib(1) = 1
fib(2) = 1
fib(3) = 2
fib(4) = 3
fib(10) = 55
fib(20) = 6765
fib(30) = 832040
[2714667 0.177725] fib_warning: Computing for 35 may take a while
fib(35) = 9227465
[32575370 1.859156] fib_warning: Computation for 35 finally completed
fib(10) = 55
[32575547 1.859171] fib_warning: Computing for 40 may take a while
fib(40) = 102334155
[363735828 20.527882] fib_warning: Computation for 40 finally completed
[363735829 20.527887] fib_error: fib is undefined for negative value -1
fib(-1) = -1

So about those columns, bestie: the first column in trace outputs is the number of events that were recorded. The second column is the time in seconds since the program started. Now you can read the vibes AND the data 🫶

The same program can also be run with additional tracing or warnings, for example:

% FIB_TRACES="recorder_location fib_loops fib_warning=3" /tmp/fib 3 4
/tmp/fib.c:33:[82 0.000496] fib_warning: Computing for 3 may take a while
/tmp/fib.c:18:[83 0.000561] fib_loops: Computing fib(3)
/tmp/fib.c:18:[84 0.000570] fib_loops: Computing fib(2)
/tmp/fib.c:20:[85 0.000575] fib_loops: Computed fib(2) = 1
/tmp/fib.c:20:[86 0.000581] fib_loops: Computed fib(3) = 2
fib(3) = 2
/tmp/fib.c:36:[87 0.000590] fib_warning: Computation for 3 finally completed
/tmp/fib.c:33:[88 0.000596] fib_warning: Computing for 4 may take a while
/tmp/fib.c:18:[89 0.000601] fib_loops: Computing fib(4)
/tmp/fib.c:18:[90 0.000607] fib_loops: Computing fib(3)
/tmp/fib.c:18:[91 0.000612] fib_loops: Computing fib(2)
/tmp/fib.c:20:[92 0.000619] fib_loops: Computed fib(2) = 1
/tmp/fib.c:20:[93 0.000625] fib_loops: Computed fib(3) = 2
/tmp/fib.c:18:[94 0.000664] fib_loops: Computing fib(2)
/tmp/fib.c:20:[95 0.000707] fib_loops: Computed fib(2) = 1
/tmp/fib.c:20:[96 0.000724] fib_loops: Computed fib(4) = 3
fib(4) = 3
/tmp/fib.c:36:[97 0.000741] fib_warning: Computation for 4 finally completed

💀 BUGS 💀

Okay so here's the not-so-slay part, and I'm gonna be real with you:

The current signal handling mechanism does not yet use sigaltstack(2), and consequently is not robust to stack overflow. It is also known to fail for repeated signals. And SIGINFO (plus the associated Control-T keyboard shortcut) does not exist on Linux, which is, quote unquote, a pity 😭

Bugs should be reported using https://github.com/c3d/recorder/issues. Go be a responsible citizen bestie 🫡

👑 SEE ALSO 👑

Additional documentation and tutorials can be found at https://github.com/c3d/recorder — go read, it's giving educational 🌈

⭐ AUTHOR ⭐

Written by Christophe de Dinechin.

And that's the whole page, bestie — you ate it 💅✨ This was Recorder Library version 1.0, dated 2019-03-09, and honestly? Timeless. Go dump some recorders and stay hydrated 🍓💜

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