punkshell/scriptlib/stdin_race.pl

#!/usr/bin/perl
use strict;
use warnings;
use Time::HiRes qw(usleep);
use IPC::Open3;
use IO::Handle;

# ANSI color codes
my $RESET = "\e[0m";
my $GREEN = "\e[32m"; # Child color
my $YELLOW = "\e[33m"; # Parent color

# Usage function
sub usage {
    my ($args) = @_;
    print STDERR "rcvd : $0 $args\n";
    print STDERR "usage:\n";
    print STDERR "       $0 pump <persecond> <maxcount>\n";
    print STDERR "       $0 parent\n";
    print STDERR "       $0 child <delay_ms>\n";
    print STDERR "\n";
    print STDERR "e.g:\n";
    print STDERR "       perl $0 pump 35 50 | perl $0 parent\n";
    exit 1;
}

# Pump role
sub pump {
    my ($persecond, $maxcount) = @_;
    if ($persecond > 1000) {
        print STDERR "WARNING: (>1000) sub millisecond scheduling not available - will go full speed\n";
        usleep(500_000);
    }

    STDOUT->autoflush(1);
    STDERR->autoflush(1);

    my $counter = -1;
    my $ms = int(1000 / $persecond);

    while ($maxcount <= 0 || $counter < $maxcount - 1) {
        $counter++;
        print ".${counter}";
        usleep($ms * 1000);
    }

    print STDERR "pump-done\n";
}

# Parent role
sub parent {
    print STDERR "${YELLOW}parent${RESET}\n";
    usleep(250_000);

    # Read the first chunk from stdin
    my $parent_chunk1;
    read(STDIN, $parent_chunk1, 8);
    print STDERR "${YELLOW}${parent_chunk1}${RESET}\n";

    # Launch the child process
    #my $child_pid = open3("<&STDIN", my $child_out, ">&STDERR", "perl", $0, "child", "150");
    open(local *CHILD_STDIN, "<&", \*STDIN) or die "Can't dup STDIN: $!";
    open(local *CHILD_STDERR, "<&", \*STDERR) or die "Can't dup STDERR: $!";
    my $child_pid = open3("<&CHILD_STDIN", my $child_out, ">&CHILD_STDERR", "perl", $0, "child", "150");

    binmode($child_out, ":utf8");

    # Handle output from the child process asynchronously
    while (my $line = <$child_out>) {
        print STDERR $line;
    }
    #close $child_out;

    waitpid($child_pid, 0);

    print STDERR "parent-tail-read\n";
    while (my $chunk = <STDIN>) {
        print STDOUT $chunk;
    }

    print STDERR "\n${YELLOW}parent-done${RESET}\n";
}

# Child role
sub child {
    my ($delay_ms) = @_;
    print STDERR "\n${GREEN}child${RESET}\n";
    usleep($delay_ms * 1000);

    # Read exactly 16 characters from stdin
    my $chunk;
    my $bytes_read = read(STDIN, $chunk, 16);
    if (defined $bytes_read) {
        if ($bytes_read > 0) {
            print STDERR "${GREEN}child-read: $bytes_read bytes${RESET}\n";
        } else {
            print STDERR "${GREEN}child-read: no data read${RESET}\n";
            exit 0;
        }
    }
    print STDOUT "${GREEN}${chunk}${RESET}\n";

    print STDERR "child-done\n";
    exit 0;
}

# Main function
sub main {
    my @args = @ARGV;
    if (@args < 1) {
        usage("");
    }

    my $role = shift @args;
    if ($role eq "pump") {
        if (@args != 2) {
            usage("pump");
        }
        my ($persecond, $maxcount) = @args;
        pump($persecond, $maxcount);
    } elsif ($role eq "parent") {
        if (@args != 0) {
            usage("parent");
        }
        parent();
    } elsif ($role eq "child") {
        if (@args != 1) {
            usage("child");
        }
        my ($delay_ms) = @args;
        child($delay_ms);
    } else {
        usage($role);
    }
}

main();