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Edit File: parcat

#!/usr/bin/perl

use Symbol qw(gensym);
use IPC::Open3;
use POSIX qw(:errno_h);
use IO::Select;
use strict;
use threads;
use threads::shared;
use Thread::Queue;

my $opened :shared;
my $q = Thread::Queue->new();
my $okq = Thread::Queue->new();
my @producers;

if(not @ARGV) {
    if(-t *STDIN) {
	print "Usage:\n";
	print "  parcat file(s)\n";
	print "  cat argfile | parcat\n";
    } else {
	# Read arguments from stdin
	chomp(@ARGV = <STDIN>);
    }
}

my $files_to_open = 0;
# Default: fd = stdout
my $fd = 1;
for (@ARGV) {
    # --rm = remove file when opened
    /^--rm$/ and do { $opt::rm = 1; next; };
    # -1 = output to fd 1, -2 = output to fd 2
    /^-(\d+)$/ and do { $fd = $1; next; };
    push @producers, threads->create('producer', $_, $fd);
    $files_to_open++;
}

sub producer {
    # Open a file/fifo, set non blocking, enqueue fileno of the file handle
    my $file = shift;
    my $output_fd = shift;
    open(my $fh, "<", $file) || do {
	print STDERR "parcat: Cannot open $file\n";
	exit(1);
    };
    # Remove file when it has been opened
    if($opt::rm) {
	unlink $file;
    }
    set_fh_non_blocking($fh);
    $opened++;
    # Pass the fileno to parent
    $q->enqueue(fileno($fh),$output_fd);
    # Get an OK that the $fh is opened and we can release the $fh
    while(1) {
	my $ok = $okq->dequeue();
	if($ok == fileno($fh)) { last; }
	# Not ours - very unlikely to happen
	$okq->enqueue($ok);
    }
    return;
}

my $s = IO::Select->new();
my %buffer;

sub add_file {
    my $infd = shift;
    my $outfd = shift;
    open(my $infh, "<&=", $infd) || die;
    open(my $outfh, ">&=", $outfd) || die;
    $s->add($infh);
    # Tell the producer now opened here and can be released
    $okq->enqueue($infd);
    # Initialize the buffer
    @{$buffer{$infh}{$outfd}} = ();
    $Global::fh{$outfd} = $outfh;
}

sub add_files {
    # Non-blocking dequeue
    my ($infd,$outfd);
    do {
	($infd,$outfd) = $q->dequeue_nb(2);
	if(defined($outfd)) {
	    add_file($infd,$outfd);
	}
    } while(defined($outfd));
}

sub add_files_block {
    # Blocking dequeue
    my ($infd,$outfd) = $q->dequeue(2);
    add_file($infd,$outfd);
}

my $fd;
my (@ready,$infh,$rv,$buf);
do {
    # Wait until at least one file is opened
    add_files_block();
    while($q->pending or keys %buffer) {
	add_files();
	while(keys %buffer) {
	    @ready = $s->can_read(0.01);
	    if(not @ready) {
		add_files();
	    }
	    for $infh (@ready) {
		# There is only one key, namely the output file descriptor
		for my $outfd (keys %{$buffer{$infh}}) {
		    $rv = sysread($infh, $buf, 65536);
		    if (!$rv) {
			if($! == EAGAIN) {
			    # Would block: Nothing read
			    next;
			} else {
			    # Nothing read, but would not block:
			    # This file is done
			    $s->remove($infh);
			    for(@{$buffer{$infh}{$outfd}}) {
				syswrite($Global::fh{$outfd},$_);
			    }
			    delete $buffer{$infh};
			    # Closing the $infh causes it to block
			    # close $infh;
			    add_files();
			    next;
			}
		    }
		    # Something read.
		    # Find \n or \r for full line
		    my $i = (rindex($buf,"\n")+1);
		    if($i) {
			# Print full line
			for(@{$buffer{$infh}{$outfd}}, substr($buf,0,$i)) {
			    syswrite($Global::fh{$outfd},$_);
			}
			# @buffer = remaining half line
			$buffer{$infh}{$outfd} = [substr($buf,$i,$rv-$i)];
		    } else {
			# Something read, but not a full line
			push @{$buffer{$infh}{$outfd}}, $buf;
		    }
		    redo;
		}
	    }
	}
    }
} while($opened < $files_to_open);

for (@producers) {
    $_->join();
}

sub set_fh_non_blocking {
    # Set filehandle as non-blocking
    # Inputs:
    #   $fh = filehandle to be blocking
    # Returns:
    #   N/A
    my $fh = shift;
    $Global::use{"Fcntl"} ||= eval "use Fcntl qw(:DEFAULT :flock); 1;";
    my $flags;
    fcntl($fh, &F_GETFL, $flags) || die $!; # Get the current flags on the filehandle
    $flags |= &O_NONBLOCK; # Add non-blocking to the flags
    fcntl($fh, &F_SETFL, $flags) || die $!; # Set the flags on the filehandle
}