parallel/src/parcat

#!/usr/bin/perl

=head1 NAME

parcat - cat files or fifos in parallel

=head1 SYNOPSIS

B<parcat> file(s)

=head1 DESCRIPTION

GNU B<parcat> reads files or fifos in parallel. It writes full lines
so there will be no problem with mixed-half-lines which you risk if
you use:

   (cat file1 & cat file2 &) | ...


=head1 EXAMPLES

=head2 Do be done

  mkfifo slot-{1..5}-digit-{0..9}
  parallel -j5 'seq 100000 | grep {} > slot-{%}-digit-{}' ::: {0..9} &
  parallel parcat slot-{1..5}-digit-{} '>' digit-{} ::: {0..9}

=head1 REPORTING BUGS

GNU B<parcat> is part of GNU B<parallel>. Report bugs to <bug-parallel@gnu.org>.


=head1 AUTHOR

Copyright (C) 2016 Ole Tange, http://ole.tange.dk and Free Software
Foundation, Inc.

=head1 LICENSE

Copyright (C) 2007,2008,2009,2010,2011 Free Software Foundation, Inc.

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
at your option any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.

=head2 Documentation license I

Permission is granted to copy, distribute and/or modify this documentation
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
Texts.  A copy of the license is included in the file fdl.txt.

=head2 Documentation license II

You are free:

=over 9

=item B<to Share>

to copy, distribute and transmit the work

=item B<to Remix>

to adapt the work

=back

Under the following conditions:

=over 9

=item B<Attribution>

You must attribute the work in the manner specified by the author or
licensor (but not in any way that suggests that they endorse you or
your use of the work).

=item B<Share Alike>

If you alter, transform, or build upon this work, you may distribute
the resulting work only under the same, similar or a compatible
license.

=back

With the understanding that:

=over 9

=item B<Waiver>

Any of the above conditions can be waived if you get permission from
the copyright holder.

=item B<Public Domain>

Where the work or any of its elements is in the public domain under
applicable law, that status is in no way affected by the license.

=item B<Other Rights>

In no way are any of the following rights affected by the license:

=over 9

=item *

Your fair dealing or fair use rights, or other applicable
copyright exceptions and limitations;

=item *

The author's moral rights;

=item *

Rights other persons may have either in the work itself or in
how the work is used, such as publicity or privacy rights.

=back

=item B<Notice>

For any reuse or distribution, you must make clear to others the
license terms of this work.

=back

A copy of the full license is included in the file as cc-by-sa.txt.

=head1 DEPENDENCIES

GNU B<parcat> uses Perl.


=head1 SEE ALSO

B<cat>(1), B<parallel>(1)

=cut


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) {
    print "Usage:\n";
    print "  parcat file(s)\n";
}

for (@ARGV) {
    push @producers, threads->create('producer', $_);
}

sub producer {
    # Open a file/fifo, set non blocking, enqueue fileno of the file handle
    my $file = shift;
    open(my $fh, "<", $file) || do {
	print STDERR "parcat: Cannot open $file\n";
	exit(1);
    };
    set_fh_non_blocking($fh);
    $q->enqueue(fileno($fh));
    $opened++;
    # 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 $fd = shift;
    open(my $fh, "<&=", $fd) || die;
    $s->add($fh);
    # Tell the producer now opened here and can be released
    $okq->enqueue($fd);
    # Initialize the buffer
    @{$buffer{$fh}} = ();
}

sub add_files {
    # Non-blocking dequeue
    while(defined(my $fd = $q->dequeue_nb())) {
	add_file($fd);
    }
}

sub add_files_block {
    # Blocking dequeue
    my $fd = $q->dequeue();
    add_file($fd);
}


my $fd;
my (@ready,$file,$rv,$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 $file (@ready) {
		$rv = sysread($file, $buf, 65536);
		if (!$rv) {
		    if($! == EAGAIN) {
			# Would block: Nothing read
			next;
		    } else {
			# This file is done
			$s->remove($file);
			print @{$buffer{$file}};
			delete $buffer{$file};
			# Closing the $file causes it to block
			# close $file;
			add_files();
			next;
		    }
		}

		# Find \n for full line
		my $i = (rindex($buf,"\n")+1);
		if($i) {
		    # Print full line
		    for(@{$buffer{$file}}, substr($buf,0,$i)) {
			syswrite(STDOUT,$_);
		    }
		    # @buffer = remaining half line
		    @{$buffer{$file}} = (substr($buf,$i,$rv-$i));
		    redo;
		} else {
		    # Something read, but not a full line
		    push @{$buffer{$file}}, $buf;
		    redo;
		}
	    }
	}
    }
} while($opened <= $#ARGV);


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
}