MCE::Relay(3pm)

NAME
MCE::Relay - Extends Many-Core Engine with relay capabilities

VERSION
This document describes MCE::Relay version 1.833

SYNOPSIS
 use MCE::Flow;

 my $file = shift || \*STDIN;

 ## Line Count #######################################

 mce_flow_f {
    max_workers => 4,
    use_slurpio => 1,
    init_relay  => 0,
 },
 sub {
    my ($mce, $slurp_ref, $chunk_id) = @_;
    my $line_count = ($$slurp_ref =~ tr/\n//);

    ## Receive and pass on updated information.
    my $lines_read = MCE::relay { $_ += $line_count };

 }, $file;

 my $total_lines = MCE->relay_final;

 print {*STDERR} "$total_lines\n";

 ## Orderly Action ###################################

 $| = 1; # Important, must flush output immediately.

 mce_flow_f {
    max_workers => 2,
    use_slurpio => 1,
    init_relay  => 0,
 },
 sub {
    my ($mce, $slurp_ref, $chunk_id) = @_;

    ## The relay value is relayed and remains 0.
    ## Writes to STDOUT orderly.

    MCE->relay_lock;
    print $$slurp_ref;
    MCE->relay_unlock;

 }, $file;

DESCRIPTION
This module enables workers to receive and pass on information orderly with zero involvement by the manager process while running. The module is loaded automatically when MCE option "init_relay" is specified.

All workers (belonging to task_id 0) must participate when relaying data.

Relaying is not meant for passing big data. The last worker will stall if exceeding the buffer size for the socket. Not exceeding 16 KiB - 7 is safe across all platforms.

API DOCUMENTATION

MCE->relay ( sub { code } )
MCE::relay { code }
    Relay is enabled by specifying the init_relay option which takes a hash or array reference, or a scalar value. Relaying is orderly and driven by chunk_id when processing data, otherwise task_wid. Omitting the code block (e.g. MCE::relay) relays forward.

    Below, relaying multiple values via a HASH reference.

     use MCE::Flow max_workers => 4;

     mce_flow {
        init_relay => { p => 0, e => 0 },
     },
     sub {
        my $wid = MCE->wid;

        ## do work
        my $pass = $wid % 3;
        my $errs = $wid % 2;

        ## relay
        my %last_rpt = MCE::relay { $_->{p} += $pass; $_->{e} += $errs };

        MCE->print("$wid: passed $pass, errors $errs\n");

        return;
     };

     my %results = MCE->relay_final;

     print "   passed $results{p}, errors $results{e} final\n\n";

     -- Output

     1: passed 1, errors 1
     2: passed 2, errors 0
     3: passed 0, errors 1
     4: passed 1, errors 0
        passed 4, errors 2 final

    Or multiple values via an ARRAY reference.

     use MCE::Flow max_workers => 4;

     mce_flow {
        init_relay => [ 0, 0 ],
     },
     sub {
        my $wid = MCE->wid;

        ## do work
        my $pass = $wid % 3;
        my $errs = $wid % 2;

        ## relay
        my @last_rpt = MCE::relay { $_->[0] += $pass; $_->[1] += $errs };

        MCE->print("$wid: passed $pass, errors $errs\n");

        return;
     };

     my ($pass, $errs) = MCE->relay_final;

     print "   passed $pass, errors $errs final\n\n";

     -- Output

     1: passed 1, errors 1
     2: passed 2, errors 0
     3: passed 0, errors 1
     4: passed 1, errors 0
        passed 4, errors 2 final

    Or simply a scalar value.

     use MCE::Flow max_workers => 4;

     mce_flow {
        init_relay => 0,
     },
     sub {
        my $wid = MCE->wid;

        ## do work
        my $bytes_read = 1000 + ((MCE->wid % 3) * 3);

        ## relay
        my $last_offset = MCE::relay { $_ += $bytes_read };

        ## output
        MCE->print("$wid: $bytes_read\n");

        return;
     };

     my $total = MCE->relay_final;

     print "   $total size\n\n";

     -- Output

     1: 1003
     2: 1006
     3: 1000
     4: 1003
        4012 size

MCE->relay_final ( void )
    Call this method to obtain the final relay value(s) after running. See included example findnull.pl for another use case.

     use MCE max_workers => 4;

     my $mce = MCE->new(
        init_relay => [ 0, 100 ],       ## initial values (two counters)

        user_func => sub {
           my ($mce) = @_;

           ## do work
           my ($acc1, $acc2) = (10, 20);

           ## relay to next worker
           MCE::relay { $_->[0] += $acc1; $_->[1] += $acc2 };

           return;
        }
     )->run;

     my ($cnt1, $cnt2) = $mce->relay_final;

     print "$cnt1 : $cnt2\n";

     -- Output

     40 : 180

MCE->relay_recv ( void )
    Call this method to obtain the next relay value before relaying. This allows serial-code to be processed orderly between workers. The following is a parallel demonstration for the fasta-benchmark on the web.

     # perl fasta.pl 25000000

     # The Computer Language Benchmarks game
     # http://benchmarksgame.alioth.debian.org/
     #
     # contributed by Barry Walsh
     # port of fasta.rb #6
     #
     # MCE::Flow version by Mario Roy
     # requires MCE 1.807+
     # requires MCE::Shared 1.806+

     use strict;
     use warnings;
     use feature 'say';

     use MCE::Flow;
     use MCE::Shared;
     use MCE::Candy;

     use constant IM => 139968;
     use constant IA => 3877;
     use constant IC => 29573;

     my $LAST = MCE::Shared->scalar( 42 );

     my $alu =
        'GGCCGGGCGCGGTGGCTCACGCCTGTAATCCCAGCACTTTGG' .
        'GAGGCCGAGGCGGGCGGATCACCTGAGGTCAGGAGTTCGAGA' .
        'CCAGCCTGGCCAACATGGTGAAACCCCGTCTCTACTAAAAAT' .
        'ACAAAAATTAGCCGGGCGTGGTGGCGCGCGCCTGTAATCCCA' .
        'GCTACTCGGGAGGCTGAGGCAGGAGAATCGCTTGAACCCGGG' .
        'AGGCGGAGGTTGCAGTGAGCCGAGATCGCGCCACTGCACTCC' .
        'AGCCTGGGCGACAGAGCGAGACTCCGTCTCAAAAA';

     my $iub = [
        [ 'a', 0.27 ], [ 'c', 0.12 ], [ 'g', 0.12 ],
        [ 't', 0.27 ], [ 'B', 0.02 ], [ 'D', 0.02 ],
        [ 'H', 0.02 ], [ 'K', 0.02 ], [ 'M', 0.02 ],
        [ 'N', 0.02 ], [ 'R', 0.02 ], [ 'S', 0.02 ],
        [ 'V', 0.02 ], [ 'W', 0.02 ], [ 'Y', 0.02 ]
     ];

     my $homosapiens = [
        [ 'a', 0.3029549426680 ],
        [ 'c', 0.1979883004921 ],
        [ 'g', 0.1975473066391 ],
        [ 't', 0.3015094502008 ]
     ];

     sub make_repeat_fasta {
        my ( $src, $n ) = @_;
        my $width = qr/(.{1,60})/;
        my $l     = length $src;
        my $s     = $src x ( ($n / $l) + 1 );
        substr( $s, $n, $l ) = '';

        while ( $s =~ m/$width/g ) { say $1 }
     }

     sub make_random_fasta {
        my ( $table, $n ) = @_;
        my $rand   = undef;
        my $width  = 60;
        my $prob   = 0.0;
        my $output = '';
        my ( $c1, $c2, $last );

        $_->[1] = ( $prob += $_->[1] ) for @$table;

        $c1  = '$rand = ( $last = ( $last * IA + IC ) % IM ) / IM;';
        $c1 .= "\$output .= '$_->[0]', next if $_->[1] > \$rand;\n" for @$table;

        my $seq = MCE::Shared->sequence(
           { chunk_size => 2000, bounds_only => 1 },
           1, $n / $width
        );

        my $code1 = q{
           while ( 1 ) {
              # --------------------------------------------
              # Process code orderly between workers.
              # --------------------------------------------

              my $chunk_id = MCE->relay_recv;
              my ( $begin, $end ) = $seq->next;

              MCE->relay, last if ( !defined $begin );

              my $last = $LAST->get;
              my $temp = $last;

              # Pre-compute $LAST value for the next worker
              for ( 1 .. ( $end - $begin + 1 ) * $width ) {
                 $temp = ( $temp * IA + IC ) % IM;
              }

              $LAST->set( $temp );

              # Increment chunk_id value
              MCE->relay( sub { $_ += 1 } );

              # --------------------------------------------
              # Also run code in parallel between workers.
              # --------------------------------------------

              for ( $begin .. $end ) {
                 for ( 1 .. $width ) { !C! }
                 $output .= "\n";
              }

              # --------------------------------------------
              # Display orderly.
              # --------------------------------------------

              MCE->gather( $chunk_id, $output );

              $output = '';
           }
        };

        $code1 =~ s/!C!/$c1/g;

        MCE::Flow->init(
           max_workers => 4, ## MCE::Util->get_ncpu || 4,
           gather      => MCE::Candy::out_iter_fh( \*STDOUT ),
           init_relay  => 1,
           use_threads => 0,
        );

        MCE::Flow->run( sub { eval $code1 } );
        MCE::Flow->finish;

        $last = $LAST->get;

        $c2  = '$rand = ( $last = ( $last * IA + IC ) % IM ) / IM;';
        $c2 .= "print('$_->[0]'), next if $_->[1] > \$rand;\n" for @$table;

        my $code2 = q{
           if ( $n % $width != 0 ) {
              for ( 1 .. $n % $width ) { !C! }
              print "\n";
           }
        };

        $code2 =~ s/!C!/$c2/g;
        eval $code2;

        $LAST->set( $last );
     }

     my $n = $ARGV[0] || 27;

     say ">ONE Homo sapiens alu";
     make_repeat_fasta( $alu, $n * 2 );

     say ">TWO IUB ambiguity codes";
     make_random_fasta( $iub, $n * 3 );

     say ">THREE Homo sapiens frequency";
     make_random_fasta( $homosapiens, $n * 5 );

MCE->relay_lock ( void )
MCE->relay_unlock ( void )
    The "relay_lock" and "relay_unlock" methods, added to MCE 1.807, are aliases for "relay_recv" and "relay" respectively. They allow one to perform an exclusive action prior to actual relaying of data.

    Below, "user_func" is taken from the "cat.pl" MCE example. Relaying is driven by "chunk_id" or "task_wid" when not processing input, thus occurs orderly.

     user_func => sub {
        my ($mce, $chunk_ref, $chunk_id) = @_;

        if ($n_flag) {
           ## Relays the total lines read.

           my $output = ''; my $line_count = ($$chunk_ref =~ tr/\n//);
           my $lines_read = MCE::relay { $_ += $line_count };

           open my $fh, '<', $chunk_ref;
           $output .= sprintf "%6d\t%s", ++$lines_read, $_ while (<$fh>);
           close $fh;

           $output .= ":$chunk_id";
           MCE->do('display_chunk', $output);
        }
        else {
           ## The following is another way to have ordered output. Workers
           ## write directly to STDOUT exclusively without any involvement
           ## from the manager process. The statement(s) between relay_lock
           ## and relay_unlock run serially and most important orderly.

           MCE->relay_lock;      # alias for MCE->relay_recv

           print $$chunk_ref;    # ensure $| = 1 in script

           MCE->relay_unlock;    # alias for MCE->relay
        }

        return;
     }

    The following is a variant of the fasta-benchmark demonstration shown above. Here, workers write exclusively and orderly to "STDOUT".

     # perl fasta.pl 25000000

     # The Computer Language Benchmarks game
     # http://benchmarksgame.alioth.debian.org/
     #
     # contributed by Barry Walsh
     # port of fasta.rb #6
     #
     # MCE::Flow version by Mario Roy
     # requires MCE 1.807+
     # requires MCE::Shared 1.806+

     use strict;
     use warnings;
     use feature 'say';

     use MCE::Flow;
     use MCE::Shared;

     use constant IM => 139968;
     use constant IA => 3877;
     use constant IC => 29573;

     my $LAST = MCE::Shared->scalar( 42 );

     my $alu =
        'GGCCGGGCGCGGTGGCTCACGCCTGTAATCCCAGCACTTTGG' .
        'GAGGCCGAGGCGGGCGGATCACCTGAGGTCAGGAGTTCGAGA' .
        'CCAGCCTGGCCAACATGGTGAAACCCCGTCTCTACTAAAAAT' .
        'ACAAAAATTAGCCGGGCGTGGTGGCGCGCGCCTGTAATCCCA' .
        'GCTACTCGGGAGGCTGAGGCAGGAGAATCGCTTGAACCCGGG' .
        'AGGCGGAGGTTGCAGTGAGCCGAGATCGCGCCACTGCACTCC' .
        'AGCCTGGGCGACAGAGCGAGACTCCGTCTCAAAAA';

     my $iub = [
        [ 'a', 0.27 ], [ 'c', 0.12 ], [ 'g', 0.12 ],
        [ 't', 0.27 ], [ 'B', 0.02 ], [ 'D', 0.02 ],
        [ 'H', 0.02 ], [ 'K', 0.02 ], [ 'M', 0.02 ],
        [ 'N', 0.02 ], [ 'R', 0.02 ], [ 'S', 0.02 ],
        [ 'V', 0.02 ], [ 'W', 0.02 ], [ 'Y', 0.02 ]
     ];

     my $homosapiens = [
        [ 'a', 0.3029549426680 ],
        [ 'c', 0.1979883004921 ],
        [ 'g', 0.1975473066391 ],
        [ 't', 0.3015094502008 ]
     ];

     sub make_repeat_fasta {
        my ( $src, $n ) = @_;
        my $width = qr/(.{1,60})/;
        my $l     = length $src;
        my $s     = $src x ( ($n / $l) + 1 );
        substr( $s, $n, $l ) = '';

        while ( $s =~ m/$width/g ) { say $1 }
     }

     sub make_random_fasta {
        my ( $table, $n ) = @_;
        my $rand   = undef;
        my $width  = 60;
        my $prob   = 0.0;
        my $output = '';
        my ( $c1, $c2, $last );

        $_->[1] = ( $prob += $_->[1] ) for @$table;

        $c1  = '$rand = ( $last = ( $last * IA + IC ) % IM ) / IM;';
        $c1 .= "\$output .= '$_->[0]', next if $_->[1] > \$rand;\n" for @$table;

        my $seq = MCE::Shared->sequence(
           { chunk_size => 2000, bounds_only => 1 },
           1, $n / $width
        );

        my $code1 = q{
           $| = 1; # Important, must flush output immediately.

           while ( 1 ) {
              # --------------------------------------------
              # Process code orderly between workers.
              # --------------------------------------------

              MCE->relay_lock;

              my ( $begin, $end ) = $seq->next;
              print( $output ), $output = '' if ( length $output );

              MCE->relay_unlock, last if ( !defined $begin );

              my $last = $LAST->get;
              my $temp = $last;

              # Pre-compute $LAST value for the next worker
              for ( 1 .. ( $end - $begin + 1 ) * $width ) {
                 $temp = ( $temp * IA + IC ) % IM;
              }

              $LAST->set( $temp );

              MCE->relay_unlock;

              # --------------------------------------------
              # Also run code in parallel.
              # --------------------------------------------

              for ( $begin .. $end ) {
                 for ( 1 .. $width ) { !C! }
                 $output .= "\n";
              }
           }
        };

        $code1 =~ s/!C!/$c1/g;

        MCE::Flow->init(
           max_workers => 4, ## MCE::Util->get_ncpu || 4,
           init_relay  => 0,
           use_threads => 0,
        );

        MCE::Flow->run( sub { eval $code1 } );
        MCE::Flow->finish;

        $last = $LAST->get;

        $c2  = '$rand = ( $last = ( $last * IA + IC ) % IM ) / IM;';
        $c2 .= "print('$_->[0]'), next if $_->[1] > \$rand;\n" for @$table;

        my $code2 = q{
           if ( $n % $width != 0 ) {
              for ( 1 .. $n % $width ) { !C! }
              print "\n";
           }
        };

        $code2 =~ s/!C!/$c2/g;
        eval $code2;

        $LAST->set( $last );
     }

     my $n = $ARGV[0] || 27;

     say ">ONE Homo sapiens alu";
     make_repeat_fasta( $alu, $n * 2 );

     say ">TWO IUB ambiguity codes";
     make_random_fasta( $iub, $n * 3 );

     say ">THREE Homo sapiens frequency";
     make_random_fasta( $homosapiens, $n * 5 );

INDEX
MCE, MCE::Core

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