NAME

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

VERSION

       This document describes MCE::Relay version 1.608

SYNOPSIS

          use MCE::Flow;

          my $file = shift || \*STDIN;

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

          mce_flow_f {
             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 ###################################

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

             ## Exclusive access to STDOUT. Relays 0.
             MCE::relay { print $$slurp_ref };

          }, $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
       init_relay is specified.

       All workers must participate when relaying data. Calling relay more than once is not
       recommended inside the block. Doing so will stall the application.

       Relaying is not met for passing big data. The last worker will likely stall if exceeding
       the buffer size for the socket. Not exceeding 8 KiB 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 values 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 )
          The relay_recv method allows one to perform an exclusive action prior to relaying.
          Below, the user_func is taken from the cat.pl example. Relaying is chunk_id driven (or
          task_wid when not processing input), thus 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 statements between relay_recv
                   ## and relay run serially and most important orderly.

                   ## STDERR/OUT flush automatically inside worker threads and
                   ## processes. Disable buffering on file handles otherwise.

                   MCE->relay_recv;             ## my $val = MCE->relay_recv;
                                                ## relay simply forwards 0 below

                   print $$chunk_ref;           ## exclusive access to STDOUT
                                                ## important, flush immediately

                   MCE->relay;
                }

                return;
             }

INDEX

       MCE

AUTHOR

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