path: root/lib/MCE/Examples.pod

=head1 NAME

MCE::Examples - Various examples and demonstrations

=head1 VERSION

This document describes MCE::Examples version 1.888

=head1 INCLUDED WITH THE DISTRIBUTION

A wrapper script for parallelizing the grep binary. Hence, processing is done
by the binary, not Perl. This wrapper resides under the bin directory.

  mce_grep
      A wrapper script with support for the following C binaries.
      agrep, grep, egrep, fgrep, and tre-agrep

      Chunking may be applied either at the [file] level, for large
      file(s), or at the [list] level when parsing many files
      recursively.

      The gain in performance is noticeable for expensive patterns,
      especially with agrep and tre-agrep.

=head1 MCE EXAMPLES ON GITHUB

The examples directory, beginning with 1.700, is maintained separately at a
GitHub repository L<https://github.com/marioroy/mce-examples> and no longer
included with the Perl MCE distribution.

=head1 PROCESSING INPUT DATA

The next section describes ways to process input data in MCE.

=head2 CHUNK_SIZE => 1 (in essence, disabling chunking)

Imagine a long running process and wanting to parallelize an array against a
pool of workers. The sequence option may be used if simply wanting to loop
through a sequence of numbers instead.

Below, a callback function is used for displaying results. The logic shows
how one can output results immediately while still preserving output order
as if processing serially. The %tmp hash is a temporary cache for
out-of-order results.

 use MCE;

 ## Return an iterator for preserving output order.

 sub preserve_order {
    my (%result_n, %result_d); my $order_id = 1;

    return sub {
       my ($chunk_id, $n, $data) = @_;

       $result_n{ $chunk_id } = $n;
       $result_d{ $chunk_id } = $data;

       while (1) {
          last unless exists $result_d{$order_id};

          printf "n: %5d sqrt(n): %7.3f\n",
             $result_n{$order_id}, $result_d{$order_id};

          delete $result_n{$order_id};
          delete $result_d{$order_id};

          $order_id++;
       }

       return;
    };
 }

 ## Use $chunk_ref->[0] or $_ to retrieve the element.
 my @input_data = (0 .. 18000 - 1);

 my $mce = MCE->new(
    gather => preserve_order, input_data => \@input_data,
    chunk_size => 1, max_workers => 3,

    user_func => sub {
       my ($mce, $chunk_ref, $chunk_id) = @_;
       MCE->gather($chunk_id, $_, sqrt($_));
    }
 );

 $mce->run;

This does the same thing using the foreach "sugar" method. 

 use MCE;

 sub preserve_order {
    ...
 }

 my $mce = MCE->new(
    chunk_size => 1, max_workers => 3,
    gather => preserve_order
 );

 ## Use $chunk_ref->[0] or $_ to retrieve the element.
 my @input_data = (0 .. 18000 - 1);

 $mce->foreach( \@input_data, sub {
    my ($mce, $chunk_ref, $chunk_id) = @_;
    MCE->gather($chunk_id, $_, sqrt($_));
 });

The 2 examples described above were done using the Core API. MCE 1.5 comes
with several models. The L<MCE::Loop> model is used below.

 use MCE::Loop;

 sub preserve_order {
    ...
 }

 MCE::Loop->init(
    chunk_size => 1, max_workers => 3,
    gather => preserve_order
 );

 ## Use $chunk_ref->[0] or $_ to retrieve the element.
 my @input_data = (0 .. 18000 - 1);

 mce_loop {
    my ($mce, $chunk_ref, $chunk_id) = @_;
    MCE->gather($chunk_id, $_, sqrt($_));

 } @input_data;

 MCE::Loop->finish;

=head2 CHUNKING INPUT DATA

Chunking has the effect of reducing IPC overhead by many folds. A chunk
containing $chunk_size items is sent to the next available worker.

 use MCE;

 ## Return an iterator for preserving output order.

 sub preserve_order {
    my (%result_n, %result_d, $size); my $order_id = 1;

    return sub {
       my ($chunk_id, $n_ref, $data_ref) = @_;

       $result_n{ $chunk_id } = $n_ref;
       $result_d{ $chunk_id } = $data_ref;

       while (1) {
          last unless exists $result_d{$order_id};
          $size = @{ $result_d{$order_id} };

          for (0 .. $size - 1) {
             printf "n: %5d sqrt(n): %7.3f\n",
                $result_n{$order_id}->[$_], $result_d{$order_id}->[$_];
          }

          delete $result_n{$order_id};
          delete $result_d{$order_id};

          $order_id++;
       }

       return;
    };
 }

 ## Chunking requires one to loop inside the code block.
 my @input_data = (0 .. 18000 - 1);

 my $mce = MCE->new(
    gather => preserve_order, input_data => \@input_data,
    chunk_size => 500, max_workers => 3,

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

       foreach ( @{ $chunk_ref } ) {
          push @n, $_;
          push @result, sqrt($_);
       }

       MCE->gather($chunk_id, \@n, \@result);
    }
 );

 $mce->run;

This does the same thing using the forchunk "sugar" method. 

 use MCE;

 sub preserve_order {
    ...
 }

 my $mce = MCE->new(
    chunk_size => 500, max_workers => 3,
    gather => preserve_order
 );

 ## Chunking requires one to loop inside the code block.
 my @input_data = (0 .. 18000 - 1);

 $mce->forchunk( \@input_data, sub {
    my ($mce, $chunk_ref, $chunk_id) = @_;
    my (@n, @result);

    foreach ( @{ $chunk_ref } ) {
       push @n, $_;
       push @result, sqrt($_);
    }

    MCE->gather($chunk_id, \@n, \@result);
 });

Finally, chunking with the L<MCE::Loop> model.

 use MCE::Loop;

 sub preserve_order {
    ...
 }

 MCE::Loop->init(
    chunk_size => 500, max_workers => 3,
    gather => preserve_order
 );

 ## Chunking requires one to loop inside the code block.
 my @input_data = (0 .. 18000 - 1);

 mce_loop {
    my ($mce, $chunk_ref, $chunk_id) = @_;
    my (@n, @result);

    foreach ( @{ $chunk_ref } ) {
       push @n, $_;
       push @result, sqrt($_);
    }

    MCE->gather($chunk_id, \@n, \@result);

 } @input_data;

 MCE::Loop->finish;

=head1 DEMO APPLYING SEQUENCES WITH USER_TASKS

The following is an extract from the seq_demo.pl example included with MCE. 
Think of having several MCEs running in parallel. The sequence and chunk_size
options may be specified uniquely per each task.

The input scalar $_ (not shown below) contains the same value as $seq_n in
user_func.

 use MCE;
 use Time::HiRes 'sleep';

 ## Run with seq_demo.pl | sort

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

    my $wid      = MCE->wid;
    my $task_id  = MCE->task_id;
    my $task_wid = MCE->task_wid;

    if (ref $seq_n eq 'ARRAY') {
       ## seq_n or $_ is an array reference when chunk_size > 1
       foreach (@{ $seq_n }) {
          MCE->printf(
             "task_id %d: seq_n %s: chunk_id %d: wid %d: task_wid %d\n",
             $task_id,    $_,       $chunk_id,   $wid,   $task_wid
          );
       }
    }
    else {
       MCE->printf(
          "task_id %d: seq_n %s: chunk_id %d: wid %d: task_wid %d\n",
          $task_id,    $seq_n,   $chunk_id,   $wid,   $task_wid
       );
    }

    sleep 0.003;

    return;
 }

 ## Each task can be configured uniquely.

 my $mce = MCE->new(
    user_tasks => [{
       max_workers => 2,
       chunk_size  => 1,
       sequence    => { begin => 11, end => 19, step => 1 },
       user_func   => \&user_func
    },{
       max_workers => 2,
       chunk_size  => 5,
       sequence    => { begin => 21, end => 29, step => 1 },
       user_func   => \&user_func
    },{
       max_workers => 2,
       chunk_size  => 3,
       sequence    => { begin => 31, end => 39, step => 1 },
       user_func   => \&user_func
    }]
 );

 $mce->run;

 -- Output

 task_id 0: seq_n 11: chunk_id 1: wid 2: task_wid 2
 task_id 0: seq_n 12: chunk_id 2: wid 1: task_wid 1
 task_id 0: seq_n 13: chunk_id 3: wid 2: task_wid 2
 task_id 0: seq_n 14: chunk_id 4: wid 1: task_wid 1
 task_id 0: seq_n 15: chunk_id 5: wid 2: task_wid 2
 task_id 0: seq_n 16: chunk_id 6: wid 1: task_wid 1
 task_id 0: seq_n 17: chunk_id 7: wid 2: task_wid 2
 task_id 0: seq_n 18: chunk_id 8: wid 1: task_wid 1
 task_id 0: seq_n 19: chunk_id 9: wid 2: task_wid 2
 task_id 1: seq_n 21: chunk_id 1: wid 3: task_wid 1
 task_id 1: seq_n 22: chunk_id 1: wid 3: task_wid 1
 task_id 1: seq_n 23: chunk_id 1: wid 3: task_wid 1
 task_id 1: seq_n 24: chunk_id 1: wid 3: task_wid 1
 task_id 1: seq_n 25: chunk_id 1: wid 3: task_wid 1
 task_id 1: seq_n 26: chunk_id 2: wid 4: task_wid 2
 task_id 1: seq_n 27: chunk_id 2: wid 4: task_wid 2
 task_id 1: seq_n 28: chunk_id 2: wid 4: task_wid 2
 task_id 1: seq_n 29: chunk_id 2: wid 4: task_wid 2
 task_id 2: seq_n 31: chunk_id 1: wid 5: task_wid 1
 task_id 2: seq_n 32: chunk_id 1: wid 5: task_wid 1
 task_id 2: seq_n 33: chunk_id 1: wid 5: task_wid 1
 task_id 2: seq_n 34: chunk_id 2: wid 6: task_wid 2
 task_id 2: seq_n 35: chunk_id 2: wid 6: task_wid 2
 task_id 2: seq_n 36: chunk_id 2: wid 6: task_wid 2
 task_id 2: seq_n 37: chunk_id 3: wid 5: task_wid 1
 task_id 2: seq_n 38: chunk_id 3: wid 5: task_wid 1
 task_id 2: seq_n 39: chunk_id 3: wid 5: task_wid 1

=head1 GLOBALLY SCOPED VARIABLES AND MCE MODELS

It is possible that Perl may create a new code ref on subsequent runs causing
MCE models to re-spawn. One solution to this is to declare global variables,
referenced by workers, with "our" instead of "my".

Let's take a look. The $i variable is declared with my and being reference in
both user_begin and mce_loop blocks. This will cause Perl to create a new code
ref for mce_loop on subsequent runs.

 use MCE::Loop;

 my $i = 0;   ## <-- this is the reason, try our instead

 MCE::Loop->init(
    user_begin => sub {
       print "process_id: $$\n" if MCE->wid == 1;
       $i++;
    },
    chunk_size => 1, max_workers => 'auto',
 );

 for (1..2) {
    ## Perl creates another code block ref causing workers
    ## to re-spawn on subsequent runs.
    print "\n"; mce_loop { print "$i: $_\n" } 1..4;
 }

 MCE::Loop->finish;

 -- Output

 process_id: 51380
 1: 1
 1: 2
 1: 3
 1: 4

 process_id: 51388
 1: 1
 1: 2
 1: 3
 1: 4

By making the one line change, we see that workers persist for the duration of
the script.

 use MCE::Loop;

 our $i = 0;  ## <-- changed my to our

 MCE::Loop->init(
    user_begin => sub {
       print "process_id: $$\n" if MCE->wid == 1;
       $i++;
    },
    chunk_size => 1, max_workers => 'auto',
 );

 for (1..2) {
    ## Workers persist between runs. No re-spawning.
    print "\n"; mce_loop { print "$i: $_\n" } 1..4;
 }

 -- Output

 process_id: 51457
 1: 1
 1: 2
 1: 4
 1: 3

 process_id: 51457
 2: 1
 2: 2
 2: 3
 2: 4

One may alternatively specify a code reference to existing routines for
user_begin and mce_loop. Take notice of the comma after \&_func though.

 use MCE::Loop;

 my $i = 0;  ## my (ok)

 sub _begin {
    print "process_id: $$\n" if MCE->wid == 1;
    $i++;
 }
 sub _func {
    print "$i: $_\n";
 }

 MCE::Loop->init(
    user_begin => \&_begin,
    chunk_size => 1, max_workers => 'auto',
 );

 for (1..2) {
    print "\n"; mce_loop \&_func, 1..4;
 }

 MCE::Loop->finish;

 -- Output

 process_id: 51626
 1: 1
 1: 2
 1: 3
 1: 4

 process_id: 51626
 2: 1
 2: 2
 2: 3
 2: 4

=head1 MANDELBROT DEMONSTRATION

For the next demonstration, L<MCE::Relay> allows a section of code to run
serially and orderly between workers. Relay capabilities is enabled with
the C<init_relay> option, which loads MCE::Relay.

 # perl mandelbrot.pl 16000 > image.pbm
 # outputs a pbm binary to STDOUT

 # The Computer Language Benchmarks Game
 # https://benchmarksgame-team.pages.debian.net/benchmarksgame/
 #
 # Started with:
 # C#  : Adapted by Antti Lankila from Isaac Gouy's implementation
 # Perl: Contributed by Mykola Zubach
 #
 # MCE::Loop version by Mario Roy
 # requires MCE 1.807+

 use strict;
 use warnings;

 use MCE::Loop;

 use constant MAXITER => 50;
 use constant LIMIT   => 4.0;
 use constant XMIN    => -1.5;
 use constant YMIN    => -1.0;

 my ( $w, $h, $m, $invN );

 sub draw_lines {
    my ( $y1, $y2 ) = @_;
    my @result;

    # Workers run simultaneously, in parallel.

    for my $y ( $y1 .. $y2 ) {
       my ( $bits, $xcounter, @line ) = ( 0, 0 );
       my $Ci = $y * $invN + YMIN;

       for my $x ( 0 .. $w - 1 ) {
          my ( $Zr, $Zi, $Tr, $Ti ) = ( 0, 0, 0, 0 );
          my $Cr = $x * $invN + XMIN;

          $bits = $bits << 1;

          for ( 1 .. MAXITER ) {
             $Zi = $Zi * 2 * $Zr + $Ci;
             $Zr = $Tr - $Ti + $Cr;
             $Ti = $Zi * $Zi, $Tr = $Zr * $Zr;

             $bits |= 1, last if ( $Tr + $Ti > LIMIT );
          }

          if ( ++$xcounter == 8 ) {
             push @line, $bits ^ 0xff;
             $bits = $xcounter = 0;
          }
       }

       if ( $xcounter ) {
          push @line, ( $bits << ( 8 - $xcounter ) ) ^ 0xff;
       }

       push @result, pack 'C*', @line;
    }

    # Statements between lock & unlock are processed serially & orderly.

    MCE->relay_lock;

    print @result;          # Workers display upper-half only.
    MCE->gather( @result ); # Gather lines for the manager-process.

    MCE->relay_unlock;
 }

 ## MAIN()

 # Important, must flush output immediately.

 $| = 1; binmode STDOUT;

 $w = $h = shift || 200;
 $m = int( $h / 2 );
 $invN = 2 / $w;

 print "P4\n$w $h\n"; # PBM image header.

 # Workers display upper-half only. Also, lines are gathered to be
 # displayed later by the manager-process after running.

 MCE::Loop->init(
    init_relay  => 0, # Enables MCE::Relay capabilities if defined.
    max_workers => 4,
    bounds_only => 1,
 );

 my @upper = mce_loop_s { draw_lines( $_[1][0], $_[1][1] ) } 0, $m;

 MCE::Loop->finish;

 # Remove first and last lines from the upper half.
 # Then, output bottom half.

 shift @upper, pop @upper;
 print reverse @upper;

=head1 MONTE CARLO SIMULATION

There is an article on the web (search for comp.lang.perl.misc MCE) suggesting
that MCE::Examples does not cover a simple simulation scenario. This section
demonstrates just that.

The serial code is based off the one by "gamo". A sleep is added to imitate
extra CPU time. The while loop is wrapped within a for loop to run 10 times.
The random number generator is seeded as well.

 use Time::HiRes qw/sleep time/;

 srand 5906;

 my ($var, $foo, $bar) = (1, 2, 3);
 my ($r, $a, $b);

 my $start = time;

 for (1..10) {
    while (1) {
       $r = rand;

       $a = $r * ($var + $foo + $bar);
       $b = sqrt($var + $foo + $bar);

       last if ($a < $b + 0.001 && $a > $b - 0.001);
       sleep 0.002;
    }

    print "$r -> $a\n";
 }

 my $end = time;

 printf {*STDERR} "\n## compute time: %0.03f secs\n\n", $end - $start;

 -- Output

 0.408246276657106 -> 2.44947765994264
 0.408099657137821 -> 2.44859794282693
 0.408285842931324 -> 2.44971505758794
 0.408342292008765 -> 2.45005375205259
 0.408333076522673 -> 2.44999845913604
 0.408344266898869 -> 2.45006560139321
 0.408084104120526 -> 2.44850462472316
 0.408197400014714 -> 2.44918440008828
 0.408344783704855 -> 2.45006870222913
 0.408248062985479 -> 2.44948837791287

 ## compute time: 93.049 secs

Next, we'd do the same with MCE. The demonstration requires at least MCE 1.509
to run properly. Folks on prior releases (1.505 - 1.508) will not see output
for the 2nd run and beyond.

 use Time::HiRes qw/sleep time/;
 use MCE::Loop;

 srand 5906;

 ## Configure MCE. Move common variables inside the user_begin
 ## block when not needed by the manager process.

 MCE::Loop->init(
    user_begin => sub {
       use vars qw($var $foo $bar);
       our ($var, $foo, $bar) = (1, 2, 3);
    },
    chunk_size => 1, max_workers => 'auto',
    input_data => \&_input, gather => \&_gather
 );

 ## Callback functions.

 my ($done, $r, $a);

 sub _input {
    return if $done;
    return rand;
 }

 sub _gather {
    my ($_r, $_a, $_b) = @_;
    return if $done;

    if ($_a < $_b + 0.001 && $_a > $_b - 0.001) {
       ($done, $r, $a) = (1, $_r, $_a);
    }
    return;
 }

 ## Compute in parallel.

 my $start = time;

 for (1..10) {
    $done = 0;      ## Reset $done before running

    mce_loop {
     # my ($mce, $chunk_ref, $chunk_id) = @_;
     # my $r = $chunk_ref->[0];

       my $r = $_;  ## Valid due to chunk_size => 1

       my $a = $r * ($var + $foo + $bar);
       my $b = sqrt($var + $foo + $bar);

       MCE->gather($r, $a, $b);
       sleep 0.002;
    };

    print "$r -> $a\n";
 }

 printf "\n## compute time: %0.03f secs\n\n", time - $start;

 -- Output

 0.408246276657106 -> 2.44947765994264
 0.408099657137821 -> 2.44859794282693
 0.408285842931324 -> 2.44971505758794
 0.408342292008765 -> 2.45005375205259
 0.408333076522673 -> 2.44999845913604
 0.408344266898869 -> 2.45006560139321
 0.408084104120526 -> 2.44850462472316
 0.408197400014714 -> 2.44918440008828
 0.408344783704855 -> 2.45006870222913
 0.408248062985479 -> 2.44948837791287

 ## compute time: 12.990 secs

Well, there you have it. MCE is able to complete the same simulation many
times faster.

=head1 MANY WORKERS RUNNING IN PARALLEL

There are occasions when one wants several workers to run in parallel without
having to specify input_data or sequence. These two options are optional in
MCE. The "do" and "sendto" methods, for sending data to the manager process,
are demonstrated below. Both process serially by the manager process on a
first come, first serve basis.

 use MCE::Flow max_workers => 4;

 sub report_stats {
    my ($wid, $msg, $h_ref) = @_;
    print "Worker $wid says $msg: ", $h_ref->{"counter"}, "\n";
 }

 mce_flow sub {
    my ($mce) = @_;
    my $wid = MCE->wid;

    if ($wid == 1) {
       my %h = ("counter" => 0);
       while (1) {
          $h{"counter"} += 1;
          MCE->do("report_stats", $wid, "Hey there", \%h);
          last if ($h{"counter"} == 4);
          sleep 2;
       }
    }
    else {
       my %h = ("counter" => 0);
       while (1) {
          $h{"counter"} += 1;
          MCE->do("report_stats", $wid, "Welcome..", \%h);
          last if ($h{"counter"} == 2);
          sleep 4;
       }
    }

    MCE->print(\*STDERR, "Worker $wid is exiting\n");
 };

 -- Output

 Note how worker 2 comes first in the 2nd run below.

 $ ./demo.pl
 Worker 1 says Hey there: 1
 Worker 2 says Welcome..: 1
 Worker 3 says Welcome..: 1
 Worker 4 says Welcome..: 1
 Worker 1 says Hey there: 2
 Worker 2 says Welcome..: 2
 Worker 3 says Welcome..: 2
 Worker 1 says Hey there: 3
 Worker 2 is exiting
 Worker 3 is exiting
 Worker 4 says Welcome..: 2
 Worker 4 is exiting
 Worker 1 says Hey there: 4
 Worker 1 is exiting

 $ ./demo.pl
 Worker 2 says Welcome..: 1
 Worker 1 says Hey there: 1
 Worker 4 says Welcome..: 1
 Worker 3 says Welcome..: 1
 Worker 1 says Hey there: 2
 Worker 2 says Welcome..: 2
 Worker 4 says Welcome..: 2
 Worker 3 says Welcome..: 2
 Worker 2 is exiting
 Worker 4 is exiting
 Worker 1 says Hey there: 3
 Worker 3 is exiting
 Worker 1 says Hey there: 4
 Worker 1 is exiting

=head1 TESTING AND CAPTURING OUTPUT

Capturing C<STDERR> and C<STDOUT> is possible with L<App::Cmd::Tester>.
MCE v1.708 or later is required to run the demonstration.

 use App::Cmd::Tester;
 use MCE;

 my $mce = MCE->new(
    max_workers => 4,

    user_func => sub {
       my $wid = MCE->wid;

       # MCE->sendto('stderr', "$wid: sendto err\n");
       # MCE->sendto(\*STDERR, "$wid: sendto err\n");
         MCE->print(\*STDERR, "$wid: print err\n");

       # MCE->sendto('stdout', "$wid: sendto out\n");
       # MCE->sendto(\*STDOUT, "$wid: sendto out\n");
       # MCE->print(\*STDOUT, "$wid: print out\n");
         MCE->print("$wid: print out\n");
    }
 );

 my $result = test_app(
    $mce => []
 );

 print "# stderr\n";
 print $result->stderr;
 print "\n";

 print "# stdout\n";
 print $result->stdout;
 print "\n";

 print "# output\n";
 print $result->output;
 print "\n";

 print "# exit code\n";
 print $result->exit_code;
 print "\n\n";

 -- Output

 # stderr
 3: print err
 4: print err
 1: print err
 2: print err

 # stdout
 3: print out
 4: print out
 1: print out
 2: print out

 # output
 3: print err
 3: print out
 4: print err
 1: print err
 4: print out
 1: print out
 2: print err
 2: print out

 # exit code
 0

The next demonstration captures a sequence of numbers orderly. The slot name
for C<IO::TieCombine> must be C<stdout> or C<stderr> for MCE->print to work.

 use MCE::Flow;
 use MCE::Candy;
 use IO::TieCombine;

 my $hub = IO::TieCombine->new;

 {
    tie local *STDOUT, $hub, 'stdout';

    MCE::Flow->init(
       max_workers => 4,
       chunk_size  => 500,
       bounds_only => 1,
       gather      => MCE::Candy::out_iter_fh(\*STDOUT),
    );

    mce_flow_s sub {
       my ($mce, $seq, $chunk_id) = @_;
       my $output = '';

       for my $n ( $seq->[0] .. $seq->[1] ) {
          $output .= "$n\n";
       }

       # do this if output order is not required
       # $mce->print(\*STDOUT, $output);

       # or this if preserving output order is desired
         $mce->gather($chunk_id, $output);

    }, 1, 100000;

    MCE::Flow->finish;
 }

 my $content = $hub->slot_contents('stdout');
 my $answer  = join("", map { "$_\n" } 1..100000);

 if ($content eq $answer) {
    print "ordered: yes\n";
 } else {
    print "ordered: no\n";
 }

 -- Output

 ordered: yes

=head1 CROSS-PLATFORM TEMPLATE FOR BINARY EXECUTABLE

Making an executable is possible with the L<PAR::Packer> module.
On the Windows platform, threads, threads::shared, and exiting via
threads are necessary for the binary to exit successfully.

 # https://metacpan.org/pod/PAR::Packer
 # https://metacpan.org/pod/pp
 #
 #   pp -o demo.exe demo.pl
 #   ./demo.exe

 use strict;
 use warnings;

 use if $^O eq "MSWin32", "threads";
 use if $^O eq "MSWin32", "threads::shared";

 use Time::HiRes (); # include minimum dependencies for MCE
 use Storable ();

 use IO::FDPass ();  # optional: for MCE::Shared->condvar, handle, queue
 use Sereal ();      # optional: faster serialization, may omit Storable

 use MCE;

 my $mce = MCE->new(
    max_workers => 4,
    user_func => sub {
       print "hello from ", MCE->wid(), "\n";
    }
 );

 $mce->run();

 threads->exit(0) if $INC{"threads.pm"};

With L<MCE::Shared> 1.808 and later releases, L<MCE::Hobo> works just
the same. The following compiles fine on UNIX and the Windows platform.

 # https://metacpan.org/pod/PAR::Packer
 # https://metacpan.org/pod/pp
 #
 #   pp -o demo.exe demo.pl
 #   ./demo.exe

 use strict;
 use warnings;

 use if $^O eq "MSWin32", "threads";
 use if $^O eq "MSWin32", "threads::shared";

 use Time::HiRes (); # include minimum dependencies for MCE::Hobo
 use Storable ();

 use IO::FDPass ();  # optional: for MCE::Shared->condvar, handle, queue
 use Sereal ();      # optional: faster serialization, may omit Storable

 use MCE::Hobo;      # 1.808 or later on Windows
 use MCE::Shared;

 my $seq_a = MCE::Shared->sequence( 1, 30 );

 sub task {
    my ( $id ) = @_;
    while ( defined ( my $num = $seq_a->next ) ) {
       print "$id: $num\n";
    }
 }

 MCE::Hobo->new( \&task, $_ ) for 1 .. 2;
 MCE::Hobo->waitall;

 threads->exit(0) if $INC{"threads.pm"};

=head1 FCGI::PROCMANAGER DEMONSTRATIONS

The demonstrations requires MCE 1.804 to run. Otherwise, the MCE C<posix_exit>
option must be specified and set to 1. This applies to UNIX only and set
automatically in 1.804 when C<(F)CGI.pm> is present.

 #!/usr/bin/perl

 # http://127.0.0.1/cgi-bin/test_mce1.fcgi
 # http://127.0.0.1/cgi-bin/test_mce1.fcgi?size=8

 use strict;
 use warnings;

 use MCE::Map max_workers => 3;

 use CGI::Fast;
 use FCGI::ProcManager;

 my $count = 0;

 my $proc_manager = FCGI::ProcManager->new({ n_processes => 4 });
 $proc_manager->pm_manage();

 while ( my $query = CGI::Fast->new() ) {
    $proc_manager->pm_pre_dispatch();

    print "Content-type: text/html\r\n\r\n";
    print "$$: ", ++$count, "<br>\n";
    print "<hr>\n";

    print "$_ = $ENV{$_}<br>\n" foreach sort keys %ENV;
    print "<hr>\n";

    my %params;

    foreach ( sort $query->param() ) {
       $params{$_} = $query->param($_);
       print $_, " = ", $params{$_}, "<br>\n";
    }

    print "<hr>\n";

    my @ret = mce_map { "$$: ".( $_ * 2 ) } 1 .. $params{'size'} || 8;

    print join("<br>\n", @ret), "<br>\n";

    $proc_manager->pm_post_dispatch();
 }

Initializing MCE options before calling C<pm_manage> is not recommended.
The following is one way to do it and does the same thing.

 #!/usr/bin/perl

 # http://127.0.0.1/cgi-bin/test_mce2.fcgi
 # http://127.0.0.1/cgi-bin/test_mce2.fcgi?size=8

 use strict;
 use warnings;

 use MCE::Map;

 use CGI::Fast;
 use FCGI::ProcManager;

 my ($first_time, $count) = (1, 0);

 my $proc_manager = FCGI::ProcManager->new({ n_processes => 4 });
 $proc_manager->pm_manage();

 while ( my $query = CGI::Fast->new() ) {
    $proc_manager->pm_pre_dispatch();

    print "Content-type: text/html\r\n\r\n";
    print "$$: ", ++$count, "<br>\n";
    print "<hr>\n";

    print "$_ = $ENV{$_}<br>\n" foreach sort keys %ENV;
    print "<hr>\n";

    my %params;

    foreach ( sort $query->param() ) {
       $params{$_} = $query->param($_);
       print $_, " = ", $params{$_}, "<br>\n";
    }

    print "<hr>\n";

    if ( $first_time ) {
       MCE::Map->init( max_workers => 3 );
    }

    my @ret = mce_map { "$$: ".( $_ * 2 ) } 1 .. $params{'size'} || 8;

    print join("<br>\n", @ret), "<br>\n";

    $proc_manager->pm_post_dispatch();
 }

Sharing data is possible via C<MCE::Shared> between C<FCGI> and C<MCE> workers.
The following is a demonstration utilizing a shared counter variable which
increments by one regardless of the C<FCGI> worker serving the request.

 #!/usr/bin/perl

 # http://127.0.0.1/cgi-bin/test_mce3.fcgi
 # http://127.0.0.1/cgi-bin/test_mce3.fcgi?size=8

 use strict;
 use warnings;

 use MCE::Map;
 use MCE::Shared;

 use CGI::Fast;
 use FCGI::ProcManager;

 # Shared variables must be defined before FCGI::ProcManager.
 my $count = MCE::Shared->scalar( 0 );
 my $first_time = 1;

 my $proc_manager = FCGI::ProcManager->new({ n_processes => 4 });
 $proc_manager->pm_manage();

 # Optional, the following statement must come after $pm->pm_manage.
 MCE::Shared->init(); # enables shared parallel-IPC capabilities

 while ( my $query = CGI::Fast->new() ) {
    $proc_manager->pm_pre_dispatch();

    print "Content-type: text/html\r\n\r\n";
    print "$$: ", $count->incr(), "<br>\n";
    print "<hr>\n";

    print "$_ = $ENV{$_}<br>\n" foreach sort keys %ENV;
    print "<hr>\n";

    my %params;

    foreach ( sort $query->param() ) {
       $params{$_} = $query->param($_);
       print $_, " = ", $params{$_}, "<br>\n";
    }

    print "<hr>\n";

    if ( $first_time ) {
       MCE::Map->init( max_workers => 3 );
       $first_time = 0;
    }

    my @ret = mce_map { "$$: ".( $_ * 2 ) } 1 .. $params{'size'} || 8;

    print join("<br>\n", @ret), "<br>\n";

    $proc_manager->pm_post_dispatch();
 }

Resetting the environment is helpful during development. The shared-manager
process stops immediately upon receiving the C<TERM> signal.

 killall -TERM perl-fcgi perl-fcgi-pm ; service httpd restart

=head1 TK DEMONSTRATIONS

The demonstrations requires MCE 1.805 to run. Otherwise, the MCE C<posix_exit>
option must be specified and set to 1. This applies to UNIX only and set
automatically in 1.805 when C<Tk.pm> is present.

 #!/usr/bin/perl

 use strict;
 use warnings;

 use MCE;
 use Tk;

 my $mw = MainWindow->new( -title => 'MCE/Tk Test' );

 $mw->geometry( '300x300' );
 $mw->Button( -text => "Test MCE", -command => \&test_mce )->pack();

 my $frame = $mw->Frame->pack( -fill => 'x' );

 my $mce = MCE->new(
    max_workers => 4,
    user_func => sub {
       my @args = @{ MCE->user_args() };
       print MCE->pid(), ": $_\n";
    },
 )->spawn;

 MainLoop;

 # Do not call $mce->shutdown on Windows ($^O eq 'MSWin32').
 # Workers terminate with the application.
 #
 # $mce->shutdown();

 print "Exiting...\n";

 sub test_mce {
    $mce->process({
       user_args  => [ 'arg1', 'arg2', 'argN' ],
       input_data => [ 1 .. 10 ],
       chunk_size => 1,
    });
 }

The following demonstration does the same thing via MCE::Flow.

 #!/usr/bin/perl

 use strict;
 use warnings;

 use MCE::Flow max_workers => 4;
 use Tk;

 my $mw = MainWindow->new( -title => 'MCE/Tk Test' );

 $mw->geometry( '300x300' );
 $mw->Button( -text => "Test MCE", -command => \&test_mce )->pack();

 my $frame = $mw->Frame->pack( -fill => 'x' );

 sub task {
    my @args = @{ MCE->user_args() };
    print MCE->pid(), ": $_\n";
 }

 MainLoop;

 print "Exiting...\n";

 sub test_mce {
    MCE::Flow->init(
       user_args  => [ 'arg1', 'arg2', 'argN' ],
       chunk_size => 1
    );
    MCE::Flow->run( \&task, [ 1 .. 10 ] );
 }

MCE::Hobo 1.804 or later is another possibility if running on a UNIX platform.

 #!/usr/bin/perl

 use strict;
 use warnings;

 use MCE::Hobo;
 use Tk;

 my $mw = MainWindow->new( -title => 'MCE/Tk Test' );

 $mw->geometry( '300x300' );
 $mw->Button( -text => "Test MCE", -command => \&test_mce )->pack();

 my $frame = $mw->Frame->pack( -fill => 'x' );

 sub task {
    my @args = @_;
    print MCE::Hobo->pid(), ": $_\n";
 }

 MainLoop;

 print "Exiting...\n";

 sub test_mce {
    MCE::Hobo->create(\&task, 'arg1', 'arg2', 'argN') for ( 1 .. 4 );
    MCE::Hobo->waitall();
 }

=head1 INDEX

L<MCE|MCE>, L<MCE::Core>

=head1 AUTHOR

Mario E. Roy, S<E<lt>marioeroy AT gmail DOT comE<gt>>

=cut