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MCE::Candy(3) User Contributed Perl Documentation MCE::Candy(3)
 

MCE::Candy - Sugar methods and output iterators

This document describes MCE::Candy version 1.837

This module provides a collection of sugar methods and helpful output iterators for preserving output order.

The sugar methods described below were created prior to the 1.5 release which added MCE Models. This module is loaded automatically upon calling a "for" method.

Forchunk, foreach, and forseq are sugar methods in MCE. Workers are spawned automatically, the code block is executed in parallel, and shutdown is called. Do not call these methods if workers must persist afterwards.
Specifying options is optional. Valid options are the same as for the process method.
 ## Declare a MCE instance.
 my $mce = MCE->new(
    max_workers => $max_workers,
    chunk_size  => 20
 );
 ## Arguments inside the code block are the same as passed to user_func.
 $mce->forchunk(\@input_array, sub {
    my ($mce, $chunk_ref, $chunk_id) = @_;
    foreach ( @{ $chunk_ref } ) {
       MCE->print("$chunk_id: $_\n");
    }
 });
 ## Input hash, current API available since 1.828.
 $mce->forchunk(\%input_hash, sub {
    my ($mce, $chunk_ref, $chunk_id) = @_;
    for my $key ( keys %{ $chunk_ref } ) {
       MCE->print("$chunk_id: [ $key ] ", $chunk_ref->{$key}, "\n");
    }
 });
 ## Passing chunk_size as an option.
 $mce->forchunk(\@input_array, { chunk_size => 30 }, sub { ... });
 $mce->forchunk(\%input_hash, { chunk_size => 30 }, sub { ... });

Foreach implies chunk_size => 1 and cannot be overwritten. Thus, looping is not necessary inside the block. Unlike forchunk above, a hash reference as input data isn't allowed.
 my $mce = MCE->new(
    max_workers => $max_workers
 );
 $mce->foreach(\@input_data, sub {
    my ($mce, $chunk_ref, $chunk_id) = @_;
    my $row = $chunk_ref->[0];
    MCE->print("$chunk_id: $row\n");
 });

Sequence may be defined using an array or hash reference.
 my $mce = MCE->new(
    max_workers => 3
 );
 $mce->forseq([ 20, 40 ], sub {
    my ($mce, $n, $chunk_id) = @_;
    my $result = `ping 192.168.1.${n}`;
    ...
 });
 $mce->forseq({ begin => 15, end => 10, step => -1 }, sub {
    my ($mce, $n, $chunk_id) = @_;
    print $n, " from ", MCE->wid, "\n";
 });
The $n_seq variable points to an array_ref of sequences. Chunk size defaults to 1 when not specified.
 $mce->forseq([ 20, 80 ], { chunk_size => 10 }, sub {
    my ($mce, $n_seq, $chunk_id) = @_;
    for my $n ( @{ $n_seq } ) {
       my $result = `ping 192.168.1.${n}`;
       ...
    }
 });

This module includes 2 output iterators which are useful for preserving output order while gathering data. These cover the 2 general use cases. The chunk_id value must be the first argument to gather. Gather must also not be called more than once inside the block.

The example utilizes the Core API with chunking disabled. Basically, setting chunk_size to 1.
 use MCE;
 use MCE::Candy;
 my @results;
 my $mce = MCE->new(
    chunk_size => 1, max_workers => 4,
    gather => MCE::Candy::out_iter_array(\@results),
    user_func => sub {
       my ($mce, $chunk_ref, $chunk_id) = @_;
       $mce->gather($chunk_id, $chunk_ref->[0] * 2);
    }
 );
 $mce->process([ 100 .. 109 ]);
 print "@results", "\n";
 -- Output
 200 202 204 206 208 210 212 214 216 218
Chunking may be desired for thousands or more items. In other words, wanting to reduce the overhead placed on IPC.
 use MCE;
 use MCE::Candy;
 my @results;
 my $mce = MCE->new(
    chunk_size => 100, max_workers => 4,
    gather => MCE::Candy::out_iter_array(\@results),
    user_func => sub {
       my ($mce, $chunk_ref, $chunk_id) = @_;
       my @output;
       foreach my $item (@{ $chunk_ref }) {
          push @output, $item * 2;
       }
       $mce->gather($chunk_id, @output);
    }
 );
 $mce->process([ 100_000 .. 200_000 - 1 ]);
 print scalar @results, "\n";
 -- Output
 100000

Let's change things a bit and use MCE::Flow for the next 2 examples. Chunking is not desired for the first example.
 use MCE::Flow;
 use MCE::Candy;
 open my $fh, '>', '/tmp/foo.txt';
 mce_flow {
    chunk_size => 1, max_workers => 4,
    gather => MCE::Candy::out_iter_fh($fh)
 },
 sub {
    my ($mce, $chunk_ref, $chunk_id) = @_;
    $mce->gather($chunk_id, $chunk_ref->[0] * 2, "\n");
 }, (100 .. 109);
 close $fh;
 -- Output sent to '/tmp/foo.txt'
 200
 202
 204
 206
 208
 210
 212
 214
 216
 218
Chunking is desired for the next example due to processing many thousands.
 use MCE::Flow;
 use MCE::Candy;
 open my $fh, '>', '/tmp/foo.txt';
 mce_flow {
    chunk_size => 100, max_workers => 4,
    gather => MCE::Candy::out_iter_fh( $fh )
 },
 sub {
    my ($mce, $chunk_ref, $chunk_id) = @_;
    my @output;
    foreach my $item (@{ $chunk_ref }) {
       push @output, ($item * 2) . "\n";
    }
    $mce->gather($chunk_id, @output);
 }, (100_000 .. 200_000 - 1);
 close $fh;
 print -s '/tmp/foo.txt', "\n";
 -- Output
 700000

Input data is not a requirement for using the output iterators included in this module. The 'chunk_id' value is set uniquely and the same as 'wid' when not processing input data.

 use MCE::Flow;
 use MCE::Candy;
 my @results;
 mce_flow {
    max_workers => 'auto', ## Note that 'auto' is never higher than 8
    gather => MCE::Candy::out_iter_array(\@results)
 },
 sub {
    my ($mce) = @_;        ## This line is not necessary
                           ## Calling via module okay; e.g: MCE->method
    ## Do work
    ## Sending a complex data structure is allowed
    ## Output will become orderly by iterator
    $mce->gather( $mce->chunk_id, {
       wid => $mce->wid, result => $mce->wid * 2
    });
 };
 foreach my $href (@results) {
    print $href->{wid} .": ". $href->{result} ."\n";
 }
 -- Output
 1: 2
 2: 4
 3: 6
 4: 8
 5: 10
 6: 12
 7: 14
 8: 16

 use MCE::Flow;
 use MCE::Candy;
 open my $fh, '>', '/tmp/out.txt';
 mce_flow {
    max_workers => 'auto', ## See get_ncpu in <MCE::Util|MCE::Util> 
    gather => MCE::Candy::out_iter_fh($fh)
 },
 sub {
    my $output = "# Worker ID: " . MCE->wid . "\n";
    ## Append results to $output string
    $output .= (MCE->wid * 2) . "\n\n";
    ## Output will become orderly by iterator
    MCE->gather( MCE->wid, $output );
 };
 close $fh;
 -- Output
 # Worker ID: 1
 2
 # Worker ID: 2
 4
 # Worker ID: 3
 6
 # Worker ID: 4
 8
 # Worker ID: 5
 10
 # Worker ID: 6
 12
 # Worker ID: 7
 14
 # Worker ID: 8
 16

MCE, MCE::Core

Mario E. Roy, <marioeroy AT gmail DOT com>
2018-08-25 perl v5.28.1

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