/ 
MCE-1.898
River stage three • 22 direct dependents • 319 total dependents
/ MCE::Map

NAME

MCE::Map - Parallel map model similar to the native map function

VERSION

This document describes MCE::Map version 1.898

SYNOPSIS

## Exports mce_map, mce_map_f, and mce_map_s
use MCE::Map;

## Array or array_ref
my @a = mce_map { $_ * $_ } 1..10000;
my @b = mce_map { $_ * $_ } \@list;

## Important; pass an array_ref for deeply input data
my @c = mce_map { $_->[1] *= 2; $_ } [ [ 0, 1 ], [ 0, 2 ], ... ];
my @d = mce_map { $_->[1] *= 2; $_ } \@deeply_list;

## File path, glob ref, IO::All::{ File, Pipe, STDIO } obj, or scalar ref
## Workers read directly and not involve the manager process
my @e = mce_map_f { chomp; $_ } "/path/to/file"; # efficient

## Involves the manager process, therefore slower
my @f = mce_map_f { chomp; $_ } $file_handle;
my @g = mce_map_f { chomp; $_ } $io;
my @h = mce_map_f { chomp; $_ } \$scalar;

## Sequence of numbers (begin, end [, step, format])
my @i = mce_map_s { $_ * $_ } 1, 10000, 5;
my @j = mce_map_s { $_ * $_ } [ 1, 10000, 5 ];

my @k = mce_map_s { $_ * $_ } {
   begin => 1, end => 10000, step => 5, format => undef
};

DESCRIPTION

This module provides a parallel map implementation via Many-Core Engine. MCE incurs a small overhead due to passing of data. A fast code block will run faster natively. However, the overhead will likely diminish as the complexity increases for the code.

my @m1 =     map { $_ * $_ } 1..1000000;               ## 0.127 secs
my @m2 = mce_map { $_ * $_ } 1..1000000;               ## 0.304 secs

Chunking, enabled by default, greatly reduces the overhead behind the scene. The time for mce_map below also includes the time for data exchanges between the manager and worker processes. More parallelization will be seen when the code incurs additional CPU time.

sub calc {
   sqrt $_ * sqrt $_ / 1.3 * 1.5 / 3.2 * 1.07
}

my @m1 =     map { calc } 1..1000000;                  ## 0.367 secs
my @m2 = mce_map { calc } 1..1000000;                  ## 0.365 secs

Even faster is mce_map_s; useful when input data is a range of numbers. Workers generate sequences mathematically among themselves without any interaction from the manager process. Two arguments are required for mce_map_s (begin, end). Step defaults to 1 if begin is smaller than end, otherwise -1.

my @m3 = mce_map_s { calc } 1, 1000000;                ## 0.270 secs

Although this document is about MCE::Map, the MCE::Stream module can write results immediately without waiting for all chunks to complete. This is made possible by passing the reference to an array (in this case @m4 and @m5).

use MCE::Stream;

sub calc {
   sqrt $_ * sqrt $_ / 1.3 * 1.5 / 3.2 * 1.07
}

my @m4; mce_stream \@m4, sub { calc }, 1..1000000;

   ## Completes in 0.272 secs. This is amazing considering the
   ## overhead for passing data between the manager and workers.

my @m5; mce_stream_s \@m5, sub { calc }, 1, 1000000;

   ## Completed in 0.176 secs. Like with mce_map_s, specifying a
   ## sequence specification turns out to be faster due to lesser
   ## overhead for the manager process.

OVERRIDING DEFAULTS

The following list options which may be overridden when loading the module.

use Sereal qw( encode_sereal decode_sereal );
use CBOR::XS qw( encode_cbor decode_cbor );
use JSON::XS qw( encode_json decode_json );

use MCE::Map
    max_workers => 4,                # Default 'auto'
    chunk_size => 100,               # Default 'auto'
    tmp_dir => "/path/to/app/tmp",   # $MCE::Signal::tmp_dir
    freeze => \&encode_sereal,       # \&Storable::freeze
    thaw => \&decode_sereal,         # \&Storable::thaw
    init_relay => 0,                 # Default undef; MCE 1.882+
    use_threads => 0,                # Default undef; MCE 1.882+
;

From MCE 1.8 onwards, Sereal 3.015+ is loaded automatically if available. Specify Sereal => 0 to use Storable instead.

use MCE::Map Sereal => 0;

CUSTOMIZING MCE

MCE::Map->init ( options )
MCE::Map::init { options }

The init function accepts a hash of MCE options. The gather option, if specified, is ignored due to being used internally by the module.

In scalar context (API available since 1.897), call MCE::Map-finish> automatically upon leaving the scope or program.

use MCE::Map;

my $guard = MCE::Map->init(
   chunk_size => 1, max_workers => 4,

   user_begin => sub {
      print "## ", MCE->wid, " started\n";
   },

   user_end => sub {
      print "## ", MCE->wid, " completed\n";
   }
);

my @a = mce_map { $_ * $_ } 1..100;

print "\n", "@a", "\n";

-- Output

## 2 started
## 1 started
## 3 started
## 4 started
## 1 completed
## 4 completed
## 2 completed
## 3 completed

1 4 9 16 25 36 49 64 81 100 121 144 169 196 225 256 289 324 361
400 441 484 529 576 625 676 729 784 841 900 961 1024 1089 1156
1225 1296 1369 1444 1521 1600 1681 1764 1849 1936 2025 2116 2209
2304 2401 2500 2601 2704 2809 2916 3025 3136 3249 3364 3481 3600
3721 3844 3969 4096 4225 4356 4489 4624 4761 4900 5041 5184 5329
5476 5625 5776 5929 6084 6241 6400 6561 6724 6889 7056 7225 7396
7569 7744 7921 8100 8281 8464 8649 8836 9025 9216 9409 9604 9801
10000

API DOCUMENTATION

MCE::Map->run ( sub { code }, list )
mce_map { code } list

Input data may be defined using a list or an array reference. Unlike MCE::Loop, Flow, and Step, specifying a hash reference as input data isn't allowed.

## Array or array_ref
my @a = mce_map { $_ * 2 } 1..1000;
my @b = mce_map { $_ * 2 } \@list;

## Important; pass an array_ref for deeply input data
my @c = mce_map { $_->[1] *= 2; $_ } [ [ 0, 1 ], [ 0, 2 ], ... ];
my @d = mce_map { $_->[1] *= 2; $_ } \@deeply_list;

## Not supported
my @z = mce_map { ... } \%hash;
MCE::Map->run_file ( sub { code }, file )
mce_map_f { code } file

The fastest of these is the /path/to/file. Workers communicate the next offset position among themselves with zero interaction by the manager process.

IO::All { File, Pipe, STDIO } is supported since MCE 1.845.

my @c = mce_map_f { chomp; $_ . "\r\n" } "/path/to/file";  # faster
my @d = mce_map_f { chomp; $_ . "\r\n" } $file_handle;
my @e = mce_map_f { chomp; $_ . "\r\n" } $io;              # IO::All
my @f = mce_map_f { chomp; $_ . "\r\n" } \$scalar;
MCE::Map->run_seq ( sub { code }, $beg, $end [, $step, $fmt ] )
mce_map_s { code } $beg, $end [, $step, $fmt ]

Sequence may be defined as a list, an array reference, or a hash reference. The functions require both begin and end values to run. Step and format are optional. The format is passed to sprintf (% may be omitted below).

my ($beg, $end, $step, $fmt) = (10, 20, 0.1, "%4.1f");

my @f = mce_map_s { $_ } $beg, $end, $step, $fmt;
my @g = mce_map_s { $_ } [ $beg, $end, $step, $fmt ];

my @h = mce_map_s { $_ } {
   begin => $beg, end => $end,
   step => $step, format => $fmt
};
MCE::Map->run ( sub { code }, iterator )
mce_map { code } iterator

An iterator reference may be specified for input_data. Iterators are described under section "SYNTAX for INPUT_DATA" at MCE::Core.

my @a = mce_map { $_ * 2 } make_iterator(10, 30, 2);

MANUAL SHUTDOWN

MCE::Map->finish
MCE::Map::finish

Workers remain persistent as much as possible after running. Shutdown occurs automatically when the script terminates. Call finish when workers are no longer needed.

use MCE::Map;

MCE::Map->init(
   chunk_size => 20, max_workers => 'auto'
);

my @a = mce_map { ... } 1..100;

MCE::Map->finish;

INDEX

MCE, MCE::Core

AUTHOR

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