Mario Roy > MCE > MCE::Grep

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Module Version: 1.515   Source  

NAME ^

MCE::Grep - Parallel grep model similar to the native grep function

VERSION ^

This document describes MCE::Grep version 1.515

SYNOPSIS ^

   ## Exports mce_grep, mce_grep_f, and mce_grep_s
   use MCE::Grep;

   ## Array or array_ref
   my @a = mce_grep { $_ % 5 == 0 } 1..10000;
   my @b = mce_grep { $_ % 5 == 0 } [ 1..10000 ];

   ## File_path, glob_ref, or scalar_ref
   my @c = mce_grep_f { /phrase/ } "/path/to/file";
   my @d = mce_grep_f { /phrase/ } $file_handle;
   my @e = mce_grep_f { /phrase/ } \$scalar;

   ## Sequence of numbers (begin, end [, step, format])
   my @f = mce_grep_s { %_ * 3 == 0 } 1, 10000, 5;
   my @g = mce_grep_s { %_ * 3 == 0 } [ 1, 10000, 5 ];

   my @h = mce_grep_s { %_ * 3 == 0 } {
      begin => 1, end => 10000, step => 5, format => undef
   };

DESCRIPTION ^

This module provides a parallel grep implementation via Many-core Engine. MCE incurs a small overhead due to passing of data. Therefore, a fast code block will likely run faster using the native grep function in Perl. The overhead quickly diminishes as the complexity of the code block increases.

   my @m1 =     grep { $_ % 5 == 0 } 1..1000000;          ## 0.137 secs
   my @m2 = mce_grep { $_ % 5 == 0 } 1..1000000;          ## 0.295 secs

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

   my @m1 =     grep { /[2357][1468][9]/ } 1..1000000;    ## 0.653 secs
   my @m2 = mce_grep { /[2357][1468][9]/ } 1..1000000;    ## 0.347 secs

The mce_grep_s function will provide better times, useful when the input data is simply a range of numbers. Workers generate sequences mathematically among themselves without any interaction from the manager process. Two arguments are required for mce_grep_s (begin, end). Step defaults to 1 if begin is smaller than end, otherwise -1.

   my @m3 = mce_grep_s { /[2357][1468][9]/ } 1, 1000000;  ## 0.271 secs

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

   use MCE::Stream default_mode => 'grep';

   my @m4; mce_stream \@m4, sub { /[2357][1468][9]/ }, 1..1000000;

      ## Completed in 0.304 secs. That is amazing considering the
      ## overhead for passing data between the manager and worker.

   my @m5; mce_stream_s \@m5, sub { /[2357][1468][9]/ }, 1, 1000000;

      ## Completed in 0.227 secs. Like with mce_grep_s, specifying a
      ## sequence specification turns out to be faster due to lesser
      ## overhead for the manager process.

A good use-case for MCE::Grep is for searching through a large log file much like one might do using the native grep function. Lets assume the file contains a hundred thousand records separated by a string "::\n\n" between each record. The imaginary pattern used also returns less than 50 records.

The native implementation is what one might do actually. What's not clearly visible here is the initial memory consumption, due to Perl reading the entire content into memory, prior to grep actually starting. A 300 MB file will consume roughly 640 MB. The time to run is 1.217 seconds for the file residing in the OS-level file-system cache.

   $/ = "::\n\n";

   open my $LOG, "<", "/path/to/log/file";
   my @match = grep { $_ =~ /pattern/ } <$LOG>;
   close $LOG;

The memory utilization is much better with MCE; 8 workers * 23 MB = 184 MB. MCE caps at some point, therefore allowing one to process a file much larger than available memory. The time to run is 0.416 seconds (2.93x faster) which includes the overhead for chunking and serializing data back to the main process as if processing serially.

   use MCE::Grep;

   MCE::Grep::init { RS => "::\n\n" };

   my @match = mce_grep_f { $_ =~ /pattern/ } "/path/to/file";

It gets even better for counting though. The native grep function takes 1.136 seconds to run whereas MCE takes just 0.155 seconds (7.33x faster).

   ## Native Grep
   my $count = grep { $_ =~ /pattern/ } <$LOG>;

   ## MCE Grep
   my $count = mce_grep_f { $_ =~ /pattern/ } "/path/to/file";

OVERRIDING DEFAULTS ^

The following list 5 options which may be overridden when loading the module.

   use Sereal qw(encode_sereal decode_sereal);

   use MCE::Grep
         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
   ;

There is a simpler way to enable Sereal with MCE 1.5. The following will attempt to use Sereal if available, otherwise will default back to using Storable for serialization.

   use MCE::Grep Sereal => 1;

   ## Serialization is through Sereal if available.
   my @m2 = mce_grep { $_ % 5 == 0 } 1..10000;

CUSTOMIZING MCE ^

init

The init function accepts a hash of MCE options. The gather option, if specified, will be set to undef due to being used internally by the module.

   use MCE::Grep;

   MCE::Grep::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_grep { $_ % 5 == 0 } 1..100;

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

   -- Output

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

   5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

API DOCUMENTATION ^

mce_grep { code } list

Input data can be defined using a list or passing a reference to an array.

   my @a = mce_grep { /[2357]/ } 1..1000;
   my @b = mce_grep { /[2357]/ } [ 1..1000 ];
mce_grep_f { code } file

The fastest of these is the /path/to/file. Workers communicate the next offset position among themselves without any interaction from the manager process.

   my @c = mce_grep_f { /phrase/ } "/path/to/file";
   my @d = mce_grep_f { /phrase/ } $file_handle;
   my @e = mce_grep_f { /phrase/ } \$scalar;
mce_grep_s { code } sequence

Sequence can 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_grep_s { /[1234]\.[5678]/ } $beg, $end, $step, $fmt;
   my @g = mce_grep_s { /[1234]\.[5678]/ } [ $beg, $end, $step, $fmt ];

   my @h = mce_grep_s { /[1234]\.[5678]/ } {
      begin => $beg, end => $end, step => $step, format => $fmt
   };
mce_grep { code } iterator

An iterator reference can by specified for input data. Iterators are described under "SYNTAX for INPUT_DATA" at MCE::Core.

   my @a = mce_grep { $_ % 3 == 0 } make_iterator(10, 30, 2);

MANUAL SHUTDOWN ^

finish

MCE workers remain persistent as much as possible after running. Shutdown occurs when the script exits. One can manually shutdown MCE by simply calling finish after running. This resets the MCE instance.

   use MCE::Grep;

   MCE::Grep::init {
      chunk_size => 20, max_workers => 'auto'
   };

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

   MCE::Grep::finish;

INDEX ^

MCE

AUTHOR ^

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

LICENSE ^

This program is free software; you can redistribute it and/or modify it under the terms of either: the GNU General Public License as published by the Free Software Foundation; or the Artistic License.

See http://dev.perl.org/licenses/ for more information.

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