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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 "::

"
       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.

          $/ = "::

";

          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 => "::

" };

          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
";
                },

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

             my @a = mce_grep { $_ % 5 == 0 } 1..100;

             print "
", "@a", "
";

             -- 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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