Provided by: libmce-perl_1.833-1_all 
NAME
MCE::Grep - Parallel grep model similar to the native grep function
VERSION
This document describes MCE::Grep version 1.833
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 { /pattern/ } "/path/to/file";
my @d = mce_grep_f { /pattern/ } $file_handle;
my @e = mce_grep_f { /pattern/ } \$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. A fast code block will run faster natively.
However, the overhead will likely diminish as the complexity increases for the code.
my @m1 = grep { $_ % 5 == 0 } 1..1000000; ## 0.065 secs
my @m2 = mce_grep { $_ % 5 == 0 } 1..1000000; ## 0.194 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 incurs additional CPU time.
my @m1 = grep { /[2357][1468][9]/ } 1..1000000; ## 0.353 secs
my @m2 = mce_grep { /[2357][1468][9]/ } 1..1000000; ## 0.218 secs
Even faster is mce_grep_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_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; ## 0.165 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 to an 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 0.203 secs. This is amazing considering the
## overhead for passing data between the manager and workers.
my @m5; mce_stream_s \@m5, sub { /[2357][1468][9]/ }, 1, 1000000;
## Completed in 0.120 secs. Like with mce_grep_s, specifying a
## sequence specification turns out to be faster due to lesser
## overhead for the manager process.
A common scenario is grepping for pattern(s) inside a massive log file. Notice how
parallelism increases as complexity increases for the pattern. Testing was done against a
300 MB file containing 250k lines.
use MCE::Grep;
my @m; open my $LOG, "<", "/path/to/log/file" or die "$!\n";
@m = grep { /pattern/ } <$LOG>; ## 0.756 secs
@m = grep { /foobar|[2357][1468][9]/ } <$LOG>; ## 24.681 secs
## Parallelism with mce_grep. This involves the manager process
## due to processing a file handle.
@m = mce_grep { /pattern/ } <$LOG>; ## 0.997 secs
@m = mce_grep { /foobar|[2357][1468][9]/ } <$LOG>; ## 7.439 secs
## Even faster with mce_grep_f. Workers access the file directly
## with zero interaction from the manager process.
my $LOG = "/path/to/file";
@m = mce_grep_f { /pattern/ } $LOG; ## 0.112 secs
@m = mce_grep_f { /foobar|[2357][1468][9]/ } $LOG; ## 6.840 secs
PARSING HUGE FILES
The MCE::Grep module lacks an optimization for quickly determining if a match is found
from not knowing the pattern inside the code block. Use the following snippet as a
template to achieve better performance. Also, take a look at examples/egrep.pl, included
with the distribution.
use MCE::Loop;
MCE::Loop::init {
max_workers => 8, use_slurpio => 1
};
my $pattern = 'karl';
my $hugefile = 'very_huge.file';
my @result = mce_loop_f {
my ($mce, $slurp_ref, $chunk_id) = @_;
## Quickly determine if a match is found.
## Process slurped chunk only if true.
if ($$slurp_ref =~ /$pattern/m) {
my @matches;
## The following is fast on Unix. Performance degrades
## drastically on Windows beyond 4 workers.
open my $MEM_FH, '<', $slurp_ref;
binmode $MEM_FH, ':raw';
while (<$MEM_FH>) { push @matches, $_ if (/$pattern/); }
close $MEM_FH;
## Therefore, use the following construct on Windows.
while ( $$slurp_ref =~ /([^\n]+\n)/mg ) {
my $line = $1; # save $1 to not lose the value
push @matches, $line if ($line =~ /$pattern/);
}
## Gather matched lines.
MCE->gather(@matches);
}
} $hugefile;
print join('', @result);
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::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
;
From MCE 1.8 onwards, Sereal 3.015+ is loaded automatically if available. Specify "Sereal
=" 0> to use Storable instead.
use MCE::Grep Sereal => 0;
CUSTOMIZING MCE
MCE::Grep->init ( options )
MCE::Grep::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.
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->run ( sub { code }, list )
mce_grep { 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.
my @a = mce_grep { /[2357]/ } 1..1000;
my @b = mce_grep { /[2357]/ } \@list;
my @z = mce_grep { /[2357]/ } \%hash; # not supported
MCE::Grep->run_file ( sub { code }, file )
mce_grep_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.
my @c = mce_grep_f { /pattern/ } "/path/to/file"; # faster
my @d = mce_grep_f { /pattern/ } $file_handle;
my @e = mce_grep_f { /pattern/ } \$scalar;
MCE::Grep->run_seq ( sub { code }, $beg, $end [, $step, $fmt ] )
mce_grep_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_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->run ( sub { code }, iterator )
mce_grep { 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_grep { $_ % 3 == 0 } make_iterator(10, 30, 2);
MANUAL SHUTDOWN
MCE::Grep->finish
MCE::Grep::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::Grep;
MCE::Grep::init {
chunk_size => 20, max_workers => 'auto'
};
my @a = mce_grep { ... } 1..100;
MCE::Grep::finish;
INDEX
MCE, MCE::Core
AUTHOR
Mario E. Roy, <marioeroy AT gmail DOT com>