1MCE::Grep(3) User Contributed Perl Documentation MCE::Grep(3)
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6 MCE::Grep - Parallel grep model similar to the native grep function
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9 This document describes MCE::Grep version 1.874
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12 ## Exports mce_grep, mce_grep_f, and mce_grep_s
13 use MCE::Grep;
14 ## Array or array_ref
16 my @a = mce_grep { $_ % 5 == 0 } 1..10000;
17 my @b = mce_grep { $_ % 5 == 0 } \@list;
18 ## Important; pass an array_ref for deeply input data
20 my @c = mce_grep { $_->[1] % 2 == 0 } [ [ 0, 1 ], [ 0, 2 ], ... ];
21 my @d = mce_grep { $_->[1] % 2 == 0 } \@deeply_list;
22 ## File path, glob ref, IO::All::{ File, Pipe, STDIO } obj, or scalar ref
24 ## Workers read directly and not involve the manager process
25 my @e = mce_grep_f { /pattern/ } "/path/to/file"; # efficient
26 ## Involves the manager process, therefore slower
28 my @f = mce_grep_f { /pattern/ } $file_handle;
29 my @g = mce_grep_f { /pattern/ } $io;
30 my @h = mce_grep_f { /pattern/ } \$scalar;
31 ## Sequence of numbers (begin, end [, step, format])
33 my @i = mce_grep_s { %_ * 3 == 0 } 1, 10000, 5;
34 my @j = mce_grep_s { %_ * 3 == 0 } [ 1, 10000, 5 ];
35 my @k = mce_grep_s { %_ * 3 == 0 } {
37 begin => 1, end => 10000, step => 5, format => undef
38 };
39
41 This module provides a parallel grep implementation via Many-Core
42 Engine. MCE incurs a small overhead due to passing of data. A fast
43 code block will run faster natively. However, the overhead will likely
44 diminish as the complexity increases for the code.
45 my @m1 = grep { $_ % 5 == 0 } 1..1000000; ## 0.065 secs
47 my @m2 = mce_grep { $_ % 5 == 0 } 1..1000000; ## 0.194 secs
48 Chunking, enabled by default, greatly reduces the overhead behind the
50 scene. The time for mce_grep below also includes the time for data
51 exchanges between the manager and worker processes. More
52 parallelization will be seen when the code incurs additional CPU time.
53 my @m1 = grep { /[2357][1468][9]/ } 1..1000000; ## 0.353 secs
55 my @m2 = mce_grep { /[2357][1468][9]/ } 1..1000000; ## 0.218 secs
56 Even faster is mce_grep_s; useful when input data is a range of
58 numbers. Workers generate sequences mathematically among themselves
59 without any interaction from the manager process. Two arguments are
60 required for mce_grep_s (begin, end). Step defaults to 1 if begin is
61 smaller than end, otherwise -1.
62 my @m3 = mce_grep_s { /[2357][1468][9]/ } 1, 1000000; ## 0.165 secs
64 Although this document is about MCE::Grep, the MCE::Stream module can
66 write results immediately without waiting for all chunks to complete.
67 This is made possible by passing the reference to an array (in this
68 case @m4 and @m5).
69 use MCE::Stream default_mode => 'grep';
71 my @m4; mce_stream \@m4, sub { /[2357][1468][9]/ }, 1..1000000;
73 ## Completed in 0.203 secs. This is amazing considering the
75 ## overhead for passing data between the manager and workers.
76 my @m5; mce_stream_s \@m5, sub { /[2357][1468][9]/ }, 1, 1000000;
78 ## Completed in 0.120 secs. Like with mce_grep_s, specifying a
80 ## sequence specification turns out to be faster due to lesser
81 ## overhead for the manager process.
82 A common scenario is grepping for pattern(s) inside a massive log file.
84 Notice how parallelism increases as complexity increases for the
85 pattern. Testing was done against a 300 MB file containing 250k lines.
86 use MCE::Grep;
88 my @m; open my $LOG, "<", "/path/to/log/file" or die "$!\n";
90 @m = grep { /pattern/ } <$LOG>; ## 0.756 secs
92 @m = grep { /foobar|[2357][1468][9]/ } <$LOG>; ## 24.681 secs
93 ## Parallelism with mce_grep. This involves the manager process
95 ## due to processing a file handle.
96 @m = mce_grep { /pattern/ } <$LOG>; ## 0.997 secs
98 @m = mce_grep { /foobar|[2357][1468][9]/ } <$LOG>; ## 7.439 secs
99 ## Even faster with mce_grep_f. Workers access the file directly
101 ## with zero interaction from the manager process.
102 my $LOG = "/path/to/file";
104 @m = mce_grep_f { /pattern/ } $LOG; ## 0.112 secs
105 @m = mce_grep_f { /foobar|[2357][1468][9]/ } $LOG; ## 6.840 secs
106
108 The MCE::Grep module lacks an optimization for quickly determining if a
109 match is found from not knowing the pattern inside the code block. Use
110 the following snippet as a template to achieve better performance.
111 Also, take a look at examples/egrep.pl, included with the distribution.
112 use MCE::Loop;
114 MCE::Loop->init(
116 max_workers => 8, use_slurpio => 1
117 );
118 my $pattern = 'karl';
120 my $hugefile = 'very_huge.file';
121 my @result = mce_loop_f {
123 my ($mce, $slurp_ref, $chunk_id) = @_;
124 ## Quickly determine if a match is found.
126 ## Process slurped chunk only if true.
127 if ($$slurp_ref =~ /$pattern/m) {
129 my @matches;
130 ## The following is fast on Unix. Performance degrades
132 ## drastically on Windows beyond 4 workers.
133 open my $MEM_FH, '<', $slurp_ref;
135 binmode $MEM_FH, ':raw';
136 while (<$MEM_FH>) { push @matches, $_ if (/$pattern/); }
137 close $MEM_FH;
138 ## Therefore, use the following construct on Windows.
140 while ( $$slurp_ref =~ /([^\n]+\n)/mg ) {
142 my $line = $1; # save $1 to not lose the value
143 push @matches, $line if ($line =~ /$pattern/);
144 }
145 ## Gather matched lines.
147 MCE->gather(@matches);
149 }
150 } $hugefile;
152 print join('', @result);
154
156 The following list options which may be overridden when loading the
157 module.
158 use Sereal qw( encode_sereal decode_sereal );
160 use CBOR::XS qw( encode_cbor decode_cbor );
161 use JSON::XS qw( encode_json decode_json );
162 use MCE::Grep
164 max_workers => 4, # Default 'auto'
165 chunk_size => 100, # Default 'auto'
166 tmp_dir => "/path/to/app/tmp", # $MCE::Signal::tmp_dir
167 freeze => \&encode_sereal, # \&Storable::freeze
168 thaw => \&decode_sereal # \&Storable::thaw
169 ;
170 From MCE 1.8 onwards, Sereal 3.015+ is loaded automatically if
172 available. Specify "Sereal => 0" to use Storable instead.
173 use MCE::Grep Sereal => 0;
175
177 MCE::Grep->init ( options )
178 MCE::Grep::init { options }
179 The init function accepts a hash of MCE options. The gather option, if
181 specified, is ignored due to being used internally by the module.
182 use MCE::Grep;
184 MCE::Grep->init(
186 chunk_size => 1, max_workers => 4,
187 user_begin => sub {
189 print "## ", MCE->wid, " started\n";
190 },
191 user_end => sub {
193 print "## ", MCE->wid, " completed\n";
194 }
195 );
196 my @a = mce_grep { $_ % 5 == 0 } 1..100;
198 print "\n", "@a", "\n";
200 -- Output
202 ## 2 started
204 ## 3 started
205 ## 1 started
206 ## 4 started
207 ## 3 completed
208 ## 4 completed
209 ## 1 completed
210 ## 2 completed
211 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
213
215 MCE::Grep->run ( sub { code }, list )
216 mce_grep { code } list
217 Input data may be defined using a list or an array reference. Unlike
219 MCE::Loop, Flow, and Step, specifying a hash reference as input data
220 isn't allowed.
221 ## Array or array_ref
223 my @a = mce_grep { /[2357]/ } 1..1000;
224 my @b = mce_grep { /[2357]/ } \@list;
225 ## Important; pass an array_ref for deeply input data
227 my @c = mce_grep { $_->[1] =~ /[2357]/ } [ [ 0, 1 ], [ 0, 2 ], ... ];
228 my @d = mce_grep { $_->[1] =~ /[2357]/ } \@deeply_list;
229 ## Not supported
231 my @z = mce_grep { ... } \%hash;
232 MCE::Grep->run_file ( sub { code }, file )
234 mce_grep_f { code } file
235 The fastest of these is the /path/to/file. Workers communicate the next
237 offset position among themselves with zero interaction by the manager
238 process.
239 "IO::All" { File, Pipe, STDIO } is supported since MCE 1.845.
241 my @c = mce_grep_f { /pattern/ } "/path/to/file"; # faster
243 my @d = mce_grep_f { /pattern/ } $file_handle;
244 my @e = mce_grep_f { /pattern/ } $io; # IO::All
245 my @f = mce_grep_f { /pattern/ } \$scalar;
246 MCE::Grep->run_seq ( sub { code }, $beg, $end [, $step, $fmt ] )
248 mce_grep_s { code } $beg, $end [, $step, $fmt ]
249 Sequence may be defined as a list, an array reference, or a hash
251 reference. The functions require both begin and end values to run.
252 Step and format are optional. The format is passed to sprintf (% may be
253 omitted below).
254 my ($beg, $end, $step, $fmt) = (10, 20, 0.1, "%4.1f");
256 my @f = mce_grep_s { /[1234]\.[5678]/ } $beg, $end, $step, $fmt;
258 my @g = mce_grep_s { /[1234]\.[5678]/ } [ $beg, $end, $step, $fmt ];
259 my @h = mce_grep_s { /[1234]\.[5678]/ } {
261 begin => $beg, end => $end,
262 step => $step, format => $fmt
263 };
264 MCE::Grep->run ( sub { code }, iterator )
266 mce_grep { code } iterator
267 An iterator reference may be specified for input_data. Iterators are
269 described under section "SYNTAX for INPUT_DATA" at MCE::Core.
270 my @a = mce_grep { $_ % 3 == 0 } make_iterator(10, 30, 2);
272
274 MCE::Grep->finish
275 MCE::Grep::finish
276 Workers remain persistent as much as possible after running. Shutdown
278 occurs automatically when the script terminates. Call finish when
279 workers are no longer needed.
280 use MCE::Grep;
282 MCE::Grep->init(
284 chunk_size => 20, max_workers => 'auto'
285 );
286 my @a = mce_grep { ... } 1..100;
288 MCE::Grep->finish;
290
292 MCE, MCE::Core
293
295 Mario E. Roy, <marioeroy AT gmail DOT com>
296perl v5.32.0 2020-08-19 MCE::Grep(3)