MCE::Stream(3)

NAME
MCE::Stream - Parallel stream model for chaining multiple maps and greps

VERSION
This document describes MCE::Stream version 1.703

SYNOPSIS
   ## Exports mce_stream, mce_stream_f, mce_stream_s
   use MCE::Stream;

   my (@m1, @m2, @m3);

   ## Default mode is map and processed from right-to-left
   @m1 = mce_stream sub { $_ * 3 }, sub { $_ * 2 }, 1..10000;
   mce_stream \@m2, sub { $_ * 3 }, sub { $_ * 2 }, 1..10000;

   ## Native Perl
   @m3 = map { $_ * $_ } grep { $_ % 5 == 0 } 1..10000;

   ## Streaming grep and map in parallel
   mce_stream \@m3,
      { mode => 'map',  code => sub { $_ * $_ } },
      { mode => 'grep', code => sub { $_ % 5 == 0 } }, 1..10000;

   ## Array or array_ref
   my @a = mce_stream sub { $_ * $_ }, 1..10000;
   my @b = mce_stream sub { $_ * $_ }, [ 1..10000 ];

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

   ## Sequence of numbers (begin, end [, step, format])
   my @f = mce_stream_s sub { $_ * $_ }, 1, 10000, 5;
   my @g = mce_stream_s sub { $_ * $_ }, [ 1, 10000, 5 ];

   my @h = mce_stream_s sub { $_ * $_ }, {
      begin => 1, end => 10000, step => 5, format => undef
   };

DESCRIPTION
This module allows one to stream multiple map and/or grep operations in parallel. Code blocks run simultaneously from right-to-left. The results are appended immediately when providing a reference to an array.

   ## Appends are serialized, even out-of-order ok, but immediately.
   ## Out-of-order chunks are held temporarily until ordered chunks
   ## arrive.

   mce_stream \@a, sub { $_ }, sub { $_ }, sub { $_ }, 1..10000;

   ##                                                    input
   ##                                        chunk1      input
   ##                            chunk3      chunk2      input
   ##                chunk2      chunk2      chunk3      input
   ##   append1      chunk3      chunk1      chunk4      input
   ##   append2      chunk1      chunk5      chunk5      input
   ##   append3      chunk5      chunk4      chunk6      ...
   ##   append4      chunk4      chunk6      ...
   ##   append5      chunk6      ...
   ##   append6      ...
   ##   ...
   ##

MCE incurs a small overhead due to passing of data. A fast code block will run faster natively when chaining multiple map functions. However, the overhead will likely diminish as the complexity increases for the code.

   ## 0.334 secs -- baseline using the native map function
   my @m1 = map { $_ * 4 } map { $_ * 3 } map { $_ * 2 } 1..1000000;

   ## 0.427 secs -- this is quite amazing considering data passing
   my @m2 = mce_stream
         sub { $_ * 4 }, sub { $_ * 3 }, sub { $_ * 2 }, 1..1000000;

   ## 0.355 secs -- appends to @m3 immediately, not after running
   my @m3; mce_stream \@m3,
         sub { $_ * 4 }, sub { $_ * 3 }, sub { $_ * 2 }, 1..1000000;

Even faster is mce_stream_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_stream_s (begin, end). Step defaults to 1 if begin is smaller than end, otherwise -1.

   ## 0.278 secs -- numbers are generated mathematically via sequence
   my @m4; mce_stream_s \@m4,
         sub { $_ * 4 }, sub { $_ * 3 }, sub { $_ * 2 }, 1, 1000000;

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::Stream
         default_mode => 'grep',          ## Default 'map'
         fast => 1,                       ## Default 0 (fast dequeue)
         max_workers => 8,                ## Default 'auto'
         chunk_size => 500,               ## 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. The following will attempt to use Sereal if available, otherwise defaults to Storable for serialization.

   use MCE::Stream Sereal => 1;

CUSTOMIZING MCE

MCE::Stream->init ( options )
MCE::Stream::init { options }
    The init function accepts a hash of MCE options. The gather and bounds_only options, if specified, are ignored due to being used internally by the module (not shown below).

       use MCE::Stream;

       MCE::Stream::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_stream sub { $_ * $_ }, 1..100;

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

       -- Output

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

Like with MCE::Stream::init above, MCE options may be specified using an anonymous hash for the first argument. Notice how both max_workers and task_name can take an anonymous array for setting values uniquely per each code block.

Remember that MCE::Stream processes from right-to-left when setting the individual values.

   use MCE::Stream;

   my @a = mce_stream {
      task_name   => [ 'c', 'b', 'a' ],
      max_workers => [  2,   4,   3, ],

      user_end => sub {
         my ($mce, $task_id, $task_name) = @_;
         print "$task_id - $task_name completed\n";
      },

      task_end => sub {
         my ($mce, $task_id, $task_name) = @_;
         MCE->print("$task_id - $task_name ended\n");
      }
   },
   sub { $_ * 4 },             ## 2 workers, named c
   sub { $_ * 3 },             ## 4 workers, named b
   sub { $_ * 2 }, 1..10000;   ## 3 workers, named a

   -- Output

   0 - a completed
   0 - a completed
   0 - a completed
   0 - a ended
   1 - b completed
   1 - b completed
   1 - b completed
   1 - b completed
   1 - b ended
   2 - c completed
   2 - c completed
   2 - c ended

Note that the anonymous hash, for specifying options, also comes first when passing an array reference.

   my @a; mce_stream {
      ...
   }, \@a, sub { ... }, sub { ... }, 1..10000;

API DOCUMENTATION
Scripts using MCE::Stream can be written using the long or short form. The long form becomes relevant when mixing modes. Again, processing occurs from right-to-left.

   my @m3 = mce_stream
      { mode => 'map',  code => sub { $_ * $_ } },
      { mode => 'grep', code => sub { $_ % 5 == 0 } }, 1..10000;

   my @m4; mce_stream \@m4,
      { mode => 'map',  code => sub { $_ * $_ } },
      { mode => 'grep', code => sub { $_ % 5 == 0 } }, 1..10000;

For multiple grep blocks, the short form can be used. Simply specify the default mode for the module. The two valid values for default_mode is 'grep' and 'map'.

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

   my @f = mce_stream_f sub { /ending$/ }, sub { /^starting/ }, $file;

The following assumes 'map' for default_mode in order to demonstrate all the possibilities of passing input data into the code block.

MCE::Stream->run ( { input_data => iterator }, sub { code } )
mce_stream { input_data => iterator }, sub { code }
    An iterator reference can by specified for input_data. The only other way is to specify input_data via MCE::Stream::init. This prevents MCE::Stream from configuring the iterator reference as another user task which will not work.

    Iterators are described under "SYNTAX for INPUT_DATA" at MCE::Core.

       MCE::Stream::init {
          input_data => iterator
       };

       my @a = mce_stream sub { $_ * 3 }, sub { $_ * 2 };

MCE::Stream->run ( sub { code }, list )
mce_stream sub { code }, list
    Input data can be defined using a list.

       my @a = mce_stream sub { $_ * 2 }, 1..1000;
       my @b = mce_stream sub { $_ * 2 }, [ 1..1000 ];

MCE::Stream->run_file ( sub { code }, file )
mce_stream_f sub { 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_stream_f sub { chomp; $_ . "\r\n" }, "/path/to/file";
       my @d = mce_stream_f sub { chomp; $_ . "\r\n" }, $file_handle;
       my @e = mce_stream_f sub { chomp; $_ . "\r\n" }, \$scalar;

MCE::Stream->run_seq ( sub { code }, $beg, $end [, $step, $fmt ] )
mce_stream_s sub { code }, $beg, $end [, $step, $fmt ]
    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_stream_s sub { $_ }, $beg, $end, $step, $fmt;
       my @g = mce_stream_s sub { $_ }, [ $beg, $end, $step, $fmt ];

       my @h = mce_stream_s sub { $_ }, {
          begin => $beg, end => $end, step => $step, format => $fmt
       };

MANUAL SHUTDOWN

MCE::Stream->finish
MCE::Stream::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::Stream;

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

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

       MCE::Stream::finish;

INDEX
MCE, MCE::Core

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