NAME

MCE::Shared - MCE extension for sharing data supporting threads and processes

VERSION

This document describes MCE::Shared version 1.007

SYNOPSIS

# OO construction

use MCE::Shared;

my $ar = MCE::Shared->array( @list );
my $cv = MCE::Shared->condvar( 0 );
my $fh = MCE::Shared->handle( '>>', \*STDOUT );
my $ha = MCE::Shared->hash( @pairs );
my $oh = MCE::Shared->ordhash( @pairs );
my $db = MCE::Shared->minidb();
my $qu = MCE::Shared->queue( await => 1, fast => 0 );
my $va = MCE::Shared->scalar( $value );
my $se = MCE::Shared->sequence( $begin, $end, $step, $fmt );
my $ob = MCE::Shared->share( $blessed_object );

# open function, MCE::Shared 1.002 and later

mce_open my $fh, ">", "/foo/bar.log" or die "$!";

# Tie construction

use feature 'say';

use MCE::Flow;
use MCE::Shared;

tie my $var, 'MCE::Shared', 'initial value';
tie my @ary, 'MCE::Shared', qw( a list of values );
tie my %ha,  'MCE::Shared', ( key1 => 'value', key2 => 'value' );
tie my %oh,  'MCE::Shared', { ordered => 1 }, ( key1 => 'value' );

tie my $cnt, 'MCE::Shared', 0;
tie my @foo, 'MCE::Shared';
tie my %bar, 'MCE::Shared';

my $m1 = MCE::Mutex->new;

mce_flow {
   max_workers => 4
},
sub {
   my ( $mce ) = @_;
   my ( $pid, $wid ) = ( MCE->pid, MCE->wid );

   ## Locking is required when multiple workers update the same element.
   ## This requires 2 trips to the manager process (fetch and store).

   $m1->synchronize( sub {
      $cnt += 1;
   });

   ## Locking is not necessary when updating unique elements.

   $foo[ $wid - 1 ] = $pid;
   $bar{ $pid }     = $wid;

   return;
};

say "scalar : $cnt";
say " array : $_" for (@foo);
say "  hash : $_ => $bar{$_}" for (sort keys %bar);

# Output

scalar : 4
 array : 37847
 array : 37848
 array : 37849
 array : 37850
  hash : 37847 => 1
  hash : 37848 => 2
  hash : 37849 => 3
  hash : 37850 => 4

DESCRIPTION

This module provides data sharing capabilities for MCE supporting threads and processes. MCE::Hobo provides threads-like parallelization for running code asynchronously.

MCE::Shared enables extra functionality on systems with IO::FDPass installed. Without it, MCE::Shared is unable to send file descriptors to the shared-manager process for queue, condvar, and possibly handle.

As of this writing, the IO::FDPass module is not a requirement for running MCE::Shared nor is the check made during installation. The reason is that IO::FDPass is not possible on Cygwin and not sure about AIX.

The following is a suggestion for systems without IO::FDPass. This restriction applies to queue, condvar, and handle only.

use MCE::Shared;

# Construct any shared queue(s) and condvar(s) first.
# These contain GLOB handles where freezing is not allowed.

my $q1  = MCE::Shared->queue();
my $q2  = MCE::Shared->queue();

my $cv1 = MCE::Shared->condvar();
my $cv2 = MCE::Shared->condvar();

# Afterwards, start the shared-manager manually.

MCE::Shared->start();

# The shared-manager process knows of \*STDOUT, \*STDERR, \*STDIN

mce_open my $fh1, ">>", \*STDOUT;                  # ok
mce_open my $fh2, "<", "/path/to/sequence.fasta";  # ok
my $h1 = MCE::Shared->hash();                      # ok

Otherwise, sharing is immediate and not delayed with IO::FDPass. It is not necessary to share queue and condvar first or worry about starting the shared-manager process.

use MCE::Shared;

my $h1 = MCE::Shared->hash();    # shares immediately
my $q1 = MCE::Shared->queue();   # IO::FDPass sends file descriptors
my $cv = MCE::Shared->condvar(); # IO::FDPass sends file descriptors
my $h2 = MCE::Shared->ordhash();

array
condvar
handle
hash
minidb
ordhash
queue
scalar
sequence

array, condvar, handle, hash, minidb, ordhash, queue, scalar, and sequence are sugar syntax for constructing a shared object.

# long form

use MCE::Shared;

use MCE::Shared::Array;
use MCE::Shared::Hash;
use MCE::Shared::OrdHash;
use MCE::Shared::Minidb;
use MCE::Shared::Queue;
use MCE::Shared::Scalar;

my $ar = MCE::Shared->share( MCE::Shared::Array->new() );
my $ha = MCE::Shared->share( MCE::Shared::Hash->new() );
my $oh = MCE::Shared->share( MCE::Shared::Ordhash->new() );
my $db = MCE::Shared->share( MCE::Shared::Minidb->new() );
my $qu = MCE::Shared->share( MCE::Shared::Queue->new() );
my $va = MCE::Shared->share( MCE::Shared::Scalar->new() );

# short form

use MCE::Shared;

my $ar = MCE::Shared->array( @list );
my $cv = MCE::Shared->condvar( 0 );
my $fh = MCE::Shared->handle( '>>', \*STDOUT );
my $ha = MCE::Shared->hash( @pairs );
my $oh = MCE::Shared->ordhash( @pairs );
my $db = MCE::Shared->minidb();
my $qu = MCE::Shared->queue( await => 1, fast => 0 );
my $va = MCE::Shared->scalar( $value );
my $se = MCE::Shared->sequence( $begin, $end, $step, $fmt );

open ( filehandle, expr )

open ( filehandle, mode, expr )

open ( filehandle, mode, reference )

In version 1.002 and later, constructs a new object by opening the file whose filename is given by expr, and associates it with filehandle. When omitting error checking at the application level, MCE::Shared emits a message and stop if open fails.

See MCE::Shared::Handle for chunk IO demonstrations.

# non-shared
use MCE::Shared::Handle;

MCE::Shared::Handle->open( my $fh, "<", "file.log" ) or die "$!";
MCE::Shared::Handle::open  my $fh, "<", "file.log"   or die "$!";

# shared
use MCE::Shared;

MCE::Shared->open( my $fh, "<", "file.log" ) or die "$!";
MCE::Shared::open  my $fh, "<", "file.log"   or die "$!";

Simple examples to open a file for reading:

# mce_open, exported
# creates a shared handle when MCE::Shared is present
# creates a non-shared handle, otherwise

mce_open my $fh, "< input.txt"     or die "open error: $!";
mce_open my $fh, "<", "input.txt"  or die "open error: $!";
mce_open my $fh, "<", \*STDIN      or die "open error: $!";

and for writing:

mce_open my $fh, "> output.txt"    or die "open error: $!";
mce_open my $fh, ">", "output.txt" or die "open error: $!";
mce_open my $fh, ">", \*STDOUT     or die "open error: $!";

num_sequence

num_sequence is an alias for sequence.

The following is a demonstration for a shared tied-hash variable. Before venturing into the actual code, notice the dump function making a call to export explicitly for objects of type MCE::Shared::Object. This is necessary in order to retrieve the data from the shared-manager process.

The export method is described later under the Common API section.

sub _dump {
   require Data::Dumper unless $INC{'Data/Dumper.pm'};
   no warnings 'once';

   local $Data::Dumper::Varname  = 'VAR';
   local $Data::Dumper::Deepcopy = 1;
   local $Data::Dumper::Indent   = 1;
   local $Data::Dumper::Purity   = 1;
   local $Data::Dumper::Sortkeys = 0;
   local $Data::Dumper::Terse    = 0;

   ( ref $_[0] eq 'MCE::Shared::Object' )
      ? print Data::Dumper::Dumper( $_[0]->export ) . "\n"
      : print Data::Dumper::Dumper( $_[0] ) . "\n";
}

use MCE::Shared;

tie my %abc, 'MCE::Shared';

my @parents = qw( a b c );
my @children = qw( 1 2 3 4 );

for my $parent ( @parents ) {
   for my $child ( @children ) {
      $abc{ $parent }{ $child } = 1;
   }
}

_dump( tied( %abc ) );

# Output

$VAR1 = bless( {
  'c' => bless( {
    '1' => '1',
    '4' => '1',
    '3' => '1',
    '2' => '1'
  }, 'MCE::Shared::Hash' ),
  'a' => bless( {
    '1' => '1',
    '4' => '1',
    '3' => '1',
    '2' => '1'
  }, 'MCE::Shared::Hash' ),
  'b' => bless( {
    '1' => '1',
    '4' => '1',
    '3' => '1',
    '2' => '1'
  }, 'MCE::Shared::Hash' )
}, 'MCE::Shared::Hash' );

Dereferencing provides hash-like behavior for hash and ordhash. Array-like behavior is allowed for array, not shown below.

use MCE::Shared;

my $abc = MCE::Shared->hash;

my @parents = qw( a b c );
my @children = qw( 1 2 3 4 );

for my $parent ( @parents ) {
   for my $child ( @children ) {
      $abc->{ $parent }{ $child } = 1;
   }
}

_dump( $abc );

Each level in a deeply structure requires a separate trip to the shared-manager process. The included MCE::Shared::Minidb module provides optimized methods for working with hash of hashes HoH and/or hash of arrays HoA. As such, do the following when performance is desired.

use MCE::Shared;

my $abc = MCE::Shared->minidb;

my @parents = qw( a b c );
my @children = qw( 1 2 3 4 );

for my $parent ( @parents ) {
   for my $child ( @children ) {
      $abc->hset( $parent, $child, 1 );
   }
}

_dump( $abc );

For further reading, see MCE::Shared::Minidb.

share

This class method transfers the blessed-object to the shared-manager process and returns a MCE::Shared::Object containing the SHARED_ID. The object must not contain any GLOB's or CODE_REF's or the transfer will fail.

Unlike with threads::shared, objects are not deeply shared. The shared object is accessible through the OO interface.

use MCE::Shared;
use Hash::Ordered;

my ($ho_shared, $ho_nonshared);

$ho_shared = MCE::Shared->share( Hash::Ordered->new() );

$ho_shared->push( @pairs );             # OO interface only
$ho_shared->mset( @pairs );

$ho_nonshared = $ho_shared->export();   # back to non-shared
$ho_nonshared = $ho_shared->destroy();  # including destruction

The following provides long and short forms for constructing a shared array, hash, or scalar object.

use MCE::Shared;

use MCE::Shared::Array;    # Loading helper classes is not necessary
use MCE::Shared::Hash;     # when using the shorter form.
use MCE::Shared::Scalar;

my $a1 = MCE::Shared->share( MCE::Shared::Array->new( @list ) );
my $a3 = MCE::Shared->share( [ @list ] );  # sugar syntax
my $a2 = MCE::Shared->array( @list );

my $h1 = MCE::Shared->share( MCE::Shared::Hash->new( @pairs ) );
my $h3 = MCE::Shared->share( { @pairs } ); # sugar syntax
my $h2 = MCE::Shared->hash( @pairs );

my $s1 = MCE::Shared->share( MCE::Shared::Scalar->new( 20 ) );
my $s2 = MCE::Shared->share( \do{ my $o = 20 } );
my $s4 = MCE::Shared->scalar( 20 );

pdl_byte
pdl_short
pdl_ushort
pdl_long
pdl_longlong
pdl_float
pdl_double
pdl_ones
pdl_sequence
pdl_zeroes
pdl_indx
pdl

pdl_byte, pdl_short, pdl_ushort, pdl_long, pdl_longlong, pdl_float, pdl_double, pdl_ones, pdl_sequence, pdl_zeroes, pdl_indx, and pdl are sugar syntax for PDL construction take place under the shared-manager process.

use PDL;                 # must load PDL before MCE::Shared
use MCE::Shared;

# makes extra copy/transfer and unnecessary destruction
my $ob1 = MCE::Shared->share( zeroes( 256, 256 ) );

# do this instead, efficient
my $ob1 = MCE::Shared->zeroes( 256, 256 );

ins_inplace

The ins_inplace method applies to shared PDL objects. It supports three forms for writing elements back to the PDL object, residing under the shared-manager process.

# --- action taken by the shared-manager process
# ins_inplace(  1 arg  ):  ins( inplace( $this ), $what, 0, 0 );
# ins_inplace(  2 args ):  $this->slice( $arg1 ) .= $arg2;
# ins_inplace( >2 args ):  ins( inplace( $this ), $what, @coords );

# --- use case
$o->ins_inplace( $result );                    #  1 arg
$o->ins_inplace( ":,$start:$stop", $result );  #  2 args
$o->ins_inplace( $result, 0, $seq_n );         # >2 args

Operations such as + 5 will not work on shared PDL objects. At this time, the OO interface is the only mechanism for communicating with the PDL piddle. For example, call slice, sever, or copy to fetch elements. Call ins_inplace to update elements.

# make a shared PDL piddle
my $b = MCE::Shared->pdl_sequence(20,20);

# fetch, add 10 to row 2 only
my $res1 = $b->slice(":,1:1") + 10;
$b->ins_inplace($res1, 0, 1);

# fetch, add 10 to rows 4 and 5
my $res2 = $b->slice(":,3:4") + 10;
$b->ins_inplace($res2, 0, 3);

# make non-shared, destroy/export
$b = $b->destroy;

print "$b\n";

The following provides parallel demonstrations using MCE::Flow.

use PDL;  # must load PDL before MCE::Shared

use MCE::Flow;
use MCE::Shared;

my $a = MCE::Shared->pdl_sequence(20,20);
my $b = MCE::Shared->pdl_zeroes(20,20);

# with chunking disabled

mce_flow_s {
   max_workers => 4, chunk_size => 1
},
sub {
   my $row = $_;
   my $result = $a->slice(":,$row:$row") + 5;
   $b->ins_inplace($result, 0, $row);
}, 0, 20 - 1;

# with chunking enabled

mce_flow_s {
   max_workers => 4, chunk_size => 5, bounds_only => 1
},
sub {
   my ($row1, $row2) = @{ $_ };
   my $result = $a->slice(":,$row1:$row2") + 5;
   $b->ins_inplace($result, 0, $row1);
}, 0, 20 - 1;

# make non-shared, destroy/export

$b = $b->destroy;

print "$b\n";

See also PDL::ParallelCPU and PDL::Parallel::threads. For further reading, the MCE-Cookbook on Github provides two PDL demonstrations.

https://github.com/marioroy/mce-cookbook

COMMON API

blessed

Returns the real blessed name, provided by the shared-manager process.

use Scalar::Util qw(blessed);
use MCE::Shared;

use MCE::Shared::Ordhash;
use Hash::Ordered;

my $oh1 = MCE::Shared->share( MCE::Shared::Ordhash->new() );
my $oh2 = MCE::Shared->share( Hash::Ordered->new() );

print blessed($oh1), "\n";    # MCE::Shared::Object
print blessed($oh2), "\n";    # MCE::Shared::Object

print $oh1->blessed(), "\n";  # MCE::Shared::Ordhash
print $oh2->blessed(), "\n";  # Hash::Ordered

destroy

Exports optionally, but destroys the shared object entirely from the shared-manager process.

my $exported_ob = $shared_ob->destroy();

$shared_ob; # becomes undef

export ( keys )

export

Exports the shared object as a non-shared object. One must export when passing the object into any dump routine. Otherwise, the shared_id value and blessed name is all one will see.

use MCE::Shared;
use MCE::Shared::Ordhash;

sub _dump {
   require Data::Dumper unless $INC{'Data/Dumper.pm'};
   no warnings 'once';

   local $Data::Dumper::Varname  = 'VAR';
   local $Data::Dumper::Deepcopy = 1;
   local $Data::Dumper::Indent   = 1;
   local $Data::Dumper::Purity   = 1;
   local $Data::Dumper::Sortkeys = 0;
   local $Data::Dumper::Terse    = 0;

   print Data::Dumper::Dumper($_[0]) . "\n";
}

my $oh1 = MCE::Shared->share( MCE::Shared::Ordhash->new() );
my $oh2 = MCE::Shared->ordhash();  # same thing

_dump($oh1);
   # bless( [ 1, 'MCE::Shared::Ordhash' ], 'MCE::Shared::Object' )

_dump($oh2);
   # bless( [ 2, 'MCE::Shared::Ordhash' ], 'MCE::Shared::Object' )

_dump( $oh1->export );  # dumps object structure and content
_dump( $oh2->export );

export can optionally take a list of indices/keys for what to export. This applies to shared array, hash, and ordhash.

use MCE::Shared;

my $h1 = MCE::Shared->hash(           # shared hash
   qw/ I Heard The Bluebirds Sing by Marty Robbins /
     # k v     k   v         k    v  k     v
);

my $h2 = $h1->export( qw/ I The / );  # non-shared hash

_dump($h2);

# Output

$VAR1 = bless( {
  'I' => 'Heard',
  'The' => 'Bluebirds'
}, 'MCE::Shared::Hash' );

next

The next method provides parallel iteration between workers for shared array, hash, ordhash, and sequence. In list context, returns the next key-value pair. This applies to array, hash, and ordhash. In scalar context, returns the next item. The undef value is returned after iteration has completed.

Internally, the list of keys to return is set when the closure is constructed. Later keys added to the shared array or hash are not included. Subsequently, the undef value is returned for deleted keys.

The following example iterates through a shared array in parallel.

use MCE::Hobo;
use MCE::Shared;

my $ob = MCE::Shared->array( 'a' .. 'j' );

sub demo1 {
   my ( $id ) = @_;
   while ( my ( $index, $value ) = $ob->next ) {
      print "$id: [ $index ] $value\n";
      sleep 1;
   }
}

sub demo2 {
   my ( $id ) = @_;
   while ( defined ( my $value = $ob->next ) ) {
      print "$id: $value\n";
      sleep 1;
   }
}

MCE::Hobo->new( \&demo2, $_ ) for 1 .. 3;

# ... do other work ...

$_->join() for MCE::Hobo->list();

# Output

1: a
2: b
3: c
2: f
1: d
3: e
2: g
3: i
1: h
2: j

The form is similar for sequence. For large sequences, the bounds_only option is recommended. Also, specify chunk_size accordingly. This reduces the amount of traffic to and from the shared-manager process.

use MCE::Hobo;
use MCE::Shared;

my $N   = shift || 4_000_000;
my $pi  = MCE::Shared->scalar( 0.0 );

my $seq = MCE::Shared->sequence(
   { chunk_size => 200_000, bounds_only => 1 },
   0, $N - 1
);

sub compute_pi {
   my ( $wid ) = @_;

   while ( my ( $beg, $end ) = $seq->next ) {
      my ( $_pi, $t ) = ( 0.0 );
      for my $i ( $beg .. $end ) {
         $t = ( $i + 0.5 ) / $N;
         $_pi += 4.0 / ( 1.0 + $t * $t );
      }
      $pi->incrby( $_pi );
   }

   return;
}

MCE::Hobo->create( \&compute_pi, $_ ) for ( 1 .. 8 );

# ... do other stuff ...

$_->join() for MCE::Hobo->list();

printf "pi = %0.13f\n", $pi->get / $N;

# Output

3.1415926535898

rewind ( index, [, index, ... ] )

rewind ( key, [, key, ... ] )

rewind ( "query string" )

Rewinds the parallel iterator for MCE::Shared::Array, MCE::Shared::Hash, or MCE::Shared::Ordhash when no arguments are given. Otherwise, resets the iterator with given criteria. The syntax for query string is described in the shared module.

# array
$ar->rewind;

$ar->rewind( 0, 1 );
$ar->rewind( "val eq some_value" );
$ar->rewind( "key >= 50 :AND val =~ /sun|moon|air|wind/" );
$ar->rewind( "val eq sun :OR val eq moon :OR val eq foo" );
$ar->rewind( "key =~ /$pattern/" );

while ( my ( $index, $value ) = $ar->next ) {
   ...
}

# hash, ordhash
$oh->rewind;

$oh->rewind( "key1", "key2" );
$oh->rewind( "val eq some_value" );
$oh->rewind( "key eq some_key :AND val =~ /sun|moon|air|wind/" );
$oh->rewind( "val eq sun :OR val eq moon :OR val eq foo" );
$oh->rewind( "key =~ /$pattern/" );

while ( my ( $key, $value ) = $oh->next ) {
   ...
}

rewind ( { options }, begin, end [, step, format ] )

rewind ( begin, end [, step, format ] )

Rewinds the parallel iterator for MCE::Shared::Sequence when no arguments are given. Otherwise, resets the iterator with given criteria.

$seq->rewind;

$seq->rewind( { chunk_size => 10, bounds_only => 1 }, 1, 100 );

while ( my ( $beg, $end ) = $seq->next ) {
   for my $i ( $beg .. $end ) {
      ...
   }
}

$seq->rewind( 1, 100 );

while ( defined ( my $num = $seq->next ) ) {
   ...
}

store ( key, value )

Deep-sharing a non-blessed structure recursively is possible with store, an alias to STORE.

use MCE::Shared;

my $h1 = MCE::Shared->hash();
my $h2 = MCE::Shared->hash();

# auto-shares deeply
$h1->store( 'key', [ 0, 2, 5, { 'foo' => 'bar' } ] );
$h2->{key}[3]{foo} = 'baz';   # via auto-vivification

my $v1 = $h1->get('key')->get(3)->get('foo');  # bar
my $v2 = $h2->get('key')->get(3)->get('foo');  # baz
my $v3 = $h2->{key}[3]{foo};                   # baz

SERVER API

init

This method is called automatically by each MCE or Hobo worker immediately after being spawned. The effect is extra parallelism during inter-process communication. The optional ID (an integer) is modded internally in a round-robin fashion.

MCE::Shared->init();
MCE::Shared->init( ID );

start

Starts the shared-manager process. This is done automatically.

MCE::Shared->start();

stop

Stops the shared-manager process, wiping all shared data content. This is called by the END block automatically when the script terminates.

MCE::Shared->stop();

REQUIREMENTS

MCE::Shared requires Perl 5.10.1 or later.

SOURCE AND FURTHER READING

The source, cookbook, and examples are hosted at GitHub.

INDEX

MCE, MCE::Hobo

AUTHOR

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

COPYRIGHT AND LICENSE

MCE::Shared is released under the same license as Perl.

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

To install MCE::Shared, copy and paste the appropriate command in to your terminal.

cpanm

cpanm MCE::Shared

CPAN shell

perl -MCPAN -e shell
install MCE::Shared

For more information on module installation, please visit the detailed CPAN module installation guide.

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NAME

VERSION

SYNOPSIS

DESCRIPTION

DATA SHARING

DEEPLY SHARING

OBJECT SHARING

PDL SHARING