++ed by:
RCUDDY AERO DEMIAN DANAJ

4 PAUSE users
4 non-PAUSE users.

Mario Roy
and 1 contributors

NAME

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

VERSION

This document describes MCE::Shared version 1.835

SYNOPSIS

 # OO construction.

 use MCE::Shared;

 my $ar = MCE::Shared->array( @list );
 my $ca = MCE::Shared->cache( max_keys => 500, max_age => 60 );
 my $cv = MCE::Shared->condvar( 0 );
 my $fh = MCE::Shared->handle( '>>', \*STDOUT ) or die "$!";
 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 );

 # The Perl-like mce_open function is available since 1.002.

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

 # Tie construction. The module API option is available since 1.825.

 use v5.10;
 use MCE::Flow;
 use MCE::Shared;

 my %args  = ( max_keys => 500, max_age => 60 );
 my @pairs = ( foo => 'bar', woo => 'baz' );
 my @list  = ( 'a' .. 'z' );

 tie my $va1, 'MCE::Shared', { module => 'MCE::Shared::Scalar' }, 'foo';
 tie my @ar1, 'MCE::Shared', { module => 'MCE::Shared::Array' }, @list;
 tie my %ca1, 'MCE::Shared', { module => 'MCE::Shared::Cache' }, %args;
 tie my %ha1, 'MCE::Shared', { module => 'MCE::Shared::Hash' }, @pairs;
 tie my %oh1, 'MCE::Shared', { module => 'MCE::Shared::Ordhash' }, @pairs;
 tie my %oh2, 'MCE::Shared', { module => 'Hash::Ordered' }, @pairs;
 tie my %oh3, 'MCE::Shared', { module => 'Tie::IxHash' }, @pairs;
 tie my $cy1, 'MCE::Shared', { module => 'Tie::Cycle' }, [ 1 .. 8 ];
 tie my $va2, 'MCE::Shared', { module => 'Tie::StdScalar' }, 'hello';
 tie my @ar3, 'MCE::Shared', { module => 'Tie::StdArray' }, @list;
 tie my %ha2, 'MCE::Shared', { module => 'Tie::StdHash' }, @pairs;
 tie my %ha3, 'MCE::Shared', { module => 'Tie::ExtraHash' }, @pairs;

 tie my @ary, 'MCE::Shared', qw( a list of values );
 tie my %ca,  'MCE::Shared', { max_keys => 500, max_age => 60 };
 tie my %ha,  'MCE::Shared', key1 => 'val1', key2 => 'val2';
 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 $mutex = MCE::Mutex->new;

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

    # Locking is necessary when multiple workers update the same
    # element. The reason is that it may involve 2 trips to the
    # shared-manager process: fetch and store in this case.

    $mutex->enter( sub { $cnt += 1 } );

    # Otherwise, locking is optional for unique elements.

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

    return;
 };

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

 __END__

 # 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.

EXTRA FUNCTIONALITY

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. The use applies to Condvar, Queue, and Handle (mce_open). IO::FDpass isn't used for anything else.

 use MCE::Shared;

 # One may want to start the shared-manager early.

 MCE::Shared->start();

 # Typically, the shared-manager is started automatically when
 # constructing a shared object.

 my $ca = MCE::Shared->cache( max_keys => 500 );

 # IO::FDPass is necessary for constructing a shared condvar or queue
 # while the manager is running in order to send file descriptors
 # associated with the object.

 # Workers block using a socket handle for ->wait and ->timedwait.

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

 # Workers block using a socket handle for ->dequeue and ->await.

 my $q1 = MCE::Shared->queue();
 my $q2 = MCE::Shared->queue( await => 1 );

For platforms where IO::FDPass isn't possible, construct condvar and queue before other classes. The manager process is delayed until sharing other classes or started explicitly.

 use MCE::Shared;

 my $has_IO_FDPass = $INC{'IO/FDPass.pm'} ? 1 : 0;

 my $cv  = MCE::Shared->condvar( 0 );
 my $que = MCE::Shared->queue( fast => 1 );

 MCE::Shared->start() unless $has_IO_FDPass;

 my $ha = MCE::Shared->hash();  # started implicitly

Note: MCE starts the shared-manager if not yet started. Ditto for MCE::Hobo.

Regarding mce_open, IO::FDPass is needed for constructing a shared-handle from a non-shared handle not yet available inside the shared-manager process. The workaround is to have the non-shared handle made before the shared-manager is started. Passing a file by reference is fine for the three STD* handles.

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

 mce_open my $shared_in,  "<",  \*STDIN;   # ok
 mce_open my $shared_out, ">>", \*STDOUT;  # ok
 mce_open my $shared_err, ">>", \*STDERR;  # ok
 mce_open my $shared_fh1, "<",  "/path/to/sequence.fasta";  # ok
 mce_open my $shared_fh2, ">>", "/path/to/results.log";     # ok

 mce_open my $shared_fh, ">>", \*NON_SHARED_FH;  # requires IO::FDPass

The IO::FDPass module is known to work reliably on most platforms. Install 1.1 or later to rid of limitations described above.

 perl -MIO::FDPass -le "print 'Cheers! Perl has IO::FDPass.'"

DATA SHARING

Below, synopsis for sharing classes included with MCE::Shared.

 # short form

 use MCE::Shared;

 $ar = MCE::Shared->array( @list );
 $ca = MCE::Shared->cache( max_keys => 500, max_age => 60 );
 $cv = MCE::Shared->condvar( 0 );
 $fh = MCE::Shared->handle( ">>", \*STDOUT ); # see mce_open below
 $ha = MCE::Shared->hash( @pairs );
 $oh = MCE::Shared->ordhash( @pairs );
 $db = MCE::Shared->minidb();
 $qu = MCE::Shared->queue( await => 1, fast => 0 );
 $va = MCE::Shared->scalar( $value );
 $se = MCE::Shared->sequence( $begin, $end, $step, $fmt );

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

 # long form, must include class module

 use MCE::Shared::Array;
 use MCE::Shared::Cache;
 use MCE::Shared::Hash;
 use MCE::Shared::Minidb;
 use MCE::Shared::Ordhash;
 use MCE::Shared::Queue;
 use MCE::Shared::Scalar;

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

The restriction for sharing classes not included with MCE::Shared is that the object must not have file-handles nor code-blocks.

 use Hash::Ordered;

 $oh = MCE::Shared->share( Hash::Ordered->new( ... ) );
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 or local construction for use by a single process
 # shorter, mce_open is an alias for MCE::Shared::Handle::open

 use MCE::Shared::Handle;

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

 mce_open my $fh, "<", "file.log" or die "$!";

 # construction for sharing with other threads and processes
 # shorter, mce_open is an alias for MCE::Shared::open

 use MCE::Shared;

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

 mce_open my $fh, "<", "file.log" or die "$!";

Simple examples to open a file for reading:

 # mce_open is exported by MCE::Shared or MCE::Shared::Handle.
 # It creates a shared file handle with MCE::Shared present
 # or 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.

DEEPLY SHARING

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.

OBJECT SHARING

share

This class method transfers the blessed-object to the shared-manager process and returns a MCE::Shared::Object containing the SHARED_ID. Starting with the 1.827 release, the module option sends parameters to the shared-manager, where the object is then constructed. This is useful for classes involving XS code or a file handle.

 use MCE::Shared;

 {
   use Math::BigFloat try => 'GMP';
   use Math::BigInt   try => 'GMP';

   my $bf  = MCE::Shared->share({ module => 'Math::BigFloat' }, 0);
   my $bi  = MCE::Shared->share({ module => 'Math::BigInt'   }, 0);
   my $y   = 1e9;

   $bf->badd($y);  # addition (add $y to shared BigFloat object)
   $bi->badd($y);  # addition (add $y to shared BigInt object)
 }

 {
   use Bio::Seq;
   use Bio::SeqIO;

   my $seq_io = MCE::Shared->share({ module => 'Bio::SeqIO' },
      -file    => ">/path/to/fasta/file.fa",
      -format  => 'Fasta',
      -verbose => -1,
   );

   my $seq_obj = Bio::Seq->new(
      -display_id => "name", -desc => "desc", -seq => "seq",
      -alphabet   => "dna"
   );

   $seq_io->write_seq($seq_obj);  # write to shared SeqIO handle
 }

 {
   use MCE::Shared::Ordhash;

   my $oh1 = MCE::Shared->share( MCE::Shared::Ordhash->new() );
   my $oh2 = MCE::Shared->share({ module => 'MCE::Shared::Ordhash' });
   my $oh3 = MCE::Shared->ordhash();  # same thing

   $oh1->assign( @pairs );
   $oh2->assign( @pairs );
   $oh3->assign( @pairs );
 }

 {
   use Hash::Ordered;

   my ($ho_shared, $ho_nonshared);

   $ho_shared = MCE::Shared->share({ module => 'Hash::Ordered' });
   $ho_shared->push( @pairs );

   $ho_nonshared = $ho_shared->export();   # back to non-shared
   $ho_nonshared = $ho_shared->destroy();  # including shared 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 isn't necessary
 use MCE::Shared::Hash;     # when using the shorter form or via the
 use MCE::Shared::Scalar;   # module option.

 my $a1 = MCE::Shared->share( MCE::Shared::Array->new( @list ) );
 my $a2 = MCE::Shared->share({ module => 'MCE::Shared::Array' }, @list );
 my $a3 = MCE::Shared->share( [ @list ] );  # sugar syntax
 my $a4 = MCE::Shared->array( @list );

 my $h1 = MCE::Shared->share( MCE::Shared::Hash->new( @pairs ) );
 my $h2 = MCE::Shared->share({ module => 'MCE::Shared::Hash' }, @pairs );
 my $h3 = MCE::Shared->share( { @pairs } ); # sugar syntax
 my $h4 = MCE::Shared->hash( @pairs );

 my $s1 = MCE::Shared->share( MCE::Shared::Scalar->new( 20 ) );
 my $s2 = MCE::Shared->share({ module => 'MCE::Shared::Scalar' }, 20 );
 my $s3 = MCE::Shared->share( \do{ my $o = 20 } );
 my $s4 = MCE::Shared->scalar( 20 );

When the module option is given, one may optionally specify the constructor function via the new option. This is necessary for the CDB_File module, which provides two different objects. One is created by new (default), and accessed by insert and finish. The other is created by TIEHASH, and accessed by FETCH.

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

 # populate CDB file
 my $cdb = MCE::Shared->share({ module => 'CDB_File' }, 't.cdb', "t.cdb.$$")
    or die "$!\n";

 $cdb->insert( $_ => $_ ) for ('aa'..'zz');
 $cdb->finish;

 # use CDB file
 my $cdb1 = tie my %hash, 'MCE::Shared', { module => 'CDB_File' }, 't.cdb';

 # same thing, without involving TIE and extra hash variable
 my $cdb2 = MCE::Shared->share(
    { module => 'CDB_File', new => 'TIEHASH' }, 't.cdb'
 );

 print $hash{'aa'}, "\n";
 print $cdb1->FETCH('bb'), "\n";
 print $cdb2->FETCH('cc'), "\n";

 # rewind may be omitted on first use for parallel iteration
 $cdb2->rewind;

 for ( 1 .. 3 ) {
    mce_async {
       while ( my ($k,$v) = $cdb2->next ) {
          print "[$$] $k => $v\n";
       }
    };
 }

 MCE::Hobo->waitall;

DBM SHARING

Construting a shared DBM object is possible starting with the 1.827 release. Supported modules are AnyDBM_File, BerkeleyDB, CDB_File, DB_File, GDBM_File, NDBM_File, ODBM_File, SDBM_File, SQLite_File, Tie::Array::DBD, and Tie::Hash::DBD. The list includes Tokyo Cabinet and Kyoto Cabinet. Also, see forked version by Altice Labs. It contains an updated kyotocabinet folder that builds successfully with recent compilers.

Freeze-thaw during STORE-FETCH (for complex data) is handled automatically using Serial 3.015+ (if available) or Storable. Below, are constructions for sharing various DBM modules. The construction for CDB_File is given in the prior section.

AnyDBM_File
 use MCE::Shared;
 use Fcntl;
 use AnyDBM_File;

 BEGIN { @AnyDBM_File::ISA = qw( DB_File GDBM_File NDBM_File ODBM_File ); }

 tie my %h1, 'MCE::Shared', { module => 'AnyDBM_File' },
    'foo_a', O_CREAT|O_RDWR or die "open error: $!";
BerkeleyDB
 use MCE::Shared;
 use BerkeleyDB;

 tie my %h1, 'MCE::Shared', { module => 'BerkeleyDB::Hash' },
    -Filename => 'foo_a', -Flags => DB_CREATE
       or die "open error: $!";
   
 tie my %h2, 'MCE::Shared', { module => 'BerkeleyDB::Btree' },
    -Filename => 'foo_b', -Flags => DB_CREATE
       or die "open error: $!";

 tie my @a1, 'MCE::Shared', { module => 'BerkeleyDB::Queue' },
    -Filename => 'foo_c', -Flags => DB_CREATE
       or die "open error: $!";

 tie my @a2, 'MCE::Shared', { module => 'BerkeleyDB::Recno' },
    -Filename => 'foo_d', -Flags => DB_CREATE -Len => 20
       or die "open error: $!";
DB_File
 use MCE::Shared;
 use Fcntl;
 use DB_File;

 # Use pre-defined references ( $DB_HASH, $DB_BTREE, $DB_RECNO ).

 tie my %h1, 'MCE::Shared', { module => 'DB_File' },
    'foo_a', O_CREAT|O_RDWR, 0640, $DB_HASH or die "open error: $!";

 tie my %h2, 'MCE::Shared', { module => 'DB_File' },
    'foo_b', O_CREAT|O_RDWR, 0640, $DB_BTREE or die "open error: $!";

 tie my @a1, 'MCE::Shared', { module => 'DB_File' },
    'foo_c', O_CREAT|O_RDWR, 0640, $DB_RECNO or die "open error: $!";

 # Changing defaults - see DB_File for valid options.

 my $opt_h = DB_File::HASHINFO->new();
 my $opt_b = DB_File::BTREEINFO->new();
 my $opt_r = DB_File::RECNOINFO->new();

 $opt_h->{'cachesize'} = 12345;

 tie my %h3, 'MCE::Shared', { module => 'DB_File' },
    'foo_d', O_CREAT|O_RDWR, 0640, $opt_h or die "open error: $!";
KyotoCabinet
TokyoCabinet
 use MCE::Shared;
 use KyotoCabinet;
 use TokyoCabinet;

 # file extension denotes hash database

 tie my %h1, 'MCE::Shared', { module => 'KyotoCabinet::DB' }, 'foo.kch',
    KyotoCabinet::DB::OWRITER | KyotoCabinet::DB::OCREATE
       or die "open error: $!";

 tie my %h2, 'MCE::Shared', { module => 'TokyoCabinet::HDB' }, 'foo.tch',
    TokyoCabinet::HDB::OWRITER | TokyoCabinet::HDB::OCREAT
       or die "open error: $!";

 # file extension denotes tree database

 tie my %h3, 'MCE::Shared', { module => 'KyotoCabinet::DB' }, 'foo.kct',
    KyotoCabinet::DB::OWRITER | KyotoCabinet::DB::OCREATE
       or die "open error: $!";

 tie my %h4, 'MCE::Shared', { module => 'TokyoCabinet::BDB' }, 'foo.tcb',
    TokyoCabinet::BDB::OWRITER | TokyoCabinet::BDB::OCREAT
       or die "open error: $!";

 # on-memory hash database

 tie my %h5, 'MCE::Shared', { module => 'KyotoCabinet::DB' }, '*';
 tie my %h6, 'MCE::Shared', { module => 'TokyoCabinet::ADB' }, '*';

 # on-memory tree database

 tie my %h7, 'MCE::Shared', { module => 'KyotoCabinet::DB' }, '%#pccap=256m';
 tie my %h8, 'MCE::Shared', { module => 'TokyoCabinet::ADB' }, '+';
Tie::Array::DBD
Tie::Hash::DBD
 use MCE::Shared;
 use Tie::Array::DBD;
 use Tie::Hash::DBD;

 # A valid string is required for the DSN argument, not a DBI handle.
 # Do not specify the 'str' option for Tie::(Array|Hash)::DBD.
 # Instead, see encoder-decoder methods described under Common API.

 tie my @a1, 'MCE::Shared', { module => 'Tie::Array::DBD' },
    'dbi:SQLite:dbname=foo_a.db', {
       tbl => 't_tie_analysis',
       key => 'h_key',
       fld => 'h_value'
    };

 tie my %h1, 'MCE::Shared', { module => 'Tie::Hash::DBD' },
    'dbi:SQLite:dbname=foo_h.db', {
       tbl => 't_tie_analysis',
       key => 'h_key',
       fld => 'h_value'
    };

 tie my %h2, 'MCE::Shared', { module => 'Tie::Hash::DBD'},
    'dbi:CSV:f_dir=.;f_ext=.csv/r;csv_null=1;csv_decode_utf8=0', {
       tbl => 'mytable',
       key => 'h_key',
       fld => 'h_value'
    };

 # By default, Sereal 3.015+ is used for serialization if available.
 # This overrides serialization from Sereal-or-Storable to JSON::XS.

 use JSON::XS ();

 tied(%ha2)->encoder( \&JSON::XS::encode_json );
 tied(%ha2)->decoder( \&JSON::XS::decode_json );

 $h2{'foo'} = 'plain value';
 $h2{'bar'} = { @pairs };
 $h2{'baz'} = [ @list ];

DBM SHARING (CONT)

DB cursors, filters, and duplicate keys are not supported, just plain array and hash functionality. The OO interface provides better performance when needed. Use iterator or next for iterating over the elements.

 use MCE::Hobo;
 use MCE::Shared;
 use Fcntl;
 use DB_File;

 unlink 'foo_a';

 my $ob = tie my %h1, 'MCE::Shared', { module => 'DB_File' },
    'foo_a', O_CREAT|O_RDWR, 0640, $DB_HASH or die "open error: $!";

 $h1{key} = 'value';
 my $val = $h1{key};

 while ( my ($k, $v) = each %h1 ) {
    print "1: $k => $v\n";
 }

 # object oriented fashion, faster

 tied(%h1)->STORE( key1 => 'value1' );
 my $val1 = tied(%h1)->FETCH('key1');

 $ob->STORE( key2 => 'value2' );
 my $val2 = $ob->FETCH('key2');

 # non-parallel iteration

 my $iter = $ob->iterator;
 while ( my ($k, $v) = $iter->() ) {
    print "2: $k => $v\n";
 }

 # parallel iteration

 sub task {
    while ( my ($k, $v) = $ob->next ) {
       print "[$$] $k => $v\n";
       sleep 1;
    }
 }

 MCE::Hobo->create(\&task) for 1 .. 3;
 MCE::Hobo->waitall;

 $ob->rewind;

 # undef $ob and $iter before %h1 when destroying manually

 undef $ob;
 undef $iter;

 untie %h1;

See also Tie::File Demonstration, at the end of the documentation.

PDL SHARING

  • 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 object, export-destroy the shared object
 $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 object, export-destroy the shared object

 $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 ( { unbless => 1 } )
destroy

Exports optionally, but destroys the shared object entirely from the shared-manager process. The unbless option is passed to export.

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

 $shared_ob;     # becomes undef
encoder ( CODE )
decoder ( CODE )

Override freeze/thaw routines. Applies to STORE and FETCH only, particularly for TIE'd objects. These are called internally for shared DB objects.

Current API available since 1.827.

 use MCE::Shared;
 use BerkeleyDB;
 use DB_File;

 my $file1 = 'file1.db';
 my $file2 = 'file2.db';

 tie my @db1, 'MCE::Shared', { module => 'DB_File' }, $file1,
    O_RDWR|O_CREAT, 0640 or die "open error '$file1': $!";

 tie my %db2, 'MCE::Shared', { module => 'BerkeleyDB::Hash' },
    -Filename => $file2, -Flags => DB_CREATE
    or die "open error '$file2': $!";

 # Called automatically by MCE::Shared for DB files.
 # tied(@db1)->encoder( MCE::Shared::Server::_get_freeze );
 # tied(@db1)->decoder( MCE::Shared::Server::_get_thaw );
 # tied(%db2)->encoder( MCE::Shared::Server::_get_freeze );
 # tied(%db2)->decoder( MCE::Shared::Server::_get_thaw );
 # et cetera.

 $db1[0] = 'foo';   # store plain and complex structure
 $db1[1] = { key => 'value' };
 $db1[2] = [ 'complex' ];

 $db2{key} = 'foo'; # ditto, plain and complex structure
 $db2{sun} = [ 'complex' ];
export ( { unbless => 1 }, keys )
export

Exports the shared object as a non-shared object. One must export the shared object when passing into any dump routine. Otherwise, the shared_id value and blessed name is all one will see. The unbless option unblesses any shared Array, Hash, and Scalar object to a non-blessed array, hash, and scalar respectively.

 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' );

Specifying the unbless option exports a non-blessed data structure instead. Unbless applies to shared MCE::Shared::{ Array, Hash, and Scalar } objects.

 my $h2 = $h1->export( { unbless => 1 }, qw/ I The / );
 my $h3 = $h1->export( { unbless => 1 } );

 _dump($h2);
 _dump($h3);

 # Output

 $VAR1 = {
   'The' => 'Bluebirds',
   'I' => 'Heard'
 };

 $VAR1 = {
   'Marty' => 'Robbins',
   'Sing' => 'by',
   'The' => 'Bluebirds',
   'I' => 'Heard'
 };
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 ...

 MCE::Hobo->waitall();

 # 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 ...

 MCE::Hobo->waitall();

 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();

LOCKING

Application-level advisory locking is possible with MCE::Mutex.

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

 my $mutex = MCE::Mutex->new();

 tie my $cntr, 'MCE::Shared', 0;

 sub work {
    for ( 1 .. 1000 ) {
       $mutex->lock;

       # The next statement involves 2 IPC ops ( get and set ).
       # Thus, locking is required.
       $cntr++;

       $mutex->unlock;
    }
 }

 MCE::Hobo->create('work') for ( 1 .. 8 );
 MCE::Hobo->waitall;

 print $cntr, "\n"; # 8000

However, locking is not necessary when using the OO interface. This is possible as MCE::Shared is implemented using a single-point of entry for commands sent to the shared-manager process. Furthermore, the shared classes include sugar methods for combining set and get in a single operation.

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

 my $cntr = MCE::Shared->scalar( 0 );

 sub work {
    for ( 1 .. 1000 ) {
       # The next statement increments the value without having
       # to call set and get explicitly.
       $cntr->incr;
    }
 }

 MCE::Hobo->create('work') for ( 1 .. 8 );
 MCE::Hobo->waitall;

 print $cntr->get, "\n"; # 8000

Another possibility when running threads is locking via threads::shared.

 use threads;
 use threads::shared;

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

 my $mutex : shared;

 tie my $cntr, 'MCE::Shared', 0;

 sub work {
    for ( 1 .. 1000 ) {
       lock $mutex;

       # the next statement involves 2 IPC ops ( get and set )
       # thus, locking is required
       $cntr++;
    }
 }

 MCE::Flow->run( { max_workers => 8 }, \&work );
 MCE::Flow->finish;

 print $cntr, "\n"; # 8000

Of the three demonstrations, the OO interface yields the best performance. This is from the lack of locking at the application level. The results were obtained from a MacBook Pro (Haswell) running at 2.6 GHz, 1600 MHz RAM.

 CentOS 7.2 VM

    -- Perl v5.16.3
    MCE::Mutex .... : 0.528 secs.
    OO Interface .. : 0.062 secs.
    threads::shared : 0.545 secs.

 FreeBSD 10.0 VM

    -- Perl v5.16.3
    MCE::Mutex .... : 0.367 secs.
    OO Interface .. : 0.083 secs.
    threads::shared : 0.593 secs.

 Mac OS X 10.11.6 ( Host OS )

    -- Perl v5.18.2
    MCE::Mutex .... : 0.397 secs.
    OO Interface .. : 0.070 secs.
    threads::shared : 0.463 secs.

 Solaris 11.2 VM

    -- Perl v5.12.5 installed with the OS
    MCE::Mutex .... : 0.895 secs.
    OO Interface .. : 0.099 secs.
    threads::shared :              Perl not built to support threads

    -- Perl v5.22.2 built with threads support
    MCE::Mutex .... : 0.788 secs.
    OO Interface .. : 0.086 secs.
    threads::shared : 0.895 secs.

 Windows 7 VM

    -- Perl v5.22.2
    MCE::Mutex .... : 1.045 secs.
    OO Interface .. : 0.312 secs.
    threads::shared : 1.061 secs.

Beginning with MCE::Shared 1.809, the pipeline method provides another way. Included in Array, Cache, Hash, Minidb, and Ordhash, it combines multiple commands for the object to be processed serially. For shared objects, the call is made atomically due to single IPC to the shared-manager process.

The pipeline method is fully wantarray-aware and receives a list of commands and their arguments. In scalar or list context, it returns data from the last command in the pipeline.

 use MCE::Mutex;
 use MCE::Shared;

 my $mutex = MCE::Mutex->new();
 my $oh = MCE::Shared->ordhash();
 my @vals;

 # mutex locking

 $mutex->lock;
 $oh->set( foo => "a_a" );
 $oh->set( bar => "b_b" );
 $oh->set( baz => "c_c" );
 @vals = $oh->mget( qw/ foo bar baz / );
 $mutex->unlock;

 # pipeline, same thing done atomically

 @vals = $oh->pipeline(
    [ "set", foo => "a_a" ],
    [ "set", bar => "b_b" ],
    [ "set", baz => "c_c" ],
    [ "mget", qw/ foo bar baz / ]
 );

 # ( "a_a", "b_b", "c_c" )

There is also pipeline_ex, same as pipeline, but returns data for every command in the pipeline.

 @vals = $oh->pipeline_ex(
    [ "set", foo => "a_a" ],
    [ "set", bar => "b_b" ],
    [ "set", baz => "c_c" ]
 );

 # ( "a_a", "b_b", "c_c" )

PYTHON DEMONSTRATION

Sharing a Python class is possible, starting with the 1.827 release. The construction is simply calling share with the module option. Methods are accessible via the OO interface.

 #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 # Share Python class. Requires MCE::Shared 1.827 or later.
 #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 use strict;
 use warnings;

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

 my $py1 = MCE::Shared->share({ module => 'My::Class' });
 my $py2 = MCE::Shared->share({ module => 'My::Class' });

 MCE::Shared->start;

 $py1->set(0, 100);
 $py2->set(1, 200);

 die "Ooops" unless $py1->get(0) eq '100';
 die "Ooops" unless $py2->get(1) eq '200';

 sub task {
     $py1->incr(0) for 1 .. 50000;
     $py2->incr(1) for 1 .. 50000;
 }

 MCE::Hobo->create(\&task) for 1 .. 3;
 MCE::Hobo->waitall;

 print $py1->get(0), "\n";  # 150100
 print $py2->get(1), "\n";  # 150200

 #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 # Python class.
 #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 package My::Class;

 use strict;
 use warnings;

 use Inline::Python qw( py_eval py_bind_class );

 py_eval ( <<'END_OF_PYTHON_CLASS' );

 class MyClass:
     def __init__(self):
         self.data = [0,0]

     def set (self, key, value):
         self.data[key] = value

     def get (self, key):
         try: return self.data[key]
         except KeyError: return None

     def incr (self, key):
         try: self.data[key] = self.data[key] + 1
         except KeyError: self.data[key] = 1

 END_OF_PYTHON_CLASS

 # Register methods for best performance.

 py_bind_class(
     'My::Class', '__main__', 'MyClass',
     'set', 'get', 'incr'
 );

 1;

LOGGER DEMONSTRATION

Often, the requirement may call for concurrent logging by many workers. Calling localtime or gmtime per each log entry is expensive. This uses the old time-stamp value until one second has elapsed.

 #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 # Concurrent logger demo. Requires MCE::Shared 1.827 or later.
 #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 use strict;
 use warnings;

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

 my $file = "log.txt";
 my $pid  = $$;

 my $ob = MCE::Shared->share( { module => 'My::Logger' }, path => $file )
     or die "open error '$file': $!";

 # $ob->autoflush(1);   # optional, flush writes immediately

 sub work {
     my $id = shift;
     for ( 1 .. 250_000 ) {
         $ob->log("Hello from $id: $_");
     }
 }

 MCE::Hobo->create('work', $_) for 1 .. 4;
 MCE::Hobo->waitall;

 # Threads and multi-process safety for closing the handle.

 sub CLONE { $pid = 0; }

 END { $ob->close if $ob && $pid == $$; }

 #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 # Logger class.
 #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 package My::Logger;

 use strict;
 use warnings;

 use Time::HiRes qw( time );

 # construction

 sub new {
     my ( $class, %self ) = @_;

     open $self{fh}, ">>", $self{path} or return '';
     binmode $self{fh};

     $self{stamp} = localtime;  # or gmtime
     $self{time } = time;

     bless \%self, $class;
 }

 # $ob->log("message");

 sub log {
     my ( $self, $stamp ) = ( shift );

     if ( time - $self->{time} > 1.0 ) {
         $self->{stamp} = $stamp = localtime;  # or gmtime
         $self->{time } = time;
     }
     else {
         $stamp = $self->{stamp};
     }

     print {$self->{fh}} "$stamp --- @_\n";
 }

 # $ob->autoflush(0);
 # $ob->autoflush(1);

 sub autoflush {
     my ( $self, $flag ) = @_;

     if ( defined fileno($self->{fh}) ) {
          $flag ? select(( select($self->{fh}), $| = 1 )[0])
                : select(( select($self->{fh}), $| = 0 )[0]);

          return 1;
     }

     return;
 }

 # $ob->binmode($layer);
 # $ob->binmode();

 sub binmode {
     my ( $self, $layer ) = @_;

     if ( defined fileno($self->{fh}) ) {
         CORE::binmode $self->{fh}, $layer // ':raw';

         return 1;
     }

     return;
 }

 # $ob->close()

 sub close {
     my ( $self ) = @_;

     if ( defined fileno($self->{fh}) ) {
         close $self->{'fh'};
     }

     return;
 }

 # $ob->flush()

 sub flush {
     my ( $self ) = @_;

     if ( defined fileno($self->{fh}) ) {
         my $old_fh = select $self->{fh};
         my $old_af = $|; $| = 1; $| = $old_af;
         select $old_fh;

         return 1;
     }

     return;
 }

 1;

TIE::FILE DEMONSTRATION

The following presents a concurrent Tie::File demonstration. Each element in the array corresponds to a record in the text file. JSON, being readable, seems appropiate for encoding complex objects.

 #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 # The MCE::Mutex module isn't needed unless IPC involves two or
 # more trips for the underlying action.
 #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 use strict;
 use warnings;

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

 use JSON::MaybeXS;

 # Safety for data having line breaks.
 use constant EOL => "\x{0a}~\x{0a}";

 my $file  = 'file.txt';
 my $mutex = MCE::Mutex->new();
 my $pid   = $$;

 my $ob = tie my @db, 'MCE::Shared', { module => 'My::File' }, $file,
     recsep => EOL or die "open error '$file': $!";

 $ob->encoder( \&JSON::MaybeXS::encode_json );
 $ob->decoder( \&JSON::MaybeXS::decode_json );

 $db[20] = 0;  # a counter at offset 20 into the array
 $db[21] = [ qw/ foo bar / ];  # store complex structure

 sub task {
     my $id  = sprintf "%02s", shift;
     my $row = int($id) - 1;
     my $chr = sprintf "%c", 97 + $id - 1;

     # A mutex isn't necessary when storing a value.
     # Ditto for fetching a value.

     $db[$row] = "Hello from $id: ";  # 1 trip
     my $val   = length $db[$row];    # 1 trip

     # A mutex may be necessary for updates involving 2 or
     # more trips (FETCH and STORE) during IPC, from and to
     # the shared-manager process, unless a unique row.

     for ( 1 .. 40 ) {
       # $db[$row] .= $id;         # 2 trips, unique row - okay
         $ob->append($row, $chr);  # 1 trip via the OO interface

       # $mu->lock;
       # $db[20] += 1;             # incrementing counter, 2 trips
       # $mu->unlock;

         $ob->incr(20);            # same thing via OO, 1 trip
     }

     my $len = length $db[$row];   # 1 trip

     printf "hobo %2d : %d\n", $id, $len;
 }

 MCE::Hobo->create('task', $_) for 1 .. 20;
 MCE::Hobo->waitall;

 printf "counter : %d\n", $db[20];
 print  $db[21]->[0], "\n";  # foo

 # Threads and multi-process safety for closing the handle.

 sub CLONE { $pid = 0; }

 END {
     if ( $pid == $$ ) {
         undef $ob;  # important, undef $ob before @db
         untie @db;  # untie @db to flush pending writes
     }
 }

 #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 # Class extending Tie::File with two sugar methods.
 # Requires MCE::Shared 1.827 or later.
 #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 package My::File;

 use strict;
 use warnings;

 use Tie::File;

 our @ISA = 'Tie::File';

 # $ob->append('string');

 sub append {
     my ($self, $key) = @_;
     my $val = $self->FETCH($key); $val .= $_[2];
     $self->STORE($key, $val);
     length $val;
 }

 # $ob->incr($key);

 sub incr {
     my ( $self, $key ) = @_;
     my $val = $self->FETCH($key); $val += 1;
     $self->STORE($key, $val);
     $val;
 }

 1;

REQUIREMENTS

MCE::Shared requires Perl 5.10.1 or later. The IO::FDPass module is highly recommended on UNIX and Windows. This module does not install it by default.

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

Copyright (C) 2016-2018 by Mario E. Roy

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

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