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MCE::Mutex - Locking for Many-Core Engine


This document describes MCE::Mutex version 1.889


 use MCE::Mutex;

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

     use MCE::Flow max_workers => 4;

     mce_flow sub {

         # access shared resource
         my $wid = MCE->wid; MCE->say($wid); sleep 1;


     use MCE::Hobo;

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

     use threads;

     threads->create('work', $_)   for 5..8;
     $_->join for ( threads->list );

 sub work {
     my ($id) = @_;

     # access shared resource
     print $id, "\n";
     sleep 1;



This module implements locking methods that can be used to coordinate access to shared data from multiple workers spawned as processes or threads.

The inspiration for this module came from reading Mutex for Ruby.


MCE::Mutex->new ( )

MCE::Mutex->new ( impl => "Channel" )

MCE::Mutex->new ( impl => "Flock", [ path => "/tmp/file.lock" ] )

MCE::Mutex->new ( path => "/tmp/file.lock" )

Creates a new mutex.

Channel locking (the default), unless path is given, is through a pipe or socket depending on the platform. The advantage of channel locking is not having to re-establish handles inside new processes and threads.

For Fcntl-based locking, it is the responsibility of the caller to remove the tempfile, associated with the mutex, when path is given. Otherwise, it establishes a tempfile internally including removal on scope exit.

$mutex->impl ( void )

Returns the implementation used for the mutex.

 $m1 = MCE::Mutex->new( );
 $m1->impl();   # Channel

 $m2 = MCE::Mutex->new( path => /tmp/my.lock );
 $m2->impl();   # Flock

 $m3 = MCE::Mutex->new( impl => "Channel" );
 $m3->impl();   # Channel

 $m4 = MCE::Mutex->new( impl => "Flock" );
 $m4->impl();   # Flock

Current API available since 1.822.

$mutex->lock ( void )

$mutex->lock_exclusive ( void )

Attempts to grab an exclusive lock and waits if not available. Multiple calls to mutex->lock by the same process or thread is safe. The mutex will remain locked until mutex->unlock is called.

The method lock_exclusive is an alias for lock, available since 1.822.

 ( my $mutex = MCE::Mutex->new( path => $0 ) )->lock_exclusive;

$mutex->lock_shared ( void )

Like lock_exclusive, but attempts to grab a shared lock instead. The lock_shared method is an alias to lock otherwise for non-Fcntl implementations.

Current API available since 1.822.

$guard = $mutex->guard_lock ( void )

This method calls lock and returns a guard object. When the guard object is destroyed, it automatically calls unlock.

Current API available since 1.889.

$mutex->unlock ( void )

Releases the lock. A held lock by an exiting process or thread is released automatically.

$mutex->synchronize ( sub { ... }, @_ )

$mutex->enter ( sub { ... }, @_ )

Obtains a lock, runs the code block, and releases the lock after the block completes. Optionally, the method is wantarray aware.

 my $val = $mutex->synchronize( sub {
     # access shared resource
     return 'scalar';

 my @ret = $mutex->enter( sub {
     # access shared resource
     return @list;

The method enter is an alias for synchronize, available since 1.822.

$mutex->timedwait ( floating_seconds )

Blocks until obtaining an exclusive lock. A false value is returned if the timeout is reached, and a true value otherwise. The default is 1 second.

 my $mutex = MCE::Mutex->new( path => $0 );

 # terminate script if a previous instance is still running

 exit unless $mutex->timedwait( 2 );


Current API available since 1.822.


MCE, MCE::Core


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