NAME

       forks::shared - drop-in replacement for Perl threads::shared with forks()

SYNOPSIS

         use forks;
         use forks::shared;

         my $variable : shared;
         my @array    : shared;
         my %hash     : shared;

         share( $variable );
         share( @array );
         share( %hash );

         $variable = shared_clone($non_shared_ref_value);
         $variable = shared_clone({'foo' => [qw/foo bar baz/]});

         lock( $variable );
         cond_wait( $variable );
         cond_wait( $variable, $lock_variable );
         cond_timedwait( $variable, abs time );
         cond_timedwait( $variable, abs time, $lock_variable );
         cond_signal( $variable );
         cond_broadcast( $variable );

         bless( $variable, class name );

         # Enable deadlock detection and resolution
         use forks::shared deadlock => {
           detect => 1,
           resolve => 1
         );
         # or
         threads::shared->set_deadlock_option(
           detect  => 1,
           resolve => 1
         );

DESCRIPTION

       The "forks::shared" pragma allows a developer to use shared variables with threads (implemented with the
       "forks" pragma) without having to have a threaded perl, or to even run 5.8.0 or higher.

       "forks::shared" is currently API compatible with CPAN threads::shared version 1.05.

EXPORT

       "share", "shared_clone", "cond_wait", "cond_timedwait", "cond_signal", "cond_broadcast", "is_shared",
       "bless"

       See "EXPORT" in threads::shared for more information.

OBJECTS

       forks::shared exports a version of bless() that works on shared objects, such that blessings propagate
       across threads.  See threads::shared for usage information and the forks test suite for additional
       examples.

EXTRA FEATURES

   Deadlock detection and resolution
       In the interest of helping programmers debug one of the most common bugs in threaded application
       software, forks::shared supports a full deadlock detection and resolution engine.

       Automated detection and resolution

       There are two ways to enable these features: either at import time in a use statement, such as:

           use forks::shared deadlock => { OPTIONS }

       or during runtime as a class method call to "set_deadlock_option", like:

           forks::shared->set_deadlock_option( OPTIONS );
           #or
           threads::shared->set_deadlock_option( OPTIONS );

       where "OPTIONS" may be a combination of any of the following:

           detect         => 1 (enable) or 0 (disable)
           period         => number of seconds between asynchronous polls
           resolve        => 1 (enable) or 0 (disable)

       The "detect" option enables deadlock detection.  By itself, this option enabled synchronous deadlock
       detection, which efficiently checks for potential deadlocks at lock() time.  If any are detected and
       warnings are enabled, it will print out details to "STDERR" like the following example:

           Deadlock detected:
               TID   SV LOCKED   SV LOCKING   Caller
                 1           3            4   t/forks06.t at line 41
                 2           4            3   t/forks06.t at line 46

       The "period" option, if set to a value greater than zero, is the number of seconds between asynchronous
       deadlock detection checks.  Asynchronous detection is useful for debugging rare, time-critical race
       conditions leading to deadlocks that may be masked by the slight time overhead introduced by synchronous
       detection on each lock() call.  Overall, it is less CPU intensive than synchronous deadlock detection.

       The "resolve" option enables auto-termination of one thread in each deadlocked thread pair that has been
       detected.  As with the "detect" option, "resolve" prints out the action it performs to STDERR, if
       warnings are enabled.  NOTE: "resolve" uses SIGKILL to break deadlocks, so this feature should not be
       used in environments where stability of the rest of your application may be adversely affected by process
       death in this manner.

       For example:

           use forks;
           use forks::shared
               deadlock => {detect=> 1, resolve => 1};

       Manual detection

       If you wish to check for deadlocks without enabling automated deadlock detection, forks provides an
       additonal thread object method,

           $thr->is_deadlocked()

       that reports whether the thread in question is currently deadlocked.  This method may be used in
       conjunction with the "resolve" deadlock option to auto-terminate offending threads.

   Splice on shared array
       As of at least threads::shared 1.05, the splice function has not been implememted for arrays; however,
       forks::shared fully supports splice on shared arrays.

   share() doesn't lose value for arrays and hashes
       In the standard Perl threads implementation, arrays and hashes are re-initialized when they become shared
       (with the share()) function.  The share() function of forks::shared does not initialize arrays and hashes
       when they become shared with the share() function.

       This could be considered a bug in the standard Perl implementation.  In any case this is an inconsistency
       of the behaviour of threads.pm and forks.pm.

       If you do not have a natively threaded perl and you have installed and are using forks in "threads.pm"
       override mode (where "use threads" loads forks.pm), then this module will explicitly emulate the behavior
       of standard threads::shared and lose value for arrays and hashes with share().  Additionally, array
       splice function will become a no-op with a warning.

       You may also enable this mode by setting the environment variable "THREADS_NATIVE_EMULATION" to a true
       value before running your script.  See "Native threads 'to-the-letter' emulation mode" in forks for more
       information.

CAVIATS

       Some caveats that you need to be aware of.

       Storing CODE refs in shared variables
         Since forks::shared requires Storable to serialize shared data structures, storing CODE refs in shared
         variables is not enabled by default (primarily for security reasons).

         If need share CODE refs between threads, the minimum you must do before storing CODE refs is:

             $Storable::Deparse = $Storable::Eval = 1;

         See "CODE_REFERENCES" in Storable for detailed information, including potential security risks and ways
         to protect yourself against them.

       test-suite exits in a weird way
         Although there are no errors in the test-suite, the test harness sometimes thinks there is something
         wrong because of an unexpected exit() value.  This is an issue with Test::More's END block, which
         wasn't designed to co-exist with a threads environment and forked processes.  Hopefully, that module
         will be patched in the future, but for now, the warnings are harmless and may be safely ignored.

CURRENT AUTHOR AND MAINTAINER

       Eric Rybski <rybskej@yahoo.com>.  Please send all module inquries to me.

ORIGINAL AUTHOR

       Elizabeth Mattijsen, <liz@dijkmat.nl>.

COPYRIGHT

       Copyright (c)
        2005-2010 Eric Rybski <rybskej@yahoo.com>,
        2002-2004 Elizabeth Mattijsen <liz@dijkmat.nl>.  All rights reserved.  This program is free software;
       you can redistribute it and/or modify it under the same terms as Perl itself.

SEE ALSO

       threads::shared, forks, forks::BerkeleyDB::shared.