Subversion Repositories Projects

package threads::shared;

use 5.008;

use strict;

use warnings;

use Scalar::Util qw(reftype refaddr blessed);

our $VERSION = '1.28';

my $XS_VERSION = $VERSION;

$VERSION = eval $VERSION;

# Declare that we have been loaded

$threads::shared::threads_shared = 1;

# Load the XS code, if applicable

if ($threads::threads) {

    require XSLoader;

    XSLoader::load('threads::shared', $XS_VERSION);

    *is_shared = \&_id;

} else {

    # String eval is generally evil, but we don't want these subs to

    # exist at all if 'threads' is not loaded successfully.

    # Vivifying them conditionally this way saves on average about 4K

    # of memory per thread.

    eval <<'_MARKER_';

        sub share          (\[$@%])         { return $_[0] }

        sub is_shared      (\[$@%])         { undef }

        sub cond_wait      (\[$@%];\[$@%])  { undef }

        sub cond_timedwait (\[$@%]$;\[$@%]) { undef }

        sub cond_signal    (\[$@%])         { undef }

        sub cond_broadcast (\[$@%])         { undef }

_MARKER_

}

### Export ###

sub import

{

    # Exported subroutines

    my @EXPORT = qw(share is_shared cond_wait cond_timedwait

                    cond_signal cond_broadcast shared_clone);

    if ($threads::threads) {

        push(@EXPORT, 'bless');

    }

    # Export subroutine names

    my $caller = caller();

    foreach my $sym (@EXPORT) {

        no strict 'refs';

        *{$caller.'::'.$sym} = \&{$sym};

    }

}

# Predeclarations for internal functions

my ($make_shared);

### Methods, etc. ###

sub threads::shared::tie::SPLICE

{

    require Carp;

    Carp::croak('Splice not implemented for shared arrays');

}

# Create a thread-shared clone of a complex data structure or object

sub shared_clone

{

    if (@_ != 1) {

        require Carp;

        Carp::croak('Usage: shared_clone(REF)');

    }

    return $make_shared->(shift, {});

}

### Internal Functions ###

# Used by shared_clone() to recursively clone

#   a complex data structure or object

$make_shared = sub {

    my ($item, $cloned) = @_;

    # Just return the item if:

    # 1. Not a ref;

    # 2. Already shared; or

    # 3. Not running 'threads'.

    return $item if (! ref($item) || is_shared($item) || ! $threads::threads);

    # Check for previously cloned references

    #   (this takes care of circular refs as well)

    my $addr = refaddr($item);

    if (exists($cloned->{$addr})) {

        # Return the already existing clone

        return $cloned->{$addr};

    }

    # Make copies of array, hash and scalar refs and refs of refs

    my $copy;

    my $ref_type = reftype($item);

    # Copy an array ref

    if ($ref_type eq 'ARRAY') {

        # Make empty shared array ref

        $copy = &share([]);

        # Add to clone checking hash

        $cloned->{$addr} = $copy;

        # Recursively copy and add contents

        push(@$copy, map { $make_shared->($_, $cloned) } @$item);

    }

    # Copy a hash ref

    elsif ($ref_type eq 'HASH') {

        # Make empty shared hash ref

        $copy = &share({});

        # Add to clone checking hash

        $cloned->{$addr} = $copy;

        # Recursively copy and add contents

        foreach my $key (keys(%{$item})) {

            $copy->{$key} = $make_shared->($item->{$key}, $cloned);

        }

    }

    # Copy a scalar ref

    elsif ($ref_type eq 'SCALAR') {

        $copy = \do{ my $scalar = $$item; };

        share($copy);

        # Add to clone checking hash

        $cloned->{$addr} = $copy;

    }

    # Copy of a ref of a ref

    elsif ($ref_type eq 'REF') {

        # Special handling for $x = \$x

        if ($addr == refaddr($$item)) {

            $copy = \$copy;

            share($copy);

            $cloned->{$addr} = $copy;

        } else {

            my $tmp;

            $copy = \$tmp;

            share($copy);

            # Add to clone checking hash

            $cloned->{$addr} = $copy;

            # Recursively copy and add contents

            $tmp = $make_shared->($$item, $cloned);

        }

    } else {

        require Carp;

        Carp::croak("Unsupported ref type: ", $ref_type);

    }

    # If input item is an object, then bless the copy into the same class

    if (my $class = blessed($item)) {

        bless($copy, $class);

    }

    # Clone READONLY flag

    if ($ref_type eq 'SCALAR') {

        if (Internals::SvREADONLY($$item)) {

            Internals::SvREADONLY($$copy, 1) if ($] >= 5.008003);

        }

    }

    if (Internals::SvREADONLY($item)) {

        Internals::SvREADONLY($copy, 1) if ($] >= 5.008003);

    }

    return $copy;

};

1;

__END__

=head1 NAME

threads::shared - Perl extension for sharing data structures between threads

=head1 VERSION

This document describes threads::shared version 1.28

=head1 SYNOPSIS

  use threads;

  use threads::shared;

  my $var :shared;

  my %hsh :shared;

  my @ary :shared;

  my ($scalar, @array, %hash);

  share($scalar);

  share(@array);

  share(%hash);

  $var = $scalar_value;

  $var = $shared_ref_value;

  $var = shared_clone($non_shared_ref_value);

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

  $hsh{'foo'} = $scalar_value;

  $hsh{'bar'} = $shared_ref_value;

  $hsh{'baz'} = shared_clone($non_shared_ref_value);

  $hsh{'quz'} = shared_clone([1..3]);

  $ary[0] = $scalar_value;

  $ary[1] = $shared_ref_value;

  $ary[2] = shared_clone($non_shared_ref_value);

  $ary[3] = shared_clone([ {}, [] ]);

  { lock(%hash); ...  }

  cond_wait($scalar);

  cond_timedwait($scalar, time() + 30);

  cond_broadcast(@array);

  cond_signal(%hash);

  my $lockvar :shared;

  # condition var != lock var

  cond_wait($var, $lockvar);

  cond_timedwait($var, time()+30, $lockvar);

=head1 DESCRIPTION

By default, variables are private to each thread, and each newly created

thread gets a private copy of each existing variable.  This module allows you

to share variables across different threads (and pseudo-forks on Win32).  It

is used together with the L<threads> module.

This module supports the sharing of the following data types only:  scalars

and scalar refs, arrays and array refs, and hashes and hash refs.

=head1 EXPORT

The following functions are exported by this module: C<share>,

C<shared_clone>, C<is_shared>, C<cond_wait>, C<cond_timedwait>, C<cond_signal>

and C<cond_broadcast>

Note that if this module is imported when L<threads> has not yet been loaded,

then these functions all become no-ops.  This makes it possible to write

modules that will work in both threaded and non-threaded environments.

=head1 FUNCTIONS

=over 4

=item share VARIABLE

C<share> takes a variable and marks it as shared:

  my ($scalar, @array, %hash);

  share($scalar);

  share(@array);

  share(%hash);

C<share> will return the shared rvalue, but always as a reference.

Variables can also be marked as shared at compile time by using the

C<:shared> attribute:

  my ($var, %hash, @array) :shared;

Shared variables can only store scalars, refs of shared variables, or

refs of shared data (discussed in next section):

  my ($var, %hash, @array) :shared;

  my $bork;

  # Storing scalars

  $var = 1;

  $hash{'foo'} = 'bar';

  $array[0] = 1.5;

  # Storing shared refs

  $var = \%hash;

  $hash{'ary'} = \@array;

  $array[1] = \$var;

  # The following are errors:

  #   $var = \$bork;                    # ref of non-shared variable

  #   $hash{'bork'} = [];               # non-shared array ref

  #   push(@array, { 'x' => 1 });       # non-shared hash ref

=item shared_clone REF

C<shared_clone> takes a reference, and returns a shared version of its

argument, performing a deep copy on any non-shared elements.  Any shared

elements in the argument are used as is (i.e., they are not cloned).

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

Object status (i.e., the class an object is blessed into) is also cloned.

  my $obj = {'foo' => [qw/foo bar baz/]};

  bless($obj, 'Foo');

  my $cpy = shared_clone($obj);

  print(ref($cpy), "\n");         # Outputs 'Foo'

For cloning empty array or hash refs, the following may also be used:

  $var = &share([]);   # Same as $var = shared_clone([]);

  $var = &share({});   # Same as $var = shared_clone({});

=item is_shared VARIABLE

C<is_shared> checks if the specified variable is shared or not.  If shared,

returns the variable's internal ID (similar to

L<refaddr()|Scalar::Util/"refaddr EXPR">).  Otherwise, returns C<undef>.

  if (is_shared($var)) {

      print("\$var is shared\n");

  } else {

      print("\$var is not shared\n");

  }

When used on an element of an array or hash, C<is_shared> checks if the

specified element belongs to a shared array or hash.  (It does not check

the contents of that element.)

  my %hash :shared;

  if (is_shared(%hash)) {

      print("\%hash is shared\n");

  }

  $hash{'elem'} = 1;

  if (is_shared($hash{'elem'})) {

      print("\$hash{'elem'} is in a shared hash\n");

  }

=item lock VARIABLE

C<lock> places a B<advisory> lock on a variable until the lock goes out of

scope.  If the variable is locked by another thread, the C<lock> call will

block until it's available.  Multiple calls to C<lock> by the same thread from

within dynamically nested scopes are safe -- the variable will remain locked

until the outermost lock on the variable goes out of scope.

C<lock> follows references exactly I<one> level:

  my %hash :shared;

  my $ref = \%hash;

  lock($ref);           # This is equivalent to lock(%hash)

Note that you cannot explicitly unlock a variable; you can only wait for the

lock to go out of scope.  This is most easily accomplished by locking the

variable inside a block.

  my $var :shared;

  {

      lock($var);

      # $var is locked from here to the end of the block

      ...

  }

  # $var is now unlocked

As locks are advisory, they do not prevent data access or modification by

another thread that does not itself attempt to obtain a lock on the variable.

You cannot lock the individual elements of a container variable:

  my %hash :shared;

  $hash{'foo'} = 'bar';

  #lock($hash{'foo'});          # Error

  lock(%hash);                  # Works

If you need more fine-grained control over shared variable access, see

L<Thread::Semaphore>.

=item cond_wait VARIABLE

=item cond_wait CONDVAR, LOCKVAR

The C<cond_wait> function takes a B<locked> variable as a parameter, unlocks

the variable, and blocks until another thread does a C<cond_signal> or

C<cond_broadcast> for that same locked variable.  The variable that

C<cond_wait> blocked on is relocked after the C<cond_wait> is satisfied.  If

there are multiple threads C<cond_wait>ing on the same variable, all but one

will re-block waiting to reacquire the lock on the variable. (So if you're only

using C<cond_wait> for synchronisation, give up the lock as soon as possible).

The two actions of unlocking the variable and entering the blocked wait state

are atomic, the two actions of exiting from the blocked wait state and

re-locking the variable are not.

In its second form, C<cond_wait> takes a shared, B<unlocked> variable followed

by a shared, B<locked> variable.  The second variable is unlocked and thread

execution suspended until another thread signals the first variable.

It is important to note that the variable can be notified even if no thread

C<cond_signal> or C<cond_broadcast> on the variable.  It is therefore

important to check the value of the variable and go back to waiting if the

requirement is not fulfilled.  For example, to pause until a shared counter

drops to zero:

  { lock($counter); cond_wait($count) until $counter == 0; }

=item cond_timedwait VARIABLE, ABS_TIMEOUT

=item cond_timedwait CONDVAR, ABS_TIMEOUT, LOCKVAR

In its two-argument form, C<cond_timedwait> takes a B<locked> variable and an

absolute timeout as parameters, unlocks the variable, and blocks until the

timeout is reached or another thread signals the variable.  A false value is

returned if the timeout is reached, and a true value otherwise.  In either

case, the variable is re-locked upon return.

Like C<cond_wait>, this function may take a shared, B<locked> variable as an

additional parameter; in this case the first parameter is an B<unlocked>

condition variable protected by a distinct lock variable.

Again like C<cond_wait>, waking up and reacquiring the lock are not atomic,

and you should always check your desired condition after this function

returns.  Since the timeout is an absolute value, however, it does not have to

be recalculated with each pass:

  lock($var);

  my $abs = time() + 15;

  until ($ok = desired_condition($var)) {

      last if !cond_timedwait($var, $abs);

  }

  # we got it if $ok, otherwise we timed out!

=item cond_signal VARIABLE

The C<cond_signal> function takes a B<locked> variable as a parameter and

unblocks one thread that's C<cond_wait>ing on that variable. If more than one

thread is blocked in a C<cond_wait> on that variable, only one (and which one

is indeterminate) will be unblocked.

If there are no threads blocked in a C<cond_wait> on the variable, the signal

is discarded. By always locking before signaling, you can (with care), avoid

signaling before another thread has entered cond_wait().

C<cond_signal> will normally generate a warning if you attempt to use it on an

unlocked variable. On the rare occasions where doing this may be sensible, you

can suppress the warning with:

  { no warnings 'threads'; cond_signal($foo); }

=item cond_broadcast VARIABLE

The C<cond_broadcast> function works similarly to C<cond_signal>.

C<cond_broadcast>, though, will unblock B<all> the threads that are blocked in

a C<cond_wait> on the locked variable, rather than only one.

=back

=head1 OBJECTS

L<threads::shared> exports a version of L<bless()|perlfunc/"bless REF"> that

works on shared objects such that I<blessings> propagate across threads.

  # Create a shared 'Foo' object

  my $foo :shared = shared_clone({});

  bless($foo, 'Foo');

  # Create a shared 'Bar' object

  my $bar :shared = shared_clone({});

  bless($bar, 'Bar');

  # Put 'bar' inside 'foo'

  $foo->{'bar'} = $bar;

  # Rebless the objects via a thread

  threads->create(sub {

      # Rebless the outer object

      bless($foo, 'Yin');

      # Cannot directly rebless the inner object

      #bless($foo->{'bar'}, 'Yang');

      # Retrieve and rebless the inner object

      my $obj = $foo->{'bar'};

      bless($obj, 'Yang');

      $foo->{'bar'} = $obj;

  })->join();

  print(ref($foo),          "\n");    # Prints 'Yin'

  print(ref($foo->{'bar'}), "\n");    # Prints 'Yang'

  print(ref($bar),          "\n");    # Also prints 'Yang'

=head1 NOTES

L<threads::shared> is designed to disable itself silently if threads are not

available.  This allows you to write modules and packages that can be used

in both threaded and non-threaded applications.

If you want access to threads, you must C<use threads> before you

C<use threads::shared>.  L<threads> will emit a warning if you use it after

L<threads::shared>.

=head1 BUGS AND LIMITATIONS

When C<share> is used on arrays, hashes, array refs or hash refs, any data

they contain will be lost.

  my @arr = qw(foo bar baz);

  share(@arr);

  # @arr is now empty (i.e., == ());

  # Create a 'foo' object

  my $foo = { 'data' => 99 };

  bless($foo, 'foo');

  # Share the object

  share($foo);        # Contents are now wiped out

  print("ERROR: \$foo is empty\n")

      if (! exists($foo->{'data'}));

Therefore, populate such variables B<after> declaring them as shared.  (Scalar

and scalar refs are not affected by this problem.)

It is often not wise to share an object unless the class itself has been

written to support sharing.  For example, an object's destructor may get

called multiple times, once for each thread's scope exit.  Another danger is

that the contents of hash-based objects will be lost due to the above

mentioned limitation.  See F<examples/class.pl> (in the CPAN distribution of

this module) for how to create a class that supports object sharing.

Does not support C<splice> on arrays!

Taking references to the elements of shared arrays and hashes does not

autovivify the elements, and neither does slicing a shared array/hash over

non-existent indices/keys autovivify the elements.

C<share()> allows you to C<< share($hashref->{key}) >> and

C<< share($arrayref->[idx]) >> without giving any error message.  But the

C<< $hashref->{key} >> or C<< $arrayref->[idx] >> is B<not> shared, causing

the error "lock can only be used on shared values" to occur when you attempt

to C<< lock($hasref->{key}) >> or C<< lock($arrayref->[idx]) >> in another

thread.

Using L<refaddr()|Scalar::Util/"refaddr EXPR">) is unreliable for testing

whether or not two shared references are equivalent (e.g., when testing for

circular references).  Use L<is_shared()/"is_shared VARIABLE">, instead:

    use threads;

    use threads::shared;

    use Scalar::Util qw(refaddr);

    # If ref is shared, use threads::shared's internal ID.

    # Otherwise, use refaddr().

    my $addr1 = is_shared($ref1) || refaddr($ref1);

    my $addr2 = is_shared($ref2) || refaddr($ref2);

    if ($addr1 == $addr2) {

        # The refs are equivalent

    }

L<each()|perlfunc/"each HASH"> does not work properly on shared references

embedded in shared structures.  For example:

    my %foo :shared;

    $foo{'bar'} = shared_clone({'a'=>'x', 'b'=>'y', 'c'=>'z'});

    while (my ($key, $val) = each(%{$foo{'bar'}})) {

        ...

    }

Either of the following will work instead:

    my $ref = $foo{'bar'};

    while (my ($key, $val) = each(%{$ref})) {

        ...

    }

    foreach my $key (keys(%{$foo{'bar'}})) {

        my $val = $foo{'bar'}{$key};

        ...

    }

View existing bug reports at, and submit any new bugs, problems, patches, etc.

to: L<http://rt.cpan.org/Public/Dist/Display.html?Name=threads-shared>

=head1 SEE ALSO

L<threads::shared> Discussion Forum on CPAN:

L<http://www.cpanforum.com/dist/threads-shared>

Annotated POD for L<threads::shared>:

L<http://annocpan.org/~JDHEDDEN/threads-shared-1.28/shared.pm>

Source repository:

L<http://code.google.com/p/threads-shared/>

L<threads>, L<perlthrtut>

L<http://www.perl.com/pub/a/2002/06/11/threads.html> and

L<http://www.perl.com/pub/a/2002/09/04/threads.html>

Perl threads mailing list:

L<http://lists.cpan.org/showlist.cgi?name=iThreads>

=head1 AUTHOR

Artur Bergman E<lt>sky AT crucially DOT netE<gt>

Documentation borrowed from the old Thread.pm.

CPAN version produced by Jerry D. Hedden E<lt>jdhedden AT cpan DOT orgE<gt>.

=head1 LICENSE

threads::shared is released under the same license as Perl.

=cut