-
-
package threads;
-use 5.7.2;
+use 5.008;
+
use strict;
use warnings;
-use overload
- '==' => \&equals,
- 'fallback' => 1;
+our $VERSION = '1.36';
+my $XS_VERSION = $VERSION;
+$VERSION = eval $VERSION;
+
+
+BEGIN {
+ # Verify this Perl supports threads
+ use Config;
+ if (! $Config{useithreads}) {
+ die("This Perl not built to support threads\n");
+ }
+
+ # Declare that we have been loaded
+ $threads::threads = 1;
+
+ # Complain if 'threads' is loaded after 'threads::shared'
+ if ($threads::shared::threads_shared) {
+ warn <<'_MSG_';
+Warning, threads::shared has already been loaded. To
+enable shared variables, 'use threads' must be called
+before threads::shared or any module that uses it.
+_MSG_
+ }
+}
-#use threads::Shared;
+# Load the XS code
+require XSLoader;
+XSLoader::load('threads', $XS_VERSION);
-require Exporter;
-require DynaLoader;
-use Devel::Peek;
+### Export ###
+sub import
+{
+ my $class = shift; # Not used
-our @ISA = qw(Exporter DynaLoader);
+ # Exported subroutines
+ my @EXPORT = qw(async);
-our %EXPORT_TAGS = ( all => [qw()]);
+ # Handle args
+ while (my $sym = shift) {
+ if ($sym =~ /^stack/) {
+ threads->set_stack_size(shift);
-our @EXPORT_OK = ( @{ $EXPORT_TAGS{'all'} } );
+ } elsif ($sym =~ /all/) {
+ push(@EXPORT, qw(yield));
-our @EXPORT = qw(
-
-);
-our $VERSION = '0.05';
+ } else {
+ push(@EXPORT, $sym);
+ }
+ }
+
+ # Export subroutine names
+ my $caller = caller();
+ foreach my $sym (@EXPORT) {
+ no strict 'refs';
+ *{$caller.'::'.$sym} = \&{$sym};
+ }
-sub new {
- my $class = shift;
- print (Dump($_[0]));
- return $class->create(@_);
+ # Set stack size via environment variable
+ if (exists($ENV{'PERL5_ITHREADS_STACK_SIZE'})) {
+ threads->set_stack_size($ENV{'PERL5_ITHREADS_STACK_SIZE'});
+ }
}
-sub equals {
- return 1 if($_[0]->tid() == $_[1]->tid());
- return 0;
+### Methods, etc. ###
+
+# Our own exit function/method
+sub exit
+{
+ CORE::exit(0);
}
-$Config::threads = 1;
+# 'Constant' args for threads->list()
+sub threads::all { }
+sub threads::running { 1 }
+sub threads::joinable { 0 }
-bootstrap threads $VERSION;
+# 'new' is an alias for 'create'
+*new = \&create;
+# 'async' is a function alias for the 'threads->create()' method
+sub async (&;@)
+{
+ unshift(@_, 'threads');
+ # Use "goto" trick to avoid pad problems from 5.8.1 (fixed in 5.8.2)
+ goto &create;
+}
-# Preloaded methods go here.
+# Thread object equality checking
+use overload (
+ '==' => \&equal,
+ '!=' => sub { ! equal(@_) },
+ 'fallback' => 1
+);
1;
+
__END__
=head1 NAME
-threads - Perl extension allowing use of interpreter based threads from perl
+threads - Perl interpreter-based threads
+
+=head1 VERSION
+
+This document describes threads version 1.36
=head1 SYNOPSIS
+ use threads ('yield', 'stack_size' => 64*4096);
-use threads;
+ sub start_thread {
+ my @args = @_;
+ print('Thread started: ', join(' ', @args), "\n");
+ }
+ my $thread = threads->create('start_thread', 'argument');
+ $thread->join();
-sub start_thread {
- print "Thread started\n";
-}
+ threads->create(sub { print("I am a thread\n"); })->join();
+ my $thread3 = async { foreach (@files) { ... } };
+ $thread3->join();
-my $thread = threads->new("start_thread","argument");
+ # Invoke thread in list context (implicit) so it can return a list
+ my ($thr) = threads->create(sub { return (qw/a b c/); });
+ # or specify list context explicitly
+ my $thr = threads->create({'context' => 'list'},
+ sub { return (qw/a b c/); });
+ my @results = $thr->join();
-$thread->new(sub { print "I am a thread"},"argument");
+ $thread->detach();
-$thread->join();
+ $thread = threads->self();
+ $thread = threads->object($tid);
-$thread->detach();
+ $tid = threads->tid();
+ $tid = threads->self->tid();
+ $tid = $thread->tid();
-$thread = threads->self();
+ threads->yield();
+ yield();
-thread->tid();
+ my @threads = threads->list();
+ my $thread_count = threads->list();
+ my @running = threads->list(threads::running);
+ my @joinable = threads->list(threads::joinable);
+ if ($thr1 == $thr2) {
+ ...
+ }
+
+ $stack_size = threads->get_stack_size();
+ $old_size = threads->set_stack_size(32*4096);
+
+ # Create a thread with a specific context and stack size
+ my $thr = threads->create({ 'context' => 'list',
+ 'stack_size' => 32*4096 },
+ \&foo);
+
+ # Get thread's context
+ my $wantarray = $thr->wantarray();
+
+ # Check thread's state
+ if ($thr->is_running()) {
+ sleep(1);
+ }
+ if ($thr->is_joinable()) {
+ $thr->join();
+ }
+
+ $thr->kill('SIGUSR1');
+
+ threads->exit();
=head1 DESCRIPTION
-Perl 5.6 has something called interpreter threads, interpreter threads are built on MULTIPLICITY and allows for several different perl interpreters to run in different threads. This has been used in win32 perl to fake forks, it has also been available to people embedding perl.
+Perl 5.6 introduced something called interpreter threads. Interpreter threads
+are different from I<5005threads> (the thread model of Perl 5.005) by creating
+a new Perl interpreter per thread, and not sharing any data or state between
+threads by default.
+
+Prior to Perl 5.8, this has only been available to people embedding Perl, and
+for emulating fork() on Windows.
+
+The I<threads> API is loosely based on the old Thread.pm API. It is very
+important to note that variables are not shared between threads, all variables
+are by default thread local. To use shared variables one must use
+L<threads::shared>.
+
+It is also important to note that you must enable threads by doing C<use
+threads> as early as possible in the script itself, and that it is not
+possible to enable threading inside an C<eval "">, C<do>, C<require>, or
+C<use>. In particular, if you are intending to share variables with
+L<threads::shared>, you must C<use threads> before you C<use threads::shared>.
+(C<threads> will emit a warning if you do it the other way around.)
=over
-=item new, function, LIST
+=item $thr = threads->create(FUNCTION, ARGS)
+
+This will create a new thread that will begin execution with the specified
+entry point function, and give it the I<ARGS> list as parameters. It will
+return the corresponding threads object, or C<undef> if thread creation failed.
+
+I<FUNCTION> may either be the name of a function, an anonymous subroutine, or
+a code ref.
+
+ my $thr = threads->create('func_name', ...);
+ # or
+ my $thr = threads->create(sub { ... }, ...);
+ # or
+ my $thr = threads->create(\&func, ...);
+
+The C<-E<gt>new()> method is an alias for C<-E<gt>create()>.
+
+=item $thr->join()
+
+This will wait for the corresponding thread to complete its execution. When
+the thread finishes, C<-E<gt>join()> will return the return value(s) of the
+entry point function.
+
+The context (void, scalar or list) for the return value(s) for C<-E<gt>join()>
+is determined at the time of thread creation.
+
+ # Create thread in list context (implicit)
+ my ($thr1) = threads->create(sub {
+ my @results = qw(a b c);
+ return (@results);
+ });
+ # or (explicit)
+ my $thr1 = threads->create({'context' => 'list'},
+ sub {
+ my @results = qw(a b c);
+ return (@results);
+ });
+ # Retrieve list results from thread
+ my @res1 = $thr1->join();
+
+ # Create thread in scalar context (implicit)
+ my $thr2 = threads->create(sub {
+ my $result = 42;
+ return ($result);
+ });
+ # Retrieve scalar result from thread
+ my $res2 = $thr2->join();
+
+ # Create a thread in void context (explicit)
+ my $thr3 = threads->create({'void' => 1},
+ sub { print("Hello, world\n"); });
+ # Join the thread in void context (i.e., no return value)
+ $thr3->join();
+
+See L</"THREAD CONTEXT"> for more details.
+
+If the program exits without all threads having either been joined or
+detached, then a warning will be issued.
+
+Calling C<-E<gt>join()> or C<-E<gt>detach()> on an already joined thread will
+cause an error to be thrown.
+
+=item $thr->detach()
+
+Makes the thread unjoinable, and causes any eventual return value to be
+discarded. When the program exits, any detached threads that are still
+running are silently terminated.
+
+If the program exits without all threads having either been joined or
+detached, then a warning will be issued.
+
+Calling C<-E<gt>join()> or C<-E<gt>detach()> on an already detached thread
+will cause an error to be thrown.
+
+=item threads->detach()
+
+Class method that allows a thread to detach itself.
+
+=item threads->exit()
+
+The usual method for terminating a thread is to
+L<return()|perlfunc/"return EXPR"> from the entry point function with the
+appropriate return value(s).
+
+If needed, a thread can be exited at any time by calling
+C<threads-E<gt>exit()>. This will cause the thread to return C<undef> in a
+scalar context, or the empty list in a list context.
+
+Calling C<die()> in a thread indicates an abnormal exit for the thread. Any
+C<$SIG{__DIE__}> handler in the thread will be called first, and then the
+thread will exit with a warning message that will contain any arguments passed
+in the C<die()> call.
+
+Calling C<exit()> in a thread is discouraged, but is equivalent to calling
+C<threads-E<gt>exit()>.
+
+If the desired affect is to truly terminate the application from a thread,
+then use L<POSIX::_exit()|POSIX/"_exit">, if available.
+
+=item threads->self()
+
+Class method that allows a thread to obtain its own I<threads> object.
+
+=item $thr->tid()
+
+Returns the ID of the thread. Thread IDs are unique integers with the main
+thread in a program being 0, and incrementing by 1 for every thread created.
+
+=item threads->tid()
-This will create a new thread with the entry point function and give it LIST as parameters.
-It will return the corresponding threads object.
+Class method that allows a thread to obtain its own ID.
-=item $threads->join
+=item threads->object($tid)
-This will wait for the corresponding thread to join. When it finishes join will return the return values of the root function.
-If a thread has been detached, join will return without wait.
+This will return the I<threads> object for the I<active> thread associated
+with the specified thread ID. Returns C<undef> if there is no thread
+associated with the TID, if the thread is joined or detached, if no TID is
+specified or if the specified TID is undef.
-=item $threads->detach
+=item threads->yield()
-Will throw away the return value from the thread and make non joinable
+This is a suggestion to the OS to let this thread yield CPU time to other
+threads. What actually happens is highly dependent upon the underlying
+thread implementation.
-=item threads->self
+You may do C<use threads qw(yield)>, and then just use C<yield()> in your
+code.
-This will return the object for the current thread.
+=item threads->list()
-=item $threads->tid
+=item threads->list(threads::all)
-This will return the id of the thread.
-threads->self->tid() is a quick way to get current thread id
+=item threads->list(threads::running)
+
+=item threads->list(threads::joinable)
+
+With no arguments (or using C<threads::all>) and in a list context, returns a
+list of all non-joined, non-detached I<threads> objects. In a scalar context,
+returns a count of the same.
+
+With a I<true> argument (using C<threads::running>), returns a list of all
+non-detached I<threads> objects that are still running.
+
+With a I<false> argument (using C<threads::joinable>), returns a list of all
+non-joined, non-detached I<threads> objects that have finished running (i.e.,
+for which C<-E<gt>join()> will not I<block>).
+
+=item $thr1->equal($thr2)
+
+Tests if two threads objects are the same thread or not. This is overloaded
+to the more natural forms:
+
+ if ($thr1 == $thr2) {
+ print("Threads are the same\n");
+ }
+ # or
+ if ($thr1 != $thr2) {
+ print("Threads differ\n");
+ }
+
+(Thread comparison is based on thread IDs.)
+
+=item async BLOCK;
+
+C<async> creates a thread to execute the block immediately following
+it. This block is treated as an anonymous subroutine, and so must have a
+semi-colon after the closing brace. Like C<threads->create()>, C<async>
+returns a I<threads> object.
+
+=item $thr->_handle()
+
+This I<private> method returns the memory location of the internal thread
+structure associated with a threads object. For Win32, this is a pointer to
+the C<HANDLE> value returned by C<CreateThread> (i.e., C<HANDLE *>); for other
+platforms, it is a pointer to the C<pthread_t> structure used in the
+C<pthread_create> call (i.e., C<pthread_t *>).
+
+This method is of no use for general Perl threads programming. Its intent is
+to provide other (XS-based) thread modules with the capability to access, and
+possibly manipulate, the underlying thread structure associated with a Perl
+thread.
+
+=item threads->_handle()
+
+Class method that allows a thread to obtain its own I<handle>.
=back
+=head1 THREAD STATE
-=head1 TODO
+The following boolean methods are useful in determining the I<state> of a
+thread.
=over
-=item Fix so the return value is returned when you join
+=item $thr->is_running()
+
+Returns true if a thread is still running (i.e., if its entry point function
+has not yet finished/exited).
+
+=item $thr->is_joinable()
+
+Returns true if the thread has finished running, is not detached and has not
+yet been joined. In other works, the thread is ready to be joined and will
+not I<block>.
+
+=item $thr->is_detached()
+
+Returns true if the thread has been detached.
-=item Add join_all
+=item threads->is_detached()
-=item Fix memory leaks!
+Class method that allows a thread to determine whether or not it is detached.
=back
-=head1 AUTHOR and COPYRIGHT
+=head1 THREAD CONTEXT
+
+As with subroutines, the type of value returned from a thread's entry point
+function may be determined by the thread's I<context>: list, scalar or void.
+The thread's context is determined at thread creation. This is necessary so
+that the context is available to the entry point function via
+L<wantarray()|perlfunc/"wantarray">. The thread may then specify a value of
+the appropriate type to be returned from C<-E<gt>join()>.
+
+=head2 Explicit context
+
+Because thread creation and thread joining may occur in different contexts, it
+may be desirable to state the context explicitly to the thread's entry point
+function. This may be done by calling C<-E<gt>create()> with a parameter hash
+as the first argument:
+
+ my $thr = threads->create({'context' => 'list'}, \&foo);
+ ...
+ my @results = $thr->join();
+
+In the above, the threads object is returned to the parent thread in scalar
+context, and the thread's entry point function C<foo> will be called in list
+context such that the parent thread can receive a list from the C<-E<gt>join()>
+call. Similarly, if you need the threads object, but your thread will not be
+returning a value (i.e., I<void> context), you would do the following:
+
+ my $thr = threads->create({'context' => 'void'}, \&foo);
+ ...
+ $thr->join();
+
+The context type may also be used as the I<key> in the parameter hash followed
+by a I<true> value:
+
+ threads->create({'scalar' => 1}, \&foo);
+ ...
+ my ($thr) = threads->list();
+ my $result = $thr->join();
+
+=head2 Implicit context
+
+If not explicitly stated, the thread's context is implied from the context
+of the C<-E<gt>create()> call:
+
+ # Create thread in list context
+ my ($thr) = threads->create(...);
+
+ # Create thread in scalar context
+ my $thr = threads->create(...);
+
+ # Create thread in void context
+ threads->create(...);
+
+=head2 $thr->wantarray()
+
+This returns the thread's context in the same manner as
+L<wantarray()|perlfunc/"wantarray">.
+
+=head2 threads->wantarray()
+
+Class method to return the current thread's context. This is the same as
+running L<wantarray()|perlfunc/"wantarray"> in the current thread.
+
+=head1 THREAD STACK SIZE
+
+The default per-thread stack size for different platforms varies
+significantly, and is almost always far more than is needed for most
+applications. On Win32, Perl's makefile explicitly sets the default stack to
+16 MB; on most other platforms, the system default is used, which again may be
+much larger than is needed.
+
+By tuning the stack size to more accurately reflect your application's needs,
+you may significantly reduce your application's memory usage, and increase the
+number of simultaneously running threads.
+
+N.B., on Windows, Address space allocation granularity is 64 KB, therefore,
+setting the stack smaller than that on Win32 Perl will not save any more
+memory.
+
+=over
+
+=item threads->get_stack_size();
+
+Returns the current default per-thread stack size. The default is zero, which
+means the system default stack size is currently in use.
+
+=item $size = $thr->get_stack_size();
+
+Returns the stack size for a particular thread. A return value of zero
+indicates the system default stack size was used for the thread.
+
+=item $old_size = threads->set_stack_size($new_size);
+
+Sets a new default per-thread stack size, and returns the previous setting.
+
+Some platforms have a minimum thread stack size. Trying to set the stack size
+below this value will result in a warning, and the minimum stack size will be
+used.
+
+Some Linux platforms have a maximum stack size. Setting too large of a stack
+size will cause thread creation to fail.
-Artur Bergman <lt>artur at contiller.se<gt>
+If needed, C<$new_size> will be rounded up to the next multiple of the memory
+page size (usually 4096 or 8192).
-threads is released under the same license as Perl
+Threads created after the stack size is set will then either call
+C<pthread_attr_setstacksize()> I<(for pthreads platforms)>, or supply the
+stack size to C<CreateThread()> I<(for Win32 Perl)>.
-Thanks to
+(Obviously, this call does not affect any currently extant threads.)
-Richard Soderberg <lt>rs at crystalflame.net<gt>
-Helping me out tons, trying to find reasons for races and other wierd bugs!
+=item use threads ('stack_size' => VALUE);
-Simon Cozens <lt>simon at brecon.co.uk<gt>
-Being there to answer zillions of annoying questions
+This sets the default per-thread stack size at the start of the application.
-Rocco Caputo <lt>troc at netrus.net<gt>
+=item $ENV{'PERL5_ITHREADS_STACK_SIZE'}
-Vipul Ved Prakash <lt>mail at vipul.net<gt>
-Helping with debugging.
+The default per-thread stack size may be set at the start of the application
+through the use of the environment variable C<PERL5_ITHREADS_STACK_SIZE>:
-please join perl-ithreads@perl.org for more information
+ PERL5_ITHREADS_STACK_SIZE=1048576
+ export PERL5_ITHREADS_STACK_SIZE
+ perl -e'use threads; print(threads->get_stack_size(), "\n")'
+
+This value overrides any C<stack_size> parameter given to C<use threads>. Its
+primary purpose is to permit setting the per-thread stack size for legacy
+threaded applications.
+
+=item threads->create({'stack_size' => VALUE}, FUNCTION, ARGS)
+
+The stack size an individual threads may also be specified. This may be done
+by calling C<-E<gt>create()> with a parameter hash as the first argument:
+
+ my $thr = threads->create({'stack_size' => 32*4096}, \&foo, @args);
+
+=item $thr2 = $thr1->create(FUNCTION, ARGS)
+
+This creates a new thread (C<$thr2>) that inherits the stack size from an
+existing thread (C<$thr1>). This is shorthand for the following:
+
+ my $stack_size = $thr1->get_stack_size();
+ my $thr2 = threads->create({'stack_size' => $stack_size}, FUNCTION, ARGS);
+
+=back
+
+=head1 THREAD SIGNALLING
+
+When safe signals is in effect (the default behavior - see L</"Unsafe signals">
+for more details), then signals may be sent and acted upon by individual
+threads.
+
+=over 4
+
+=item $thr->kill('SIG...');
+
+Sends the specified signal to the thread. Signal names and (positive) signal
+numbers are the same as those supported by
+L<kill()|perlfunc/"kill SIGNAL, LIST">. For example, 'SIGTERM', 'TERM' and
+(depending on the OS) 15 are all valid arguments to C<-E<gt>kill()>.
+
+Returns the thread object to allow for method chaining:
+
+ $thr->kill('SIG...')->join();
+
+=back
+
+Signal handlers need to be set up in the threads for the signals they are
+expected to act upon. Here's an example for I<cancelling> a thread:
+
+ use threads;
+
+ sub thr_func
+ {
+ # Thread 'cancellation' signal handler
+ $SIG{'KILL'} = sub { threads->exit(); };
+
+ ...
+ }
+
+ # Create a thread
+ my $thr = threads->create('thr_func');
+
+ ...
+
+ # Signal the thread to terminate, and then detach
+ # it so that it will get cleaned up automatically
+ $thr->kill('KILL')->detach();
+
+Here's another simplistic example that illustrates the use of thread
+signalling in conjunction with a semaphore to provide rudimentary I<suspend>
+and I<resume> capabilities:
+
+ use threads;
+ use Thread::Semaphore;
+
+ sub thr_func
+ {
+ my $sema = shift;
+
+ # Thread 'suspend/resume' signal handler
+ $SIG{'STOP'} = sub {
+ $sema->down(); # Thread suspended
+ $sema->up(); # Thread resumes
+ };
+
+ ...
+ }
+
+ # Create a semaphore and send it to a thread
+ my $sema = Thread::Semaphore->new();
+ my $thr = threads->create('thr_func', $sema);
+
+ # Suspend the thread
+ $sema->down();
+ $thr->kill('STOP');
+
+ ...
+
+ # Allow the thread to continue
+ $sema->up();
+
+CAVEAT: The thread signalling capability provided by this module does not
+actually send signals via the OS. It I<emulates> signals at the Perl-level
+such that signal handlers are called in the appropriate thread. For example,
+sending C<$thr-E<gt>kill('STOP')> does not actually suspend a thread (or the
+whole process), but does cause a C<$SIG{'STOP'}> handler to be called in that
+thread (as illustrated above).
+
+As such, signals that would normally not be appropriate to use in the
+C<kill()> command (e.g., C<kill('KILL', $$)>) are okay to use with the
+C<-E<gt>kill()> method (again, as illustrated above).
+
+Correspondingly, sending a signal to a thread does not disrupt the operation
+the thread is currently working on: The signal will be acted upon after the
+current operation has completed. For instance, if the thread is I<stuck> on
+an I/O call, sending it a signal will not cause the I/O call to be interrupted
+such that the signal is acted up immediately.
+
+=head1 WARNINGS
+
+=over 4
+
+=item Perl exited with active threads:
+
+If the program exits without all threads having either been joined or
+detached, then this warning will be issued.
+
+NOTE: This warning cannot be suppressed using C<no warnings 'threads';> as
+suggested below.
+
+=item Thread creation failed: pthread_create returned #
+
+See the appropriate I<man> page for C<pthread_create> to determine the actual
+cause for the failure.
+
+=item Thread # terminated abnormally: ...
+
+A thread terminated in some manner other than just returning from its entry
+point function. For example, the thread may have terminated using C<die>.
+
+=item Using minimum thread stack size of #
+
+Some platforms have a minimum thread stack size. Trying to set the stack size
+below this value will result in the above warning, and the stack size will be
+set to the minimum.
+
+=item Thread creation failed: pthread_attr_setstacksize(I<SIZE>) returned 22
+
+The specified I<SIZE> exceeds the system's maximum stack size. Use a smaller
+value for the stack size.
+
+=back
+
+If needed, thread warnings can be suppressed by using:
+
+ no warnings 'threads';
+
+in the appropriate scope.
+
+=head1 ERRORS
+
+=over 4
+
+=item This Perl not built to support threads
+
+The particular copy of Perl that you're trying to use was not built using the
+C<useithreads> configuration option.
+
+Having threads support requires all of Perl and all of the XS modules in the
+Perl installation to be rebuilt; it is not just a question of adding the
+L<threads> module (i.e., threaded and non-threaded Perls are binary
+incompatible.)
+
+=item Cannot change stack size of an existing thread
+
+The stack size of currently extant threads cannot be changed, therefore, the
+following results in the above error:
+
+ $thr->set_stack_size($size);
+
+=item Cannot signal threads without safe signals
+
+Safe signals must be in effect to use the C<-E<gt>kill()> signalling method.
+See L</"Unsafe signals"> for more details.
+
+=item Unrecognized signal name: ...
+
+The particular copy of Perl that you're trying to use does not support the
+specified signal being used in a C<-E<gt>kill()> call.
+
+=back
=head1 BUGS
=over
-=item creating a thread from within a thread is unsafe under win32
+=item Parent-child threads
+
+On some platforms, it might not be possible to destroy I<parent> threads while
+there are still existing I<child> threads.
+
+=item Creating threads inside special blocks
+
+Creating threads inside C<BEGIN>, C<CHECK> or C<INIT> blocks should not be
+relied upon. Depending on the Perl version and the application code, results
+may range from success, to (apparently harmless) warnings of leaked scalar, or
+all the way up to crashing of the Perl interpreter.
+
+=item Unsafe signals
+
+Since Perl 5.8.0, signals have been made safer in Perl by postponing their
+handling until the interpreter is in a I<safe> state. See
+L<perl58delta/"Safe Signals"> and L<perlipc/"Deferred Signals (Safe Signals)">
+for more details.
+
+Safe signals is the default behavior, and the old, immediate, unsafe
+signalling behavior is only in effect in the following situations:
+
+=over 4
+
+=item * Perl was been built with C<PERL_OLD_SIGNALS> (see C<perl -V>).
+
+=item * The environment variable C<PERL_SIGNALS> is set to C<unsafe> (see L<perlrun/"PERL_SIGNALS">).
+
+=item * The module L<Perl::Unsafe::Signals> is used.
=back
+If unsafe signals is in effect, then signal handling is not thread-safe, and
+the C<-E<gt>kill()> signalling method cannot be used.
+
+=item Returning closures from threads
+
+Returning closures from threads should not be relied upon. Depending of the
+Perl version and the application code, results may range from success, to
+(apparently harmless) warnings of leaked scalar, or all the way up to crashing
+of the Perl interpreter.
+
+=item Perl Bugs and the CPAN Version of L<threads>
+
+Support for threads extents beyond the code in this module (i.e.,
+F<threads.pm> and F<threads.xs>), and into the Perl iterpreter itself. Older
+versions of Perl contain bugs that may manifest themselves despite using the
+latest version of L<threads> from CPAN. There is no workaround for this other
+than upgrading to the lastest version of Perl.
+
+(Before you consider posting a bug report, please consult, and possibly post a
+message to the discussion forum to see if what you've encountered is a known
+problem.)
+
+=back
+
+=head1 REQUIREMENTS
+
+Perl 5.8.0 or later
+
=head1 SEE ALSO
-L<perl>, L<perlcall>, L<perlembed>, L<perlguts>
+L<threads> Discussion Forum on CPAN:
+L<http://www.cpanforum.com/dist/threads>
-=cut
+Annotated POD for L<threads>:
+L<http://annocpan.org/~JDHEDDEN/threads-1.36/threads.pm>
+L<threads::shared>, 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>
+Stack size discussion:
+L<http://www.perlmonks.org/?node_id=532956>
+
+=head1 AUTHOR
+
+Artur Bergman E<lt>sky AT crucially DOT netE<gt>
+
+threads is released under the same license as Perl.
+
+CPAN version produced by Jerry D. Hedden <jdhedden AT cpan DOT org>
+
+=head1 ACKNOWLEDGEMENTS
+
+Richard Soderberg E<lt>perl AT crystalflame DOT netE<gt> -
+Helping me out tons, trying to find reasons for races and other weird bugs!
+
+Simon Cozens E<lt>simon AT brecon DOT co DOT ukE<gt> -
+Being there to answer zillions of annoying questions
+
+Rocco Caputo E<lt>troc AT netrus DOT netE<gt>
+
+Vipul Ved Prakash E<lt>mail AT vipul DOT netE<gt> -
+Helping with debugging
+
+Dean Arnold E<lt>darnold AT presicient DOT comE<gt> -
+Stack size API
+
+=cut
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