package threads;
-use 5.7.2;
+use 5.008;
+
use strict;
use warnings;
-use overload
- '==' => \&equal,
- 'fallback' => 1;
+our $VERSION = '1.71';
+my $XS_VERSION = $VERSION;
+$VERSION = eval $VERSION;
-#use threads::Shared;
+# Verify this Perl supports threads
+require Config;
+if (! $Config::Config{useithreads}) {
+ die("This Perl not built to support threads\n");
+}
-BEGIN {
- warn "Warning, threads::shared has already been loaded. ".
- "To enable shared variables for these modules 'use threads' ".
- "must be called before any of those modules are loaded\n"
- if($threads::shared::threads_shared);
+# Complain if 'threads' is loaded after 'threads::shared'
+if ($threads::shared::threads_shared) {
+ warn <<'_MSG_';
+Warning, threads::shared has already been loaded. To
+enable shared variables, 'use threads' must be called
+before threads::shared or any module that uses it.
+_MSG_
}
-require Exporter;
-require DynaLoader;
+# Declare that we have been loaded
+$threads::threads = 1;
-our @ISA = qw(Exporter DynaLoader);
+# Load the XS code
+require XSLoader;
+XSLoader::load('threads', $XS_VERSION);
+
+
+### Export ###
+
+sub import
+{
+ my $class = shift; # Not used
+
+ # Exported subroutines
+ my @EXPORT = qw(async);
+
+ # Handle args
+ while (my $sym = shift) {
+ if ($sym =~ /^(?:stack|exit)/i) {
+ if (defined(my $arg = shift)) {
+ if ($sym =~ /^stack/i) {
+ threads->set_stack_size($arg);
+ } else {
+ $threads::thread_exit_only = $arg =~ /^thread/i;
+ }
+ } else {
+ require Carp;
+ Carp::croak("threads: Missing argument for option: $sym");
+ }
+
+ } elsif ($sym =~ /^str/i) {
+ import overload ('""' => \&tid);
+
+ } elsif ($sym =~ /^(?::all|yield)$/) {
+ push(@EXPORT, qw(yield));
+
+ } else {
+ require Carp;
+ Carp::croak("threads: Unknown import option: $sym");
+ }
+ }
+
+ # Export subroutine names
+ my $caller = caller();
+ foreach my $sym (@EXPORT) {
+ no strict 'refs';
+ *{$caller.'::'.$sym} = \&{$sym};
+ }
+
+ # Set stack size via environment variable
+ if (exists($ENV{'PERL5_ITHREADS_STACK_SIZE'})) {
+ threads->set_stack_size($ENV{'PERL5_ITHREADS_STACK_SIZE'});
+ }
+}
-our %EXPORT_TAGS = ( all => [qw()]);
-our @EXPORT_OK = ( @{ $EXPORT_TAGS{'all'} } );
+### Methods, etc. ###
-our @EXPORT = qw(
-
-);
-our $VERSION = '0.05';
+# Exit from a thread (only)
+sub exit
+{
+ my ($class, $status) = @_;
+ if (! defined($status)) {
+ $status = 0;
+ }
+ # Class method only
+ if (ref($class)) {
+ require Carp;
+ Carp::croak('Usage: threads->exit(status)');
+ }
-sub equal {
- return 1 if($_[0]->tid() == $_[1]->tid());
- return 0;
+ $class->set_thread_exit_only(1);
+ CORE::exit($status);
}
-$threads::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;
-# Preloaded methods go here.
+# '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;
+}
+
+# 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 1.71
=head1 SYNOPSIS
-use threads;
+ use threads ('yield',
+ 'stack_size' => 64*4096,
+ 'exit' => 'threads_only',
+ 'stringify');
+
+ sub start_thread {
+ my @args = @_;
+ print('Thread started: ', join(' ', @args), "\n");
+ }
+ my $thr = threads->create('start_thread', 'argument');
+ $thr->join();
+
+ threads->create(sub { print("I am a thread\n"); })->join();
+
+ my $thr2 = async { foreach (@files) { ... } };
+ $thr2->join();
+ if (my $err = $thr2->error()) {
+ warn("Thread error: $err\n");
+ }
+
+ # Invoke thread in list context (implicit) so it can return a list
+ my ($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();
+
+ $thr->detach();
+
+ # Get a thread's object
+ $thr = threads->self();
+ $thr = threads->object($tid);
+
+ # Get a thread's ID
+ $tid = threads->tid();
+ $tid = $thr->tid();
+ $tid = "$thr";
+
+ # Give other threads a chance to run
+ threads->yield();
+ yield();
+
+ # Lists of non-detached threads
+ my @threads = threads->list();
+ my $thread_count = threads->list();
+
+ my @running = threads->list(threads::running);
+ my @joinable = threads->list(threads::joinable);
+
+ # Test thread objects
+ if ($thr1 == $thr2) {
+ ...
+ }
+
+ # Manage thread stack size
+ $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,
+ 'exit' => 'thread_only' },
+ \&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();
+ }
+
+ # Send a signal to a thread
+ $thr->kill('SIGUSR1');
+
+ # Exit a thread
+ threads->exit();
-sub start_thread {
- print "Thread started\n";
-}
+=head1 DESCRIPTION
-my $thread = threads->new("start_thread","argument");
+Perl 5.6 introduced something called interpreter threads. Interpreter threads
+are different from I<5005threads> (the thread model of Perl 5.005) by creating
+a new Perl interpreter per thread, and not sharing any data or state between
+threads by default.
-$thread->new(sub { print "I am a thread"},"argument");
+Prior to Perl 5.8, this has only been available to people embedding Perl, and
+for emulating fork() on Windows.
-$thread->join();
+The I<threads> API is loosely based on the old Thread.pm API. It is very
+important to note that variables are not shared between threads, all variables
+are by default thread local. To use shared variables one must also use
+L<threads::shared>:
-$thread->detach();
+ use threads;
+ use threads::shared;
-$thread = threads->self();
+It is also important to note that you must enable threads by doing C<use
+threads> as early as possible in the script itself, and that it is not
+possible to enable threading inside an C<eval "">, C<do>, C<require>, or
+C<use>. In particular, if you are intending to share variables with
+L<threads::shared>, you must C<use threads> before you C<use threads::shared>.
+(C<threads> will emit a warning if you do it the other way around.)
-threads->tid();
-threads->self->tid();
+=over
-$thread->tid();
+=item $thr = threads->create(FUNCTION, ARGS)
-=head1 DESCRIPTION
+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->self()
+
+Class method that allows a thread to obtain its own I<threads> object.
+
+=item $thr->tid()
+
+Returns the ID of the thread. Thread IDs are unique integers with the main
+thread in a program being 0, and incrementing by 1 for every thread created.
+
+=item threads->tid()
+
+Class method that allows a thread to obtain its own ID.
+
+=item "$thr"
+
+If you add the C<stringify> import option to your C<use threads> declaration,
+then using a threads object in a string or a string context (e.g., as a hash
+key) will cause its ID to be used as the value:
+
+ use threads qw(stringify);
+
+ my $thr = threads->create(...);
+ print("Thread $thr started...\n"); # Prints out: Thread 1 started...
+
+=item threads->object($tid)
+
+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->yield()
+
+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.
+
+You may do C<use threads qw(yield)>, and then just use C<yield()> in your
+code.
+
+=item threads->list()
+
+=item threads->list(threads::all)
+
+=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-joined, 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
+semicolon after the closing brace. Like C<threads-E<gt>create()>, C<async>
+returns a I<threads> object.
+
+=item $thr->error()
-Perl 5.6 introduced something called interpreter threads. Interpreter
-threads are different from "5005threads" (the thread model of Perl
-5.005) by creating a new perl interpreter per thread and not sharing
-any data or state between threads.
+Threads are executed in an C<eval> context. This method will return C<undef>
+if the thread terminates I<normally>. Otherwise, it returns the value of
+C<$@> associated with the thread's execution status in its C<eval> context.
-Prior to perl 5.8 this has only been available to people embedding
-perl and for emulating fork() on windows.
+=item $thr->_handle()
-The 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 per default thread local. To use shared variables one
-must use threads::shared.
+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 *>).
-It is also important to note that you preferably enable threads by
-doing C<use threads> as early as possible and that it is not possible
-to enable threading inside an eval ""; In particular, if you are
-intending to share variables with threads::shared, you must
-C<use threads> before you C<use threads::shared> and threads will emit
-a warning if you do it the other way around.
+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 EXITING A THREAD
+
+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).
=over
-=item $thread = new(function, LIST)
+=item threads->exit()
+
+If needed, a thread can be exited at any time by calling
+C<threads-E<gt>exit()>. This will cause the thread to return C<undef> in a
+scalar context, or the empty list in a list context.
+
+When called from the I<main> thread, this behaves the same as C<exit(0)>.
+
+=item threads->exit(status)
+
+When called from a thread, this behaves like C<threads-E<gt>exit()> (i.e., the
+exit status code is ignored).
+
+When called from the I<main> thread, this behaves the same as C<exit(status)>.
+
+=item die()
+
+Calling C<die()> in a thread indicates an abnormal exit for the thread. Any
+C<$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.
+
+=item exit(status)
+
+Calling L<exit()|perlfunc/"exit EXPR"> inside a thread causes the whole
+application to terminate. Because of this, the use of C<exit()> inside
+threaded code, or in modules that might be used in threaded applications, is
+strongly discouraged.
+
+If C<exit()> really is needed, then consider using the following:
-This will create a new thread with the entry point function and give
-it LIST as parameters. It will return the corresponding threads
-object.
+ threads->exit() if threads->can('exit'); # Thread friendly
+ exit(status);
-create() is an alias to new.
+=item use threads 'exit' => 'threads_only'
-=item $thread->join
+This globally overrides the default behavior of calling C<exit()> inside a
+thread, and effectively causes such calls to behave the same as
+C<threads-E<gt>exit()>. In other words, with this setting, calling C<exit()>
+causes only the thread to terminate.
-This will wait for the corresponding thread to join. When it finishes
-join will return the return values of the entry point function. If a
-thread has been detached, join will return without wait.
+Because of its global effect, this setting should not be used inside modules
+or the like.
-=item $thread->detach
+The I<main> thread is unaffected by this setting.
-Will throw away the return value from the thread and make it
-non-joinable.
+=item threads->create({'exit' => 'thread_only'}, ...)
-=item threads->self
+This overrides the default behavior of C<exit()> inside the newly created
+thread only.
-This will return the object for the current thread.
+=item $thr->set_thread_exit_only(boolean)
-=item $thread->tid
+This can be used to change the I<exit thread only> behavior for a thread after
+it has been created. With a I<true> argument, C<exit()> will cause only the
+thread to exit. With a I<false> argument, C<exit()> will terminate the
+application.
-This will return the id of the thread. threads->self->tid() is a
-quick way to get current thread id.
+The I<main> thread is unaffected by this call.
+
+=item threads->set_thread_exit_only(boolean)
+
+Class method for use inside a thread to change its own behavior for C<exit()>.
+
+The I<main> thread is unaffected by this call.
=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 or exited).
+
+=item $thr->is_joinable()
+
+Returns true if the thread has finished running, is not detached and has not
+yet been joined. In other words, the thread is ready to be joined, and a call
+to C<$thr-E<gt>join()> 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
-Arthur Bergman E<lt>arthur at contiller.seE<gt>
+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()>.
-threads is released under the same license as Perl.
+=head2 Explicit context
-Thanks to
+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 hash reference
+as the first argument:
-Richard Soderberg E<lt>rs at crystalflame.netE<gt>
-Helping me out tons, trying to find reasons for races and other weird bugs!
+ my $thr = threads->create({'context' => 'list'}, \&foo);
+ ...
+ my @results = $thr->join();
-Simon Cozens E<lt>simon at brecon.co.ukE<gt>
-Being there to answer zillions of annoying questions
+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
+(array) context such that the parent thread can receive a list (array) from
+the C<-E<gt>join()> call. (C<'array'> is synonymous with C<'list'>.)
+
+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);
+ ...
+ $thr->join();
+
+The context type may also be used as the I<key> in the hash reference followed
+by a I<true> value:
+
+ threads->create({'scalar' => 1}, \&foo);
+ ...
+ my ($thr) = threads->list();
+ my $result = $thr->join();
+
+=head2 Implicit context
-Rocco Caputo E<lt>troc at netrus.netE<gt>
+If not explicitly stated, the thread's context is implied from the context
+of the C<-E<gt>create()> call:
-Vipul Ved Prakash E<lt>mail at vipul.netE<gt>
-Helping with debugging.
+ # Create thread in list context
+ my ($thr) = threads->create(...);
-please join perl-ithreads@perl.org for more information
+ # Create thread in scalar context
+ my $thr = threads->create(...);
-=head1 BUGS
+ # 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 returns the same
+value as running L<wantarray()|perlfunc/"wantarray"> inside the current
+thread's entry point function.
+
+=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.
+
+Note that 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 creating a thread from within a thread is unsafe under win32
+=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.
+
+If needed, C<$new_size> will be rounded up to the next multiple of the memory
+page size (usually 4096 or 8192).
-=item PERL_OLD_SIGNALS are not threadsafe, will not be.
+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)>.
+(Obviously, this call does not affect any currently extant threads.)
+
+=item use threads ('stack_size' => VALUE);
+
+This sets the default per-thread stack size at the start of the application.
+
+=item $ENV{'PERL5_ITHREADS_STACK_SIZE'}
+
+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>:
+
+ 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)
+
+To specify a particular stack size for any individual thread, call
+C<-E<gt>create()> with a hash reference 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 pass 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.
+
+Sending a signal to a terminated thread is ignored.
+
+=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: If the I<main> thread exits, then 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, or by using C<threads-E<gt>exit()>. For example, the thread
+may have terminated because of an error, or by 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 AND LIMITATIONS
+
+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.
+
+=over
+
+=item Thread-safe modules
+
+See L<perlmod/"Making your module threadsafe"> when creating modules that may
+be used in threaded applications, especially if those modules use non-Perl
+data, or XS code.
+
+=item Using non-thread-safe modules
+
+Unfortunately, you may encounter Perl modules that are not I<thread-safe>.
+For example, they may crash the Perl interpreter during execution, or may dump
+core on termination. Depending on the module and the requirements of your
+application, it may be possible to work around such difficulties.
+
+If the module will only be used inside a thread, you can try loading the
+module from inside the thread entry point function using C<require> (and
+C<import> if needed):
+
+ sub thr_func
+ {
+ require Unsafe::Module
+ # Unsafe::Module->import(...);
+
+ ....
+ }
+
+If the module is needed inside the I<main> thread, try modifying your
+application so that the module is loaded (again using C<require> and
+C<-E<gt>import()>) after any threads are started, and in such a way that no
+other threads are started afterwards.
+
+If the above does not work, or is not adequate for your application, then file
+a bug report on L<http://rt.cpan.org/Public/> against the problematic module.
+
+=item Current working directory
+
+On all platforms except MSWin32, the setting for the current working directory
+is shared among all threads such that changing it in one thread (e.g., using
+C<chdir()>) will affect all the threads in the application.
+
+On MSWin32, each thread maintains its own the current working directory
+setting.
+
+=item Environment variables
+
+Currently, on all platforms except MSWin32, all I<system> calls (e.g., using
+C<system()> or back-ticks) made from threads use the environment variable
+settings from the I<main> thread. In other words, changes made to C<%ENV> in
+a thread will not be visible in I<system> calls made by that thread.
+
+To work around this, set environment variables as part of the I<system> call.
+For example:
+
+ my $msg = 'hello';
+ system("FOO=$msg; echo \$FOO"); # Outputs 'hello' to STDOUT
+
+On MSWin32, each thread maintains its own set of environment variables.
+
+=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 has 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 Returning objects from threads
+
+Returning objects from threads does not work. Depending on the classes
+involved, you may be able to work around this by returning a serialized
+version of the object (e.g., using L<Data::Dumper> or L<Storable>), and then
+reconstituting it in the joining thread. If you're using Perl 5.10.0 or
+later, and if the class supports L<shared objects|threads::shared/"OBJECTS">,
+you can pass them via L<shared queues| Thread::Queue>.
+
+=item END blocks in threads
+
+It is possible to add L<END blocks|perlmod/"BEGIN, UNITCHECK, CHECK, INIT and
+END"> to threads by using L<require|perlfunc/"require VERSION"> or
+L<eval|perlfunc/"eval EXPR"> with the appropriate code. These C<END> blocks
+will then be executed when the thread's interpreter is destroyed (i.e., either
+during a C<-E<gt>join()> call, or at program termination).
+
+However, calling any L<threads> methods in such an C<END> block will most
+likely I<fail> (e.g., the application may hang, or generate an error) due to
+mutexes that are needed to control functionality within the L<threads> module.
+
+For this reason, the use of C<END> blocks in threads is B<strongly>
+discouraged.
+
+=item Perl Bugs and the CPAN Version of L<threads>
+
+Support for threads extends beyond the code in this module (i.e.,
+F<threads.pm> and F<threads.xs>), and into the Perl interpreter 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 latest version of Perl.
+
+Even with the latest version of Perl, it is known that certain constructs
+with threads may result in warning messages concerning leaked scalars or
+unreferenced scalars. However, such warnings are harmless, and may safely be
+ignored.
+
+You can search for L<threads> related bug reports at
+L<http://rt.cpan.org/Public/>. If needed submit any new bugs, problems,
+patches, etc. to: L<http://rt.cpan.org/Public/Dist/Display.html?Name=threads>
+
+=back
+
+=head1 REQUIREMENTS
+
+Perl 5.8.0 or later
+
=head1 SEE ALSO
-L<perl>, L<threads::shared>, L<perlcall>, L<perlembed>, L<perlguts>
+L<threads> Discussion Forum on CPAN:
+L<http://www.cpanforum.com/dist/threads>
+
+Annotated POD for L<threads>:
+L<http://annocpan.org/~JDHEDDEN/threads-1.71/threads.pm>
+
+Source repository:
+L<http://code.google.com/p/threads-shared/>
+
+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>
+
+CPAN version produced by Jerry D. Hedden <jdhedden AT cpan DOT org>
+
+=head1 LICENSE
+
+threads is released under the same license as Perl.
+
+=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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