ext/Thread/sync.tx Test thread synchronisation
ext/Thread/sync2.tx Test thread synchronisation
ext/Thread/thr5005.t Test 5.005-style threading (skipped if no use5005threads)
-ext/Thread/Thread.pm Thread extension Perl module
ext/Thread/Thread.xs Thread extension external subroutines
ext/Thread/Thread/Queue.pm Thread synchronised queue objects
ext/Thread/Thread/Semaphore.pm Thread semaphore objects
lib/Text/TabsWrap/t/tabs.t See if Text::Tabs works
lib/Text/TabsWrap/t/wrap.t See if Text::Wrap::wrap works
lib/Text/Wrap.pm Paragraph formatter
+lib/Thread.pm Thread extensions frontend
lib/Tie/Array.pm Base class for tied arrays
lib/Tie/Array/push.t Test for Tie::Array
lib/Tie/Array/splice.t Test for Tie::Array::SPLICE
use ExtUtils::MakeMaker;
WriteMakefile(
NAME => 'Thread',
- VERSION_FROM => 'Thread.pm',
- MAN3PODS => {}
+ VERSION => '2.00',
+ MAN3PODS => {}
);
+++ /dev/null
-package Thread;
-require Exporter;
-use XSLoader ();
-our($VERSION, @ISA, @EXPORT);
-
-$VERSION = "1.01";
-
-@ISA = qw(Exporter);
-@EXPORT_OK = qw(yield cond_signal cond_broadcast cond_wait async);
-
-=head1 NAME
-
-Thread - manipulate threads in Perl (EXPERIMENTAL, subject to change)
-
-=head1 CAVEAT
-
-The Thread extension requires Perl to be built in a particular way to
-enable the older 5.005 threading model. Just to confuse matters, there
-is an alternate threading model known as "ithreads" that does NOT
-support this extension. If you are using a binary distribution such
-as ActivePerl that is built with ithreads support, this extension CANNOT
-be used.
-
-=head1 SYNOPSIS
-
- use Thread;
-
- my $t = new Thread \&start_sub, @start_args;
-
- $result = $t->join;
- $result = $t->eval;
- $t->detach;
- $flags = $t->flags;
-
- if ($t->done) {
- $t->join;
- }
-
- if($t->equal($another_thread)) {
- # ...
- }
-
- my $tid = Thread->self->tid;
- my $tlist = Thread->list;
-
- lock($scalar);
- yield();
-
- use Thread 'async';
-
-=head1 DESCRIPTION
-
- WARNING: Threading is an experimental feature. Both the interface
- and implementation are subject to change drastically. In fact, this
- documentation describes the flavor of threads that was in version
- 5.005. Perl 5.6.0 and later have the beginnings of support for
- interpreter threads, which (when finished) is expected to be
- significantly different from what is described here. The information
- contained here may therefore soon be obsolete. Use at your own risk!
-
-The C<Thread> module provides multithreading support for perl.
-
-=head1 FUNCTIONS
-
-=over 8
-
-=item new \&start_sub
-
-=item new \&start_sub, LIST
-
-C<new> starts a new thread of execution in the referenced subroutine. The
-optional list is passed as parameters to the subroutine. Execution
-continues in both the subroutine and the code after the C<new> call.
-
-C<new Thread> returns a thread object representing the newly created
-thread.
-
-=item lock VARIABLE
-
-C<lock> places a 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. C<lock> is recursive, so multiple calls to C<lock> are
-safe--the variable will remain locked until the outermost lock on the
-variable goes out of scope.
-
-Locks on variables only affect C<lock> calls--they do I<not> affect normal
-access to a variable. (Locks on subs are different, and covered in a bit)
-If you really, I<really> want locks to block access, then go ahead and tie
-them to something and manage this yourself. This is done on purpose. While
-managing access to variables is a good thing, perl doesn't force you out of
-its living room...
-
-If a container object, such as a hash or array, is locked, all the elements
-of that container are not locked. For example, if a thread does a C<lock
-@a>, any other thread doing a C<lock($a[12])> won't block.
-
-You may also C<lock> a sub, using C<lock &sub>. Any calls to that sub from
-another thread will block until the lock is released. This behaviour is not
-equivalent to declaring the sub with the C<locked> attribute. The C<locked>
-attribute serializes access to a subroutine, but allows different threads
-non-simultaneous access. C<lock &sub>, on the other hand, will not allow
-I<any> other thread access for the duration of the lock.
-
-Finally, C<lock> will traverse up references exactly I<one> level.
-C<lock(\$a)> is equivalent to C<lock($a)>, while C<lock(\\$a)> is not.
-
-=item async BLOCK;
-
-C<async> creates a thread to execute the block immediately following
-it. This block is treated as an anonymous sub, and so must have a
-semi-colon after the closing brace. Like C<new Thread>, C<async> returns a
-thread object.
-
-=item Thread->self
-
-The C<Thread-E<gt>self> function returns a thread object that represents
-the thread making the C<Thread-E<gt>self> call.
-
-=item Thread->list
-
-C<Thread-E<gt>list> returns a list of thread objects for all running and
-finished but un-C<join>ed threads.
-
-=item cond_wait VARIABLE
-
-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 reblock waiting to reaquire the lock on the variable. (So if
-you're only using C<cond_wait> for synchronization, give up the lock as
-soon as possible)
-
-=item cond_signal VARIABLE
-
-The C<cond_signal> function takes a 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.
-
-=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.
-
-=item yield
-
-The C<yield> function allows another thread to take control of the
-CPU. The exact results are implementation-dependent.
-
-=back
-
-=head1 METHODS
-
-=over 8
-
-=item join
-
-C<join> waits for a thread to end and returns any values the thread exited
-with. C<join> will block until the thread has ended, though it won't block
-if the thread has already terminated.
-
-If the thread being C<join>ed C<die>d, the error it died with will be
-returned at this time. If you don't want the thread performing the C<join>
-to die as well, you should either wrap the C<join> in an C<eval> or use the
-C<eval> thread method instead of C<join>.
-
-=item eval
-
-The C<eval> method wraps an C<eval> around a C<join>, and so waits for a
-thread to exit, passing along any values the thread might have returned.
-Errors, of course, get placed into C<$@>.
-
-=item detach
-
-C<detach> tells a thread that it is never going to be joined i.e.
-that all traces of its existence can be removed once it stops running.
-Errors in detached threads will not be visible anywhere - if you want
-to catch them, you should use $SIG{__DIE__} or something like that.
-
-=item equal
-
-C<equal> tests whether two thread objects represent the same thread and
-returns true if they do.
-
-=item tid
-
-The C<tid> method returns the tid of a thread. The tid is a monotonically
-increasing integer assigned when a thread is created. The main thread of a
-program will have a tid of zero, while subsequent threads will have tids
-assigned starting with one.
-
-=item flags
-
-The C<flags> method returns the flags for the thread. This is the
-integer value corresponding to the internal flags for the thread, and
-the value may not be all that meaningful to you.
-
-=item done
-
-The C<done> method returns true if the thread you're checking has
-finished, and false otherwise.
-
-=back
-
-=head1 LIMITATIONS
-
-The sequence number used to assign tids is a simple integer, and no
-checking is done to make sure the tid isn't currently in use. If a program
-creates more than 2^32 - 1 threads in a single run, threads may be assigned
-duplicate tids. This limitation may be lifted in a future version of Perl.
-
-=head1 SEE ALSO
-
-L<attributes>, L<Thread::Queue>, L<Thread::Semaphore>, L<Thread::Specific>.
-
-=cut
-
-#
-# Methods
-#
-
-#
-# Exported functions
-#
-sub async (&) {
- return new Thread $_[0];
-}
-
-sub eval {
- return eval { shift->join; };
-}
-
-XSLoader::load 'Thread';
-
-1;
print "1..0 # Skip: no Config\n";
exit(0);
}
- if ($Config{extensions} !~ /\bThread\b/) {
- print "1..0 # Skip: no use5005threads\n";
- exit(0);
- }
}
use Thread 'async';
print "1..0 # Skip: no Config\n";
exit(0);
}
- if ($Config{extensions} !~ /\bThread\b/) {
- print "1..0 # Skip: no use5005threads\n";
- exit(0);
- }
}
use Thread 'async';
print "1..0 # Skip: no Config\n";
exit(0);
}
- if ($Config{extensions} !~ /\bThread\b/) {
- print "1..0 # Skip: no use5005threads\n";
- exit(0);
- }
}
use Thread 'async';
print "1..0 # Skip: no Config\n";
exit(0);
}
- if ($Config{extensions} !~ /\bThread\b/) {
- print "1..0 # Skip: no use5005threads\n";
- exit(0);
- }
}
use Thread;
print "1..0 # Skip: no Config\n";
exit(0);
}
- if ($Config{extensions} !~ /\bThread\b/) {
- print "1..0 # Skip: no use5005threads\n";
- exit(0);
- }
}
use Thread;
print "1..0 # Skip: no Config\n";
exit(0);
}
- if ($Config{extensions} !~ /\bThread\b/) {
- print "1..0 # Skip: no use5005threads\n";
- exit(0);
- }
}
use Thread;
print "1..0 # Skip: no Config\n";
exit(0);
}
- if ($Config{extensions} !~ /\bThread\b/) {
- print "1..0 # Skip: no use5005threads\n";
- exit(0);
- }
}
use Thread qw(async);
print "1..0 # Skip: no Config\n";
exit(0);
}
- if ($Config{extensions} !~ /\bThread\b/) {
- print "1..0 # Skip: no use5005threads\n";
- exit(0);
- }
}
use Thread;
print "1..0 # Skip: no Config\n";
exit(0);
}
- if ($Config{extensions} !~ /\bThread\b/) {
- print "1..0 # Skip: no use5005threads\n";
- exit(0);
- }
}
use Thread;
print "1..0 # Skip: no Config\n";
exit(0);
}
- if ($Config{extensions} !~ /\bThread\b/) {
- print "1..0 # Skip: no use5005threads\n";
- exit(0);
- }
}
use Thread;
print "1..0 # Skip: no Config\n";
exit(0);
}
- if ($Config{extensions} !~ /\bThread\b/) {
- print "1..0 # Skip: no use5005threads\n";
- exit(0);
- }
}
use Thread;
print "1..0 # Skip: no Config\n";
exit(0);
}
- if ($Config{extensions} !~ /\bThread\b/) {
- print "1..0 # Skip: no use5005threads\n";
- exit(0);
- }
}
use Thread;
print "1..0 # Skip: no Config\n";
exit(0);
}
- if ($Config{extensions} !~ /\bThread\b/) {
- print "1..0 # Skip: no use5005threads\n";
- exit(0);
- }
}
use Thread;
print "1..0 # Skip: no Config\n";
exit(0);
}
- if ($Config{extensions} !~ /\bThread\b/) {
- print "1..0 # Skip: no use5005threads\n";
- exit(0);
- }
}
use Thread;
print "1..0 # Skip: no Config\n";
exit(0);
}
- if ($Config{extensions} !~ /\bThread\b/) {
- print "1..0 # Skip: no use5005threads\n";
- exit(0);
- }
}
use Thread;
print "1..0 # Skip: no Config\n";
exit(0);
}
- if ($Config{extensions} !~ /\bThread\b/) {
- print "1..0 # Skip: no use5005threads\n";
- exit(0);
- }
}
use Thread;
use warnings;
use overload
- '==' => \&equals,
+ '==' => \&equal,
'fallback' => 1;
#use threads::Shared;
our $VERSION = '0.05';
-sub equals {
+sub equal {
return 1 if($_[0]->tid() == $_[1]->tid());
return 0;
}
=head1 DESCRIPTION
-Perl 5.6 introduced something called interpreter threads. Interpreter
-threads are different from 5005 threads by creating a new perl
-interpreter per thread and not sharing any data or state between threads.
+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.
-Prior to perl 5.8 this has only been available to people embedding perl and
-for emulating fork() on windows.
+Prior to perl 5.8 this has only been available to people embedding
+perl and for emulating fork() on windows.
-The threads API is loosly 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.
+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.
-It is also important to note that you preferebly enable threads by doing
-C<use threads> as early as possible and it is not possible to enable threading
-by in an eval "";
+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 "";
=over
-=item new, function, LIST
+=item $thread = new(function, LIST)
This will create a new thread with the entry point function and give
it LIST as parameters. It will return the corresponding threads
object.
-create is an alias to new
+create() is an alias to new.
=item $thread->join
-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 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.
=item $thread->detach
-Will throw away the return value from the thread and make non joinable
+Will throw away the return value from the thread and make it
+non-joinable.
=item threads->self
=item $thread->tid
-This will return the id of the thread.
-threads->self->tid() is a quick way to get current thread id
+This will return the id of the thread. threads->self->tid() is a
+quick way to get current thread id.
=back
=over
-=item Fix so the return value is returned when you join
+=item Fix so the return value is returned when you join.
-=item Add join_all
+=item Add join_all.
=item Fix memory leaks!
Arthur Bergman E<lt>arthur at contiller.seE<gt>
-threads is released under the same license as Perl
+threads is released under the same license as Perl.
Thanks to
--- /dev/null
+package Thread;
+
+$VERSION = '2.00';
+
+BEGIN {
+ use Config;
+ our $ithreads = $Config{useithreads};
+ our $othreads = $Config{use5005threads};
+}
+
+require Exporter;
+use XSLoader ();
+our($VERSION, @ISA, @EXPORT);
+
+@ISA = qw(Exporter);
+
+BEGIN {
+ if ($ithreads) {
+ @EXPORT = qw(share cond_wait cond_broadcast cond_signal unlock)
+ } elsif ($othreads) {
+ @EXPORT_OK = qw(cond_signal cond_broadcast cond_wait);
+ }
+ push @EXPORT_OK, qw(async yield);
+}
+
+=head1 NAME
+
+Thread - manipulate threads in Perl
+
+=head1 CAVEAT
+
+Perl has two thread models.
+
+In Perl 5.005 the thread model was that all data is implicitly shared
+and shared access to data has to be explicitly synchronized.
+This model is called "5005threads".
+
+In Perl 5.6 a new model was introduced in which all is was thread
+local and shared access to data has to be explicitly declared.
+This model is called "ithreads", for "interpreter threads".
+
+In Perl 5.6 the ithreads model was not available as a public API,
+only as an internal API that was available for extension writers,
+and to implement fork() emulation on Win32 platforms.
+
+In Perl 5.8 the ithreads model became available through the C<threads>
+module.
+
+Neither model is configured by default into Perl (except, as mentioned
+above, in Win32 ithreads are always available.)
+
+For backwards compatibility, the Thread module has been reworked
+to function as a frontend for both 5005threads and ithreads.
+Note that the compatibility is not complete: because the data sharing
+models are directly opposed, anything to do with data sharing has to
+be thought differently. With the ithreads you must explicitly share()
+variables between the threads.
+
+Finally, note that there are many known serious problems with the
+5005threads, one of the least of which is that regular expression
+match variables like $1 are not threadsafe, that is, they easily get
+corrupted by competing threads. Other problems include more insidious
+data corruption and mysterious crashes. You are seriously urged to
+use ithreads instead.
+
+=head1 SYNOPSIS
+
+ use Thread;
+
+ my $t = Thread->new(\&start_sub, @start_args);
+
+ $result = $t->join;
+ $result = $t->eval;
+ $t->detach;
+
+ if ($t->done) {
+ $t->join;
+ }
+
+ if($t->equal($another_thread)) {
+ # ...
+ }
+
+ yield();
+
+ my $tid = Thread->self->tid;
+
+ lock($scalar);
+ lock(@array);
+ lock(%hash);
+
+ lock(\&sub); # not available with ithreads
+
+ $flags = $t->flags; # not available with ithreads
+
+ my @list = Thread->list; # not available with ithreads
+
+ unlock(...); # not available with the 5.005 threads
+
+ use Thread 'async';
+
+=head1 DESCRIPTION
+
+The C<Thread> module provides multithreading support for perl.
+
+=head1 FUNCTIONS
+
+=over 8
+
+=item $thread = Thread->new(\&start_sub)
+
+=item $thread = Thread->new(\&start_sub, LIST)
+
+C<new> starts a new thread of execution in the referenced subroutine. The
+optional list is passed as parameters to the subroutine. Execution
+continues in both the subroutine and the code after the C<new> call.
+
+C<Thread->new> returns a thread object representing the newly created
+thread.
+
+=item lock VARIABLE
+
+C<lock> places a lock on a variable until the lock goes out of scope
+(with ithreads you can also explicitly unlock()).
+
+If the variable is locked by another thread, the C<lock> call will
+block until it's available. C<lock> is recursive, so multiple calls
+to C<lock> are safe--the variable will remain locked until the
+outermost lock on the variable goes out of scope.
+
+Locks on variables only affect C<lock> calls--they do I<not> affect normal
+access to a variable. (Locks on subs are different, and covered in a bit.)
+If you really, I<really> want locks to block access, then go ahead and tie
+them to something and manage this yourself. This is done on purpose.
+While managing access to variables is a good thing, Perl doesn't force
+you out of its living room...
+
+If a container object, such as a hash or array, is locked, all the
+elements of that container are not locked. For example, if a thread
+does a C<lock @a>, any other thread doing a C<lock($a[12])> won't
+block.
+
+With 5005threads you may also C<lock> a sub, using C<lock &sub>.
+Any calls to that sub from another thread will block until the lock
+is released. This behaviour is not equivalent to declaring the sub
+with the C<locked> attribute. The C<locked> attribute serializes
+access to a subroutine, but allows different threads non-simultaneous
+access. C<lock &sub>, on the other hand, will not allow I<any> other
+thread access for the duration of the lock.
+
+Finally, C<lock> will traverse up references exactly I<one> level.
+C<lock(\$a)> is equivalent to C<lock($a)>, while C<lock(\\$a)> is not.
+
+=item async BLOCK;
+
+C<async> creates a thread to execute the block immediately following
+it. This block is treated as an anonymous sub, and so must have a
+semi-colon after the closing brace. Like C<Thread->new>, C<async>
+returns a thread object.
+
+=item Thread->self
+
+The C<Thread-E<gt>self> function returns a thread object that represents
+the thread making the C<Thread-E<gt>self> call.
+
+=item cond_wait VARIABLE
+
+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 reblock waiting
+to reaquire the lock on the variable. (So if you're only using
+C<cond_wait> for synchronization, give up the lock as soon as
+possible.)
+
+=item cond_signal VARIABLE
+
+The C<cond_signal> function takes a 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.
+
+=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.
+
+=item yield
+
+The C<yield> function allows another thread to take control of the
+CPU. The exact results are implementation-dependent.
+
+=back
+
+=head1 METHODS
+
+=over 8
+
+=item join
+
+C<join> waits for a thread to end and returns any values the thread
+exited with. C<join> will block until the thread has ended, though
+it won't block if the thread has already terminated.
+
+If the thread being C<join>ed C<die>d, the error it died with will
+be returned at this time. If you don't want the thread performing
+the C<join> to die as well, you should either wrap the C<join> in
+an C<eval> or use the C<eval> thread method instead of C<join>.
+
+=item eval
+
+The C<eval> method wraps an C<eval> around a C<join>, and so waits for
+a thread to exit, passing along any values the thread might have returned.
+Errors, of course, get placed into C<$@>. (Not available with ithreads.)
+
+=item detach
+
+C<detach> tells a thread that it is never going to be joined i.e.
+that all traces of its existence can be removed once it stops running.
+Errors in detached threads will not be visible anywhere - if you want
+to catch them, you should use $SIG{__DIE__} or something like that.
+
+=item equal
+
+C<equal> tests whether two thread objects represent the same thread and
+returns true if they do.
+
+=item tid
+
+The C<tid> method returns the tid of a thread. The tid is
+a monotonically increasing integer assigned when a thread is
+created. The main thread of a program will have a tid of zero,
+while subsequent threads will have tids assigned starting with one.
+
+=item flags
+
+The C<flags> method returns the flags for the thread. This is the
+integer value corresponding to the internal flags for the thread,
+and the value may not be all that meaningful to you.
+(Not available with ithreads.)
+
+=item done
+
+The C<done> method returns true if the thread you're checking has
+finished, and false otherwise. (Not available with ithreads.)
+
+=back
+
+=head1 LIMITATIONS
+
+The sequence number used to assign tids is a simple integer, and no
+checking is done to make sure the tid isn't currently in use. If a
+program creates more than 2**32 - 1 threads in a single run, threads
+may be assigned duplicate tids. This limitation may be lifted in
+a future version of Perl.
+
+=head1 SEE ALSO
+
+L<threads::shared> (not available with 5005threads)
+
+L<attributes>, L<Thread::Queue>, L<Thread::Semaphore>,
+L<Thread::Specific> (not available with ithreads)
+
+=cut
+
+#
+# Methods
+#
+
+#
+# Exported functions
+#
+
+sub async (&) {
+ return Thread->new($_[0]);
+}
+
+sub eval {
+ return eval { shift->join; };
+}
+
+sub unimplemented {
+ print $_[0], " unimplemented with ",
+ $Config{useithreads} ? "ithreads" : "5005threads", "\n";
+
+}
+
+sub unimplement {
+ for my $m (@_) {
+ *{"Thread::$m"} = sub { unimplemented $m };
+ }
+}
+
+BEGIN {
+ if ($ithreads) {
+ XSLoader::load 'threads';
+ for my $m (qw(new join detach yield self tid equal)) {
+ *{"Thread::$m"} = \&{"threads::$m"};
+ }
+ XSLoader::load 'threads::shared';
+ for my $m (qw(cond_signal cond_broadcast cond_wait unlock share)) {
+ *{"Thread::$m"} = \&{"threads::shared::${m}_enabled"};
+ }
+ unimplement(qw(list done eval flags));
+ } elsif ($othreads) {
+ XSLoader::load 'Thread';
+ unimplement(qw(unlock));
+ } else {
+ require Carp;
+ Carp::croak("This Perl has neither ithreads not 5005threads");
+ }
+}
+
+1;
This function places an advisory lock on a variable, subroutine,
or referenced object contained in I<THING> until the lock goes out
of scope. This is a built-in function only if your version of Perl
-was built with threading enabled, and if you've said C<use Threads>.
-Otherwise a user-defined function by this name will be called. See
-L<Thread>.
+was built with threading enabled, and if you've said C<use Thread>.
+Otherwise a user-defined function by this name will be called.
+See L<Thread>.
=item log EXPR