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threads(3) |
User Contributed Perl Documentation |
threads(3) |
threads - Perl interpreter-based threads
This document describes threads version 2.21
The "interpreter-based threads" provided by Perl are not the fast,
lightweight system for multitasking that one might expect or hope for. Threads
are implemented in a way that make them easy to misuse. Few people know how to
use them correctly or will be able to provide help.
The use of interpreter-based threads in perl is officially
discouraged.
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();
Since Perl 5.8, thread programming has been available using a model called
interpreter threads which provides a new Perl interpreter for each
thread, and, by default, results in no data or state information being shared
between threads.
(Prior to Perl 5.8, 5005threads was available through the
"Thread.pm" API. This threading model has
been deprecated, and was removed as of Perl 5.10.0.)
As just mentioned, all variables are, by default, thread local. To
use shared variables, you need to also load threads::shared:
use threads;
use threads::shared;
When loading threads::shared, you must "use
threads" before you "use
threads::shared". ("threads"
will emit a warning if you do it the other way around.)
It is strongly recommended that you enable threads via
"use threads" as early as possible in your
script.
If needed, scripts can be written so as to run on both threaded
and non-threaded Perls:
my $can_use_threads = eval 'use threads; 1';
if ($can_use_threads) {
# Do processing using threads
...
} else {
# Do it without using threads
...
}
- $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 ARGS list as parameters. It
will return the corresponding threads object, or
"undef" if thread creation failed.
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 "->new()" method is
an alias for "->create()".
- $thr->join()
- This will wait for the corresponding thread to complete its execution.
When the thread finishes, "->join()"
will return the return value(s) of the entry point function.
The context (void, scalar or list) for the return value(s) for
"->join()" is determined at the
time of thread creation.
# Create thread in list context (implicit)
my ($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 "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 "->join()" or
"->detach()" on an already joined
thread will cause an error to be thrown.
- $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 "->join()" or
"->detach()" on an already detached
thread will cause an error to be thrown.
- threads->detach()
- Class method that allows a thread to detach itself.
- threads->self()
- Class method that allows a thread to obtain its own threads
object.
- $thr->tid()
- Returns the ID of the thread. Thread IDs are unique integers with the main
thread in a program being 0, and incrementing by 1 for every thread
created.
- threads->tid()
- Class method that allows a thread to obtain its own ID.
- "$thr"
- If you add the "stringify" import option
to your "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 $thr started\n"); # Prints: Thread 1 started
- threads->object($tid)
- This will return the threads object for the active thread
associated with the specified thread ID. If $tid
is the value for the current thread, then this call works the same as
"->self()". Otherwise, returns
"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.
- 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 "use threads
qw(yield)", and then just use
"yield()" in your code.
- threads->list()
- threads->list(threads::all)
- threads->list(threads::running)
- threads->list(threads::joinable)
- With no arguments (or using
"threads::all") and in a list context,
returns a list of all non-joined, non-detached threads objects. In
a scalar context, returns a count of the same.
With a true argument (using
"threads::running"), returns a list of
all non-joined, non-detached threads objects that are still
running.
With a false argument (using
"threads::joinable"), returns a list
of all non-joined, non-detached threads objects that have
finished running (i.e., for which
"->join()" will not
block).
- $thr1->equal($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.)
- async BLOCK;
- "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
"threads->create()",
"async" returns a threads
object.
- $thr->error()
- Threads are executed in an "eval"
context. This method will return "undef"
if the thread terminates normally. Otherwise, it returns the value
of $@ associated with the thread's execution
status in its "eval" context.
- $thr->_handle()
- This private method returns a pointer (i.e., the memory location
expressed as an unsigned integer) to the internal thread structure
associated with a threads object. For Win32, this is a pointer to the
"HANDLE" value returned by
"CreateThread" (i.e.,
"HANDLE *"); for other platforms, it is
a pointer to the "pthread_t" structure
used in the "pthread_create" call (i.e.,
"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.
- threads->_handle()
- Class method that allows a thread to obtain its own handle.
The usual method for terminating a thread is to return() from the entry
point function with the appropriate return value(s).
- threads->exit()
- If needed, a thread can be exited at any time by calling
"threads->exit()". This will cause
the thread to return "undef" in a scalar
context, or the empty list in a list context.
When called from the main thread, this behaves the same
as exit(0).
- threads->exit(status)
- When called from a thread, this behaves like
"threads->exit()" (i.e., the exit
status code is ignored).
When called from the main thread, this behaves the same
as "exit(status)".
- die()
- Calling "die()" in a thread indicates an
abnormal exit for the thread. Any $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
"die()" call.
- exit(status)
- Calling exit() inside a thread causes the whole application to
terminate. Because of this, the use of
"exit()" inside threaded code, or in
modules that might be used in threaded applications, is strongly
discouraged.
If "exit()" really is
needed, then consider using the following:
threads->exit() if threads->can('exit'); # Thread friendly
exit(status);
- use threads 'exit' => 'threads_only'
- This globally overrides the default behavior of calling
"exit()" inside a thread, and
effectively causes such calls to behave the same as
"threads->exit()". In other words,
with this setting, calling "exit()"
causes only the thread to terminate.
Because of its global effect, this setting should not be used
inside modules or the like.
The main thread is unaffected by this setting.
- threads->create({'exit' => 'thread_only'}, ...)
- This overrides the default behavior of
"exit()" inside the newly created thread
only.
- $thr->set_thread_exit_only(boolean)
- This can be used to change the exit thread only behavior for a
thread after it has been created. With a true argument,
"exit()" will cause only the thread to
exit. With a false argument,
"exit()" will terminate the application.
The main thread is unaffected by this call.
- threads->set_thread_exit_only(boolean)
- Class method for use inside a thread to change its own behavior for
"exit()".
The main thread is unaffected by this call.
The following boolean methods are useful in determining the state of a
thread.
- $thr->is_running()
- Returns true if a thread is still running (i.e., if its entry point
function has not yet finished or exited).
- $thr->is_joinable()
- Returns true if the thread has finished running, is not detached and has
not yet been joined. In other words, the thread is ready to be joined, and
a call to "$thr->join()" will not
block.
- $thr->is_detached()
- Returns true if the thread has been detached.
- threads->is_detached()
- Class method that allows a thread to determine whether or not it is
detached.
As with subroutines, the type of value returned from a thread's entry point
function may be determined by the thread's 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
wantarray(). The thread may then specify a value of the appropriate
type to be returned from "->join()".
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
"->create()" with a hash reference 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
"foo" will be called in list (array)
context such that the parent thread can receive a list (array) from the
"->join()" call.
('array' is synonymous with
'list'.)
Similarly, if you need the threads object, but your thread will
not be returning a value (i.e., void context), you would do the
following:
my $thr = threads->create({'context' => 'void'}, \&foo);
...
$thr->join();
The context type may also be used as the key in the hash
reference followed by a true value:
threads->create({'scalar' => 1}, \&foo);
...
my ($thr) = threads->list();
my $result = $thr->join();
If not explicitly stated, the thread's context is implied from the context of
the "->create()" call:
# Create thread in list context
my ($thr) = threads->create(...);
# Create thread in scalar context
my $thr = threads->create(...);
# Create thread in void context
threads->create(...);
This returns the thread's context in the same manner as wantarray().
Class method to return the current thread's context. This returns the same value
as running wantarray() inside the current thread's entry point
function.
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.
- 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.
- $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.
- $old_size = threads->set_stack_size($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, $new_size will be rounded
up to the next multiple of the memory page size (usually 4096 or
8192).
Threads created after the stack size is set will then either
call "pthread_attr_setstacksize()"
(for pthreads platforms), or supply the stack size to
"CreateThread()" (for Win32
Perl).
(Obviously, this call does not affect any currently extant
threads.)
- use threads ('stack_size' => VALUE);
- This sets the default per-thread stack size at the start of the
application.
- $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
"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
"stack_size" parameter given to
"use threads". Its primary purpose is
to permit setting the per-thread stack size for legacy threaded
applications.
- threads->create({'stack_size' => VALUE}, FUNCTION, ARGS)
- To specify a particular stack size for any individual thread, call
"->create()" with a hash reference as
the first argument:
my $thr = threads->create({'stack_size' => 32*4096},
\&foo, @args);
- $thr2 = $thr1->create(FUNCTION, ARGS)
- This creates a new thread ($thr2) that inherits
the stack size from an existing thread ($thr1).
This is shorthand for the following:
my $stack_size = $thr1->get_stack_size();
my $thr2 = threads->create({'stack_size' => $stack_size},
FUNCTION, ARGS);
When safe signals is in effect (the default behavior - see "Unsafe
signals" for more details), then signals may be sent and acted upon by
individual threads.
- $thr->kill('SIG...');
- Sends the specified signal to the thread. Signal names and (positive)
signal numbers are the same as those supported by kill(). For
example, 'SIGTERM', 'TERM' and (depending on the OS) 15 are all valid
arguments to "->kill()".
Returns the thread object to allow for method chaining:
$thr->kill('SIG...')->join();
Signal handlers need to be set up in the threads for the signals
they are expected to act upon. Here's an example for 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
suspend and 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
$sema->up();
CAVEAT: The thread signalling capability provided by this module
does not actually send signals via the OS. It emulates signals at the
Perl-level such that signal handlers are called in the appropriate thread.
For example, sending
"$thr->kill('STOP')" does not actually
suspend a thread (or the whole process), but does cause a
$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 "kill()" command (e.g.,
"kill('KILL', $$)") are okay to use with
the "->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
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/finished thread is ignored.
- 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 main thread exits, then this warning
cannot be suppressed using "no warnings
'threads';" as suggested below.
- Thread creation failed: pthread_create returned #
- See the appropriate man page for
"pthread_create" to determine the actual
cause for the failure.
- Thread # terminated abnormally: ...
- A thread terminated in some manner other than just returning from its
entry point function, or by using
"threads->exit()". For example, the
thread may have terminated because of an error, or by using
"die".
- 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.
- Thread creation failed: pthread_attr_setstacksize(SIZE) returned
22
- The specified SIZE exceeds the system's maximum stack size. Use a
smaller value for the stack size.
If needed, thread warnings can be suppressed by using:
no warnings 'threads';
in the appropriate scope.
- This Perl not built to support threads
- The particular copy of Perl that you're trying to use was not built using
the "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 threads module (i.e., threaded and non-threaded
Perls are binary incompatible).
- 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);
- Cannot signal threads without safe signals
- Safe signals must be in effect to use the
"->kill()" signalling method. See
"Unsafe signals" for more details.
- Unrecognized signal name: ...
- The particular copy of Perl that you're trying to use does not support the
specified signal being used in a
"->kill()" call.
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.
- Thread-safe modules
- See "Making your module threadsafe" in perlmod when creating
modules that may be used in threaded applications, especially if those
modules use non-Perl data, or XS code.
- Using non-thread-safe modules
- Unfortunately, you may encounter Perl modules that are not
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
"require" (and
"import" if needed):
sub thr_func
{
require Unsafe::Module
# Unsafe::Module->import(...);
....
}
If the module is needed inside the main thread, try
modifying your application so that the module is loaded (again using
"require" and
"->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
<http://rt.cpan.org/Public/> against the problematic module.
- Memory consumption
- On most systems, frequent and continual creation and destruction of
threads can lead to ever-increasing growth in the memory footprint of the
Perl interpreter. While it is simple to just launch threads and then
"->join()" or
"->detach()" them, for long-lived
applications, it is better to maintain a pool of threads, and to reuse
them for the work needed, using queues to notify threads of pending work.
The CPAN distribution of this module contains a simple example
(examples/pool_reuse.pl) illustrating the creation, use and
monitoring of a pool of reusable threads.
- 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 "chdir()") will affect all
the threads in the application.
On MSWin32, each thread maintains its own the current working
directory setting.
- Environment variables
- Currently, on all platforms except MSWin32, all system calls (e.g.,
using "system()" or back-ticks) made
from threads use the environment variable settings from the main
thread. In other words, changes made to %ENV in a
thread will not be visible in system calls made by that thread.
To work around this, set environment variables as part of the
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.
- Catching signals
- Signals are caught by the main thread (thread ID = 0) of a script.
Therefore, setting up signal handlers in threads for purposes other than
"THREAD SIGNALLING" as documented above will not accomplish what
is intended.
This is especially true if trying to catch
"SIGALRM" in a thread. To handle
alarms in threads, set up a signal handler in the main thread, and then
use "THREAD SIGNALLING" to relay the signal to the thread:
# Create thread with a task that may time out
my $thr = threads->create(sub {
threads->yield();
eval {
$SIG{ALRM} = sub { die("Timeout\n"); };
alarm(10);
... # Do work here
alarm(0);
};
if ($@ =~ /Timeout/) {
warn("Task in thread timed out\n");
}
};
# Set signal handler to relay SIGALRM to thread
$SIG{ALRM} = sub { $thr->kill('ALRM') };
... # Main thread continues working
- Parent-child threads
- On some platforms, it might not be possible to destroy parent
threads while there are still existing child threads.
- Unsafe signals
- Since Perl 5.8.0, signals have been made safer in Perl by postponing their
handling until the interpreter is in a safe state. See "Safe
Signals" in perl58delta and "Deferred Signals (Safe
Signals)" in perlipc for more details.
Safe signals is the default behavior, and the old, immediate,
unsafe signalling behavior is only in effect in the following
situations:
- Perl has been built with
"PERL_OLD_SIGNALS" (see
"perl -V").
- The environment variable "PERL_SIGNALS"
is set to "unsafe" (see
"PERL_SIGNALS" in perlrun).
- The module Perl::Unsafe::Signals is used.
If unsafe signals is in effect, then signal handling is not
thread-safe, and the "->kill()"
signalling method cannot be used.
- Identity of objects returned from threads
- When a value is returned from a thread through a
"join" operation, the value and
everything that it references is copied across to the joining thread, in
much the same way that values are copied upon thread creation. This works
fine for most kinds of value, including arrays, hashes, and subroutines.
The copying recurses through array elements, reference scalars, variables
closed over by subroutines, and other kinds of reference.
However, everything referenced by the returned value is a
fresh copy in the joining thread, even if a returned object had in the
child thread been a copy of something that previously existed in the
parent thread. After joining, the parent will therefore have a duplicate
of each such object. This sometimes matters, especially if the object
gets mutated; this can especially matter for private data to which a
returned subroutine provides access.
- Returning blessed objects from threads
- Returning blessed 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 Data::Dumper or Storable),
and then reconstituting it in the joining thread. If you're using Perl
5.10.0 or later, and if the class supports shared objects, you can pass
them via shared queues.
- END blocks in threads
- It is possible to add END blocks to threads by using require or eval with
the appropriate code. These "END" blocks
will then be executed when the thread's interpreter is destroyed (i.e.,
either during a "->join()" call, or
at program termination).
However, calling any threads methods in such an
"END" block will most likely
fail (e.g., the application may hang, or generate an error) due
to mutexes that are needed to control functionality within the threads
module.
For this reason, the use of
"END" blocks in threads is
strongly discouraged.
- Open directory handles
- In perl 5.14 and higher, on systems other than Windows that do not support
the "fchdir" C function, directory
handles (see opendir) will not be copied to new threads. You can use the
"d_fchdir" variable in Config.pm to
determine whether your system supports it.
In prior perl versions, spawning threads with open directory
handles would crash the interpreter. [perl #75154]
<http://rt.perl.org/rt3/Public/Bug/Display.html?id=75154>
- Detached threads and global destruction
- If the main thread exits while there are detached threads which are still
running, then Perl's global destruction phase is not executed because
otherwise certain global structures that control the operation of threads
and that are allocated in the main thread's memory may get destroyed
before the detached thread is destroyed.
If you are using any code that requires the execution of the
global destruction phase for clean up (e.g., removing temp files), then
do not use detached threads, but rather join all threads before exiting
the program.
- Perl Bugs and the CPAN Version of threads
- Support for threads extends beyond the code in this module (i.e.,
threads.pm and threads.xs), and into the Perl interpreter
itself. Older versions of Perl contain bugs that may manifest themselves
despite using the latest version of 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 threads related bug reports at
<http://rt.cpan.org/Public/>. If needed submit any new bugs,
problems, patches, etc. to:
<http://rt.cpan.org/Public/Dist/Display.html?Name=threads>
threads on MetaCPAN: <https://metacpan.org/release/threads>
Code repository for CPAN distribution:
<https://github.com/Dual-Life/threads>
threads::shared, perlthrtut
<http://www.perl.com/pub/a/2002/06/11/threads.html> and
<http://www.perl.com/pub/a/2002/09/04/threads.html>
Perl threads mailing list:
<http://lists.perl.org/list/ithreads.html>
Stack size discussion:
<http://www.perlmonks.org/?node_id=532956>
Sample code in the examples directory of this distribution
on CPAN.
Artur Bergman <sky AT crucially DOT net>
CPAN version produced by Jerry D. Hedden <jdhedden AT cpan DOT
org>
threads is released under the same license as Perl.
Richard Soderberg <perl AT crystalflame DOT net> - Helping me out tons,
trying to find reasons for races and other weird bugs!
Simon Cozens <simon AT brecon DOT co DOT uk> - Being there
to answer zillions of annoying questions
Rocco Caputo <troc AT netrus DOT net>
Vipul Ved Prakash <mail AT vipul DOT net> - Helping with
debugging
Dean Arnold <darnold AT presicient DOT com> - Stack size
API
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