threads - Perl interpreter-based threads
This document describes threads version 2.27
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 makes 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 <https://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.
- Locales
- Prior to Perl 5.28, locales could not be used with threads,
due to various race conditions. Starting in that release, on systems that
implement thread-safe locale functions, threads can be used, with some
caveats. This includes Windows starting with Visual Studio 2005, and
systems compatible with POSIX 2008. See "Multi-threaded
operation" in perllocale.
Each thread (except the main thread) is started using the C locale. The main
thread is started like all other Perl programs; see
"ENVIRONMENT" in perllocale. You can switch locales in any
thread as often as you like.
If you want to inherit the parent thread's locale, you can, in the parent,
set a variable like so:
$foo = POSIX::setlocale(LC_ALL, NULL);
and then pass to threads-> create() a sub that closes over $foo.
Then, in the child, you say
POSIX::setlocale(LC_ALL, $foo);
Or you can use the facilities in threads::shared to pass $foo; or if the
environment hasn't changed, in the child, do
POSIX::setlocale(LC_ALL, "");
- 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]
<https://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
<https://rt.cpan.org/Public/>. If needed submit any new bugs,
problems, patches, etc. to:
<https://rt.cpan.org/Public/Dist/Display.html?Name=threads>
Perl 5.8.0 or later
threads on MetaCPAN: <
https://metacpan.org/release/threads>
Code repository for CPAN distribution:
<
https://github.com/Dual-Life/threads>
threads::shared, perlthrtut
<
https://www.perl.com/pub/a/2002/06/11/threads.html> and
<
https://www.perl.com/pub/a/2002/09/04/threads.html>
Perl threads mailing list: <
https://lists.perl.org/list/ithreads.html>
Stack size discussion: <
https://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