0,0 → 1,1056 |
package threads; |
|
use 5.008; |
|
use strict; |
use warnings; |
|
our $VERSION = '1.71'; |
my $XS_VERSION = $VERSION; |
$VERSION = eval $VERSION; |
|
# Verify this Perl supports threads |
require Config; |
if (! $Config::Config{useithreads}) { |
die("This Perl not built to support threads\n"); |
} |
|
# Complain if 'threads' is loaded after 'threads::shared' |
if ($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_ |
} |
|
# Declare that we have been loaded |
$threads::threads = 1; |
|
# 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'}); |
} |
} |
|
|
### Methods, etc. ### |
|
# 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)'); |
} |
|
$class->set_thread_exit_only(1); |
CORE::exit($status); |
} |
|
# 'Constant' args for threads->list() |
sub threads::all { } |
sub threads::running { 1 } |
sub threads::joinable { 0 } |
|
# 'new' is an alias for 'create' |
*new = \&create; |
|
# 'async' is a function alias for the 'threads->create()' method |
sub async (&;@) |
{ |
unshift(@_, 'threads'); |
# Use "goto" trick to avoid pad problems from 5.8.1 (fixed in 5.8.2) |
goto &create; |
} |
|
# Thread object equality checking |
use overload ( |
'==' => \&equal, |
'!=' => sub { ! equal(@_) }, |
'fallback' => 1 |
); |
|
1; |
|
__END__ |
|
=head1 NAME |
|
threads - Perl interpreter-based threads |
|
=head1 VERSION |
|
This document describes threads version 1.71 |
|
=head1 SYNOPSIS |
|
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(); |
|
=head1 DESCRIPTION |
|
Perl 5.6 introduced something called interpreter threads. Interpreter threads |
are different from I<5005threads> (the thread model of Perl 5.005) by creating |
a new Perl interpreter per thread, and not sharing any data or state between |
threads by default. |
|
Prior to Perl 5.8, this has only been available to people embedding Perl, and |
for emulating fork() on Windows. |
|
The I<threads> API is loosely based on the old Thread.pm API. It is very |
important to note that variables are not shared between threads, all variables |
are by default thread local. To use shared variables one must also use |
L<threads::shared>: |
|
use threads; |
use threads::shared; |
|
It is also important to note that you must enable threads by doing C<use |
threads> as early as possible in the script itself, and that it is not |
possible to enable threading inside an C<eval "">, C<do>, C<require>, or |
C<use>. In particular, if you are intending to share variables with |
L<threads::shared>, you must C<use threads> before you C<use threads::shared>. |
(C<threads> will emit a warning if you do it the other way around.) |
|
=over |
|
=item $thr = threads->create(FUNCTION, ARGS) |
|
This will create a new thread that will begin execution with the specified |
entry point function, and give it the I<ARGS> list as parameters. It will |
return the corresponding threads object, or C<undef> if thread creation failed. |
|
I<FUNCTION> may either be the name of a function, an anonymous subroutine, or |
a code ref. |
|
my $thr = threads->create('func_name', ...); |
# or |
my $thr = threads->create(sub { ... }, ...); |
# or |
my $thr = threads->create(\&func, ...); |
|
The C<-E<gt>new()> method is an alias for C<-E<gt>create()>. |
|
=item $thr->join() |
|
This will wait for the corresponding thread to complete its execution. When |
the thread finishes, C<-E<gt>join()> will return the return value(s) of the |
entry point function. |
|
The context (void, scalar or list) for the return value(s) for C<-E<gt>join()> |
is determined at the time of thread creation. |
|
# Create thread in list context (implicit) |
my ($thr1) = threads->create(sub { |
my @results = qw(a b c); |
return (@results); |
}); |
# or (explicit) |
my $thr1 = threads->create({'context' => 'list'}, |
sub { |
my @results = qw(a b c); |
return (@results); |
}); |
# Retrieve list results from thread |
my @res1 = $thr1->join(); |
|
# Create thread in scalar context (implicit) |
my $thr2 = threads->create(sub { |
my $result = 42; |
return ($result); |
}); |
# Retrieve scalar result from thread |
my $res2 = $thr2->join(); |
|
# Create a thread in void context (explicit) |
my $thr3 = threads->create({'void' => 1}, |
sub { print("Hello, world\n"); }); |
# Join the thread in void context (i.e., no return value) |
$thr3->join(); |
|
See L</"THREAD CONTEXT"> for more details. |
|
If the program exits without all threads having either been joined or |
detached, then a warning will be issued. |
|
Calling C<-E<gt>join()> or C<-E<gt>detach()> on an already joined thread will |
cause an error to be thrown. |
|
=item $thr->detach() |
|
Makes the thread unjoinable, and causes any eventual return value to be |
discarded. When the program exits, any detached threads that are still |
running are silently terminated. |
|
If the program exits without all threads having either been joined or |
detached, then a warning will be issued. |
|
Calling C<-E<gt>join()> or C<-E<gt>detach()> on an already detached thread |
will cause an error to be thrown. |
|
=item threads->detach() |
|
Class method that allows a thread to detach itself. |
|
=item threads->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 $thr->error() |
|
Threads are executed in an C<eval> context. This method will return C<undef> |
if the thread terminates I<normally>. Otherwise, it returns the value of |
C<$@> associated with the thread's execution status in its C<eval> context. |
|
=item $thr->_handle() |
|
This I<private> method returns the memory location of the internal thread |
structure associated with a threads object. For Win32, this is a pointer to |
the C<HANDLE> value returned by C<CreateThread> (i.e., C<HANDLE *>); for other |
platforms, it is a pointer to the C<pthread_t> structure used in the |
C<pthread_create> call (i.e., C<pthread_t *>). |
|
This method is of no use for general Perl threads programming. Its intent is |
to provide other (XS-based) thread modules with the capability to access, and |
possibly manipulate, the underlying thread structure associated with a Perl |
thread. |
|
=item threads->_handle() |
|
Class method that allows a thread to obtain its own I<handle>. |
|
=back |
|
=head1 EXITING A THREAD |
|
The usual method for terminating a thread is to |
L<return()|perlfunc/"return EXPR"> from the entry point function with the |
appropriate return value(s). |
|
=over |
|
=item threads->exit() |
|
If needed, a thread can be exited at any time by calling |
C<threads-E<gt>exit()>. This will cause the thread to return C<undef> in a |
scalar context, or the empty list in a list context. |
|
When called from the I<main> thread, this behaves the same as C<exit(0)>. |
|
=item threads->exit(status) |
|
When called from a thread, this behaves like C<threads-E<gt>exit()> (i.e., the |
exit status code is ignored). |
|
When called from the I<main> thread, this behaves the same as C<exit(status)>. |
|
=item die() |
|
Calling C<die()> in a thread indicates an abnormal exit for the thread. Any |
C<$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: |
|
threads->exit() if threads->can('exit'); # Thread friendly |
exit(status); |
|
=item use threads 'exit' => 'threads_only' |
|
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. |
|
Because of its global effect, this setting should not be used inside modules |
or the like. |
|
The I<main> thread is unaffected by this setting. |
|
=item threads->create({'exit' => 'thread_only'}, ...) |
|
This overrides the default behavior of C<exit()> inside the newly created |
thread only. |
|
=item $thr->set_thread_exit_only(boolean) |
|
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. |
|
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 |
|
The following boolean methods are useful in determining the I<state> of a |
thread. |
|
=over |
|
=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 threads->is_detached() |
|
Class method that allows a thread to determine whether or not it is detached. |
|
=back |
|
=head1 THREAD CONTEXT |
|
As with subroutines, the type of value returned from a thread's entry point |
function may be determined by the thread's I<context>: list, scalar or void. |
The thread's context is determined at thread creation. This is necessary so |
that the context is available to the entry point function via |
L<wantarray()|perlfunc/"wantarray">. The thread may then specify a value of |
the appropriate type to be returned from C<-E<gt>join()>. |
|
=head2 Explicit context |
|
Because thread creation and thread joining may occur in different contexts, it |
may be desirable to state the context explicitly to the thread's entry point |
function. This may be done by calling C<-E<gt>create()> with a 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 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 = $thr->join(); |
|
=head2 Implicit context |
|
If not explicitly stated, the thread's context is implied from the context |
of the C<-E<gt>create()> call: |
|
# Create thread in list context |
my ($thr) = threads->create(...); |
|
# Create thread in scalar context |
my $thr = threads->create(...); |
|
# Create thread in void context |
threads->create(...); |
|
=head2 $thr->wantarray() |
|
This returns the thread's context in the same manner as |
L<wantarray()|perlfunc/"wantarray">. |
|
=head2 threads->wantarray() |
|
Class method to return the current thread's context. This 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 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). |
|
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<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 |