threads.pm

视频监控网络部分的协议ddns,的模块的实现代码,请大家大胆指正.

    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