threads::shared.3

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.

\&      print("\e$var is not shared\en");
\&  }
.Ve
.IP "lock \s-1VARIABLE\s0" 4
.IX Item "lock VARIABLE"
\&\f(CW\*(C`lock\*(C'\fR places a lock on a variable until the lock goes out of scope.  If the
variable is locked by another thread, the \f(CW\*(C`lock\*(C'\fR call will block until it's
available.  Multiple calls to \f(CW\*(C`lock\*(C'\fR by the same thread from within
dynamically nested scopes are safe \*(-- the variable will remain locked until
the outermost lock on the variable goes out of scope.
.Sp
Locking a container object, such as a hash or array, doesn't lock the elements
of that container. For example, if a thread does a \f(CW\*(C`lock(@a)\*(C'\fR, any other
thread doing a \f(CW\*(C`lock($a[12])\*(C'\fR won't block.
.Sp
\&\f(CW\*(C`lock()\*(C'\fR follows references exactly \fIone\fR level.  \f(CW\*(C`lock(\e$a)\*(C'\fR is equivalent
to \f(CW\*(C`lock($a)\*(C'\fR, while \f(CW\*(C`lock(\e\e$a)\*(C'\fR is not.
.Sp
Note that you cannot explicitly unlock a variable; you can only wait for the
lock to go out of scope.  This is most easily accomplished by locking the
variable inside a block.
.Sp
.Vb 7
\&  my $var :shared;
\&  {
\&      lock($var);
\&      # $var is locked from here to the end of the block
\&      ...
\&  }
\&  # $var is now unlocked
.Ve
.Sp
If you need more fine-grained control over shared variable access, see
Thread::Semaphore.
.IP "cond_wait \s-1VARIABLE\s0" 4
.IX Item "cond_wait VARIABLE"
.PD 0
.IP "cond_wait \s-1CONDVAR\s0, \s-1LOCKVAR\s0" 4
.IX Item "cond_wait CONDVAR, LOCKVAR"
.PD
The \f(CW\*(C`cond_wait\*(C'\fR function takes a \fBlocked\fR variable as a parameter, unlocks
the variable, and blocks until another thread does a \f(CW\*(C`cond_signal\*(C'\fR or
\&\f(CW\*(C`cond_broadcast\*(C'\fR for that same locked variable.  The variable that
\&\f(CW\*(C`cond_wait\*(C'\fR blocked on is relocked after the \f(CW\*(C`cond_wait\*(C'\fR is satisfied.  If
there are multiple threads \f(CW\*(C`cond_wait\*(C'\fRing on the same variable, all but one
will re-block waiting to reacquire the lock on the variable. (So if you're only
using \f(CW\*(C`cond_wait\*(C'\fR for synchronisation, give up the lock as soon as possible).
The two actions of unlocking the variable and entering the blocked wait state
are atomic, the two actions of exiting from the blocked wait state and
re-locking the variable are not.
.Sp
In its second form, \f(CW\*(C`cond_wait\*(C'\fR takes a shared, \fBunlocked\fR variable followed
by a shared, \fBlocked\fR variable.  The second variable is unlocked and thread
execution suspended until another thread signals the first variable.
.Sp
It is important to note that the variable can be notified even if no thread
\&\f(CW\*(C`cond_signal\*(C'\fR or \f(CW\*(C`cond_broadcast\*(C'\fR on the variable.  It is therefore
important to check the value of the variable and go back to waiting if the
requirement is not fulfilled.  For example, to pause until a shared counter
drops to zero:
.Sp
.Vb 1
\&  { lock($counter); cond_wait($count) until $counter == 0; }
.Ve
.IP "cond_timedwait \s-1VARIABLE\s0, \s-1ABS_TIMEOUT\s0" 4
.IX Item "cond_timedwait VARIABLE, ABS_TIMEOUT"
.PD 0
.IP "cond_timedwait \s-1CONDVAR\s0, \s-1ABS_TIMEOUT\s0, \s-1LOCKVAR\s0" 4
.IX Item "cond_timedwait CONDVAR, ABS_TIMEOUT, LOCKVAR"
.PD
In its two-argument form, \f(CW\*(C`cond_timedwait\*(C'\fR takes a \fBlocked\fR variable and an
absolute timeout as parameters, unlocks the variable, and blocks until the
timeout is reached or another thread signals the variable.  A false value is
returned if the timeout is reached, and a true value otherwise.  In either
case, the variable is re-locked upon return.
.Sp
Like \f(CW\*(C`cond_wait\*(C'\fR, this function may take a shared, \fBlocked\fR variable as an
additional parameter; in this case the first parameter is an \fBunlocked\fR
condition variable protected by a distinct lock variable.
.Sp
Again like \f(CW\*(C`cond_wait\*(C'\fR, waking up and reacquiring the lock are not atomic,
and you should always check your desired condition after this function
returns.  Since the timeout is an absolute value, however, it does not have to
be recalculated with each pass:
.Sp
.Vb 6
\&  lock($var);
\&  my $abs = time() + 15;
\&  until ($ok = desired_condition($var)) {
\&      last if !cond_timedwait($var, $abs);
\&  }
\&  # we got it if $ok, otherwise we timed out!
.Ve
.IP "cond_signal \s-1VARIABLE\s0" 4
.IX Item "cond_signal VARIABLE"
The \f(CW\*(C`cond_signal\*(C'\fR function takes a \fBlocked\fR variable as a parameter and
unblocks one thread that's \f(CW\*(C`cond_wait\*(C'\fRing on that variable. If more than one
thread is blocked in a \f(CW\*(C`cond_wait\*(C'\fR on that variable, only one (and which one
is indeterminate) will be unblocked.
.Sp
If there are no threads blocked in a \f(CW\*(C`cond_wait\*(C'\fR on the variable, the signal
is discarded. By always locking before signaling, you can (with care), avoid
signaling before another thread has entered \fIcond_wait()\fR.
.Sp
\&\f(CW\*(C`cond_signal\*(C'\fR will normally generate a warning if you attempt to use it on an
unlocked variable. On the rare occasions where doing this may be sensible, you
can suppress the warning with:
.Sp
.Vb 1
\&  { no warnings \*(Aqthreads\*(Aq; cond_signal($foo); }
.Ve
.IP "cond_broadcast \s-1VARIABLE\s0" 4
.IX Item "cond_broadcast VARIABLE"
The \f(CW\*(C`cond_broadcast\*(C'\fR function works similarly to \f(CW\*(C`cond_signal\*(C'\fR.
\&\f(CW\*(C`cond_broadcast\*(C'\fR, though, will unblock \fBall\fR the threads that are blocked in
a \f(CW\*(C`cond_wait\*(C'\fR on the locked variable, rather than only one.
.SH "OBJECTS"
.IX Header "OBJECTS"
threads::shared exports a version of \fIbless()\fR that
works on shared objects such that \fIblessings\fR propagate across threads.
.PP
.Vb 5
\&  # Create a shared \*(Aqfoo\*(Aq object
\&  my $foo;
\&  share($foo);
\&  $foo = &share({});
\&  bless($foo, \*(Aqfoo\*(Aq);
\&
\&  # Create a shared \*(Aqbar\*(Aq object
\&  my $bar;
\&  share($bar);
\&  $bar = &share({});
\&  bless($bar, \*(Aqbar\*(Aq);
\&
\&  # Put \*(Aqbar\*(Aq inside \*(Aqfoo\*(Aq
\&  $foo\->{\*(Aqbar\*(Aq} = $bar;
\&
\&  # Rebless the objects via a thread
\&  threads\->create(sub {
\&      # Rebless the outer object
\&      bless($foo, \*(Aqyin\*(Aq);
\&
\&      # Cannot directly rebless the inner object
\&      #bless($foo\->{\*(Aqbar\*(Aq}, \*(Aqyang\*(Aq);
\&
\&      # Retrieve and rebless the inner object
\&      my $obj = $foo\->{\*(Aqbar\*(Aq};
\&      bless($obj, \*(Aqyang\*(Aq);
\&      $foo\->{\*(Aqbar\*(Aq} = $obj;
\&
\&  })\->join();
\&
\&  print(ref($foo),          "\en");    # Prints \*(Aqyin\*(Aq
\&  print(ref($foo\->{\*(Aqbar\*(Aq}), "\en");    # Prints \*(Aqyang\*(Aq
\&  print(ref($bar),          "\en");    # Also prints \*(Aqyang\*(Aq
.Ve
.SH "NOTES"
.IX Header "NOTES"
threads::shared is designed to disable itself silently if threads are not
available. If you want access to threads, you must \f(CW\*(C`use threads\*(C'\fR before you
\&\f(CW\*(C`use threads::shared\*(C'\fR.  threads will emit a warning if you use it after
threads::shared.
.SH "BUGS AND LIMITATIONS"
.IX Header "BUGS AND LIMITATIONS"
When \f(CW\*(C`share\*(C'\fR is used on arrays, hashes, array refs or hash refs, any data
they contain will be lost.
.PP
.Vb 3
\&  my @arr = qw(foo bar baz);
\&  share(@arr);
\&  # @arr is now empty (i.e., == ());
\&
\&  # Create a \*(Aqfoo\*(Aq object
\&  my $foo = { \*(Aqdata\*(Aq => 99 };
\&  bless($foo, \*(Aqfoo\*(Aq);
\&
\&  # Share the object
\&  share($foo);        # Contents are now wiped out
\&  print("ERROR: \e$foo is empty\en")
\&      if (! exists($foo\->{\*(Aqdata\*(Aq}));
.Ve
.PP
Therefore, populate such variables \fBafter\fR declaring them as shared.  (Scalar
and scalar refs are not affected by this problem.)
.PP
It is often not wise to share an object unless the class itself has been
written to support sharing.  For example, an object's destructor may get
called multiple times, once for each thread's scope exit.  Another danger is
that the contents of hash-based objects will be lost due to the above
mentioned limitation.  See \fIexamples/class.pl\fR (in the \s-1CPAN\s0 distribution of
this module) for how to create a class that supports object sharing.
.PP
Does not support \f(CW\*(C`splice\*(C'\fR on arrays!
.PP
Taking references to the elements of shared arrays and hashes does not
autovivify the elements, and neither does slicing a shared array/hash over
non-existent indices/keys autovivify the elements.
.PP
\&\f(CW\*(C`share()\*(C'\fR allows you to \f(CW\*(C`share($hashref\->{key})\*(C'\fR without giving any
error message.  But the \f(CW\*(C`$hashref\->{key}\*(C'\fR is \fBnot\fR shared, causing the
error \*(L"locking can only be used on shared values\*(R" to occur when you attempt to
\&\f(CW\*(C`lock($hasref\->{key})\*(C'\fR.
.PP
View existing bug reports at, and submit any new bugs, problems, patches, etc.
to: <http://rt.cpan.org/NoAuth/Bugs.html?Dist=threads\-shared>
.SH "SEE ALSO"
.IX Header "SEE ALSO"
threads::shared Discussion Forum on \s-1CPAN:\s0
<http://www.cpanforum.com/dist/threads\-shared>
.PP
Annotated \s-1POD\s0 for threads::shared:
<http://annocpan.org/~JDHEDDEN/threads\-shared\-1.14/shared.pm>
.PP
Source repository:
<http://code.google.com/p/threads\-shared/>
.PP
threads, perlthrtut
.PP
<http://www.perl.com/pub/a/2002/06/11/threads.html> and
<http://www.perl.com/pub/a/2002/09/04/threads.html>
.PP
Perl threads mailing list:
<http://lists.cpan.org/showlist.cgi?name=iThreads>
.SH "AUTHOR"
.IX Header "AUTHOR"
Artur Bergman <sky \s-1AT\s0 crucially \s-1DOT\s0 net>
.PP
threads::shared is released under the same license as Perl.
.PP
Documentation borrowed from the old Thread.pm.
.PP
\&\s-1CPAN\s0 version produced by Jerry D. Hedden <jdhedden \s-1AT\s0 cpan \s-1DOT\s0 org>.