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Initial commit of OpenSPARC T2 design and verification files.
[OpenSPARC-T2-DV] / tools / perl-5.8.0 / man / man3 / threads::shared.3
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129.\" ========================================================================
130.\"
131.IX Title "threads::shared 3"
132.TH threads::shared 3 "2002-06-01" "perl v5.8.0" "Perl Programmers Reference Guide"
133.SH "NAME"
134threads::shared \- Perl extension for sharing data structures between threads
135.SH "SYNOPSIS"
136.IX Header "SYNOPSIS"
137.Vb 2
138\& use threads;
139\& use threads::shared;
140.Ve
141.PP
142.Vb 1
143\& my $var : shared;
144.Ve
145.PP
146.Vb 6
147\& my($scalar, @array, %hash);
148\& share($scalar);
149\& share(@array);
150\& share(%hash);
151\& my $bar = &share([]);
152\& $hash{bar} = &share({});
153.Ve
154.PP
155.Vb 1
156\& { lock(%hash); ... }
157.Ve
158.PP
159.Vb 3
160\& cond_wait($scalar);
161\& cond_broadcast(@array);
162\& cond_signal(%hash);
163.Ve
164.SH "DESCRIPTION"
165.IX Header "DESCRIPTION"
166By default, variables are private to each thread, and each newly created
167thread gets a private copy of each existing variable. This module allows
168you to share variables across different threads (and pseudoforks on Win32).
169It is used together with the threads module.
170.SH "EXPORT"
171.IX Header "EXPORT"
172\&\f(CW\*(C`share\*(C'\fR, \f(CW\*(C`lock\*(C'\fR, \f(CW\*(C`cond_wait\*(C'\fR, \f(CW\*(C`cond_signal\*(C'\fR, \f(CW\*(C`cond_broadcast\*(C'\fR
173.PP
174Note that if this module is imported when \f(CW\*(C`threads\*(C'\fR has not yet been
175loaded, then these functions all become no\-ops. This makes it possible
176to write modules that will work in both threaded and non-threaded
177environments.
178.SH "FUNCTIONS"
179.IX Header "FUNCTIONS"
180.IP "share \s-1VARIABLE\s0" 4
181.IX Item "share VARIABLE"
182\&\f(CW\*(C`share\*(C'\fR takes a value and marks it as shared. You can share a scalar,
183array, hash, scalar ref, array ref or hash ref. \f(CW\*(C`share\*(C'\fR will return
184the shared rvalue.
185.Sp
186\&\f(CW\*(C`share\*(C'\fR will traverse up references exactly \fIone\fR level.
187\&\f(CW\*(C`share(\e$a)\*(C'\fR is equivalent to \f(CW\*(C`share($a)\*(C'\fR, while \f(CW\*(C`share(\e\e$a)\*(C'\fR is not.
188.Sp
189A variable can also be marked as shared at compile time by using the
190\&\f(CW\*(C`shared\*(C'\fR attribute: \f(CW\*(C`my $var : shared\*(C'\fR.
191.Sp
192If you want to share a newly created reference unfortunately you
193need to use \f(CW\*(C`&share([])\*(C'\fR and \f(CW\*(C`&share({})\*(C'\fR syntax due to problems
194with Perl's prototyping.
195.IP "lock \s-1VARIABLE\s0" 4
196.IX Item "lock VARIABLE"
197\&\f(CW\*(C`lock\*(C'\fR places a lock on a variable until the lock goes out of scope.
198If the variable is locked by another thread, the \f(CW\*(C`lock\*(C'\fR call will
199block until it's available. \f(CW\*(C`lock\*(C'\fR is recursive, so multiple calls
200to \f(CW\*(C`lock\*(C'\fR are safe \*(-- the variable will remain locked until the
201outermost lock on the variable goes out of scope.
202.Sp
203If a container object, such as a hash or array, is locked, all the
204elements of that container are not locked. For example, if a thread
205does a \f(CW\*(C`lock @a\*(C'\fR, any other thread doing a \f(CW\*(C`lock($a[12])\*(C'\fR won't block.
206.Sp
207\&\f(CW\*(C`lock\*(C'\fR will traverse up references exactly \fIone\fR level.
208\&\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.
209.Sp
210Note that you cannot explicitly unlock a variable; you can only wait
211for the lock to go out of scope. If you need more fine-grained
212control, see Thread::Semaphore.
213.IP "cond_wait \s-1VARIABLE\s0" 4
214.IX Item "cond_wait VARIABLE"
215The \f(CW\*(C`cond_wait\*(C'\fR function takes a \fBlocked\fR variable as a parameter,
216unlocks the variable, and blocks until another thread does a
217\&\f(CW\*(C`cond_signal\*(C'\fR or \f(CW\*(C`cond_broadcast\*(C'\fR for that same locked variable.
218The variable that \f(CW\*(C`cond_wait\*(C'\fR blocked on is relocked after the
219\&\f(CW\*(C`cond_wait\*(C'\fR is satisfied. If there are multiple threads
220\&\f(CW\*(C`cond_wait\*(C'\fRing on the same variable, all but one will reblock waiting
221to reacquire the lock on the variable. (So if you're only using
222\&\f(CW\*(C`cond_wait\*(C'\fR for synchronisation, give up the lock as soon as
223possible). The two actions of unlocking the variable and entering the
224blocked wait state are atomic, The two actions of exiting from the
225blocked wait state and relocking the variable are not.
226.Sp
227It is important to note that the variable can be notified even if
228no thread \f(CW\*(C`cond_signal\*(C'\fR or \f(CW\*(C`cond_broadcast\*(C'\fR on the variable.
229It is therefore important to check the value of the variable and
230go back to waiting if the requirement is not fulfilled.
231.IP "cond_signal \s-1VARIABLE\s0" 4
232.IX Item "cond_signal VARIABLE"
233The \f(CW\*(C`cond_signal\*(C'\fR function takes a \fBlocked\fR variable as a parameter
234and unblocks one thread that's \f(CW\*(C`cond_wait\*(C'\fRing on that variable. If
235more than one thread is blocked in a \f(CW\*(C`cond_wait\*(C'\fR on that variable,
236only one (and which one is indeterminate) will be unblocked.
237.Sp
238If there are no threads blocked in a \f(CW\*(C`cond_wait\*(C'\fR on the variable,
239the signal is discarded. By always locking before signaling, you can
240(with care), avoid signaling before another thread has entered \fIcond_wait()\fR.
241.Sp
242\&\f(CW\*(C`cond_signal\*(C'\fR will normally generate a warning if you attempt to use it
243on an unlocked variable. On the rare occasions where doing this may be
244sensible, you can skip the warning with
245.Sp
246.Vb 1
247\& { no warnings 'threads'; cond_signal($foo) }
248.Ve
249.IP "cond_broadcast \s-1VARIABLE\s0" 4
250.IX Item "cond_broadcast VARIABLE"
251The \f(CW\*(C`cond_broadcast\*(C'\fR function works similarly to \f(CW\*(C`cond_signal\*(C'\fR.
252\&\f(CW\*(C`cond_broadcast\*(C'\fR, though, will unblock \fBall\fR the threads that are
253blocked in a \f(CW\*(C`cond_wait\*(C'\fR on the locked variable, rather than only one.
254.SH "NOTES"
255.IX Header "NOTES"
256threads::shared is designed to disable itself silently if threads are
257not available. If you want access to threads, you must \f(CW\*(C`use threads\*(C'\fR
258before you \f(CW\*(C`use threads::shared\*(C'\fR. threads will emit a warning if you
259use it after threads::shared.
260.SH "BUGS"
261.IX Header "BUGS"
262\&\f(CW\*(C`bless\*(C'\fR is not supported on shared references. In the current version,
263\&\f(CW\*(C`bless\*(C'\fR will only bless the thread local reference and the blessing
264will not propagate to the other threads. This is expected to be
265implemented in a future version of Perl.
266.PP
267Does not support splice on arrays!
268.PP
269Taking references to the elements of shared arrays and hashes does not
270autovivify the elements, and neither does slicing a shared array/hash
271over non-existent indices/keys autovivify the elements.
272.PP
273\&\fIshare()\fR allows you to \f(CW\*(C`share $hashref\-\*(C'\fR{key}> without giving any error
274message. But the \f(CW\*(C`$hashref\-\*(C'\fR{key}> is \fBnot\fR shared, causing the error
275\&\*(L"locking can only be used on shared values\*(R" to occur when you attempt to
276\&\f(CW\*(C`lock $hasref\-\*(C'\fR{key}>.
277.SH "AUTHOR"
278.IX Header "AUTHOR"
279Arthur Bergman <arthur at contiller.se>
280.PP
281threads::shared is released under the same license as Perl
282.PP
283Documentation borrowed from the old Thread.pm
284.SH "SEE ALSO"
285.IX Header "SEE ALSO"
286threads, perlthrtut, <http://www.perl.com/pub/a/2002/06/11/threads.html>
Full OpenSPARC design & verification tarball including full HDL.