1Thread(3pm) Perl Programmers Reference Guide Thread(3pm)
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6 Thread - Manipulate threads in Perl (for old code only)
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9 The "Thread" module served as the frontend to the old-style thread
10 model, called 5005threads, that was introduced in release 5.005. That
11 model was deprecated, and has been removed in version 5.10.
12 For old code and interim backwards compatibility, the "Thread" module
14 has been reworked to function as a frontend for the new interpreter
15 threads (ithreads) model. However, some previous functionality is not
16 available. Further, the data sharing models between the two thread
17 models are completely different, and anything to do with data sharing
18 has to be thought differently. With ithreads, you must explicitly
19 "share()" variables between the threads.
20 You are strongly encouraged to migrate any existing threaded code to
22 the new model (i.e., use the "threads" and "threads::shared" modules)
23 as soon as possible.
24
26 In Perl 5.005, the thread model was that all data is implicitly shared,
27 and shared access to data has to be explicitly synchronized. This
28 model is called 5005threads.
29 In Perl 5.6, a new model was introduced in which all is was thread
31 local and shared access to data has to be explicitly declared. This
32 model is called ithreads, for "interpreter threads".
33 In Perl 5.6, the ithreads model was not available as a public API; only
35 as an internal API that was available for extension writers, and to
36 implement fork() emulation on Win32 platforms.
37 In Perl 5.8, the ithreads model became available through the "threads"
39 module, and the 5005threads model was deprecated.
40 In Perl 5.10, the 5005threads model was removed from the Perl
42 interpreter.
43
45 use Thread qw(:DEFAULT async yield);
46 my $t = Thread->new(\&start_sub, @start_args);
48 $result = $t->join;
50 $t->detach;
51 if ($t->done) {
53 $t->join;
54 }
55 if($t->equal($another_thread)) {
57 # ...
58 }
59 yield();
61 my $tid = Thread->self->tid;
63 lock($scalar);
65 lock(@array);
66 lock(%hash);
67 my @list = Thread->list;
69
71 The "Thread" module provides multithreading support for Perl.
72
74 $thread = Thread->new(\&start_sub)
75 $thread = Thread->new(\&start_sub, LIST)
76 "new" starts a new thread of execution in the referenced
77 subroutine. The optional list is passed as parameters to the
78 subroutine. Execution continues in both the subroutine and the
79 code after the "new" call.
80 "Thread->new" returns a thread object representing the newly
82 created thread.
83 lock VARIABLE
85 "lock" places a lock on a variable until the lock goes out of
86 scope.
87 If the variable is locked by another thread, the "lock" call
89 will block until it's available. "lock" is recursive, so
90 multiple calls to "lock" are safe--the variable will remain
91 locked until the outermost lock on the variable goes out of
92 scope.
93 Locks on variables only affect "lock" calls--they do not affect
95 normal access to a variable. (Locks on subs are different, and
96 covered in a bit.) If you really, really want locks to block
97 access, then go ahead and tie them to something and manage this
98 yourself. This is done on purpose. While managing access to
99 variables is a good thing, Perl doesn't force you out of its
100 living room...
101 If a container object, such as a hash or array, is locked, all
103 the elements of that container are not locked. For example, if
104 a thread does a "lock @a", any other thread doing a
105 "lock($a[12])" won't block.
106 Finally, "lock" will traverse up references exactly one level.
108 "lock(\$a)" is equivalent to "lock($a)", while "lock(\\$a)" is
109 not.
110 async BLOCK;
112 "async" creates a thread to execute the block immediately
113 following it. This block is treated as an anonymous sub, and
114 so must have a semi-colon after the closing brace. Like
115 "Thread->new", "async" returns a thread object.
116 Thread->self
118 The "Thread->self" function returns a thread object that
119 represents the thread making the "Thread->self" call.
120 Thread->list
122 Returns a list of all non-joined, non-detached Thread objects.
123 cond_wait VARIABLE
125 The "cond_wait" function takes a locked variable as a
126 parameter, unlocks the variable, and blocks until another
127 thread does a "cond_signal" or "cond_broadcast" for that same
128 locked variable. The variable that "cond_wait" blocked on is
129 relocked after the "cond_wait" is satisfied. If there are
130 multiple threads "cond_wait"ing on the same variable, all but
131 one will reblock waiting to re-acquire the lock on the
132 variable. (So if you're only using "cond_wait" for
133 synchronization, give up the lock as soon as possible.)
134 cond_signal VARIABLE
136 The "cond_signal" function takes a locked variable as a
137 parameter and unblocks one thread that's "cond_wait"ing on that
138 variable. If more than one thread is blocked in a "cond_wait"
139 on that variable, only one (and which one is indeterminate)
140 will be unblocked.
141 If there are no threads blocked in a "cond_wait" on the
143 variable, the signal is discarded.
144 cond_broadcast VARIABLE
146 The "cond_broadcast" function works similarly to "cond_signal".
147 "cond_broadcast", though, will unblock all the threads that are
148 blocked in a "cond_wait" on the locked variable, rather than
149 only one.
150 yield The "yield" function allows another thread to take control of
152 the CPU. The exact results are implementation-dependent.
153
155 join "join" waits for a thread to end and returns any values the
156 thread exited with. "join" will block until the thread has
157 ended, though it won't block if the thread has already
158 terminated.
159 If the thread being "join"ed "die"d, the error it died with
161 will be returned at this time. If you don't want the thread
162 performing the "join" to die as well, you should either wrap
163 the "join" in an "eval" or use the "eval" thread method instead
164 of "join".
165 detach "detach" tells a thread that it is never going to be joined
167 i.e. that all traces of its existence can be removed once it
168 stops running. Errors in detached threads will not be visible
169 anywhere - if you want to catch them, you should use
170 $SIG{__DIE__} or something like that.
171 equal "equal" tests whether two thread objects represent the same
173 thread and returns true if they do.
174 tid The "tid" method returns the tid of a thread. The tid is a
176 monotonically increasing integer assigned when a thread is
177 created. The main thread of a program will have a tid of zero,
178 while subsequent threads will have tids assigned starting with
179 one.
180 done The "done" method returns true if the thread you're checking
182 has finished, and false otherwise.
183
185 The following were implemented with 5005threads, but are no longer
186 available with ithreads.
187 lock(\&sub)
189 With 5005threads, you could also "lock" a sub such that any
190 calls to that sub from another thread would block until the
191 lock was released.
192 Also, subroutines could be declared with the ":locked"
194 attribute which would serialize access to the subroutine, but
195 allowed different threads non-simultaneous access.
196 eval The "eval" method wrapped an "eval" around a "join", and so
198 waited for a thread to exit, passing along any values the
199 thread might have returned and placing any errors into $@.
200 flags The "flags" method returned the flags for the thread - an
202 integer value corresponding to the internal flags for the
203 thread.
204
206 threads, threads::shared, Thread::Queue, Thread::Semaphore
207perl v5.32.1 2021-05-31 Thread(3pm)