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47 .TH PTHREAD_SIGMASK 3C "Mar 23, 2005"
49 pthread_sigmask \- change or examine calling thread's signal mask
53 cc -mt [ \fIflag\fR... ] \fIfile\fR... -lpthread [ \fIlibrary\fR... ]
57 \fBint\fR \fBpthread_sigmask\fR(\fBint\fR \fIhow\fR, \fBconst sigset_t *\fR\fIset\fR, \fBsigset_t *\fR\fIoset\fR);
63 The \fBpthread_sigmask()\fR function changes or examines a calling thread's
64 signal mask. Each thread has its own signal mask. A new thread inherits the
65 calling thread's signal mask and priority; however, pending signals are not
66 inherited. Signals pending for a new thread will be empty.
69 If the value of the argument \fIset\fR is not \fINULL\fR, \fIset\fR points to a
70 set of signals that can modify the currently blocked set. If the value of
71 \fIset\fR is \fINULL\fR, the value of \fIhow\fR is insignificant and the
72 thread's signal mask is unmodified; thus, \fBpthread_sigmask()\fR can be used
73 to inquire about the currently blocked signals.
76 The value of the argument \fIhow\fR specifies the method in which the set is
77 changed and takes one of the following values:
84 \fIset\fR corresponds to a set of signals to block. They are added to the
91 \fB\fBSIG_UNBLOCK\fR\fR
94 \fIset\fR corresponds to a set of signals to unblock. These signals are deleted
95 from the current signal mask.
101 \fB\fBSIG_SETMASK\fR\fR
104 \fIset\fR corresponds to the new signal mask. The current signal mask is
105 replaced by \fBset\fR.
110 If the value of \fIoset\fR is not \fINULL\fR, it points to the location where
111 the previous signal mask is stored.
115 Upon successful completion, the \fBpthread_sigmask()\fR function returns
116 \fB0\fR. Otherwise, it returns a non-zero value.
120 The \fBpthread_sigmask()\fR function will fail if:
127 The value of \fIhow\fR is not defined and \fIoset\fR is \fINULL\fR.
132 \fBExample 1 \fRCreate a default thread that can serve as a signal
133 catcher/handler with its own signal mask.
136 The following example shows how to create a default thread that can serve as a
137 signal catcher/handler with its own signal mask. \fBnew\fR will have a
138 different value from the creator's signal mask.
142 As POSIX threads and Solaris threads are fully compatible even within the same
143 process, this example uses \fBpthread_create\fR(3C) if you execute \fBa.out
144 0\fR, or \fBthr_create\fR(3C) if you execute \fBa.out 1\fR.
154 The \fBsigemptyset\fR(3C) function initializes a null signal set, \fBnew\fR.
155 The \fBsigaddset\fR(3C) function packs the signal, \fBSIGINT\fR, into that new
162 Either \fBpthread_sigmask()\fR or \fBthr_sigsetmask()\fR is used to mask the
163 signal, \fBSIGINT\fR (CTRL-C), from the calling thread, which is \fBmain()\fR.
164 The signal is masked to guarantee that only the new thread will receive this
171 \fBpthread_create()\fR or \fBthr_create()\fR creates the signal-handling
178 Using \fBpthread_join\fR(3C) or \fBthr_join\fR(3C), \fBmain()\fR then waits for
179 the termination of that signal-handling thread, whose \fBID\fR number is
180 \fBuser_threadID\fR; \fBmain()\fR will then \fBsleep\fR(3C) for 2 seconds,
181 after which the program terminates.
187 The signal-handling thread, \fBhandler\fR:
192 Assigns the handler \fBinterrupt()\fR to handle the signal \fBSIGINT\fR, by the
193 call to \fBsigaction\fR(2).
199 Resets its own signal set to \fInot block\fR the signal, \fBSIGINT\fR.
205 Sleeps for 8 seconds to allow time for the user to deliver the signal,
206 \fBSIGINT\fR, by pressing the \fBCTRL-C\fR.
212 /* cc thisfile.c -lthread -lpthread */
213 #define _REENTRANT /* basic first 3-lines for threads */
216 thread_t user_threadID;
218 void *handler(\|), interrupt(\|);
221 main( int argc, char *argv[\|] ) {
225 sigaddset(&new, SIGINT);
228 case '0': /* POSIX */
229 pthread_sigmask(SIG_BLOCK, &new, NULL);
230 pthread_create(&user_threadID, NULL, handler,
232 pthread_join(user_threadID, NULL);
235 case '1': /* Solaris */
236 thr_sigsetmask(SIG_BLOCK, &new, NULL);
237 thr_create(NULL, 0, handler, argv[1], 0,
239 thr_join(user_threadID, NULL, NULL);
243 printf("thread handler, # %d, has exited\en",user_threadID);
245 printf("main thread, # %d is done\en", thr_self(\|));
249 struct sigaction act;
254 act.sa_handler = interrupt;
255 sigaction(SIGINT, &act, NULL);
257 case '0': /* POSIX */
258 pthread_sigmask(SIG_UNBLOCK, &new, NULL);
260 case '1': /* Solaris */
261 thr_sigsetmask(SIG_UNBLOCK, &new, NULL);
264 printf("\en Press CTRL-C to deliver SIGINT signal to the
266 sleep(8); /* give user time to hit CTRL-C */
273 printf("thread %d caught signal %d\en", thr_self(\|), sig);
276 void test_argv(char argv1[\|]) {
278 printf("use 0 as arg1 to use thr_create(\|);\en \e
279 or use 1 as arg1 to use pthread_create(\|)\en");
288 In the last example, the \fBhandler\fR thread served as a signal-handler while
289 also taking care of activity of its own (in this case, sleeping, although it
290 could have been some other activity). A thread could be completely dedicated to
291 signal-handling simply by waiting for the delivery of a selected signal by
292 blocking with \fBsigwait\fR(2). The two subroutines in the previous example,
293 \fBhandler()\fR and \fBinterrupt()\fR, could have been replaced with the
300 handler(void *unused)
303 printf("thread %d is waiting for you to press the CTRL-C keys\en",
305 sigwait(&new, &signal);
306 printf("thread %d has received the signal %d \en", thr_self(\|),
310 /* pthread_create(\|) and thr_create(\|) would use NULL instead
311 of argv[1] for the arg passed to handler(\|) */
317 In this routine, one thread is dedicated to catching and handling the signal
318 specified by the set \fBnew\fR, which allows \fBmain()\fR and all of its other
319 sub-threads, created \fIafter\fR \fBpthread_sigmask()\fR or
320 \fBthr_sigsetmask()\fR masked that signal, to continue uninterrupted. Any use
321 of \fBsigwait\fR(2) should be such that all threads block the signals passed
322 to \fBsigwait\fR(2) at all times. Only the thread that calls \fBsigwait()\fR
323 will get the signals. The call to \fBsigwait\fR(2) takes two arguments.
327 For this type of background dedicated signal-handling routine, a Solaris daemon
328 thread can be used by passing the argument \fBTHR_DAEMON\fR to
329 \fBthr_create\fR(3C).
334 See \fBattributes\fR(5) for descriptions of the following attributes:
342 ATTRIBUTE TYPE ATTRIBUTE VALUE
344 Interface Stability Standard
346 MT-Level MT-Safe and Async-Signal-Safe
352 \fBsigaction\fR(2), \fBsigprocmask\fR(2), \fBsigwait\fR(2),
353 \fBcond_wait\fR(3C), \fBpthread_cancel\fR(3C), \fBpthread_create\fR(3C),
354 \fBpthread_join\fR(3C), \fBpthread_self\fR(3C), \fBsigaddset\fR(3C),
355 \fBsigemptyset\fR(3C), \fBsigsetops\fR(3C), \fBsleep\fR(3C),
356 \fBattributes\fR(5), \fBcancellation\fR(5), \fBstandards\fR(5)
360 It is not possible to block signals that cannot be caught or ignored (see
361 \fBsigaction\fR(2)). It is also not possible to block or unblock
362 \fBSIGCANCEL\fR, as \fBSIGCANCEL\fR is reserved for the implementation of POSIX
363 thread cancellation (see \fBpthread_cancel\fR(3C) and \fBcancellation\fR(5)).
364 This restriction is quietly enforced by the standard C library.
367 Using \fBsigwait\fR(2) in a dedicated thread allows asynchronously generated
368 signals to be managed synchronously; however, \fBsigwait\fR(2) should never be
369 used to manage synchronously generated signals.
372 Synchronously generated signals are exceptions that are generated by a thread
373 and are directed at the thread causing the exception. Since \fBsigwait()\fR
374 blocks waiting for signals, the blocking thread cannot receive a synchronously
378 The \fBsigprocmask\fR(2) function behaves the same as if
379 \fBpthread_sigmask()\fR has been called. POSIX leaves the semantics of the call
380 to \fBsigprocmask\fR(2) unspecified in a multi-threaded process, so programs
381 that care about POSIX portability should not depend on this semantic.
384 If a signal is delivered while a thread is waiting on a condition variable, the
385 \fBcond_wait\fR(3C) function will be interrupted and the handler will be
386 executed. The state of the lock protecting the condition variable is undefined
387 while the thread is executing the signal handler.
390 Although \fBpthread_sigmask()\fR is Async-Signal-Safe with respect to the
391 Solaris environment, this safeness is not guaranteed to be portable to other
395 Signals that are generated synchronously should not be masked. If such a signal
396 is blocked and delivered, the receiving process is killed.