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26 .TH PTHREAD_CLEANUP_PUSH 3 2008-11-24 "Linux" "Linux Programmer's Manual"
28 pthread_cleanup_push, pthread_cleanup_pop \- push and pop
29 thread cancellation clean-up handlers
32 .B #include <pthread.h>
34 .BI "void pthread_cleanup_push(void (*" routine ")(void *),"
36 .BI "void pthread_cleanup_pop(int " execute );
38 Compile and link with \fI\-pthread\fP.
41 These functions manipulate the calling thread's stack of
42 thread-cancellation clean-up handlers.
43 A clean-up handler is a function that is automatically executed
44 when a thread is canceled (or in various other circumstances
46 it might, for example, unlock a mutex so that
47 it becomes available to other threads in the process.
50 .BR pthread_cleanup_push ()
53 onto the top of the stack of clean-up handlers.
56 is later invoked, it will be given
61 .BR pthread_cleanup_pop ()
62 function removes the routine at the top of the stack of clean-up handlers,
63 and optionally executes it if
67 A cancellation clean-up handler is popped from the stack
68 and executed in the following circumstances:
70 When a thread is canceled,
71 all of the stacked clean-up handlers are popped and executed in
72 the reverse of the order in which they were pushed onto the stack.
74 When a thread terminates by calling
76 all clean-up handlers are executed as described in the preceding point.
77 (Clean-up handlers are \fInot\fP called if the thread terminates by
80 from the thread start function.)
83 .BR pthread_cleanup_pop ()
86 argument, the top-most clean-up handler is popped and executed.
89 .BR pthread_cleanup_push ()
91 .BR pthread_cleanup_pop ()
92 to be implemented as macros that expand to text
93 containing \(aq\fB{\fP\(aq and \(aq\fB}\fP\(aq, respectively.
94 For this reason, the caller must ensure that calls to these
95 functions are paired within the same function,
96 and at the same lexical nesting level.
97 (In other words, a clean-up handler is established only
98 during the execution of a specified section of code.)
102 .RB ( siglongjmp (3))
103 produces undefined results if any call has been made to
104 .BR pthread_cleanup_push ()
106 .BR pthread_cleanup_pop ()
107 without the matching call of the pair since the jump buffer
110 .RB ( sigsetjmp (3)).
113 .RB ( siglongjmp (3))
114 from inside a clean-up handler produces undefined results
115 unless the jump buffer was also filled by
120 These functions do not return a value.
124 .\" Available since glibc 2.0
129 .BR pthread_cleanup_push ()
131 .BR pthread_cleanup_pop ()
132 functions \fIare\fP implemented as macros that expand to text
133 containing \(aq\fB{\fP\(aq and \(aq\fB}\fP\(aq, respectively.
134 This means that variables declared within the scope of
135 paired calls to these functions will be visible within only that scope.
138 .\" The text was actually added in the 2004 TC2
139 says that the effect of using
145 to prematurely leave a block bracketed
146 .BR pthread_cleanup_push ()
148 .BR pthread_cleanup_pop ()
150 Portable applications should avoid doing this.
152 The program below provides a simple example of the use of the functions
153 described in this page.
154 The program creates a thread that executes a loop bracketed by
155 .BR pthread_cleanup_push ()
157 .BR pthread_cleanup_pop ().
158 This loop increments a global variable,
161 Depending on what command-line arguments are supplied,
162 the main thread sends the other thread a cancellation request,
163 or sets a global variable that causes the other thread
164 to exit its loop and terminate normally (by doing a
167 In the following shell session,
168 the main thread sends a cancellation request to the other thread:
177 Called clean-up handler
178 Thread was canceled; cnt = 0
182 From the above, we see that the thread was canceled,
183 and that the cancellation clean-up handler was called
184 and it reset the value of the global variable
188 In the next run, the main program sets a
189 global variable that causes other thread to terminate normally:
197 Thread terminated normally; cnt = 2
201 From the above, we see that the clean-up handler was not executed (because
203 was 0), and therefore the value of
207 In the next run, the main program sets a global variable that
208 causes the other thread to terminate normally,
209 and supplies a nonzero value for
210 .IR cleanup_pop_arg :
218 Called clean-up handler
219 Thread terminated normally; cnt = 0
223 In the above, we see that although the thread was not canceled,
224 the clean-up handler was executed, because the argument given to
225 .BR pthread_cleanup_pop ()
231 #include <sys/types.h>
237 #define handle_error_en(en, msg) \\
238 do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)
241 static int cleanup_pop_arg = 0;
245 cleanup_handler(void *arg)
247 printf("Called clean\-up handler\\n");
252 thread_start(void *arg)
256 printf("New thread started\\n");
258 pthread_cleanup_push(cleanup_handler, NULL);
260 curr = start = time(NULL);
263 pthread_testcancel(); /* A cancellation point */
264 if (curr < time(NULL)) {
266 printf("cnt = %d\\n", cnt); /* A cancellation point */
271 pthread_cleanup_pop(cleanup_pop_arg);
276 main(int argc, char *argv[])
282 s = pthread_create(&thr, NULL, thread_start, NULL);
284 handle_error_en(s, "pthread_create");
286 sleep(2); /* Allow new thread to run a while */
290 cleanup_pop_arg = atoi(argv[2]);
294 printf("Canceling thread\\n");
295 s = pthread_cancel(thr);
297 handle_error_en(s, "pthread_cancel");
300 s = pthread_join(thr, &res);
302 handle_error_en(s, "pthread_join");
304 if (res == PTHREAD_CANCELED)
305 printf("Thread was canceled; cnt = %d\\n", cnt);
307 printf("Thread terminated normally; cnt = %d\\n", cnt);
312 .BR pthread_cancel (3),
313 .BR pthread_cleanup_push_defer_np (3),
314 .BR pthread_setcancelstate (3),
315 .BR pthread_testcancel (3),