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     pthread_cleanup_push, pthread_cleanup_pop - push and pop thread cancel-
     lation clean-up handlers


     #include <pthread.h>
     void pthread_cleanup_push(void (*routine)(void *),
                               void *arg);
     void pthread_cleanup_pop(int execute);
     Compile and link with -pthread.


     These functions manipulate the calling thread's stack of thread-cancel-
     lation  clean-up  handlers.   A  clean-up handler is a function that is
     automatically executed when a thread is canceled (or in  various  other
     circumstances  described  below); it might, for example, unlock a mutex
     so that it becomes available to other threads in the process.
     The pthread_cleanup_push() function pushes routine onto the top of  the
     stack  of clean-up handlers.  When routine is later invoked, it will be
     given arg as its argument.
     The pthread_cleanup_pop() function removes the routine at  the  top  of
     the  stack  of clean-up handlers, and optionally executes it if execute
     is nonzero.
     A cancellation clean-up handler is popped from the stack  and  executed
     in the following circumstances:
     1. When  a thread is canceled, all of the stacked clean-up handlers are
        popped and executed in the reverse of the order in which  they  were
        pushed onto the stack.
     2. When  a  thread  terminates by calling pthread_exit(3), all clean-up
        handlers are executed as described in the preceding point.   (Clean-
        up  handlers are not called if the thread terminates by performing a
        return from the thread start function.)
     3. When a thread calls pthread_cleanup_pop()  with  a  nonzero  execute
        argument, the top-most clean-up handler is popped and executed.
     POSIX.1  permits pthread_cleanup_push() and pthread_cleanup_pop() to be
     implemented as macros that expand  to  text  containing  '{'  and  '}',
     respectively.   For  this  reason, the caller must ensure that calls to
     these functions are paired within the same function, and  at  the  same
     lexical  nesting  level.  (In other words, a clean-up handler is estab-
     lished only during the execution of a specified section of code.)
     Calling longjmp(3) (siglongjmp(3)) produces undefined  results  if  any
     call  has  been made to pthread_cleanup_push() or pthread_cleanup_pop()
     without the matching call of the pair since the jump buffer was  filled
     by   setjmp(3)  (sigsetjmp(3)).   Likewise,  calling  longjmp(3)  (sig-
     longjmp(3)) from inside a clean-up handler produces  undefined  results
     unless  the  jump  buffer  was  also filled by setjmp(3) (sigsetjmp(3))
     inside the handler.


     These functions do not return a value.


     There are no errors.


     For  an  explanation  of  the  terms  used   in   this   section,   see
     |Interface               | Attribute     | Value   |
     |pthread_cleanup_push(), | Thread safety | MT-Safe |
     |pthread_cleanup_pop()   |               |         |


     POSIX.1-2001, POSIX.1-2008.


     On Linux, the pthread_cleanup_push()  and  pthread_cleanup_pop()  func-
     tions  are implemented as macros that expand to text containing '{' and
     '}', respectively.  This means that variables declared within the scope
     of  paired  calls  to  these functions will be visible within only that
     POSIX.1 says that the effect of using return, break, continue, or  goto
     to  prematurely  leave  a  block  bracketed  pthread_cleanup_push() and
     pthread_cleanup_pop() is undefined.  Portable applications should avoid
     doing this.


     The program below provides a simple example of the use of the functions
     described in this page.  The program creates a thread that  executes  a
     loop  bracketed  by  pthread_cleanup_push()  and pthread_cleanup_pop().
     This loop increments a global variable, cnt, once each second.  Depend-
     ing  on what command-line arguments are supplied, the main thread sends
     the other thread a cancellation request, or sets a global variable that
     causes  the  other  thread  to exit its loop and terminate normally (by
     doing a return).
     In the following shell session, the main thread  sends  a  cancellation
     request to the other thread:
         $  ./a.out  New  thread  started  cnt  = 0 cnt = 1 Canceling thread
         Called clean-up handler Thread was canceled; cnt = 0
     From the above, we see that the thread was canceled, and that the  can-
     cellation  clean-up  handler  was  called and it reset the value of the
     global variable cnt to 0.
     In the next run, the main program sets a global  variable  that  causes
     other thread to terminate normally:
         $  ./a.out  x  New thread started cnt = 0 cnt = 1 Thread terminated
         normally; cnt = 2
     From the above, we see that  the  clean-up  handler  was  not  executed
     (because cleanup_pop_arg was 0), and therefore the value of cnt was not
     In the next run, the main program sets a global  variable  that  causes
     the  other  thread  to terminate normally, and supplies a nonzero value
     for cleanup_pop_arg:
         $ ./a.out x 1 New thread started cnt = 0 cnt =  1  Called  clean-up
         handler Thread terminated normally; cnt = 0
     In  the  above,  we  see that although the thread was not canceled, the
     clean-up  handler  was  executed,  because  the   argument   given   to
     pthread_cleanup_pop() was nonzero.
 Program source
        #include   <pthread.h>  #include  <sys/types.h>  #include  <stdio.h>
     #include <stdlib.h> #include <unistd.h> #include <errno.h>
     #define handle_error_en(en, msg) \
             do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)
     static int done = 0; static int cleanup_pop_arg = 0; static int  cnt  =
     static void cleanup_handler(void *arg) {
         printf("Called clean-up handler\n");
         cnt = 0; }
     static void * thread_start(void *arg) {
         time_t start, curr;
         printf("New thread started\n");
         pthread_cleanup_push(cleanup_handler, NULL);
         curr = start = time(NULL);
         while (!done) {
             pthread_testcancel();           /* A cancellation point */
             if (curr < time(NULL)) {
                 curr = time(NULL);
                 printf("cnt = %d\n", cnt);  /* A cancellation point */
         return NULL; }
     int main(int argc, char *argv[]) {
         pthread_t thr;
         int s;
         void *res;
         s = pthread_create(&thr, NULL, thread_start, NULL);
         if (s != 0)
             handle_error_en(s, "pthread_create");
         sleep(2);           /* Allow new thread to run a while */
         if (argc > 1) {
             if (argc > 2)
                 cleanup_pop_arg = atoi(argv[2]);
             done = 1;
         } else {
             printf("Canceling thread\n");
             s = pthread_cancel(thr);
             if (s != 0)
                 handle_error_en(s, "pthread_cancel");
         s = pthread_join(thr, &res);
         if (s != 0)
             handle_error_en(s, "pthread_join");
         if (res == PTHREAD_CANCELED)
             printf("Thread was canceled; cnt = %d\n", cnt);
             printf("Thread terminated normally; cnt = %d\n", cnt);
         exit(EXIT_SUCCESS); }


     pthread_cancel(3), pthread_cleanup_push_defer_np(3), pthread_setcancel-
     state(3), pthread_testcancel(3), pthreads(7)


     This page is part of release 4.16 of the Linux  man-pages  project.   A
     description  of  the project, information about reporting bugs, and the
     latest    version    of    this    page,    can     be     found     at

Linux 2017-09-15 PTHREAD_CLEANUP_PUSH(3)

/data/webs/external/dokuwiki/data/pages/man/pthread_cleanup_push.txt · Last modified: 2019/05/17 09:32 by

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