pthread_cleanup_push(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | NOTES | EXAMPLES | SEE ALSO | COLOPHON

PTHREAD_CLEANUP_PUSH(3) Linux Programmer's ManualPTHREAD_CLEANUP_PUSH(3)

NAME         top

       pthread_cleanup_push, pthread_cleanup_pop - push and pop thread
       cancellation clean-up handlers

SYNOPSIS         top

       #include <pthread.h>

       void pthread_cleanup_push(void (*routine)(void *), void *arg);
       void pthread_cleanup_pop(int execute);

       Compile and link with -pthread.

DESCRIPTION         top

       These functions manipulate the calling thread's stack of thread-
       cancellation 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 established 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) (siglongjmp(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.

RETURN VALUE         top

       These functions do not return a value.

ERRORS         top

       There are no errors.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       attributes(7).

       ┌──────────────────────────────────────┬───────────────┬─────────┐
       │Interface                             Attribute     Value   │
       ├──────────────────────────────────────┼───────────────┼─────────┤
       │pthread_cleanup_push(),               │ Thread safety │ MT-Safe │
       │pthread_cleanup_pop()                 │               │         │
       └──────────────────────────────────────┴───────────────┴─────────┘

CONFORMING TO         top

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

NOTES         top

       On Linux, the pthread_cleanup_push() and pthread_cleanup_pop()
       functions 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 scope.

       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.

EXAMPLES         top

       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.  Depending 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
       cancellation 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 reset.

       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 = 0;

       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 */
                   cnt++;
               }
           }

           pthread_cleanup_pop(cleanup_pop_arg);
           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);
           else
               printf("Thread terminated normally; cnt = %d\n", cnt);
           exit(EXIT_SUCCESS);
       }

SEE ALSO         top

       pthread_cancel(3), pthread_cleanup_push_defer_np(3),
       pthread_setcancelstate(3), pthread_testcancel(3), pthreads(7)

COLOPHON         top

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       https://www.kernel.org/doc/man-pages/.

Linux                          2021-03-22        PTHREAD_CLEANUP_PUSH(3)

Pages that refer to this page: pthread_cancel(3)pthread_cleanup_push_defer_np(3)pthread_exit(3)pthread_setcancelstate(3)pthread_testcancel(3)pthreads(7)