pthread_mutexattr_setrobust(3) — Linux manual page

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

PTHREAD_MUTEXATTR_SETROBUST(3)Programmer'sPManual_MUTEXATTR_SETROBUST(3)

NAME         top

       pthread_mutexattr_getrobust, pthread_mutexattr_setrobust - get
       and set the robustness attribute of a mutex attributes object

SYNOPSIS         top

       #include <pthread.h>

       int pthread_mutexattr_getrobust(const pthread_mutexattr_t *attr,
                                       int *robustness);
       int pthread_mutexattr_setrobust(const pthread_mutexattr_t *attr,
                                       int robustness);

       Compile and link with -pthread.

   Feature Test Macro Requirements for glibc (see
   feature_test_macros(7)):

       pthread_mutexattr_getrobust(), pthread_mutexattr_setrobust():
           _POSIX_C_SOURCE >= 200809L

DESCRIPTION         top

       The pthread_mutexattr_getrobust() function places the value of
       the robustness attribute of the mutex attributes object referred
       to by attr in *robustness.  The pthread_mutexattr_setrobust()
       function sets the value of the robustness attribute of the mutex
       attributes object referred to by attr to the value specified in
       *robustness.

       The robustness attribute specifies the behavior of the mutex when
       the owning thread dies without unlocking the mutex.  The
       following values are valid for robustness:

       PTHREAD_MUTEX_STALLED
              This is the default value for a mutex attributes object.
              If a mutex is initialized with the PTHREAD_MUTEX_STALLED
              attribute and its owner dies without unlocking it, the
              mutex remains locked afterwards and any future attempts to
              call pthread_mutex_lock(3) on the mutex will block
              indefinitely.

       PTHREAD_MUTEX_ROBUST
              If a mutex is initialized with the PTHREAD_MUTEX_ROBUST
              attribute and its owner dies without unlocking it, any
              future attempts to call pthread_mutex_lock(3) on this
              mutex will succeed and return EOWNERDEAD to indicate that
              the original owner no longer exists and the mutex is in an
              inconsistent state.  Usually after EOWNERDEAD is returned,
              the next owner should call pthread_mutex_consistent(3) on
              the acquired mutex to make it consistent again before
              using it any further.

              If the next owner unlocks the mutex using
              pthread_mutex_unlock(3) before making it consistent, the
              mutex will be permanently unusable and any subsequent
              attempts to lock it using pthread_mutex_lock(3) will fail
              with the error ENOTRECOVERABLE.  The only permitted
              operation on such a mutex is pthread_mutex_destroy(3).

              If the next owner terminates before calling
              pthread_mutex_consistent(3), further pthread_mutex_lock(3)
              operations on this mutex will still return EOWNERDEAD.

       Note that the attr argument of pthread_mutexattr_getrobust() and
       pthread_mutexattr_setrobust() should refer to a mutex attributes
       object that was initialized by pthread_mutexattr_init(3),
       otherwise the behavior is undefined.

RETURN VALUE         top

       On success, these functions return 0.  On error, they return a
       positive error number.

       In the glibc implementation, pthread_mutexattr_getrobust() always
       return zero.

ERRORS         top

       EINVAL A value other than PTHREAD_MUTEX_STALLED or
              PTHREAD_MUTEX_ROBUST was passed to
              pthread_mutexattr_setrobust().

VERSIONS         top

       pthread_mutexattr_getrobust() and pthread_mutexattr_setrobust()
       were added to glibc in version 2.12.

CONFORMING TO         top

       POSIX.1-2008.

NOTES         top

       In the Linux implementation, when using process-shared robust
       mutexes, a waiting thread also receives the EOWNERDEAD
       notification if the owner of a robust mutex performs an execve(2)
       without first unlocking the mutex.  POSIX.1 does not specify this
       detail, but the same behavior also occurs in at least some other
       implementations.

       Before the addition of pthread_mutexattr_getrobust() and
       pthread_mutexattr_setrobust() to POSIX, glibc defined the
       following equivalent nonstandard functions if _GNU_SOURCE was
       defined:

       int pthread_mutexattr_getrobust_np(const pthread_mutexattr_t *attr,
                                          int *robustness);
       int pthread_mutexattr_setrobust_np(const pthread_mutexattr_t *attr,
                                          int robustness);

       Correspondingly, the constants PTHREAD_MUTEX_STALLED_NP and
       PTHREAD_MUTEX_ROBUST_NP were also defined.

       These GNU-specific APIs, which first appeared in glibc 2.4, are
       nowadays obsolete and should not be used in new programs.

EXAMPLES         top

       The program below demonstrates the use of the robustness
       attribute of a mutex attributes object.  In this program, a
       thread holding the mutex dies prematurely without unlocking the
       mutex.  The main thread subsequently acquires the mutex
       successfully and gets the error EOWNERDEAD, after which it makes
       the mutex consistent.

       The following shell session shows what we see when running this
       program:

           $ ./a.out
           [original owner] Setting lock...
           [original owner] Locked. Now exiting without unlocking.
           [main] Attempting to lock the robust mutex.
           [main] pthread_mutex_lock() returned EOWNERDEAD
           [main] Now make the mutex consistent
           [main] Mutex is now consistent; unlocking

   Program source
       #include <stdlib.h>
       #include <stdio.h>
       #include <unistd.h>
       #include <pthread.h>
       #include <errno.h>

       #define handle_error_en(en, msg) \
               do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)

       static pthread_mutex_t mtx;

       static void *
       original_owner_thread(void *ptr)
       {
           printf("[original owner] Setting lock...\n");
           pthread_mutex_lock(&mtx);
           printf("[original owner] Locked. Now exiting without unlocking.\n");
           pthread_exit(NULL);
       }

       int
       main(int argc, char *argv[])
       {
           pthread_t thr;
           pthread_mutexattr_t attr;
           int s;

           pthread_mutexattr_init(&attr);

           pthread_mutexattr_setrobust(&attr, PTHREAD_MUTEX_ROBUST);

           pthread_mutex_init(&mtx, &attr);

           pthread_create(&thr, NULL, original_owner_thread, NULL);

           sleep(2);

           /* "original_owner_thread" should have exited by now. */

           printf("[main] Attempting to lock the robust mutex.\n");
           s = pthread_mutex_lock(&mtx);
           if (s == EOWNERDEAD) {
               printf("[main] pthread_mutex_lock() returned EOWNERDEAD\n");
               printf("[main] Now make the mutex consistent\n");
               s = pthread_mutex_consistent(&mtx);
               if (s != 0)
                   handle_error_en(s, "pthread_mutex_consistent");
               printf("[main] Mutex is now consistent; unlocking\n");
               s = pthread_mutex_unlock(&mtx);
               if (s != 0)
                   handle_error_en(s, "pthread_mutex_unlock");

               exit(EXIT_SUCCESS);
           } else if (s == 0) {
               printf("[main] pthread_mutex_lock() unexpectedly succeeded\n");
               exit(EXIT_FAILURE);
           } else {
               printf("[main] pthread_mutex_lock() unexpectedly failed\n");
               handle_error_en(s, "pthread_mutex_lock");
           }
       }

SEE ALSO         top

       get_robust_list(2), set_robust_list(2),
       pthread_mutex_consistent(3), pthread_mutex_init(3),
       pthread_mutex_lock(3), pthreads(7)

COLOPHON         top

       This page is part of release 5.11 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
       https://www.kernel.org/doc/man-pages/.

Linux                          2021-03-22 PTHREAD_MUTEXATTR_SETROBUST(3)

Pages that refer to this page: get_robust_list(2)pthread_mutexattr_init(3)pthread_mutex_consistent(3)