pthread_mutexattr_getrobust

PTHREAD_MUTEXATTR_SETROBUSTLinux Programmer's MaPTHREAD_MUTEXATTR_SETROBUST(3)



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

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

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

CONFORMING TO
       POSIX.1-2008.

NOTES
       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.

EXAMPLE
       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 thread] Attempting to lock the robust mutex.
           [main thread] pthread_mutex_lock() returned EOWNERDEAD
           [main thread] Now make the mutex consistent
           [main thread] 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);
                                       /* initialize the attributes object */
           pthread_mutexattr_setrobust(&attr, PTHREAD_MUTEX_ROBUST);
                                      /* set robustness */

           pthread_mutex_init(&mtx, &attr);   /* initialize the mutex */

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

           sleep(2);

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

           printf("[main thread] Attempting to lock the robust mutex.\n");
           s = pthread_mutex_lock(&mtx);
           if (s == EOWNERDEAD) {
               printf("[main thread] pthread_mutex_lock() returned EOWNERDEAD\n");
               printf("[main thread] Now make the mutex consistent\n");
               s = pthread_mutex_consistent(&mtx);
               if (s != 0)
                   handle_error_en(s, "pthread_mutex_consistent");
               printf("[main thread] 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 thread] pthread_mutex_lock() unexpectedly succeeded\n");
               exit(EXIT_FAILURE);
           } else {
               printf("[main thread] pthread_mutex_lock() unexpectedly failed\n");
               handle_error_en(s, "pthread_mutex_lock");
           }
       }

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

COLOPHON
       This page is part of release 5.04 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                             2019-10-10    PTHREAD_MUTEXATTR_SETROBUST(3)