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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | STANDARDS | HISTORY | EXAMPLES | SEE ALSO | COLOPHON |
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pthread_...setrobust(3) Library Functions Manual pthread_...setrobust(3)
pthread_mutexattr_getrobust, pthread_mutexattr_setrobust - get
and set the robustness attribute of a mutex attributes object
POSIX threads library (libpthread, -lpthread)
#include <pthread.h>
int pthread_mutexattr_getrobust(const pthread_mutexattr_t *attr,
int *robustness);
int pthread_mutexattr_setrobust(pthread_mutexattr_t *attr,
int robustness);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
pthread_mutexattr_getrobust(), pthread_mutexattr_setrobust():
_POSIX_C_SOURCE >= 200809L
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.
On success, these functions return 0. On error, they return a
positive error number.
In the glibc implementation, pthread_mutexattr_getrobust() always
return zero.
EINVAL A value other than PTHREAD_MUTEX_STALLED or
PTHREAD_MUTEX_ROBUST was passed to
pthread_mutexattr_setrobust().
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.
POSIX.1-2008.
glibc 2.12. POSIX.1-2008.
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:
[[deprecated]]
int pthread_mutexattr_getrobust_np(const pthread_mutexattr_t *attr,
int *robustness);
[[deprecated]]
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; since
glibc 2.34 these APIs are marked as deprecated.
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 <errno.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.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(void)
{
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");
}
}
get_robust_list(2), set_robust_list(2),
pthread_mutex_consistent(3), pthread_mutex_init(3),
pthread_mutex_lock(3), pthreads(7)
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Linux man-pages 6.9.1 2024-06-15 pthread_...setrobust(3)
Pages that refer to this page: get_robust_list(2), pthread_mutexattr_init(3), pthread_mutex_consistent(3)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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