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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON |
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PTHREAD_MUTEXATTR_SETROBUST(3)x Programmer's ManualAD_MUTEXATTR_SETROBUST(3)
pthread_mutexattr_getrobust, pthread_mutexattr_setrobust - get and
set the robustness attribute of a mutex attributes object
#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
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().
pthread_mutexattr_getrobust() and pthread_mutexattr_setrobust() were
added to glibc in version 2.12.
POSIX.1-2008.
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.
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");
}
}
get_robust_list(2), set_robust_list(2), pthread_mutex_init(3),
pthread_mutex_consistent(3), pthread_mutex_lock(3), pthreads(7)
This page is part of release 4.15 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 2017-08-20 PTHREAD_MUTEXATTR_SETROBUST(3)
Pages that refer to this page: get_robust_list(2), pthread_mutexattr_init(3), pthread_mutex_consistent(3)
Copyright and license for this manual page
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