pthread_mutexattr_setrobust(3) - Linux manual page (original) (raw)
pthread...setrobust(3) Library Functions Manual pthread...setrobust(3)
NAME top
pthread_mutexattr_getrobust, pthread_mutexattr_setrobust - get and
set the robustness attribute of a mutex attributes objectLIBRARY top
POSIX threads library (_libpthread_, _-lpthread_)SYNOPSIS top
**#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 >= 200809LDESCRIPTION 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)](../man3/pthread%5Fmutex%5Flock.3.html) 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)](../man3/pthread%5Fmutex%5Flock.3.html) 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)](../man3/pthread%5Fmutex%5Fconsistent.3.html) 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)](../man3/pthread%5Fmutex%5Funlock.3.html) before making it consistent, the
mutex will be permanently unusable and any subsequent
attempts to lock it using [pthread_mutex_lock(3)](../man3/pthread%5Fmutex%5Flock.3.html) will fail
with the error **ENOTRECOVERABLE**. The only permitted
operation on such a mutex is [pthread_mutex_destroy(3)](../man3/pthread%5Fmutex%5Fdestroy.3.html).
If the next owner terminates before calling
[pthread_mutex_consistent(3)](../man3/pthread%5Fmutex%5Fconsistent.3.html), further [pthread_mutex_lock(3)](../man3/pthread%5Fmutex%5Flock.3.html)
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)](../man3/pthread%5Fmutexattr%5Finit.3.html),
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
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)](../man2/execve.2.html)
without first unlocking the mutex. POSIX.1 does not specify this
detail, but the same behavior also occurs in at least some other
implementations.STANDARDS top
POSIX.1-2008.HISTORY top
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.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; unlockingProgram 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");
}
}SEE ALSO top
[get_robust_list(2)](../man2/get%5Frobust%5Flist.2.html), [set_robust_list(2)](../man2/set%5Frobust%5Flist.2.html),
[pthread_mutex_consistent(3)](../man3/pthread%5Fmutex%5Fconsistent.3.html), [pthread_mutex_init(3)](../man3/pthread%5Fmutex%5Finit.3.html),
[pthread_mutex_lock(3)](../man3/pthread%5Fmutex%5Flock.3.html), [pthreads(7)](../man7/pthreads.7.html)COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2024-07-23 pthread...setrobust(3)
Pages that refer to this page:get_robust_list(2), pthread_mutexattr_init(3), pthread_mutex_consistent(3)