pthread_mutexattr_getpshared¶

Synopsis¶

#include <pthread.h>

int pthread_mutexattr_getpshared(const pthread_mutexattr_t *restrict attr,
                                 int *restrict pshared);

int pthread_mutexattr_setpshared(pthread_mutexattr_t *attr, int pshared);

Status¶

Implemented

Conformance¶

IEEE Std 1003.1-2017

Description¶

The pthread_mutexattr_getpshared() function shall obtain the value of the process-shared attribute from the attributes object referenced by attr.

The pthread_mutexattr_setpshared() function shall set the process-shared attribute in an initialized attributes object referenced by attr.

The process-shared attribute is set to PTHREAD_PROCESS_SHARED to permit a mutex to be operated upon by any thread that has access to the memory where the mutex is allocated, even if the mutex is allocated in memory that is shared by multiple processes. The default value of the attribute shall be PTHREAD_PROCESS_PRIVATE.

The behavior is undefined if the value specified by the attr argument to pthread_mutexattr_getpshared() or pthread_mutexattr_setpshared() does not refer to an initialized mutex attributes object.

Return value¶

Upon successful completion, pthread_mutexattr_setpshared() shall return zero; otherwise, an error number shall be returned to indicate the error.

Upon successful completion, pthread_mutexattr_getpshared() shall return zero and store the value of the process-shared attribute of attr into the object referenced by the pshared parameter. Otherwise, an error number shall be returned to indicate the error.

Errors¶

The pthread_mutexattr_setpshared() function shall fail if:

ENOTSUP - The value of pshared is PTHREAD_PROCESS_SHARED (see POSIX deviations).

The pthread_mutexattr_setpshared() function may fail if:

EINVAL - The new value specified for the attribute is outside the range of legal values for that attribute.

These functions shall not return an error code of EINTR.

POSIX deviations¶

Phoenix-RTOS doesn’t support process-shared mutexes (the Thread Process-Shared Synchronization option, _POSIX_THREAD_PROCESS_SHARED is not defined). pthread_mutexattr_setpshared() fails with ENOTSUP when pshared is PTHREAD_PROCESS_SHARED, an error that the standard does not define for it, and pthread_mutexattr_getpshared() always reports PTHREAD_PROCESS_PRIVATE. A Phoenix-RTOS mutex is a kernel object identified by a handle which is valid only in the process that created it, so a mutex placed in memory shared by several processes can’t be used by threads of the other processes.