pthread_rwlockattr_getpshared¶

Synopsis¶

#include <pthread.h>

int pthread_rwlockattr_getpshared(const pthread_rwlockattr_t *restrict attr,
                                  int *restrict pshared);

int pthread_rwlockattr_setpshared(pthread_rwlockattr_t *attr, int pshared);

Status¶

Implemented

Conformance¶

IEEE Std 1003.1-2017

Description¶

The pthread_rwlockattr_getpshared() function shall obtain the value of the process-shared attribute from the initialized attributes object referenced by attr. The pthread_rwlockattr_setpshared() function shall set the process-shared attribute in an initialized attributes object referenced by attr.

The process-shared attribute shall be set to PTHREAD_PROCESS_SHARED to permit a read-write lock to be operated upon by any thread that has access to the memory where the read-write lock is allocated, even if the read-write lock is allocated in memory that is shared by multiple processes. The default value of the process-shared attribute shall be PTHREAD_PROCESS_PRIVATE. Phoenix-RTOS supports only PTHREAD_PROCESS_PRIVATE (see POSIX deviations).

The behavior is undefined if the value specified by the attr argument to pthread_rwlockattr_getpshared() or pthread_rwlockattr_setpshared() does not refer to an initialized read-write lock attributes object.

Return value¶

Upon successful completion, the pthread_rwlockattr_getpshared() function 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.

If successful, the pthread_rwlockattr_setpshared() function shall return zero; otherwise, an error number shall be returned to indicate the error.

Errors¶

The pthread_rwlockattr_setpshared() function shall fail if:

ENOTSUP - The value of pshared is PTHREAD_PROCESS_SHARED.

The pthread_rwlockattr_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¶

IEEE Std 1003.1-2017 defines these functions as part of the Thread Process-Shared Synchronization option and requires pthread_rwlockattr_setpshared() to accept PTHREAD_PROCESS_SHARED, so that a read-write lock can be shared between processes. Phoenix-RTOS does not support this option (_POSIX_THREAD_PROCESS_SHARED is not defined), and pthread_rwlockattr_setpshared() returns ENOTSUP for PTHREAD_PROCESS_SHARED, an error that the standard does not define for it. A Phoenix-RTOS read-write lock is built on a kernel mutex and kernel condition variables, which are resources of the process that created them and cannot be used by another process.