pthread_mutexattr

Synopsis:

#include <pthread.h>

int pthread_mutexattr_settype( 
                      pthread_mutexattr_t * attr, 
                      int type );

Arguments:

attr

A pointer to the pthread_mutexattr_t object that you want to set the attribute in.

type

The new type; one of:

PTHREAD_MUTEX_NORMAL
PTHREAD_MUTEX_ERRORCHECK
PTHREAD_MUTEX_RECURSIVE
PTHREAD_MUTEX_DEFAULT

In QNX Neutrino, PTHREAD_MUTEX_DEFAULT mutexes are treated in the same way as PTHREAD_MUTEX_ERRORCHECK ones.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The pthread_mutexattr_settype() function sets the mutex type in the mutex attribute object attr to the value given by type.

To make the mutext robust (PTHREAD_MUTEX_ROBUST) or nonrobust (PTHREAD_MUTEX_STALLED), call pthread_mutexattr_setrobust().

The type and the robustness govern the behavior of the mutex when you relock the mutex without first unlocking it, and when you try to unlock a mutex that you don't own or that isn't locked:

Mutex type	Robustness	Relock	Unlock when not the owner
NORMAL	STALLED	Deadlock	Undefined behavior
NORMAL	ROBUST	Deadlock	pthread_mutex_unlock() returns EPERM
ERRORCHECK	Either	pthread_mutex_lock() and pthread_mutex_timedlock() return EDEADLK	pthread_mutex_unlock() returns EPERM
RECURSIVE	Either	The lock count is incremented. You must unlock it the same number of times before another thread can acquire the mutex.	pthread_mutex_unlock() returns EPERM
DEFAULT	Either	pthread_mutex_lock() and pthread_mutex_timedlock() return EDEADLK	pthread_mutex_unlock() returns EPERM

Note: You can't use a robust mutex with SyncMutexEvent(). The two mechanisms achieve the same goal in different ways.

Returns:

EOK: Success.
EINVAL: The value specified by attr or type is invalid.

Classification:

POSIX 1003.1

Safety:
Cancellation point	No
Interrupt handler	No
Signal handler	Yes
Thread	Yes

Caveats:

An application shouldn't use a PTHREAD_MUTEX_RECURSIVE mutex with condition variables because the implicit unlock performed for a pthread_cond_wait() or pthread_cond_timedwait() may not actually release the mutex (if it's been locked multiple times). If this happens, no other thread can satisfy the condition of the predicate.