pthread_mutexattr_gettype(3pthread)

Synopsis

   cc [options] -Kthread file
   

   #include <pthread.h>
   

   int pthread_mutexattr_gettype(pthread_mutexattr_t *attr, int *type);
   int pthread_mutexattr_settype(pthread_mutexattr_t,*attr, int type);

Description

The type of mutex is contained in the type attribute of the mutex attributes. Valid mutex types include the following:

PTHREAD_MUTEX_NORMAL

This type of mutex does not detect deadlock. A thread attempting to relock this mutex without first unlocking it will deadlock. Attempting to unlock a mutex locked by a different thread results in undefined behavior. Attempting to unlock an unlocked mutex results in undefined behavior.

PTHREAD_MUTEX_ERRORCHECK

This type of mutex provides error checking. A thread attempting to relock this mutex without first unlocking it will return with an error. A thread attempting to unlock a mutex which another thread has locked will return with an error. A thread attempting to unlock an unlocked mutex will return with an error.

PTHREAD_MUTEX_RECURSIVE

A thread attempting to relock this mutex without first unlocking it will succeed in locking the mutex. The relocking deadlock which can occur with mutexes of type PTHREAD_MUTEX_NORMAL cannot occur with this type of mutex. Multiple locks of this mutex require the same number of unlocks to release the mutex before another thread can acquire the mutex. A thread attempting to unlock a mutex which another thread has locked will return with an error. A thread attempting to unlock an unlocked mutex will return with an error.

PTHREAD_MUTEX_DEFAULT

This type of mutex behaves exactly as described for PTHREAD_MUTEX_NORMAL, above.

An application should not 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 had been locked multiple times). If this happens, no other thread can satisfy the condition of the predicate.

Return values

pthread_mutexattr_gettype returns zero on success and stores the value of the type attribute of attr into the object referenced by the type parameter. Otherwise, an error number is returned.

Diagnostics

EINVAL

The value type is invalid.

EINVAL

The value specified by attr is invalid.

Standards compliance

References