NAME

pthread_mutexattr_setkind_np - Specifies the mutex type attribute

SYNOPSIS

#include <pthread.h> int pthread_mutexattr_setkind_np( pthread_mutexattr_t *attr, int kind);

PARAMETERS

attrMutex attributes object modified. 

kindNew value for the mutex type attribute. The kind parameter specifies the type of mutex that is created. Valid values are MUTEX_FAST_NP (default), MUTEX_RECURSIVE_NP, and MUTEX_NONRECURSIVE_NP. 

DESCRIPTION

The pthread_mutexattr_setkind_np() routine sets the mutex type attribute that is used when a mutex is created. A fast mutex is locked and unlocked in the fastest manner possible. A fast mutex can only be locked (obtained) once. All subsequent calls to pthread_mutex_lock() cause the calling thread to block until the mutex is freed by the thread that owns it. If the thread that owns the mutex attempts to lock it again, the thread waits for itself to release the mutex (causing a deadlock). A recursive mutex can be locked more than once by the same thread without causing that thread to deadlock. In other words, a single thread can make consecutive calls to pthread_mutex_lock() without blocking. The thread must then call pthread_mutex_unlock() the same number of times as it called pthread_mutex_lock() before another thread can lock the mutex. A nonrecursive mutex is locked only once by a thread, like a fast mutex.  If the thread tries to lock the mutex again without first unlocking it, the thread receives an error.  Thus, nonrecursive mutexes are more informative than fast mutexes because fast mutexes block in such a case, leaving it up to you to determine why the thread no longer executes.  Also, if someone other than the owner tries to unlock a nonrecursive mutex, an error is returned. Never use a recursive mutex with condition variables because the implicit unlock performed for a pthread_cond_wait() or pthread_cond_timedwait() might not actually release the mutex. In that case, no other thread can satisfy the condition of the predicate. This routine is a new primitive.

RETURN VALUES

If the function fails, errno may be set to one of the following values:

RELATED INFORMATION

Functions:  pthread_mutexattr_create(3), pthread_mutexattr_getkind_np(3), pthread_mutex_init(3). 

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