NAME

pthread_mutexattr_gettype, pthread_mutexattr_settype - get and set the mutex type attribute

SYNOPSIS

#include <pthread.h>

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


DESCRIPTION

The pthread_mutexattr_gettype() and pthread_mutexattr_settype() functions, respectively, shall get and set the mutex type attribute. This attribute is set in the type parameter to these functions. The default value of the type attribute is PTHREAD_MUTEX_DEFAULT.

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

PTHREAD_MUTEX_NORMAL

This type of mutex does not detect deadlock. A thread attempting to relock this mutex without first unlocking it shall 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 shall return with an error. A thread attempting to unlock a mutex which another thread has locked shall return with an error. A thread attempting to unlock an unlocked mutex shall return with an error.

PTHREAD_MUTEX_RECURSIVE

A thread attempting to relock this mutex without first unlocking it shall 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 shall 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 shall return with an error. A thread attempting to unlock an unlocked mutex shall return with an error.

PTHREAD_MUTEX_DEFAULT

Attempting to recursively lock a mutex of this type results in undefined behavior. Attempting to unlock a mutex of this type which was not locked by the calling thread results in undefined behavior. Attempting to unlock a mutex of this type which is not locked results in undefined behavior. An implementation may map this mutex to one of the other mutex types.

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

RETURN VALUE

Upon successful completion, the pthread_mutexattr_gettype() function shall return zero and store the value of the type attribute of attr into the object referenced by the type parameter. Otherwise, an error shall be returned to indicate the error.

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

ERRORS

The pthread_mutexattr_settype() function shall fail if:

[EINVAL]

The value type is invalid.

These functions shall not return an error code of [EINTR].

EXAMPLES

None.

APPLICATION USAGE

It is advised that an application should not use a PTHREAD_MUTEX_RECURSIVE mutex with condition variables because the implicit unlock performed for a pthread_cond_timedwait() or pthread_cond_wait() 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.

RATIONALE

If an implementation detects that the value specified by the attr argument to pthread_mutexattr_gettype() or pthread_mutexattr_settype() does not refer to an initialized mutex attributes object, it is recommended that the function should fail and report an [EINVAL] error.

FUTURE DIRECTIONS

None.

SEE ALSO

pthread_cond_timedwait

XBD <pthread.h>

CHANGE HISTORY

First released in Issue 5.

Issue 6

The Open Group Corrigendum U033/3 is applied. The SYNOPSIS for pthread_mutexattr_gettype() is updated so that the first argument is of type const pthread_mutexattr_t *.

The restrict keyword is added to the pthread_mutexattr_gettype() prototype for alignment with the ISO/IEC 9899:1999 standard.

Issue 7

The pthread_mutexattr_gettype() and pthread_mutexattr_settype() functions are moved from the XSI option to the Base.

The [EINVAL] error for an uninitialized mutex attributes object is removed; this condition results in undefined behavior.