The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition
Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.

#### NAME

> pthread_mutexattr_gettype, pthread_mutexattr_settype - get and set the mutex type attribute

#### SYNOPSIS

> ``[XSI] #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.

#### 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.

> The pthread_mutexattr_gettype() and pthread_mutexattr_settype() functions may fail if:

> [EINVAL]
>   The value specified by attr is invalid.

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

The following sections are informative.

#### 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

> None.

#### FUTURE DIRECTIONS

> None.

#### SEE ALSO

> pthread_cond_timedwait(), the Base Definitions volume of IEEE Std 1003.1-2001, <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.

End of informative text.

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