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

PTHREAD_MUTEX_ERRORCHECK

PTHREAD_MUTEX_RECURSIVE

PTHREAD_MUTEX_DEFAULT

The mutex type affects the behavior of calls which lock and unlock the mutex. See pthread_mutex_lock for details. An implementation may map PTHREAD_MUTEX_DEFAULT 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, pthread_mutex_lock

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.

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0464 [121] is applied.