PTHREAD_MUTEXATTR_GETTYPE(P) POSIX Programmer's Manual PTHREAD_MUTEXATTR_GETTYPE(P)
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.
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 per-
formed 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>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE
and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained
online at http://www.opengroup.org/unix/online.html .
IEEE
/The Open Group 2003 PTHREAD_MUTEXATTR_GETTYPE(P)