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() func-
tions, 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
error.
ERRORS
The pthread_mutexattr_settype() function shall fail if:
EINVAL The value type is invalid.
The pthread_mutexattr_gettype() and pthread_mutexattr_settype() func-
tions 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_RECUR-
SIVE 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 predi-
cate.
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 Technology
-- 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 .
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