PTHREAD_MUTEXATTR_GETTYPE(3C) Standard C Library Functions


NAME


pthread_mutexattr_gettype, pthread_mutexattr_settype - get or set mutex
type

SYNOPSIS


cc -mt [ flag... ] file... -lpthread [ library... ]
#include <pthread.h>

int pthread_mutexattr_gettype(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 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 will 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 will return with
an error. A thread attempting to unlock a
mutex that another thread has locked will
return with an error. A thread attempting to
unlock an unlocked mutex will return with an
error.


PTHREAD_MUTEX_RECURSIVE
A thread attempting to relock this mutex
without first unlocking it will succeed in
locking the mutex. The relocking deadlock
that can occur with mutexes of type
PTHREAD_MUTEX_NORMAL cannot occur with this
type of mutex. Multiple locks of this mutex
require the same number of unlocks to release
the mutex before another thread can acquire
the mutex. A thread attempting to unlock a
mutex that another thread has locked will
return with an error. A thread attempting to
unlock an unlocked mutex will return with an
error. This type of mutex is only supported
for mutexes whose process shared attribute is
PTHREAD_PROCESS_PRIVATE.


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


RETURN VALUES


Upon successful completion, the pthread_mutexattr_settype() function
returns 0. Otherwise, an error number is returned to indicate the error.


Upon successful completion, the pthread_mutexattr_gettype() function
returns 0 and stores the value of the type attribute of attr in the
object referenced by the type parameter. Otherwise an error number is
returned to indicate the error.

ERRORS


The pthread_mutexattr_gettype() and pthread_mutexattr_settype() functions
will 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.


ATTRIBUTES


See attributes(5) for descriptions of the following attributes:


+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Standard |
+--------------------+-----------------+
|MT-Level | MT-Safe |
+--------------------+-----------------+

SEE ALSO


pthread_cond_timedwait(3C), pthread_cond_wait(3C), attributes(5),
standards(5)

NOTES


Application should not use a PTHREAD_MUTEX_RECURSIVE mutex with condition
variables because the implicit unlock performed for pthread_cond_wait()
or pthread_cond_timedwait() will not actually release the mutex (if it
had been locked multiple times). If this occurs, no other thread can
satisfy the condition of the predicate.


March 23, 2005 PTHREAD_MUTEXATTR_GETTYPE(3C)