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(7) 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(7),
standards(7)

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)