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)