pthread_mutexattr_gettype

, pthread_mutexattr_settype

- get or set mutex type

Synopsis

cc –mt [ flag... ] file... [ 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:

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.