PTHREAD_RWLOCK_INIT(3C) Standard C Library Functions PTHREAD_RWLOCK_INIT(3C)


NAME


pthread_rwlock_init, pthread_rwlock_destroy - initialize or destroy read-
write lock object

SYNOPSIS


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

int pthread_rwlock_init(pthread_rwlock_t *restrict rwlock,
const pthread_rwlockattr_t *restrict attr);


int pthread_rwlock_destroy(pthread_rwlock_t **rwlock);


pthread_rwlock_t rwlock=PTHREAD_RWLOCK_INITIALIZER;


DESCRIPTION


The pthread_rwlock_init() function initializes the read-write lock
referenced by rwlock with the attributes referenced by attr. If attr is
NULL, the default read-write lock attributes are used; the effect is the
same as passing the address of a default read-write lock attributes
object. Once initialized, the lock can be used any number of times
without being re-initialized. Upon successful initialization, the state
of the read-write lock becomes initialized and unlocked. Results are
undefined if pthread_rwlock_init() is called specifying an already
initialized read-write lock. Results are undefined if a read-write lock
is used without first being initialized.


If the pthread_rwlock_init() function fails, rwlock is not initialized
and the contents of rwlock are undefined.


The pthread_rwlock_destroy() function destroys the read-write lock object
referenced by rwlock and releases any resources used by the lock. The
effect of subsequent use of the lock is undefined until the lock is re-
initialized by another call to pthread_rwlock_init(). An implementation
may cause pthread_rwlock_destroy() to set the object referenced by
rwlock to an invalid value. Results are undefined if
pthread_rwlock_destroy() is called when any thread holds rwlock.
Attempting to destroy an uninitialized read-write lock results in
undefined behaviour. A destroyed read-write lock object can be re-
initialized using pthread_rwlock_init(); the results of otherwise
referencing the read-write lock object after it has been destroyed are
undefined.


In cases where default read-write lock attributes are appropriate, the
macro PTHREAD_RWLOCK_INITIALIZER can be used to initialize read-write
locks that are statically allocated. The effect is equivalent to dynamic
initialization by a call to pthread_rwlock_init() with the parameter
attr specified as NULL, except that no error checks are performed.

RETURN VALUES


If successful, the pthread_rwlock_init() and pthread_rwlock_destroy()
functions return 0. Otherwise, an error number is returned to indicate
the error.

ERRORS


The pthread_rwlock_init() and pthread_rwlock_destroy() functions will
fail if:

EINVAL
The value specified by attr is invalid.


EINVAL
The value specified by rwlock 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_rwlock_rdlock(3C), pthread_rwlock_unlock(3C),
pthread_rwlock_wrlock(3C), pthread_rwlockattr_init(3C), attributes(5),
standards(5)


March 23, 2005 PTHREAD_RWLOCK_INIT(3C)