The
pthread_rwlock_init() function is used to initialize a read/write lock, with attributes specified by
attr. If
attr is
NULL, the default read/write lock attributes are used.
The results of calling
pthread_rwlock_init() with an already initialized lock are undefined.
The macro
PTHREAD_RWLOCK_INITIALIZER can be used to initialize a read/write lock when the allocation can be done statically, no error checking is required, and the default attributes are appropriate. The behavior is similar to calling
pthread_rwlock_init() with
attr specified as
NULL.
The
pthread_rwlock_destroy() function is used to destroy a read/write lock previously created with
pthread_rwlock_init().
The
pthread_rwlock_rdlock() function acquires a read lock on
lock provided that
lock is not presently held for writing and no writer threads are presently blocked on the lock. If the read lock cannot be immediately acquired, the calling thread blocks until it can acquire the lock.
The
pthread_rwlock_timedrdlock() performs the same action, but will not wait beyond
abstime to obtain the lock before returning.
The
pthread_rwlock_tryrdlock() function performs the same action as
pthread_rwlock_rdlock(), but does not block if the lock cannot be immediately obtained (i.e., the lock is held for writing or there are waiting writers).
A thread may hold multiple concurrent read locks. If so,
pthread_rwlock_unlock() must be called once for each lock obtained.
The results of acquiring a read lock while the calling thread holds a write lock are undefined.
The
pthread_rwlock_wrlock() function blocks until a write lock can be acquired against
lock.
The
pthread_rwlock_timedwrlock() performs the same action, but will not wait beyond
abstime to obtain the lock before returning.
The
pthread_rwlock_trywrlock() function performs the same action as
pthread_rwlock_wrlock(), but does not block if the lock cannot be immediately obtained.
The results are undefined if the calling thread already holds the lock at the time the call is made.
The
pthread_rwlock_unlock() function is used to release the read/write lock previously obtained by
pthread_rwlock_rdlock(),
pthread_rwlock_wrlock(),
pthread_rwlock_tryrdlock(), or
pthread_rwlock_trywrlock().