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PTHREAD_RWLOCK(3)          Library Functions Manual          PTHREAD_RWLOCK(3)

NAME
     pthread_rwlock -- read/write lock interface

LIBRARY
     POSIX Threads Library (libpthread, -lpthread)

SYNOPSIS
     #include <&lt;pthread.h>&gt;

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

     pthread_rwlock_t lock = PTHREAD_RWLOCK_INITIALIZER;
     int
     pthread_rwlock_destroy(pthread_rwlock_t *lock);

     int
     pthread_rwlock_rdlock(pthread_rwlock_t *lock);

     int
     pthread_rwlock_timedrdlock(pthread_rwlock_t * restrict lock, const struct
     timespec * restrict abstime);

     int
     pthread_rwlock_tryrdlock(pthread_rwlock_t *lock);

     int
     pthread_rwlock_wrlock(pthread_rwlock_t *lock);

     int
     pthread_rwlock_timedwrlock(pthread_rwlock_t * restrict lock, const struct
     timespec * restrict abstime);

     int
     pthread_rwlock_trywrlock(pthread_rwlock_t *lock);

     int
     pthread_rwlock_unlock(pthread_rwlock_t *lock);

DESCRIPTION
     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().

RETURN VALUES
     If successful, the pthread_rwlock_init() function will return zero.
     Otherwise an error number will be returned to indicate the error.

     If successful, the pthread_rwlock_destroy(), pthread_rwlock_rdlock(),
     pthread_rwlock_timedrdlock(), pthread_rwlock_tryrdlock(),
     pthread_rwlock_wrlock(), pthread_rwlock_timedwrlock(),
     pthread_rwlock_trywrlock(), and pthread_rwlock_unlock() will return zero.
     Otherwise an error number will be returned to indicate the error.

     The results are undefined if lock is not held by the calling thread.

ERRORS
     The pthread_rwlock_init() function may fail if:

     [EAGAIN]           The system lacks the resources to initialize another
                        read-write lock.

     [EBUSY]            The system has detected an attempt to re-initialize
                        the object referenced by lock, a previously
                        initialized but not yet destroyed read/write lock.

     [EINVAL]           The value specified by attr is invalid.

     [ENOMEM]           Insufficient memory exists to initialize the read-
                        write lock.

     The pthread_rwlock_destroy() function may fail if:

     [EBUSY]            The system has detected an attempt to destroy the
                        object referenced by lock while it is locked.

     [EINVAL]           The value specified by lock is invalid.

     The pthread_rwlock_tryrdlock() function shall fail if:

     [EBUSY]            The lock could not be acquired because a writer holds
                        the lock or was blocked on it.

     The pthread_rwlock_timedrdlock() function shall fail if:

     [ETIMEDOUT]        The time specified by abstime was reached before the
                        lock could be obtained.

     The pthread_rwlock_rdlock(), pthread_rwlock_timedrdlock(), and
     pthread_rwlock_tryrdlock() functions may fail if:

     [EAGAIN]           The lock could not be acquired because the maximum
                        number of read locks against lock has been exceeded.

     [EDEADLK]          The current thread already owns lock for writing.

     [EINVAL]           The value specified by lock is invalid.

     The pthread_rwlock_trywrlock() function shall fail if:

     [EBUSY]            The calling thread is not able to acquire the lock
                        without blocking.

     The pthread_rwlock_timedrdlock() function shall fail if:

     [ETIMEDOUT]        The time specified by abstime was reached before the
                        lock could be obtained.

     The pthread_rwlock_wrlock(), pthread_rwlock_timedwrlock(), and
     pthread_rwlock_trywrlock() functions may fail if:

     [EDEADLK]          The calling thread already owns the read/write lock
                        (for reading or writing).

     [EINVAL]           The value specified by lock is invalid.

     The pthread_rwlock_unlock() function may fail if:

     [EINVAL]           The value specified by lock is invalid.

     [EPERM]            The current thread does not own the read/write lock.

SEE ALSO
     pthread(3), pthread_barrier(3), pthread_cond(3), pthread_mutex(3),
     pthread_rwlockattr(3), pthread_spin(3)

STANDARDS
     These functions conform to IEEE Std 1003.1-2001 (``POSIX.1'').

BUGS
     The PTHREAD_PROCESS_SHARED attribute is not supported.

NetBSD 6.1.5                     July 8, 2010                     NetBSD 6.1.5