Updated: 2022/Sep/29
Please read Privacy Policy. It's for your privacy.
PTHREAD_RWLOCK(3) Library Functions Manual PTHREAD_RWLOCK(3)
NAME
pthread_rwlock, pthread_rwlock_init, pthread_rwlock_destroy,
pthread_rwlock_rdlock, pthread_rwlock_timedrdlock,
pthread_rwlock_tryrdlock, pthread_rwlock_wrlock,
pthread_rwlock_timedwrlock, pthread_rwlock_trywrlock,
pthread_rwlock_unlock - read/write lock interface
LIBRARY
POSIX Threads Library (libpthread, -lpthread)
SYNOPSIS
#include <pthread.h>
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 10.99 July 8, 2010 NetBSD 10.99