SyncRWLock() , SyncRWLock

Note:

Don't use the SyncRWLock() or SyncRWLock_r() kernel call directly; instead, use the POSIX functions for read-write locks.

Synopsis:

#include <sys/neutrino.h>

int SyncRWLock( sync_t * sync, unsigned op);

int SyncRWLock_r( sync_t * sync, unsigned op);

Arguments:

sync

A pointer to a pthread_rwlock_t object that you want to lock for writing.

op

The operation type; one of:

_NTO_RWLOCK_READ_LOCK — acquire the lock as a reader.
_NTO_RWLOCK_READ_TRYLOCK — attempt to acquire the lock as a reader, but return immediately if the lock is busy.
_NTO_RWLOCK_READ_UNLOCK — release the lock as a reader.
_NTO_RWLOCK_WRITE_LOCK — acquire the lock as a writer.
_NTO_RWLOCK_WRITE_TRYLOCK — attempt to acquire the lock as a writer, but return immediately if the lock is busy.
_NTO_RWLOCK_WRITE_UNLOCK — release the lock as a writer.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The SyncRWLock() and SyncRWLock_r() kernel calls lock or unlock a read-write lock. These kernel calls work on the given sync_t object and perform the action specified by the operation argument op.

Note:

Writers and readers are sorted in equal priority, with no preference given to writers, based on the order of their arrival.

Blocking states

STATE_RWLOCK_READ: The calling thread blocks waiting for a write-lock to be unlocked.
STATE_RWLOCK_WRITE: The calling thread blocks waiting for all read-locks to be unlocked.

Returns:

The only difference between these functions is the way they indicate errors:

SyncRWLock(): If an error occurs, the function returns -1 and sets errno. Returns 0 on success.
SyncRWLock_r(): Returns EOK on success. This function does NOT set errno. If an error occurs, this function returns any value listed in the Errors section.

Errors:

EAGAIN

Couldn't acquire read lock because the maximum number of read locks would be exceeded.

EBUSY

One of the following occurred:

An _NTO_RWLOCK_READ_TRYLOCK operation found the object write-locked.
An _NTO_RWLOCK_WRITE_TRYLOCK operation found the object already locked.

EDEADLK

The calling thread already has a write lock.

EFAULT

A fault occurred when the kernel tried to access the sync memory provided.

EINTR

A signal was received while waiting for the lock.

EINVAL

The read-write lock is invalid.

EPERM

An _NTO_RWLOCK_WRITE_UNLOCK attempted to release a write-lock held by another thread.

ETIMEDOUT

The lock couldn't be acquired before the specified timeout expired.

Classification:

QNX OS


Safety:
Cancellation point	No
Signal handler	Yes
Thread	Yes

SyncRWLock() , SyncRWLock_r()