Locking Operations

The x-kernel provides a readers/writers lock synchronization type, ReadWriteLock. This type is currently built on top of the x-kernel Semaphore type. Although originally developed for the machNetIPC protocols, the lock can be used for more general synchronization. The ReadWriteLock implementation favors writers (i.e., if queues of readers and writers both exist, writers will always be favored.)

Note that we expect these locking operations to be used in a multiprocessor environment, although we have not yet used them for this purpose. Protocol developers working in an MP environment should attempt to adhere to this interface. However, we consider locking on an MP to be an unresolved issue, and so we are eager to hear about experiences using these operations in such an environment.

rwLockInit

Initializes the lock for subsequent operations.

void rwLockInit (ReadWriteLock *)

rwLockDestroy

All threads waiting on this lock will be released and their locking operations will return XK_FAILURE. When both the reader and writer queue are empty, the user-supplied RwlDestroyFunc will be called with a pointer to the lock and the void* argument.

void rwLockDestroy ( ReadWriteLock *, RwlDestroyFunc, void *)

typedef void (*RwlDestroyFunc ) ( ReadWriteLock *, void * );

readerLock

Acquires a reader lock. Many readers may hold the lock at one time, but no writers will acquire the lock while at least one reader holds the lock. Will return XK_FAILURE if the lock was destroyed before the lock was acquired.

xkern_return_t readerLock ( ReadWriteLock * )

readerUnlock

Releases a reader lock. It is an error to call readerUnlock without holding a reader lock.

void readerUnlock ( ReadWriteLock * )

writerLock

Acquires a writer lock. While a writer lock is held, no other reader or writer may acquire the lock. Will return XK_FAILURE if the lock was destroyed before the lock was acquired.

xkern_return_t writerLock ( ReadWriteLock * )

writerUnlock

Releases a writer lock. It is an error to call writerUnlock without holding a writer lock.

void writerUnlock ( ReadWriteLock * )