/**
* Releases the write lock held by the provided tx. If it is null then an attempt to acquire the
* current transaction from the transaction manager will be made. This is to make safe calling
* this method as an <code>afterCompletion()</code> hook where the transaction context is not
* necessarily available. If write count is zero and there are waiting transactions in the queue
* they will be interrupted if they can acquire the lock.
*/
synchronized void releaseWriteLock(Object tx) throws LockNotFoundException {
TxLockElement tle = getLockElement(tx);
if (tle.writeCount == 0) {
throw new LockNotFoundException("" + tx + " don't have writeLock");
}
totalWriteCount--;
tle.writeCount--;
if (tle.isFree()) {
txLockElementMap.remove(tx);
ragManager.lockReleased(this, tx);
}
// the threads in the waitingList cannot be currentThread
// so we only have to wake other elements if writeCount is down to zero
// (that is: If writeCount > 0 a waiting thread in the queue cannot be
// the thread that holds the write locks because then it would never
// have been put into wait mode)
if (totalWriteCount == 0 && waitingThreadList.size() > 0) {
// wake elements in queue until a write lock is found or queue is
// empty
do {
WaitElement we = waitingThreadList.removeLast();
if (!we.element.movedOn) {
we.waitingThread.interrupt();
if (we.lockType == LockType.WRITE) {
break;
}
}
} while (waitingThreadList.size() > 0);
}
}
/**
* Tries to acquire write lock for a given transaction. If <CODE>this.writeCount</CODE> is greater
* than the currents tx's write count or the read count is greater than the currents tx's read
* count the transaction has to wait and the {@link RagManager#checkWaitOn} method is invoked for
* deadlock detection.
*
* <p>If the lock can be acquires the lock count is updated on <CODE>this</CODE> and the
* transaction lock element (tle).
*
* @throws DeadlockDetectedException if a deadlock is detected
*/
synchronized void acquireWriteLock(Object tx) throws DeadlockDetectedException {
TxLockElement tle = getOrCreateLockElement(tx);
try {
tle.movedOn = false;
boolean shouldAddWait = true;
Thread currentThread = currentThread();
while (totalWriteCount > tle.writeCount || totalReadCount > tle.readCount) {
ragManager.checkWaitOn(this, tx);
if (shouldAddWait) {
waitingThreadList.addFirst(new WaitElement(tle, WRITE, currentThread));
}
try {
wait();
shouldAddWait = false;
} catch (InterruptedException e) {
interrupted();
shouldAddWait = true;
}
ragManager.stopWaitOn(this, tx);
}
registerWriteLockAcquired(tx, tle);
} finally {
// if deadlocked, remove marking so lock is removed when empty
tle.movedOn = true;
marked--;
}
}
/**
* Tries to acquire write lock for a given transaction. If <CODE>this.writeCount</CODE> is greater
* than the currents tx's write count or the read count is greater than the currents tx's read
* count the transaction has to wait and the {@link RagManager#checkWaitOn} method is invoked for
* deadlock detection.
*
* <p>If the lock can be acquires the lock count is updated on <CODE>this</CODE> and the
* transaction lock element (tle).
*
* @throws DeadlockDetectedException if a deadlock is detected
*/
synchronized void acquireWriteLock(Object tx) throws DeadlockDetectedException {
TxLockElement tle = getOrCreateLockElement(tx);
try {
tle.movedOn = false;
while (totalWriteCount > tle.writeCount || totalReadCount > tle.readCount) {
deadlockGuardedWait(tx, tle, WRITE);
}
registerWriteLockAcquired(tx, tle);
} finally {
// if deadlocked, remove marking so lock is removed when empty
tle.movedOn = true;
marked--;
}
}
synchronized boolean tryAcquireWriteLock(Object tx) {
TxLockElement tle = getOrCreateLockElement(tx);
try {
tle.movedOn = false;
if (totalWriteCount > tle.writeCount || totalReadCount > tle.readCount) {
return false;
}
registerWriteLockAcquired(tx, tle);
return true;
} finally {
// if deadlocked, remove marking so lock is removed when empty
tle.movedOn = true;
marked--;
}
}
private void registerLockAcquired(Object tx, TxLockElement tle) {
if (tle.isFree()) {
ragManager.lockAcquired(this, tx);
}
}
/**
* Releases the read lock held by the provided transaction. If it is null then an attempt to
* acquire the current transaction will be made. This is to make safe calling the method from the
* context of an <code>afterCompletion()</code> hook where the tx is locally stored and not
* necessarily available through the tm. If there are waiting transactions in the queue they will
* be interrupted if they can acquire the lock.
*/
synchronized void releaseReadLock(Object tx) throws LockNotFoundException {
TxLockElement tle = getLockElement(tx);
if (tle.readCount == 0) {
throw new LockNotFoundException("" + tx + " don't have readLock");
}
totalReadCount--;
tle.readCount--;
if (tle.isFree()) {
txLockElementMap.remove(tx);
ragManager.lockReleased(this, tx);
}
if (waitingThreadList.size() > 0) {
WaitElement we = waitingThreadList.getLast();
if (we.lockType == LockType.WRITE) {
// this one is tricky...
// if readCount > 0 we either have to find a waiting read lock
// in the queue or a waiting write lock that has all read
// locks, if none of these are found it means that there
// is a (are) thread(s) that will release read lock(s) in the
// near future...
if (totalReadCount == we.element.readCount) {
// found a write lock with all read locks
waitingThreadList.removeLast();
if (!we.element.movedOn) {
we.waitingThread.interrupt();
}
} else {
ListIterator<WaitElement> listItr =
waitingThreadList.listIterator(waitingThreadList.lastIndexOf(we));
// hm am I doing the first all over again?
// think I am if cursor is at lastIndex + 0.5 oh well...
while (listItr.hasPrevious()) {
we = listItr.previous();
if (we.lockType == LockType.WRITE && totalReadCount == we.element.readCount) {
// found a write lock with all read locks
listItr.remove();
if (!we.element.movedOn) {
we.waitingThread.interrupt();
// ----
break;
}
} else if (we.lockType == LockType.READ) {
// found a read lock, let it do the job...
listItr.remove();
if (!we.element.movedOn) {
we.waitingThread.interrupt();
}
}
}
}
} else {
// some thread may have the write lock and released a read lock
// if writeCount is down to zero we can interrupt the waiting
// read lock
if (totalWriteCount == 0) {
waitingThreadList.removeLast();
if (!we.element.movedOn) {
we.waitingThread.interrupt();
}
}
}
}
}
