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public class PLock {
private Map<Thread, Integer> readLocks = new HashMap<Thread, Integer>();
private Thread writeLock = null;
private int writeLockCount = 0;
public synchronized void getReadLock() {
Thread currentThread = Thread.currentThread();
long startTimeMillis = System.currentTimeMillis();
boolean gotStuck = false;
while (canClaimReadLock(currentThread) == false) {
gotStuck = true;
try {
wait();
} catch (InterruptedException ex) {
Log.warn("Interrupted while attempting to get read lock.", ex);
}
}
report(gotStuck, startTimeMillis, "read");
if (readLocks.containsKey(currentThread)) {
readLocks.put(currentThread, 1 + readLocks.get(currentThread));
} else {
readLocks.put(currentThread, 1);
}
}
...
public synchronized void relinquishReadLock() {
Thread currentThread = Thread.currentThread();
if (readLocks.containsKey(currentThread) == false) {
throw new RuntimeException("Cannot relinquish read lock on thread " + currentThread + " because it does not hold a lock.");
}
int newLockCount = readLocks.get(currentThread) - 1;
if (newLockCount == 0) {
readLocks.remove(currentThread);
notifyAll(); // IMPORTANT: allow other threads to wake up and check if they can get locks now.
} else {
readLocks.put(currentThread, newLockCount);
}
}
public synchronized void getWriteLock() {
//Log.warn("getWriteLock() in thread " + Thread.currentThread());
//dumpLocks();
Thread currentThread = Thread.currentThread();
long startTimeMillis = System.currentTimeMillis();
boolean gotStuck = false;
while (canClaimWriteLock(currentThread) == false) {
gotStuck = true;
try {
wait();
} catch (InterruptedException ex) {
Log.warn("Interrupted while attempting to get write lock.", ex);
}
}
report(gotStuck, startTimeMillis, "write");
writeLock = currentThread;
writeLockCount++;
}
...
public synchronized void relinquishWriteLock() {
//Log.warn("relinquishWriteLock() in thread " + Thread.currentThread());
Thread currentThread = Thread.currentThread();
if (writeLock != currentThread) {
throw new RuntimeException("Cannot relinquish write lock on thread " + currentThread + " because it does not hold the lock.");
}
if (writeLockCount <= 0) {
throw new RuntimeException("Tried to relinquish write lock on thread " + currentThread + " while write lock count is " + writeLockCount);
}
writeLockCount--;
if (writeLockCount == 0) {
writeLock = null;
notifyAll(); // IMPORTANT: allow other threads to wake up and check if they can get locks now.
}
}
...
}
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