Our own reentrant lock

The following code shows how we could implement the reentrant lock ourselves. The code shows the reentrancy semantics, too. We just show the lock and unlock method:

public class YetAnotherReentrantLock {
 private Thread lockedBy = null;
 private int lockCount = 0;

The class has two fields—a lockedBy thread reference and a lockcount—which are used to track how many times the thread recursively locked itself:

private boolean isLocked() {
  return lockedBy != null;
}

private boolean isLockedByMe() {
  return Thread.currentThread() == lockedBy;
}

The preceding snippet shows two helper methods. Using such helpers help make the code more readable:

public synchronized void lock() throws InterruptedException {
  while (isLocked() && !isLockedByMe()) {
    this.wait();
 }
 lockedBy = Thread.currentThread();
 lockCount++;
}

Here is a pictorial analysis...