I recently added a basic deadlock detection mechanism to tempus-fugit. The DeadlockDetector class allows you to programmatically detect basic deadlocks in your Java code. You can output deadlocks using the following code (note that printing a thread dump using the ThreadDump class will automatically attempt to find any deadlocks).

DeadlockDetector.printDeadlocks(System.out);

The DeadlockDetector class will spot Java monitor cyclic locking problems and additionally detect Lock based cyclic problems. It’s implementation is basically the same as that used by jconsole and jstack. An example is illustrated in the example below.

@Test
public void potentialDeadlock() {
  new Kidnapper().start();
  new Negotiator().start();
}

public class Kidnapper extends Thread {
  public void run() {
     synchronized (nibbles) {
        synchronized (cash) {
            take(cash);
        }
     }
  }
}

public class Negotiator extends Thread {
  public void run() {
     synchronized (cash) {
        synchronized (nibbles) {
            take(nibbles);
        }
     }
  }
}

Here, the Kidnapper is unwilling to release poor Nibbles the Cat until he has the Cash but our Negotiator is unwilling to part with the Cash until he has poor Nibbles back in his arms. The deadlock detector displays this woeful situation as follows.

 Deadlock detected  
 =================  

 "Negotiator-Thread-1":  
    waiting to lock Monitor of ...DeadlockDetectorTest$Cat@ce4a8a  
    which is held by "Kidnapper-Thread-0"  

 "Kidnapper-Thread-0":  
    waiting to lock Monitor of ...DeadlockDetectorTest$Cash@7fc8b2  
    which is held by "Negotiator-Thread-1"  

I don’t imagine you’ll need to print out information about deadlocks or thread dumps from within your code very often, but on the off chance you’ll need to during debugging, they are both available for you to use in the tempus-fugit project.