Deadlocks

If you are not careful in coding multithreaded applications, you can encounter deadlocks, which will bring your system to a screeching halt. Suppose you have an object alpha running in one thread and an object beta running in another thread. Alpha executes a synchronized method (which by definition holds a lock on alpha) that calls a synchronized method defined on beta. If at the same time beta is executing a synchronized method, and this method in turn calls a synchronized method on alpha, each thread will wait for the other thread to relinquish its lock before proceeding. Deadlock!^[13]

^[13] [Arnold2000].

Solutions for resolving deadlock:

1. Order the objects to be locked and ensure the locks are acquired in this order.

2. Use a common object to lock.