![]() and if they grab the locks in the opposite order to each other, then you should observe a deadlock. If you changed the two methods to do this: grab one lock. I will not describe here a complex concurrency problem, but a simple problem that you may face it if you use CountDownLatch careless.Īssume you have 2 threads (Thread-1 and Thread-2) that share a single and you want to synchronize them using a CountDownLatch. It will then release them and exit, and the second thread will be able to grab the locks i.e. Thread 1 can never get B, and thread 2 can never get A. when thread A holds lock L and tries to acquire lock M, while thread B holds lock M and tries to acquire lock L. 2 - Run the jstack command with the pid as argument. 1 - By using jps command I can get the pid of the Java application. Below is an example of a deadlock situation: If thread 1 locks A, and tries to lock B, and thread 2 has already locked B, and tries to lock A, a deadlock arises. For example, if I run the program where deadlock was created due to nested synchronization, then I can get the thread dump using following steps. And as concurrency use cases can be very complex, developers must be very careful. If you prefer video, I have a video version of this deadlock tutorial here: Deadlock in Java. In simple terms, thread1 hold object1 lock and wait for object2 lock and thread 2 hold object 2 lock and wait for object 1 lock. ![]() CountDownLatch can save your time in suitable cases and you have to be aware of this class.Īs always synchronization of threads can raise deadlocks if code is not good. ![]() Example : Program to exhibit deadlock in Java. It’s a very convenience class to achieve synchronization between two or more threads, where allows one or more threads to wait until a set of operations being performed in other threads completes (check javadoc and this post). In deadlock situation, both the threads keep waiting for each other to release the lock.
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