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#Thread deadlock how to
#Thread deadlock code

Though this could have many answers, first, I would look at the code to see if a nested synchronized block is calling a synchronized method from another or if it is trying to get a lock on a different object. It will only happen in the case of multitasking or multi-threading. So, what is a deadlock? The answer is simple - when two or more threads are waiting for each other to release the resource they need (lock) and get stuck for infinite time, the situation is called deadlock. Even though the question looks very basic, most of the Java developers get stuck once you start going deeper.

#Thread deadlock how to

If something is missing or you have something to share about the topic please write a comment.Want to learn how to avoid deadlock in Java? The question of avoiding deadlock is one of the popular Java interview questions, with multi-threading being asked mostly at a senior level interview with lots of follow up questions. That’s all for the topic Deadlock in Java With Examples.

Why wait(), notify() and notifyAll() Methods Must be Called From a Synchronized Method or Block.

Java stack information for the threads listed above: waiting on (a $Lock)Īt .tryHandlePending(Unknown Source) waiting on (a $Lock)Īt .remove(Unknown Source) : BLOCKED (on object monitor)Īt (DLDemo.java:33) Here some of the relevant portion of the thread dump is displayed. Jstack 7408ģ– Get the thread dump and analyze it. JpsĢ– Run the jstack command with the pid as argument. That pid can be obtained by running jps command.Īs example– If I run the program where deadlock was created due to nested synchronization, then I can get the thread dump using following steps.ġ– By using jps command I can get the pid of the Java application. You can use jstack utility to get a thread dump by providing the pid of the Java application. If you observe that your multi-threaded code is not performing as well as it was then it may be due to a deadlock and best thing is to get a thread dump of the application and analyze it. How to debug a deadlock in Javaĭetecting a deadlock in Java is not easy, even logs may be of little help. Static synchronization helps in this case because the lock will be acquired at the class level then.

If two object instances are used two threads using two separate objects can still enter a synchronized method or block with their separate object locks. class ThreadA implements Runnableģ– By using static synchronization in Java. Deadlock in Java exampleįirst example shows the scenario when there are nested synchronized blocks with reverse ordering of objects. Calling one synchronized method from another where methods are not using the same object to synchronize.Nested synchronized blocks with reverse ordering of objects.Scenarios when deadlock may happen are as follows. You may get deadlock in Java because of the improper use of the synchronized keyword. How to debug a deadlock in Java Deadlock in Java scenarios.