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What is a Deadlock situation in Java? What are the minimum requirements for a Deadlock situation in a program in Java? How can we prevent a Deadlock in Java?

 

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What is a Deadlock situation in Java? 

A Deadlock is a situation in which two or more threads are waiting on each other to release a resource. Each thread is waiting for a resource that is held by the other waiting thread. At times there is a circular wait when more than two threads are waiting on each other’s resources.


What are the minimum requirements for a Deadlock situation in a program in Java?

For a deadlock to occur following are the minimum requirements:

1. Mutual exclusion: There has to be a resource that can be accessed by only one thread at any point of time.

2. Resource holding: One thread locks one resource and holds it, and at the same time it tries to acquire lock on another mutually exclusive resource.

3. No preemption: There is no pre-emption mechanism by which resource held by a thread can be freed after a specific period of time.

4. Circular wait: There can be a scenario in which two or more threads lock one resource each and they wait for each other’s resource to get free. 

This causes circular wait among threads for same set of resources.


How can we prevent a Deadlock in Java?

To prevent a Deadlock from occurring at least one requirement for a deadlock has to be removed:

1. Mutual exclusion: We can use optimistic locking to prevent mutual exclusion among resources.

2. Resource holding: A thread has to release all its exclusive locks if it does not succeed in acquiring all exclusive locks for resources required.

3. No preemption: We can use timeout period for an exclusive lock to get free after a given amount of time.

4. Circular wait: We can check and ensure that circular wait does not occur, when all exclusive locks have been acquired by all the threads in the same sequence.

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