Woudn't just synchronized (lock) {} be enough?

Question about the task

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Why do we need to lock (this) as well? I see it that way: The thread goes into the first method -> locks the 'lock' mutex -> then goes to the second method and tries to go into the synchronize (lock) {} block but it can't because the 'lock' mutex was already acquired in the first method -> waits until it is released (which never happens) -> deadlock

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Guadalupe Gagnon

Level 37 , Tampa, United States

29 April 2021, 15:34

solution

Threads can't lock themselves out. They can enter any lock that they hold the lock for (object or class). It is other threads that can not. The task is asking that you create a deadlock, but that would never occur in this scenario. The deadlock occurs when one thread holds one lock while another thread holds another lock. Then both threads need to access to an area of code already locked by the other thread before they themselves can release their lock. So: Thread1 -> hold an object lock Thread2 -> holds a class lock Thread1 -> to release the hold on the object lock it needs access to code that is locked by the class lock Thread2 -> to release the hold on the class lock it needs access to code that is locked by the object lock In this scenario deadlock occurs.