Deadlocks

A deadlock occurs when two threads (or processes) are waiting for each other to release a resource and thus neither can complete its job since it waits forever.

Two threads wait for a different mutex, which the other thread holds.

A degenerate case is when a single thread is blocked, waiting for a mutex that it already holds (like a dog chasing its own tail.)

How to Avoid Deadlocks:

• Have a clear hierarchy of data and understanding of what mutexes do to the data.
• Consider the ABBA deadlock. For example: Thread 1 holds resource A and Thread 2 holds resource B, and then when Thread 1 wants to use resource B and Thread 2 wants to use resource A, a deadlock happens.
• Fixing this situation requires clear rules: A thread that wants to use a resource must first free the resources that it holds.