What methods can be used to eliminate resource deadlock in a multithreaded program?

Mutual blocking (deadlock) occurs when several threads are waiting for resources held by each other, and none can continue working. To eliminate or prevent deadlock, the following approaches are used:

• Avoid cyclic waiting: always request resources in the same order to eliminate dependency cycles.
• Use timeouts: set a timeout when attempting to acquire a resource, after which the thread gives up and releases already acquired resources.
• Apply detection and recovery algorithms: periodically check for deadlocks and interrupt or restart the relevant threads.
• Minimize resource holding time: release resources as quickly as possible to reduce the likelihood of deadlocks.

In iOS, GCD and queue operations are often used for synchronization, which helps avoid complex deadlocks. You can also use NSLock with a timeout or dispatch_semaphore to control access.