How can mutual resource locking be prevented in a multithreaded environment?

Mutual resource deadlocks occur when two or more threads permanently block each other, waiting for resources held by the other. To prevent deadlocks in a multithreaded environment, the following approaches can be used:

1. Single order of resource acquisition — always acquire resources in the same order across all threads. This prevents cyclic waiting.

2. Use timeouts when acquiring locks — if a resource is unavailable for a certain period, the thread releases already acquired resources and retries later.

3. Avoid nested locking — minimize the number of resources acquired simultaneously.

4. Use deadlock detection and resolution algorithms — periodically check the state of locks and interrupt or restart threads upon detecting mutual locking.

5. Use high-level synchronization primitives (e.g., DispatchQueue in iOS), which minimize the risk of deadlock.

Example of ordered resource acquisition:

let resourceA = NSLock()
let resourceB = NSLock()

func safeAccess() {
    // Always acquire resourceA, then resourceB
    resourceA.lock()
    resourceB.lock()
    // Work with resources
    resourceB.unlock()
    resourceA.unlock()
}

This approach prevents cyclic locking.