Can you explain what a race condition is in the context of parallel program execution?

A race condition occurs when multiple threads or processes access and modify shared data simultaneously without proper synchronization. As a result, the final state of the data depends on the order of operations, leading to unpredictable errors.

For example, if two threads try to increment a counter at the same time and both read the old value, the final value will only increase by 1 instead of 2.

In iOS, this can manifest when working with multithreading (e.g., GCD or OperationQueue) if synchronization mechanisms (locks, queues, atomic operations) are not used. To avoid race conditions, sequential access to shared resources must be ensured.