Concurrency interview questions

Implement a countdown latch whose wait resolves once countDown has been called the required number of times.

Implement an async mutex whose acquire returns a release function, serializing access so only one holder runs at a time.

Implement an async semaphore that admits up to N concurrent holders and queues the rest until a permit frees.

Implement a task queue that runs async jobs under a concurrency limit and resolves an idle promise when drained.

Schedule async requests under a concurrency limit, always running the highest-priority waiter next with a stable FIFO tiebreak.

Implement a read-write lock that allows many concurrent readers or one exclusive writer without starving writers.