Interview Q&A / Operating Systems

1. What is the difference between a mutex and a semaphore?

   A mutex is a lock that lets only one thread into a critical section at a time, and only the thread that locked it should unlock it. A semaphore is a counter that allows up to N threads to use a resource at once, and any thread can signal it, which also makes it useful for one thread to notify another.

   BeginnerIn-depth3 min read
2. What is a counting semaphore and when would you use one?

   A counting semaphore holds a non-negative integer that tracks how many units of a resource are free. wait() takes one unit (blocking at zero) and signal() returns one. It limits how many threads use a pool at once.

   BeginnerQuick answer1 min read
3. How do you solve the producer-consumer problem using semaphores?

   Use three semaphores: empty (counts free slots, starts at N), full (counts filled slots, starts at 0) and mutex (starts at 1). Producers wait on empty, consumers wait on full, and mutex guards the buffer.

   IntermediateQuick answer1 min read