Interview Q&A / Operating Systems

1. What is a race condition, and what is the critical section problem?

   A race condition happens when two or more threads access shared data at the same time and the result depends on the exact timing of their steps. The critical section is the part of code that touches that shared data, and the critical section problem is designing a way so only one thread runs it at a time, with progress and bounded waiting.

   BeginnerIn-depth3 min read
2. 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
3. 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