What is the difference between mutex and semaphore? How are they implemented?

Mutex (mutual exclusion) and semaphore are synchronization mechanisms, but with different purposes and behaviors:

• Mutex is a binary lock that allows only one thread to own the resource at any given time. It is used to protect critical sections.
• Semaphore is a counter that limits the number of threads that can access a resource simultaneously. It can have an arbitrary number of permissions.

Implementation:

• Mutex is usually implemented through atomic operations and kernel locks, ensuring exclusive access.
• Semaphore stores a counter that decreases when acquired and increases when released. If the counter is zero, threads are blocked until it is released.

Example: mutex — a door with one key, semaphore — a room with several chairs, where a limited number of people can enter.