What is a Mutex and what is under its hood?

Mutex (mutual exclusion) is a synchronization primitive that provides exclusive access to a shared resource in a multithreaded environment. It guarantees that only one thread (goroutine in Go) can own the mutex and execute the critical section of code at a time.

Under the hood in Go, sync.Mutex is implemented using atomic operations and system calls:

• It has a state field (usually an integer) that stores information about whether the mutex is locked.
• When attempting to acquire the mutex, an atomic Compare-And-Swap operation is used to set the state to "locked".
• If the mutex is already locked, the goroutine is blocked and placed in a waiting queue.
• When the mutex is released, one of the waiting goroutines is awakened.

Thus, the mutex implements an efficient locking mechanism with minimal system calls, transitioning to wait mode only in case of conflict.

Example usage:

var mu sync.Mutex

mu.Lock()
// critical section
mu.Unlock()