How does sync.Mutex work under the hood?

sync.Mutex in Go is implemented based on system synchronization primitives and atomic operations. Under the hood, it contains a state field (usually an integer) that reflects whether the mutex is locked.

When Lock() is called, an atomic attempt is made to set the lock flag. If the mutex is free, the flag is set, and the thread continues execution. If the mutex is already locked, the thread is blocked and placed in a waiting queue.

Unlock() clears the lock flag and unblocks one of the waiting threads, if any.

The implementation uses the low-level runtime package, which interacts with the Go scheduler and system calls for efficient goroutine switching and minimizing wait costs.

Example usage:

var mu sync.Mutex

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

Thus, sync.Mutex provides mutual exclusion with minimal overhead thanks to its integration with the Go runtime.