Mis on pessimistic locking?

Pessimistic locking is an approach to managing concurrent access to data, where the resource is locked immediately at the start of an operation to prevent conflicts. That is, when a transaction wants to modify data, it acquires a lock, and other transactions wait until the lock is released.

In Go, this can be implemented using mutexes (sync.Mutex), which block access to shared data:

var mu sync.Mutex

func updateData() {
    mu.Lock()   // pessimistic lock
    defer mu.Unlock()
    // critical section
}

This approach guarantees that only one goroutine can modify data at a time, but it may reduce parallelism and cause locking.