A mutual-exclusion locking object that allows multiple threads to synchronize access to shared resources. A mutex has two states: locked and unlocked. Once a mutex has been locked by a thread, other threads attempting to lock it block. When the locking thread unlocks (releases) the mutex, one of the blocked threads (if any) acquires (locks) it and uses the resource. The thread that locks the mutex must be the one that unlocks it. The work-loop lock (which is used by a command gate) is based on a mutex. See also lock, work loop