Module Stdlib.Mutex

Locks for mutual exclusion.

Mutexes (mutual-exclusion locks) are used to implement critical sections and protect shared mutable data structures against concurrent accesses. The typical use is (if m is the mutex associated with the data structure D):

Mutex.lock m;
(* Critical section that operates over D *);
Mutex.unlock m
type t

The type of mutexes.

val create : unit -> t

Return a new mutex.

val lock : t -> unit

Lock the given mutex. Only one thread can have the mutex locked at any time. A thread that attempts to lock a mutex already locked by another thread will suspend until the other thread unlocks the mutex.

  • before 4.12

    Sys_error was not raised for recursive locking (platform-dependent behaviour)

val try_lock : t -> bool

Same as Mutex.lock, but does not suspend the calling thread if the mutex is already locked: just return false immediately in that case. If the mutex is unlocked, lock it and return true.

val unlock : t -> unit

Unlock the given mutex. Other threads suspended trying to lock the mutex will restart. The mutex must have been previously locked by the thread that calls Mutex.unlock.

  • raises Sys_error

    if the mutex is unlocked or was locked by another thread.

  • before 4.12

    Sys_error was not raised when unlocking an unlocked mutex or when unlocking a mutex from a different thread.

val protect : t -> (unit -> 'a) -> 'a

protect mutex f runs f() in a critical section where mutex is locked (using lock); it then takes care of releasing mutex, whether f() returned a value or raised an exception.

The unlocking operation is guaranteed to always takes place, even in the event an asynchronous exception (e.g. Sys.Break) is raised in some signal handler.

  • since 5.1