Module Mutex

module Mutex: sig .. end

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)
Raises Sys_error if the mutex is already locked by the thread calling Mutex.lock.

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.

Before 4.12 Sys_error was not raised when unlocking an unlocked mutex or when unlocking a mutex from a different thread.
Raises Sys_error if the mutex is unlocked or was locked by another thread.

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

protect mutex f runs f() in a critical section where mutex is locked (using Mutex.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