Mutex.3o - Man Page

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.

Before4.12

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 .

Before4.12

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