NAME

       Semaphore - Semaphores

Module

       Module   Semaphore

Documentation

       Module Semaphore
        : sig end

       Semaphores

       A  semaphore  is  a  thread synchronization device that can be used to control access to a
       shared resource.

       Two flavors of semaphores are provided: counting semaphores and binary semaphores.

       Since 4.12

   Counting semaphores
       A counting semaphore is a counter that can be accessed concurrently  by  several  threads.
       The  typical  use  is to synchronize producers and consumers of a resource by counting how
       many units of the resource are available.

       The two basic operations on semaphores are:

       -"release" (also called "V", "post", "up", and "signal"), which increments  the  value  of
       the  counter.   This  corresponds  to  producing  one more unit of the shared resource and
       making it available to others.

       -"acquire" (also called "P", "wait", "down", and "pend"), which waits until the counter is
       greater than zero and decrements it.  This corresponds to consuming one unit of the shared
       resource.

       module Counting : sig end

   Binary semaphores
       Binary semaphores are a variant of counting semaphores where semaphores can only take  two
       values, 0 and 1.

       A binary semaphore can be used to control access to a single shared resource, with value 1
       meaning "resource is available" and value 0 meaning "resource is unavailable".

       The "release" operation of a binary semaphore sets its value to  1,  and  "acquire"  waits
       until the value is 1 and sets it to 0.

       A  binary  semaphore  can  be  used  instead of a mutex (see module Mutex ) when the mutex
       discipline (of unlocking the mutex from the thread that locked  it)  is  too  restrictive.
       The  "acquire"  operation corresponds to locking the mutex, and the "release" operation to
       unlocking it, but "release" can be performed in a  thread  different  than  the  one  that
       performed  the  "acquire".   Likewise,  it  is  safe to release a binary semaphore that is
       already available.

       module Binary : sig end