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module Semaphore

: sig
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type 'a t

Type of semaphores

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val init : 'a option -> 'a t

init v initializes a semaphore with an optional value v. If it is Some x, then Semaphore.wait will return immediately with x, otherwise it will block until Semaphore.signal is called.

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val signal : 'a t -> 'a -> unit

signal sem v allows one thread blocked in Semaphore.wait on semaphore sem to continue. The semaphore will then block again further threads.

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val wait : 'a t -> 'a

wait sem blocks the calling thread on semaphore sem if it was not initialized with Some x or not signalled before. The semaphore is reset to None, i.e. calling wait again will block unless the semaphore was signalled inbetween.

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val get : 'a t -> 'a option

get sem

Returns None if semaphore is not set, Some value otherwise. The semaphore is reset to None, and a subsequent wait will block again.
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val look : 'a t -> 'a option

look sem

Returns None if semaphore is not set, Some value otherwise. The state of the semaphore remains unchanged.
end