System.Posix.Semaphore

semCreate :: Bool	If true, create the semaphore if it does not yet exist.
semExclusive :: Bool	If true, throw an exception if the semaphore already exists.

data Semaphore

semOpen :: String -> OpenSemFlags -> FileMode -> Int -> IO Semaphore

Open a named semaphore with the given name, flags, mode, and initial value.

semUnlink :: String -> IO ()

Delete the semaphore with the given name.

semWait :: Semaphore -> IO ()

Lock the semaphore, blocking until it becomes available. Since this is done through a system call, this will block the *entire runtime*, not just the current thread. If this is not the behaviour you want, use semThreadWait instead.

semTryWait :: Semaphore -> IO Bool

Attempt to lock the semaphore without blocking. Immediately return False if it is not available.

semThreadWait :: Semaphore -> IO ()

Poll the semaphore until it is available, then lock it. Unlike semWait, this will block only the current thread rather than the entire process.

semPost :: Semaphore -> IO ()

Unlock the semaphore.

semGetValue :: Semaphore -> IO Int

Return the semaphore's current value.

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