unix-2.3.1.0: POSIX functionality Contents Index

System.Posix.Semaphore Portability non-portable (requires POSIX) Stability experimental Maintainer libraries@haskell.org

Description

POSIX named semaphore support.

Synopsis

data OpenSemFlags = OpenSemFlags { semCreate :: Bool semExclusive :: Bool } data Semaphore semOpen :: String -> OpenSemFlags -> FileMode -> Int -> IO Semaphore semUnlink :: String -> IO () semWait :: Semaphore -> IO () semTryWait :: Semaphore -> IO Bool semThreadWait :: Semaphore -> IO () semPost :: Semaphore -> IO () semGetValue :: Semaphore -> IO Int

Documentation

data OpenSemFlags

Constructors OpenSemFlags 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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