Copyright	(c) Sam Derbyshire 2022
License	BSD-style (see the file libraries/base/LICENSE)
Maintainer	Sam Derbyshire
Stability	provisional
Portability	portable
Safe Haskell	Safe
Language	Haskell2010

Semaphores

newtype Semaphore Source

A Windows semaphore.

To obtain a Semaphore, use createSemaphore to create a new one, or openSemaphore to open an existing one.

To wait on a semaphore, use waitForSingleObject.

To release resources on a semaphore, use releaseSemaphore.

To free a semaphore, use closeHandle. The semaphore object is destroyed when its last handle has been closed. Closing the handle does not affect the semaphore count; therefore, be sure to call releaseSemaphore before closing the handle or before the process terminates. Otherwise, pending wait operations will either time out or continue indefinitely, depending on whether a time-out value has been specified.

Access modes

type AccessMode = UINT Source

sEMAPHORE_ALL_ACCESS :: AccessMode Source

sEMAPHORE_MODIFY_STATE :: AccessMode Source

Managing semaphores

createSemaphore Source

Open a Semaphore with the given name, or create a new semaphore if no such semaphore exists, with initial count i and maximum count m.

The counts must satisfy i >= 0, m > 0 and i <= m.

The returned Bool is True if the function found an existing semaphore with the given name, in which case a handle to that semaphore is returned and the counts are ignored.

Use openSemaphore if you don't want to create a new semaphore.

openSemaphore Source

Open an existing Semaphore.

releaseSemaphore :: Semaphore -> LONG -> IO LONG Source

Increase the count of the Semaphore by the specified amount.

Returns the count of the semaphore before the increase.

Throws an error if the count would exceeded the maximum count of the semaphore.