Maintainer | Bas van Dijk <v.dijk.bas@gmail.com> , Roel van Dijk <vandijk.roel@gmail.com> |
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Multiple-reader, single-writer locks. Used to protect shared resources which may be concurrently read, but only sequentially written.
All functions are exception safe. Throwing asynchronous exceptions will not
compromise the internal state of an RWLock
. This means it is perfectly safe
to kill a thread that is blocking on, for example, acquireRead
.
See also Java's version: http://java.sun.com/javase/7/docs/api/java/util/concurrent/locks/ReadWriteLock.html
This module is designed to be imported qualified. We suggest importing it like:
import Control.Concurrent.ReadWriteLock ( RWLock ) import qualified Control.Concurrent.ReadWriteLock as RWL ( ... )
- data RWLock
- new :: IO RWLock
- acquireRead :: RWLock -> IO ()
- releaseRead :: RWLock -> IO ()
- withRead :: RWLock -> IO α -> IO α
- tryAcquireRead :: RWLock -> IO Bool
- tryWithRead :: RWLock -> IO α -> IO (Maybe α)
- acquireWrite :: RWLock -> IO ()
- releaseWrite :: RWLock -> IO ()
- withWrite :: RWLock -> IO α -> IO α
- tryAcquireWrite :: RWLock -> IO Bool
- tryWithWrite :: RWLock -> IO α -> IO (Maybe α)
Documentation
Multiple-reader, single-writer lock. Is in one of three states:
- "Free": Read or write access can be acquired without blocking.
- "Read": One or more threads have acquired read access. Blocks write access.
- "Write": A single thread has acquired write access. Blocks other threads from acquiring both read and write access.
Creating Read-Write Locks
Create a new RWLock
. The initial state is "free"; either read or write
access can be acquired without blocking.
Read access
Blocking
acquireRead :: RWLock -> IO ()Source
Acquire the read lock.
Blocks if another thread has acquired write access. If acquireRead
terminates
without throwing an exception the state of the RWLock
will be "read".
Implementation note: Throws an exception when more than (maxBound :: Int) simultaneous threads acquire the read lock. But that is unlikely.
releaseRead :: RWLock -> IO ()Source
Release the read lock.
If the calling thread was the last one to relinquish read access the state will revert to "free".
It is an error to release read access to an RWLock
which is not in the
"read" state.
withRead :: RWLock -> IO α -> IO αSource
A convenience function wich first acquires read access and then performs the computation. When the computation terminates, whether normally or by raising an exception, the read lock is released.
Non-blocking
tryAcquireRead :: RWLock -> IO BoolSource
Try to acquire the read lock; non blocking.
Like acquireRead
, but doesn't block. Returns True
if the resulting state is
"read", False
otherwise.
Write access
Blocking
acquireWrite :: RWLock -> IO ()Source
Acquire the write lock.
Blocks if another thread has acquired either read or write access. If
acquireWrite
terminates without throwing an exception the state of the
RWLock
will be "write".
releaseWrite :: RWLock -> IO ()Source
Release the write lock.
If releaseWrite
terminates without throwing an exception the state will be
"free".
It is an error to release write access to an RWLock
which is not in the
"write" state.
withWrite :: RWLock -> IO α -> IO αSource
A convenience function wich first acquires write access and then performs the computation. When the computation terminates, whether normally or by raising an exception, the write lock is released.
Non-blocking
tryAcquireWrite :: RWLock -> IO BoolSource
Try to acquire the write lock; non blocking.
Like acquireWrite
, but doesn't block. Returns True
if the resulting state is
"write", False
otherwise.