Mutex: Difference between revisions
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(Added an explaination of Haskell's MVars.) |
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The value passed on the channel is not accessed here, just as the internal state of a mutex is not accessed. Rather, it is only the effect of the value being available that is important. (Of course if you wanted to send something meaningful on the channel, a reference to the shared resource would be a good start...) |
The value passed on the channel is not accessed here, just as the internal state of a mutex is not accessed. Rather, it is only the effect of the value being available that is important. (Of course if you wanted to send something meaningful on the channel, a reference to the shared resource would be a good start...) |
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=={{header|Haskell}}== |
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Haskell has a slight variation on the mutex, namely the MVar. MVars, unlike mutexes, are containers. However, they are similar enough that MVar () is essentially a mutex. A MVar can be in two states: empty or full, only storing a value when full. There are 4 main ways to deal with MVars: |
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<lang haskell>takeMVar :: MVar a -> IO a |
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putMVar :: MVar a -> a -> IO () |
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tryTakeMVar :: MVar a -> IO (Maybe a) |
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tryPutMVar :: MVar a -> a -> IO Bool |
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takeMVar will attempt to fetch a value from the MVar, and will block while the MVar is empty. After using this, the MVar will be left empty. |
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putMVar will attempt to put a value in a MVar, and will block while there already is a value in the MVar. This will leave the MVar full. |
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The last two functions are non-blocking versions of takeMVar and putMVar, returning Nothing and False, respectively, if their blocking counterpart would have blocked. |
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For more information see the [http://www.haskell.org/ghc/docs/latest/html/libraries/base/Control-Concurrent-MVar.html documentation]. |
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==Icon and {{header|Unicon}}== |
==Icon and {{header|Unicon}}== |
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