Question about withMVar

[Eric Mertens]

The action is atomic as long as while one thread is using withMVar another
thread isn't using putMVar

On Sun, Jul 18, 2021 at 6:49 AM Harendra Kumar <harendra.kumar at gmail.com>
wrote:

> The documentation of withMVar (in Control.Concurrent.MVar module of base
> package) says:
>
> {-|  'withMVar' is an exception-safe wrapper for operating on the contents  of an 'MVar'.  This operation is exception-safe: it will replace the  original contents of the 'MVar' if an exception is raised (see  "Control.Exception").  However, it is only atomic if there are no  other producers for this 'MVar'.-}withMVar :: MVar a -> (a -> IO b) -> IO bwithMVar m io =  mask $ \restore -> do    a <- takeMVar m    b <- restore (io a) `onException` putMVar m a    putMVar m a    return b
>
> Can someone shed some light on what is meant by the statement -
> "However, it is only atomic if there are no other producers for this 'MVar'."?
>
> I hope this is the right mailing list for this question.
>
> Thanks,
> Harendra
>
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-- 
Eric Mertens
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