Documentation in Control.Monad.STM.TMVar - isEmptyTMVar
Edward Z. Yang
ezyang at MIT.EDU
Thu Oct 6 21:05:49 CEST 2011
Excerpts from Heinrich Apfelmus's message of Wed Oct 05 11:38:46 -0400 2011:
> As of stm-188.8.131.52, the documentation for the isEmptyTMVar function
>  reads
> isEmptyTMVar :: TMVar a -> STM BoolSource
> Check whether a given TMVar is empty.
> Notice that the boolean value returned is just a snapshot of the state
> of the TMVar. By the time you get to react on its result, the TMVar
> may have been filled (or emptied) - so be extremely careful when using
> this operation. Use tryTakeTMVar instead if possible.
> This being software transactional memory, where everything is wrapped
> into a call to the atomically function, I believe that the second
> paragraph is now completely obsolete, to the point of being misleading
> (it sure scared me). I would be relieved if someone could remove it.
> Most likely, it was originally copied directly from the corresponding
> documentation of Control.Concurrent.MVar .
> Best regards,
> Heinrich Apfelmus
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