Re: Asynchronous exceptions and laziness bugs in Control.Concurrent.QSem/QSemN

This was coincidentaly widely discussed at Galois recently, in two talks: * http://www.galois.com/~dons/talks/strict-concurrency-feb-26-2010/strict-conc... * http://www.galois.com/~dons/talks/jl-march-2010-async.pdf So good to see you're looking at these. bos:

Looks good to me. Thanks.

On Thu, Mar 18, 2010 at 1:54 PM, Bas van Dijk wrote:

Hello,

after discovering the bugs regarding asynchronous exceptions and laziness in Data.Unique and Control.Concurrent.SampleVar I became a bit suspicious about the other concurrency mechanisms.

It looks like Control.Concurrent.Chan is safe because it uses modifyMVar_ internally which performs the necessary block.

Control.Concurrent.QSem and QSemN are not alright however! They both suffer the same bugs:

* Potential dead-lock due to not blocking asynchronous exceptions. * Potential space-leak because of lazily putting numeric expression in a MVar.

The attached patch fixes these bugs.

regards,

Bas

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