On 24/11/2014 11:12, Yuras Shumovich wrote:
On Mon, 2014-11-24 at 10:09 +0000, Simon Marlow wrote:
On 14/11/2014 21:23, Yuras Shumovich wrote:
I was reviewing some exception handling code in base library, and I found this line: https://phabricator.haskell.org/diffusion/GHC/browse/master/libraries/base/C...
Here mask is used, but I looks completely useless for me. waitQSem itself should be called with async exceptions masked, otherwise there is no way to prevent resource leak.
Do anyone know why mask is used here?
I wrote that code. It looks like mask_ is important, otherwise an async exception might leave the MVar empty, no? We can't assume that waitQSem is always called inside a mask_, so it does its own mask_.
Hmm, yes, you are right.
Note, that in case of failure (and without external `mask`) it is not possible to determine, whether a unit of resource was reserved or not. It makes the particular instance of `QSem` unusable anymore, and we have to create other one. Probably there are situations where it is OK though.
I don't think that's true: if waitQSem fails, then the semaphore has not been acquired. This guarantee is important for "bracket waitQSem signalSQem" to work. I just peered at the code again and I believe this is true - have you spotted a case where it might be false? If so that's a bug. Cheers, Simon
Thanks, Yuras
Cheers, Simon
I wonder whether an author of the code tried to do something different, so there actually can be a bug hidden here. Probably uninterruptibleMask_ should be used here? (I don't think so though.)
Thanks, Yuras
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