Allow async exceptions to pierce masked waitForProcess#101
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snoyberg merged 3 commits intohaskell:masterfrom Aug 8, 2017
Merged
Allow async exceptions to pierce masked waitForProcess#101snoyberg merged 3 commits intohaskell:masterfrom
snoyberg merged 3 commits intohaskell:masterfrom
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This looks good, I feel much better about the usage of |
snoyberg
requested changes
Aug 3, 2017
| unless (e1 == ExitSuccess && e2 == ExitSuccess) | ||
| $ error "sleep exited with non-zero exit code!" | ||
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| do |
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The test implementation is pretty fragile.
- The sleep value is low enough that the process could legitimately finish before the
waitForProcessbegins - I'd rather not rely on
BlockedIndefinitelyOnMVar, but instead useonExceptiontoputMVara value in the case of an exception - It's worth reporting the
ecin theRightcase; an exit code of 0 vs 127 will be highly informative, for instance
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Updated - how's that?
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Looks good! One last request: can you add a comment to the ChangeLog explaining the change in semantics here?
snoyberg
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Aug 8, 2017
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Thanks! |
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Hello!
I believe I found a bug in
waitForProcess. When run in theMaskedInterruptiblestate, an async exception doesn't actually bring the thread down.For example, the
typed-processlibrary exportswithProcesswhich is similar towithCreateProcess, but ends up callingwaitForProcessin the cleanup action of abracket.Even though
waitForProcessis aninterruptibleforeign call, I think what's happening is:waitForProcesscallinterruptibleforeign call, sendsSIGPIPE(GHC docs)c_waitForProcessreturns-1with errno =EINTRMaskedInterruptiblec_waitForProcessis retried because it's wrapped bythrowErrnoIfMinus1Retry_So our "interruptible"
waitForProcessis only half-interrupted :)My fix in this patch is to simply poll for any async exceptions before entering
c_waitForProcess. Here is some related discussion I had with @snoyberg.Thanks!