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After interrupting a build with Ctrl-C (SIGINT), cabal install just goes on to the next package #971

andersk opened this Issue · 8 comments

3 participants

Anders Kaseorg Ben Millwood Roman Cheplyaka
Anders Kaseorg

After interrupting a build with Ctrl-C (SIGINT), cabal install just goes on to the next package. So it takes way more Ctrl-Cs than it should to stop a running cabal install command. For example:

$ cabal install cabal-dev
Resolving dependencies...
Configuring HTTP-4000.2.3...
Building HTTP-4000.2.3...
Preprocessing library HTTP-4000.2.3...
[ 1 of 18] Compiling Network.HTTP.Base64 ( Network/HTTP/Base64.hs, dist/build/Network/HTTP/Base64.o )
^CConfiguring tar-
Building tar-
Preprocessing library tar-
[1 of 8] Compiling Codec.Archive.Tar.Types ( Codec/Archive/Tar/Types.hs, dist/build/Codec/Archive/Tar/Types.o )
^Ccabal: Error: some packages failed to install:
HTTP-4000.2.3 failed during the building phase. The exception was:
ExitFailure 1
cabal-dev-0.9.1 depends on tar- which failed to install.
tar- failed during the building phase. The exception was:
ExitFailure 1

This problem can be prevented by using the WCE method when launching subprocesses.

Ben Millwood

It looks like the information necessary to determine if a process was killed by a signal is not provided by the process library. Should probably take that up as a bug with them.

Ben Millwood

I opened a related bug for the process library on the GHC trac.

Anders Kaseorg

As a workaround for this missing functionality, can cabal use the WUE method instead? (That is: while running a subprocess, install a SIGINT handler that sets a flag; when the subprocess ends, if the flag is set, reraise the signal.) WUE is inferior to WCE, but the difference isn’t very noticable for noninteractive subprocesses.

Roman Cheplyaka

I believe the correct way to do this on POSIX systems is via process groups.

Anders Kaseorg

The process library ticket has been closed for GHC 7.8. The library now provides the negative signal number as the exit status for terminated processes, which allows WCE to be implemented. On previous GHC versions, we could still use WUE, which is better than nothing.

(@feuerbach, process groups have nothing to do with this problem. The child processes are correctly exiting with SIGINT. The bug is just that cabal is ignoring the SIGINT exit status from its child, as well as the SIGINT that it received itself.)

Roman Cheplyaka

@andersk thanks for clarifying. But why does it ignore its own SIGINT and have to get this information indirectly through its children?

Anders Kaseorg

@feuerbach, this is all explained in detail in the link I posted with the original report:

Roman Cheplyaka

I just realized that it has to do that so as not to die when running a ghci session inside cabal repl (as it used to some time ago).

But I'll make sure to read that article. Thanks.

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