Race condition when quitting and kill(::Process) is in a finalizer

[iamed2]

ericdavies@mccreary ~/r/julia0p5 (release-0.5)> julia
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  (_)     | (_) (_)    |  Documentation: http://docs.julialang.org
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  | | |_| | | | (_| |  |  Version 0.5.1-pre+27 (2016-11-04 08:41 UTC)
 _/ |\__'_|_|_|\__'_|  |  Commit 25f7066* (3 days old release-0.5)
|__/                   |  x86_64-apple-darwin16.1.0

julia> type Foo
           proc::Base.Process
       end

julia> a = Foo(spawn(`python -m SimpleHTTPServer`))
Foo(Process(`python -m SimpleHTTPServer`, ProcessRunning))

julia> finalizer(a, x->kill(x.proc))

julia> quit()
error in running finalizer: Base.AssertionError(msg="p.handle != C_NULL")

This only happens about half the time. When it does happen, the process is left as an orphan. When it doesn't, the kill executes correctly and kills the process.

I was able to replicate on the latest master (f9a6bbd) as well.

[yuyichao]

The order of finalizer run is undefined.

[iamed2]

How about making the finalizer for Process kill an un-detached process?

[vtjnash]

It better to let the kernel deal with that (since it knows how to do exactly this), since running finalizers at exit is unreliable

[iamed2]

But if the process just sits around listening on a port or something, the kernel won't kill it.

[StefanKarpinski]

At least trying to kill a zombie child seems better than not trying at all just because it might not work.

[vtjnash]

In general, you should avoid using kill and use a proper synchronization mechanism such as pipes.

@StefanKarpinski Zombies are already dead, you can't kill them.

[iamed2]

To be clear the problem here is orphans, not zombies. But I do think trying to kill is the best course of action.

In this case, the program being called expects SIGINT to tell it to close. I don't think any other method of communication is available. This is fairly common for command-line test servers.