Misbehaving exit status from Hotspot

[Charles Oliver Nutter]

A bit more background and info...

This investigation was spawned by a JRuby bug:
https://github.com/jruby/jruby/issues/5224

Zhengyu Gu pointed out that -XX:+ReduceSignalUsage allows my gisted example
to work as expected.

$ ./sigtest `which java`  -XX:+ReduceSignalUsage Loop
pid: 28705
status: 15
exited: 0, stop signal: 0, term signal: 15, exit status: 0

That isn't too surprising to me, but it's also undesirable to have to pass
this flag. Shouldn't Hotspot's shutdown handler be propagating SIGTERM to
the system-default handler as its final step? It seems like that's the
missing piece here, if I'm reading the tea leaves correctly.

Interestingly, just setting this flag and running JRuby is not enough to
"fix" our bug...I also need to add a downcall to raise(3) as part of
termination.

Bottom line for me: Hotspot is not being a good actor wrt exit statuses and
signal handling, and it should at *least* produce valid exit conditions for
the process when terminated prematurely by a signal.

- Charlie

On Tue, Jun 26, 2018 at 2:05 PM, Charles Oliver Nutter <headius at headius.com>
wrote:

> (mods: previous version of this was sent without subscription complete;
> disregard)
>
> Hello all!
>
> I've been struggling to fix some signal-handling issues in JRuby and I've
> come to the determination that Hotspot is not being a good actor as far as
> signals and exit statuses go.
>
> I've put together some C and Java code to demonstrate the problem. I could
> have flaws in my understanding of signal handling and exit statuses.
>
> The test program just spawns a given command, waits for termination, and
> uses the wait(2) W macros to parse out the process exit states.
>
> "loop.c" just loops.
> "loop2.c" has the loop but also installs a TERM signal handler, closer in
> behavior to shutdown hooks in Ruby and JVM.
> "Loop.java" just loops.
>
> The first two produce the expected results...
>
> $ ./sigtest `pwd`/loop
> pid: 22130
> status: 15
> exited: 0, stop signal: 0, term signal: 15, exit status: 0
>
> $ ./sigtest `pwd`/loop2
> term received
> pid: 22173
> status: 15
> exited: 0, stop signal: 0, term signal: 15, exit status: 0
>
> Java produces nonsense results...
>
> $ ./sigtest `which java` Loop
> pid: 22136
> status: 36608
> exited: 1, stop signal: 143, term signal: 0, exit status: 143
>
> I have tried various combinations of using the sun.misc.Signal stuff,
> doing a native downcall to raise(3), and so on...but nothing helps,
> probably because the Hotspot's own TERM handler is swallowing or otherwise
> mutilating the exit status.
>
> We do get bug reports about JRuby's exit statuses not making any sense. I
> assumed it was our fault until this week.
>
> Help?
>
> - Charlie
>
>