Janet erases stacktrace for an error while it is dying..

[amano-kenji]

Janet erases stacktrace for an error while it is dying..

[bakpakin]

If you apply the link mentioned here : #1378 (comment), does that fix the issue?

Whatever the issue is, I don't think the stacktrace is being "erased" as is suspected.

[bakpakin]

I suspect janet shut down before stacktrace was printed?

Should I mechanically replace all invocations of exit with _exit and compile janet?

Yeah, that is what I'm suggesting. After _exit called, nothing should be returning, as that is the root of all of this strange cleanup behavior

[bakpakin]

The description of the problem doesn't make sense to me, I would need some sample code to debug. It sounds like there is some multithreading involved.

[amano-kenji]

Yes, there are a lot of threads that stall the shutdown process.... Expect at least 7 threads.

file/read is called in a separate thread, too.

[amano-kenji]

I think file/read didn't have time to return nil if the shutdown was fast.

If there are many threads that stall the shutdown, then file/read has enough time to return nil which causes json/decode to throw an error because json/decode doesn't like nil.

Because janet is shutting down, it doesn't have stacktrace for json/decode.

It is basically a race condition.

[amano-kenji]

I suspect janet shut down before stacktrace was printed?

Should I mechanically replace all invocations of exit with _exit and compile janet?

[amano-kenji]

Is it possible for file/read to return nil during shut down?

[amano-kenji]

I was able to reproduce this issue partially.

test.janet

(import spork/json)

(ev/spawn-thread
  (with [proc (os/spawn ["sleep" "100000000000"] :p {:out :pipe :err :pipe})]
    (os/proc-wait proc)))

(ev/spawn-thread
  (forever
    (json/decode (file/read stdin :line))))

(forever
  (ev/sleep 1))

Execute

$ sleep 1000 | janet test.janet

If you kill sleep, you will get an error message like

$ sleep 10000 | janet test.janet
error: bad slot #0, expected string, symbol, keyword or buffer, got nil
  in json/decode
  in _spawn-thread [test.janet] on line 9, column 5

So, I should check whether (file/read stdin :line) returns nil anyway.

My suspicion is that if you kill sleep and then test.janet very fast in sequence, you can kill the script before stacktrace is printed. That's probably why I could sometimes see the stacktrace and could not most of the time.

What do you think?

[amano-kenji]

I think I'm just closing this issue.... for now...