Creating a spawn blocks application closure

[matkuki]

Hi,

• Windows 10 x64
• Nim almost devel
• malebolgia: nimble install malebolgia
• niup: nimble install niup

I have a niup application that uses malebolgia to spawn a sound effect in a {.cdecl.} callback. This is the callback:

import malebolgia
import niup
import soundutils

var
    ...
    malebolgia_master = malebolgia.createMaster()
    malebolgia_results = newSeq[PlaybackResult](10)

niup.init()

...

# Countdown timer callback
proc countdown_tick(arg: PtrIhandle): cint {.cdecl.} =
    const filename = "alarm.wav"
    malebolgia_master.awaitAll:
        malebolgia_master.spawn soundutils.play_wav(filename) -> malebolgia_results[0]
    echo "Sound playback completed."

...

main_window.showXY(IUP_CENTER, IUP_CENTER)

niup.mainLoop()
niup.close()

echo "Application closed."

Now, running the application and closing it without the callback countdown_tick not being executed: no problems, application closes.
But running it and executing the callback, everything is fine, the soundutils.play_wav spawning works great and "Sound playback completed." is echoed, but closing the application echo's "Application closed." and then hangs indefinitely, until Ctrl+C is pressed.
If I change the callback to a synchronous execution, like so:

proc countdown_tick(arg: PtrIhandle): cint {.cdecl.} =
    const filename = "alarm.wav"
    let result = soundutils.play_wav(filename)
    echo "Sound playback completed."

... it also works without problems.

Any ideas of what's blocking the closing of the application when a spawn is created?

P.S.:
I tried adding malebolgia_master.cancel() at the end after the echo, no difference.
Also tried malebolgia.panicStop(), but that call itself also hangs indefinitely.

[Araq]

What does valgrind say?

[matkuki]

I'm on Windows, any simple way to install valgrind on it?
I have Visual Studio 2022, if maybe I can give you some information with it?

[matkuki]

@Araq
Note that the code has no main function, all of it is directly in the file. which looks roughly like this:

all imports
...

niup.open()

all variable and callback definitions
...

main_window.showXY(IUP_CENTER, IUP_CENTER)

niup.mainLoop()

niup.close()

malebolgia.panicStop() # <- THIS HANGS FOREVER!

echo "END"

Added echo's into the panicStop() call ( the call added at the bottom of the code) and it stops here:

proc panicStop*() =
  ## Stops all threads.
  echo 1
  globalStopToken.store(true, moRelaxed)
  echo 2
  joinThreads(thr) # <- HANGS HERE!
  echo 3
  deinitCond(chan.dataAvailable)
  echo 4
  deinitCond(chan.spaceAvailable)
  echo 5
  deinitLock(chan.L)
  echo 6

[matkuki]

@Araq
The joinThreads line inside panicStop always blocks, even when not spawning anything.
I assume it's a Windows issue with joinThreads. Is there an issue for this already open in Nim's repository?

[Araq]

Pretty sure it's something else, joinThreads is used heavily, even on Windows.

[matkuki]

Hey @Araq
If I change this in malebolgia.nim:

... to this:

... it works!
Any ideas?

P.S.:
Any number higher than 1 for ThreadPoolSize makes it hang, only 1 works.

[Araq]

Yeah well, you need to setup WSL and run it via valgrind under Linux. Most likely one of your dependencies doesn't play nice and it's the most reasonable way to debug these things.