HCtl event callback gives "Fatal Python error: drop_gil: drop_gil: GIL is not locked"

[HEnquist]

I'm running the hctltest2.py test.

Then change one of the controls, I tried the "Z Test Volume" that gets numid 4:
amixer -D hw:0 cset numid=4 5

This generates and event, which runs the callback function. That results in the test script crashing, with:

Fatal Python error: drop_gil: drop_gil: GIL is not locked
Python runtime state: initialized

Thread 0x00007cae1adbc740 (most recent call first):
  File "/home/henrik/repos/camilladsp-controller/hctltest2.py", line 25 in event_callback

Current thread 0x00007cae1adbc740 (most recent call first):
  File "/home/henrik/repos/camilladsp-controller/hctltest2.py", line 63 in <module>

Extension modules: pyalsa.alsahcontrol (total: 1)
Aborted (core dumped)

Tested on manjaro with python 3.11, and latest alsa-python.

Also tested on Python 3.8.19, using the latest alsa-python code directly from this repo, with the same result.

[HEnquist]

Update on this, maybe not a solution but perhaps a clue on what to do?
Commenting out the Py_BEGIN_ALLOW_THREADS and Py_END_ALLOW_THREADS ain the handle_events() function at https://github.com/alsa-project/alsa-python/blob/master/pyalsa/alsahcontrol.c#L127
makes things work properly.

static PyObject *
pyalsahcontrol_handleevents(struct pyalsahcontrol *self, PyObject *args)
{
	int err;
	
	//Py_BEGIN_ALLOW_THREADS;
	err = snd_hctl_handle_events(self->handle);
	//Py_END_ALLOW_THREADS;
	if (err < 0)
		PyErr_Format(PyExc_IOError,
		     "HControl handle events error: %s", strerror(-err));
	Py_RETURN_NONE;
}

[perexg]

Unfortunately, I cannot reproduce this with latest master:

$ ./setup.py build
running build
running build_py
copying pyalsa/__init__.py -> build/lib.linux-x86_64-cpython-312/pyalsa
running build_ext
pyalsa/alsacard.so -> build/lib.linux-x86_64-cpython-312/pyalsa/alsacard.cpython-312-x86_64-linux-gnu.so
pyalsa/alsacontrol.so -> build/lib.linux-x86_64-cpython-312/pyalsa/alsacontrol.cpython-312-x86_64-linux-gnu.so
pyalsa/alsahcontrol.so -> build/lib.linux-x86_64-cpython-312/pyalsa/alsahcontrol.cpython-312-x86_64-linux-gnu.so
pyalsa/alsamixer.so -> build/lib.linux-x86_64-cpython-312/pyalsa/alsamixer.cpython-312-x86_64-linux-gnu.so
pyalsa/alsaseq.so -> build/lib.linux-x86_64-cpython-312/pyalsa/alsaseq.cpython-312-x86_64-linux-gnu.so
$ ./hctltest2.py
Watching (DEF): HDMI/DP,pcm=3 Jack,0
Watching (CLASS): HDMI/DP,pcm=4 Jack,0
Watching (DEF): Z Test Volume,1
Poll OK!
CALLBACK (DEF)! [VALUE] Z Test Volume:1
   (33, 33)

The command on the other console:

$ amixer -c 0 cset name="Z Test Volume",index=1 33
numid=51,iface=MIXER,name='Z Test Volume',index=1
  ; type=INTEGER,access=rw----W-,values=2,min=0,max=100,step=1
  : values=33,33

[perexg]

Could you test code from PR #12 , if it solves something for you ?

[HEnquist]

It works great!
I tested both master and #12 a couple of times to make sure:

• master -> fails as before
• PR 12 -> works fine
• master again -> still fails
• PR 12 again -> works

Thanks for fixing!