Async mode server: dynamic attribute read/write/is_allowed are not called by worker

[tiagocoutinho]

In async mode (gevent, asyncio, ...) the dynamic attributes read, write and is_allowed methods are not called through the worker like the standard attributes

[mliszcz]

Probably got the same issue:

sys:1: RuntimeWarning: coroutine 'AsyncioDevice.getter' was never awaited

As a workaround I needed to decorate my methods:

def run_in_executor(fn):
    @functools.wraps(fn)
    def wrapper(*args, **kwargs):
        get_worker().execute(wrapper, *args, **kwargs)
    return wrapper

Howeve it would be nice to have this handled by PyTango.

[stanislaw55]

Hi
I just hit this issue. Is there any chance that it will be fixed any time soon?

[ajoubertza]

Hi @stanislaw55

I wasn't planning on working on this. Would you consider helping by submitting a pull request?

[stanislaw55]

Hi @ajoubertza
Actually, I would like to make time for contribution but the fix proposed by @mliszcz did not worked for me for some reason. I did not investigated in depth since docs mentioned experimental state of server GreenMode. However, now I will come back to this issue and try to generate more detailed bug report.

My setup:
pytango 9.2.5
Libtango 9.2.5
Python 3.6.8

I did not tested this fix with (Py)Tango 9.3.x because of lack of such libraries compiled. However, I'll try to test it and maybe latest version from develop.

Stay tuned!

[stanislaw55]

Okay, that was quick one

The fix that worker for me

import functools

from tango.server import get_worker

def run_in_executor(fn):
    @functools.wraps(fn)
    def wrapper(*args, **kwargs):
        get_worker().execute(fn, *args, **kwargs)
    return wrapper

(mind that now in execute call there's fn, not wrapper)

[ajoubertza]

@stanislaw55 Well spotted - the fn makes more sense than a recursive call!

If you're working on a PR, I suggest starting by adding one or more failing tests at the end of https://github.com/tango-controls/pytango/blob/develop/tests/test_server.py. I see there are actually no tests for is_allowed!

You could base them on something like the one below. The typed_values fixture will repeat the test for lots of different types of attributes. The server_green_mode will repeat the test for all the different green modes.

pytango/tests/test_server.py

Lines 153 to 171 in fa1193e

	def test_read_write_attribute(typed_values, server_green_mode):
	dtype, values, expected = typed_values
	class TestDevice(Device):
	green_mode = server_green_mode
	@attribute(dtype=dtype, max_dim_x=10,
	access=AttrWriteType.READ_WRITE)
	def attr(self):
	return self.attr_value
	@attr.write
	def attr(self, value):
	self.attr_value = value
	with DeviceTestContext(TestDevice) as proxy:
	for value in values:
	proxy.attr = value
	assert_close(proxy.attr, expected(value))

If you explicitly need async or await keywords in the test, you have to jump through some hoops to keep the code readable in Python versions prior to 3.5.

pytango/tests/test_server.py

Lines 383 to 391 in fa1193e

	if server_green_mode == GreenMode.Asyncio:
	code = textwrap.dedent("""\
	@asyncio.coroutine
	def dev_status(self):
	coro = super(type(self), self).dev_status()
	result = {YIELD_FROM}(coro)
	{RETURN}(3*result)
	""").format(**globals())
	exec(code)

[stanislaw55]

Thanks for detailed instrution on test, @ajoubertza!

I'll try to make some time for PR in days to come