Bug: issue with callbacks that also call proxy methods:

[tlambert03]

something is broken when a signal callback connected to a proxy event itself calls proxy methods:

def test_cb(proxy: CMMCorePlus) -> None:
    mock = Mock()

    @proxy.events.imageSnapped.connect
    def callback() -> None:
        proxy.getLoadedDevices()  # test fails unless you comment out this line
        mock()

    proxy.snapImage()
    mock.assert_called_once()

[tlambert03]

https://pyro5.readthedocs.io/en/latest/clientcode.html#proxy-sharing-between-threads

and

https://github.com/irmen/Pyro5/blob/master/examples/threadproxysharing/client.py#L14

however... if I use _pyroClaimOwnership, I deadlock, because we're doing exactly what they discourage doing (circular communication) in the tips and tricks

[tlambert03]

it's going to be extremely hard to support the use case as posed in the original post here.

if I try to use _pyroClaimOwnership on a single proxy object, inside of the callback, then I get deadlocks (that can also be explored).

One solution is to have the callback itself create an independent proxy to the same URI... but if we want the end-user (e.g. napari-micromanager or other users of pymmcore-remote) to be able to call core methods within callbacks as if they weren't using the proxy at all (which we kind of do), then the only solution I can currently think of is some rather dark magic of mucking with the locals() and closures of the callback (swapping in a new proxy object) before calling the callback... and that would require deep mucking with psygnal itself, and is probably incompatible with Qt.

[tlambert03]

this works:

def test_cb_with_core_method(proxy: CMMCorePlus) -> None:
    mock = Mock()
    from psygnal import emit_queued

    @proxy.events.imageSnapped.connect(thread="main")
    def callback() -> None:
        d = proxy.getLoadedDevices()  # test fails unless you comment out this line
        mock()

    proxy.snapImage()
    emit_queued()
    mock.assert_called_once()

see psygnal docs: https://psygnal.readthedocs.io/en/latest/usage/#connecting-across-threads