fix: max recursion depth exceeded

[zermelo-wisen]

Fixes #321.

• Disables recording while executingevent.py::describe_value.
• Prevents "Fatal Python error: Cannot recover from stack overflow." in sympy project while running tests with AppMap. This problem occurs while describing the return_value since describing Params are already protected by recording_disabled here.
• Adds a test to ensure that calling instrumented methods as a side effect of describing the return value does not produce additional events.

[apotterri]

Thanks for this. I think it would cleaner to fix recording_disabled. Have a look and let me know if that makes sense.

[apotterri]

Instead of doing this, let's fix recording_disabled:

@contextmanager
def recording_disabled():
    tls = appmap_tls()
    orig = tls.get("instrumentation_disabled")
    tls["instrumentation_disabled"] = True
    try:
        yield
    finally:
        tls["instrumentation_disabled"] = orig

Then you can just change describe_value to start with

def describe_value(name, val, max_depth=5):
    with recording_disabled():

[zermelo-wisen]

Sure, I thought about this but wasn't sure if it wasn't intended to be that way. I'll change it now.

[apotterri]

I think we need to consider the performance impact of this change. Please see my suggestions.

[apotterri]

Seeing this led me to think a bit more about these changes.

In the work we've been going to generate large numbers of AppMaps, it's become clear that there's a significant performance penalty to running with the agent. We'll certainly need to take other steps to address this, but we it's something we should start thinking about.

Here, rather than calling is_instrumentation_disabled(), which will incur 4 or 5 extra function calls, let's just do

Suggested change

	original_value = is_instrumentation_disabled()
	original_value = tls.get("instrumentation_disabled")

Let's also remove with recording_disabled(): from describe_value, and add it to FuncReturnEvent.__init__. It's already here, so there's no need to call it again when creating call event.

[apotterri]

LGTM, thanks!