Debugging+Logging: find out when sync function run in asynq context

As we migrate our code to use asynq, we would love a way to detect usages of sync calls within asynq contexts.

For example, imagine:

@asynq.async()
def data_fetch_1():
    return 5

@asynq.async()
def data_fetch_times_2():
    data = data_fetch_1()
    return data + data

This will incur a sync fetch within an already asynq call which should be fixed since it incurs performance penalties especially when data_fetch_2 is batched.

I have not seen a way to log/debug/add a hook to figure out when this happens

[manannayak]

Yep

[JelleZijlstra]

We should really document that options mechanism.