Performance regression with Tasks after upgrading from 1.6 to 1.7 (persisting up to 1.8.2)

[ricobeck]

After updating our code base to 1.7 (ObservableState), we have noticed that after opening and successfully completing many tasks, we run into a performance problem at a later point in time. This manifests itself in a 100% CPU load (resulting in a low frame rate and high power consumption).

If we leave out the part with the many tasks when running the app, the performance is fine. However, as soon as we load a lot of data in a client, parse it and render an image from it, this has negative effects.

In Instruments (Swift Concurrency Profiling Template) you can see how the tasks no longer disappear, even though they are actually finished. Profiling with TCA 1.6 does not show this anomaly.

We have tried to reproduce this in a sample, but the performance deterioration does not occur there. However, the same result is visible in Instruments:

The assumption is that an await is still blocking the termination at some point, but all methods are provided with Task.checkCancellation and manual canceling should not be necessary.

[ricobeck]

Here's the sample:
https://github.com/ricobeck/TCATaskTest