Incomplete cleanup in scheduler leading to bugs

The test that caused the error was added in ktbarrett/cocotb@d589303f9ae8cca17789b21b597e4bec66cf80bf. The failure can be observed by running the failing test and at least one other test after it.

cd tests/test_cases/test_cocotb
make MODULE=test_concurrency_primitives COCOTB_SCHEDULER_DEBUG=1 TESTCASE="test_exceptions_forked_late,test_exceptions_first"

sim.log

You can see from the log that the coroutine test_exceptions_forked_late.<locals>.await_later that was scheduled in the first test was not cleaned up and fires in the second test and causes it to fail.

[ktbarrett]

@eric-wieser Did you check the log from the OP? You can see a couroutine from the first test is still being scheduled during the second test (line 59). After the Timer returns it reschedules that coroutine where it awaits on the outcome from raise_soon, which is stored.

[ktbarrett]

The correct solution is to not use fork, but prefer start_soon instead.