Add optimizations for scheduler

src/cocotb/_scheduler.py

@@ -260,8 +260,6 @@ def __init__(self, test_complete_cb: Callable[[], None]) -> None:
 
         self._current_task = None
 
-        self._is_reacting = False
-
         self._write_task = None
         self._writes_pending = Event()
 
@@ -338,30 +336,6 @@ def _test_completed(self, trigger=None):
             # if it did, make sure we handle the test completing
             self._check_termination()
 
-    def _react(self, trigger):
-        """
-        Called when a trigger fires.
-
-        We ensure that we only start the event loop once, rather than
-        letting it recurse.
-        """
-        if self._is_reacting:
-            # queue up the trigger, the event loop will get to it
-            self._pending_triggers.append(trigger)
-            return
-
-        if self._pending_triggers:
-            raise InternalError(
-                f"Expected all triggers to be handled but found {self._pending_triggers}"
-            )
-
-        # start the event loop
-        self._is_reacting = True
-        try:
-            self._event_loop(trigger)
-        finally:
-            self._is_reacting = False
-
     def _event_loop(self, trigger):
         """
         Run an event loop triggered by the given trigger.
@@ -524,7 +498,7 @@ def _unschedule(self, task):
                 self._cleanup()
 
         elif Join(task) in self._trigger2tasks:
-            self._react(Join(task))
+            self._pending_triggers.append(Join(task))
         else:
             try:
                 # throws an error if the background task errored
@@ -581,7 +555,10 @@ def _resume_task_upon(self, task, trigger):
                 raise InternalError("More than one task waiting on an unprimed trigger")
 
             try:
-                trigger._prime(self._react)
+                if isinstance(trigger, GPITrigger):
+                    trigger._prime(self._event_loop)
+                else:
+                    trigger._prime(self._pending_triggers.append)
             except Exception as e:
                 # discard the trigger we associated, it will never fire
                 self._trigger2tasks.pop(trigger)
@@ -716,16 +693,26 @@ def start_soon(self, task: Union[Coroutine, Task]) -> Task:
         self._queue(task)
         return task
 
-    def _add_test(self, test_task):
+    def _add_test(self, test_task: Task[None]) -> None:
         """Called by the regression manager to queue the next test"""
+        if self._mode != self._MODE_NORMAL:
+            raise InternalError("Test was not started in Normal Mode.")
+
         if self._test is not None:
-            raise InternalError("Test was added while another was in progress")
+            raise InternalError("Test was added while another was in progress.")
 
         self._test = test_task
-        self._resume_task_upon(
-            test_task,
-            NullTrigger(name=f"Start {test_task!s}", outcome=_outcomes.Value(None)),
+
+        # like _resume_task_upon, but forcing the NullTrigger to go through the main entry point
+        trigger = NullTrigger(
+            name=f"Start {test_task!s}", outcome=_outcomes.Value(None)
         )
+        test_task._trigger = trigger
+        trigger_tasks = self._trigger2tasks.setdefault(trigger, [])
+        trigger_tasks.append(test_task)
+
+        # call into main entry point
+        trigger._prime(self._event_loop)
 
     # This collection of functions parses a trigger out of the object
     # that was yielded by a task, converting `list` -> `Waitable`,

tests/test_cases/test_cocotb/test_scheduler.py

@@ -521,7 +521,7 @@ def react_wrapper(trigger):
         log = logging.getLogger("cocotb.test")
         log.debug("react_wrapper start")
         assert coro_scheduled is False
-        cocotb._scheduler._react(trigger)
+        cocotb._scheduler._event_loop(trigger)
         assert coro_scheduled is True
         log.debug("react_wrapper end")
 
@@ -651,7 +651,7 @@ def react_wrapper(trigger):
         log = logging.getLogger("cocotb.test")
         log.debug("react_wrapper start")
         sim_resumed = False
-        cocotb._scheduler._react(trigger)
+        cocotb._scheduler._event_loop(trigger)
         sim_resumed = True
         log.debug("react_wrapper end")