Re-factor WorkflowHandler.run_step() so user manually emits Event to start next step in worfklow

docs/docs/understanding/workflows/observability.md

@@ -107,13 +107,19 @@ In a notebook environment it can be helpful to run a workflow step by step. You
 w = ConcurrentFlow(timeout=10, verbose=True)
 handler = w.run()
 
-async for _ in handler.run_step():
-    # inspect context
+while not handler.is_done():
+    # run_step returns the step's output event
+    ev = await handler.run_step()
+    # can make modifications to the results before dispatching the event
+    # val = ev.get("some_key")
+    # ev.set("some_key", new_val)
+    # can also inspect context
     # val = await handler.ctx.get("key")
+    handler.ctx.send_event(ev)
     continue
 
 # get the result
-result = await handler
+result = handler.result()
 ```
 
 You can call `run_step` multiple times to step through the workflow one step at a time.

llama-index-core/llama_index/core/workflow/context.py

@@ -30,6 +30,14 @@ def __init__(self, workflow: "Workflow", stepwise: bool = False) -> None:
         self._tasks: Set[asyncio.Task] = set()
         self._broker_log: List[Event] = []
         self._step_flags: Dict[str, asyncio.Event] = {}
+        self._step_event_holding: Optional[Event] = None
+        self._step_lock: asyncio.Lock = asyncio.Lock()
+        self._step_condition: asyncio.Condition = asyncio.Condition(
+            lock=self._step_lock
+        )
+        self._step_event_written: asyncio.Condition = asyncio.Condition(
+            lock=self._step_lock
+        )
         self._accepted_events: List[Tuple[str, str]] = []
         self._retval: Any = None
         # Streaming machinery

llama-index-core/llama_index/core/workflow/handler.py

@@ -31,44 +31,75 @@ async def stream_events(self) -> AsyncGenerator[Event, None]:
             if type(ev) is StopEvent:
                 break
 
-    async def run_step(self) -> Optional[Any]:
+    async def run_step(self) -> Optional[Event]:
+        """Runs the next workflow step and returns the output Event.
+
+        If return is None, then the workflow is considered done.
+
+        Examples:
+            ```python
+            handler = workflow.run(stepwise=True)
+            while not handler.is_done():
+                ev = await handler.run_step()
+                handler.ctx.send_event(ev)
+
+            result = handler.result()
+            print(result)
+            ```
+        """
+        # since event is sent before calling this method, we need to unblock the event loop
+        await asyncio.sleep(0)
+
         if self.ctx and not self.ctx.stepwise:
             raise ValueError("Stepwise context is required to run stepwise.")
 
         if self.ctx:
-            # Unblock all pending steps
-            for flag in self.ctx._step_flags.values():
-                flag.set()
-
-            # Yield back control to the event loop to give an unblocked step
-            # the chance to run (we won't actually sleep here).
-            await asyncio.sleep(0)
-
-            # See if we're done, or if a step raised any error
-            we_done = False
-            exception_raised = None
-            for t in self.ctx._tasks:
-                # Check if we're done
-                if not t.done():
-                    continue
-
-                we_done = True
-                e = t.exception()
-                if type(e) != WorkflowDone:
-                    exception_raised = e
-
-            retval = None
-            if we_done:
-                # Remove any reference to the tasks
+            try:
+                # Unblock all pending steps
+                for flag in self.ctx._step_flags.values():
+                    flag.set()
+
+                # Yield back control to the event loop to give an unblocked step
+                # the chance to run (we won't actually sleep here).
+                await asyncio.sleep(0)
+
+                # check if we're done, or if a step raised error
+                we_done = False
+                exception_raised = None
+                retval = None
                 for t in self.ctx._tasks:
-                    t.cancel()
-                    await asyncio.sleep(0)
-                retval = self.ctx.get_result()
-
-                self.set_result(retval)
-
-            if exception_raised:
-                raise exception_raised
+                    # Check if we're done
+                    if not t.done():
+                        continue
+
+                    we_done = True
+                    e = t.exception()
+                    if type(e) != WorkflowDone:
+                        exception_raised = e
+
+                if we_done:
+                    # Remove any reference to the tasks
+                    for t in self.ctx._tasks:
+                        t.cancel()
+                        await asyncio.sleep(0)
+
+                    if exception_raised:
+                        raise exception_raised
+
+                    self.set_result(self.ctx.get_result())
+                else:  # continue with running next step
+                    # notify unblocked task that we're ready to accept next event
+                    async with self.ctx._step_condition:
+                        self.ctx._step_condition.notify()
+
+                    # Wait to be notified that the new_ev has been written
+                    async with self.ctx._step_event_written:
+                        await self.ctx._step_event_written.wait()
+                        retval = self.ctx._step_event_holding
+            except Exception as e:
+                if not self.is_done():  # Avoid InvalidStateError edge case
+                    self.set_exception(e)
+                raise
         else:
             raise ValueError("Context is not set!")
 

llama-index-core/llama_index/core/workflow/workflow.py

@@ -161,6 +161,7 @@ def _start(self, stepwise: bool = False, ctx: Optional[Context] = None) -> Conte
             ctx._queues = {}
             ctx._step_flags = {}
             ctx._retval = None
+            ctx._step_event_holding = None
 
         for name, step_func in self._get_steps().items():
             ctx._queues[name] = asyncio.Queue()
@@ -258,7 +259,13 @@ async def _task(
                     elif isinstance(new_ev, InputRequiredEvent):
                         ctx.write_event_to_stream(new_ev)
                     else:
-                        ctx.send_event(new_ev)
+                        if stepwise:
+                            async with ctx._step_condition:
+                                await ctx._step_condition.wait()
+                                ctx._step_event_holding = new_ev
+                                ctx._step_event_written.notify()  # shares same lock
+                        else:
+                            ctx.send_event(new_ev)
 
             for _ in range(step_config.num_workers):
                 ctx._tasks.add(
@@ -351,59 +358,6 @@ async def _run_workflow() -> None:
         asyncio.create_task(_run_workflow())
         return result
 
-    @dispatcher.span
-    async def run_step(self, **kwargs: Any) -> Optional[Any]:
-        """Runs the workflow stepwise until completion."""
-        warnings.warn(
-            "run_step() is deprecated, use `workflow.run(stepwise=True)` instead.\n"
-            "handler = workflow.run(stepwise=True)\n"
-            "while not handler.is_done():\n"
-            "    result = await handler.run_step()\n"
-            "    print(result)\n"
-        )
-
-        # Check if we need to start a new session
-        if self._stepwise_context is None:
-            self._validate()
-            self._stepwise_context = self._start(stepwise=True)
-            # Run the first step
-            self._stepwise_context.send_event(StartEvent(**kwargs))
-
-        # Unblock all pending steps
-        for flag in self._stepwise_context._step_flags.values():
-            flag.set()
-
-        # Yield back control to the event loop to give an unblocked step
-        # the chance to run (we won't actually sleep here).
-        await asyncio.sleep(0)
-
-        # See if we're done, or if a step raised any error
-        we_done = False
-        exception_raised = None
-        for t in self._stepwise_context._tasks:
-            # Check if we're done
-            if not t.done():
-                continue
-
-            we_done = True
-            e = t.exception()
-            if type(e) != WorkflowDone:
-                exception_raised = e
-
-        retval = None
-        if we_done:
-            # Remove any reference to the tasks
-            for t in self._stepwise_context._tasks:
-                t.cancel()
-                await asyncio.sleep(0)
-            retval = self._stepwise_context._retval
-            self._stepwise_context = None
-
-        if exception_raised:
-            raise exception_raised
-
-        return retval
-
     def is_done(self) -> bool:
         """Checks if the workflow is done."""
         return self._stepwise_context is None

llama-index-core/tests/workflow/test_workflow.py

@@ -37,54 +37,31 @@ async def test_workflow_run(workflow):
     assert result == "Workflow completed"
 
 
-@pytest.mark.asyncio()
-async def test_deprecated_workflow_run_step(workflow):
-    workflow._verbose = True
-
-    # First step
-    result = await workflow.run_step()
-    assert result is None
-    assert not workflow.is_done()
-
-    # Second step
-    result = await workflow.run_step()
-    assert result is None
-    assert not workflow.is_done()
-
-    # Final step
-    result = await workflow.run_step()
-    assert not workflow.is_done()
-    assert result is None
-
-    # Cleanup step
-    result = await workflow.run_step()
-    assert result == "Workflow completed"
-    assert workflow.is_done()
-
-
 @pytest.mark.asyncio()
 async def test_workflow_run_step(workflow):
     handler = workflow.run(stepwise=True)
 
-    result = await handler.run_step()
-    assert result is None
+    event = await handler.run_step()
+    assert isinstance(event, OneTestEvent)
     assert not handler.is_done()
+    handler.ctx.send_event(event)
 
-    result = await handler.run_step()
-    assert result is None
+    event = await handler.run_step()
+    assert isinstance(event, LastEvent)
     assert not handler.is_done()
+    handler.ctx.send_event(event)
 
-    result = await handler.run_step()
-    assert result is None
+    event = await handler.run_step()
+    assert isinstance(event, StopEvent)
     assert not handler.is_done()
+    handler.ctx.send_event(event)
 
-    result = await handler.run_step()
-    assert result is None
-    assert not handler.is_done()
+    event = await handler.run_step()
+    assert event is None
 
-    result = await handler.run_step()
-    assert result == "Workflow completed"
+    result = await handler
     assert handler.is_done()
+    assert result == "Workflow completed"
 
 
 @pytest.mark.asyncio()