docs: Enhance documentation for SingleThreadedAgentRuntime with usage…

… examples and clarifications; undeprecate process_next (#5230)

Resolves #5046

python/packages/autogen-core/src/autogen_core/_single_threaded_agent_runtime.py

@@ -27,7 +27,6 @@
 else:
     from ._queue import Queue, QueueShutDown  # type: ignore
 
-from typing_extensions import deprecated
 
 from ._agent import Agent
 from ._agent_id import AgentId
@@ -147,6 +146,103 @@ def _warn_if_none(value: Any, handler_name: str) -> None:
 
 
 class SingleThreadedAgentRuntime(AgentRuntime):
+    """A single-threaded agent runtime that processes all messages using a single asyncio queue.
+    Messages are delivered in the order they are received, and the runtime processes
+    each message in a separate asyncio task concurrently.
+
+    .. note::
+
+        This runtime is suitable for development and standalone applications.
+        It is not suitable for high-throughput or high-concurrency scenarios.
+
+    Args:
+        intervention_handlers (List[InterventionHandler], optional): A list of intervention
+            handlers that can intercept messages before they are sent or published. Defaults to None.
+        tracer_provider (TracerProvider, optional): The tracer provider to use for tracing. Defaults to None.
+
+    Examples:
+
+        A simple example of creating a runtime, registering an agent, sending a message and stopping the runtime:
+
+        .. code-block:: python
+
+            import asyncio
+            from dataclasses import dataclass
+
+            from autogen_core import AgentId, MessageContext, RoutedAgent, SingleThreadedAgentRuntime, message_handler
+
+
+            @dataclass
+            class MyMessage:
+                content: str
+
+
+            class MyAgent(RoutedAgent):
+                @message_handler
+                async def handle_my_message(self, message: MyMessage, ctx: MessageContext) -> None:
+                    print(f"Received message: {message.content}")
+
+
+            async def main() -> None:
+                # Create a runtime and register the agent
+                runtime = SingleThreadedAgentRuntime()
+                await MyAgent.register(runtime, "my_agent", lambda: MyAgent("My agent"))
+
+                # Start the runtime, send a message and stop the runtime
+                runtime.start()
+                await runtime.send_message(MyMessage("Hello, world!"), recipient=AgentId("my_agent", "default"))
+                await runtime.stop()
+
+
+            asyncio.run(main())
+
+        An example of creating a runtime, registering an agent, publishing a message and stopping the runtime:
+
+        .. code-block:: python
+
+            import asyncio
+            from dataclasses import dataclass
+
+            from autogen_core import (
+                DefaultTopicId,
+                MessageContext,
+                RoutedAgent,
+                SingleThreadedAgentRuntime,
+                default_subscription,
+                message_handler,
+            )
+
+
+            @dataclass
+            class MyMessage:
+                content: str
+
+
+            # The agent is subscribed to the default topic.
+            @default_subscription
+            class MyAgent(RoutedAgent):
+                @message_handler
+                async def handle_my_message(self, message: MyMessage, ctx: MessageContext) -> None:
+                    print(f"Received message: {message.content}")
+
+
+            async def main() -> None:
+                # Create a runtime and register the agent
+                runtime = SingleThreadedAgentRuntime()
+                await MyAgent.register(runtime, "my_agent", lambda: MyAgent("My agent"))
+
+                # Start the runtime.
+                runtime.start()
+                # Publish a message to the default topic that the agent is subscribed to.
+                await runtime.publish_message(MyMessage("Hello, world!"), DefaultTopicId())
+                # Wait for the message to be processed and then stop the runtime.
+                await runtime.stop_when_idle()
+
+
+            asyncio.run(main())
+
+    """
+
     def __init__(
         self,
         *,
@@ -455,8 +551,8 @@ async def _process_response(self, message_envelope: ResponseMessageEnvelope) ->
                 message_envelope.future.set_result(message_envelope.message)
             self._message_queue.task_done()
 
-    @deprecated("Manually stepping the runtime processing is deprecated. Use start() instead.")
     async def process_next(self) -> None:
+        """Process the next message in the queue."""
         await self._process_next()
 
     async def _process_next(self) -> None: