extmod/uasyncio: Implement Loop.stop() to stop the event loop.

docs/library/uasyncio.rst

@@ -251,13 +251,17 @@ Event Loop
 
 .. method:: Loop.run_forever()
 
-    Run the event loop forever.
+    Run the event loop until `stop()` is called.
 
 .. method:: Loop.run_until_complete(awaitable)
 
     Run the given *awaitable* until it completes.  If *awaitable* is not a task
     then it will be promoted to one.
 
+.. method:: Loop.stop()
+
+    Stop the event loop.
+
 .. method:: Loop.close()
 
     Close the event loop.

extmod/uasyncio/core.py

@@ -214,17 +214,33 @@ def run(coro):
 # Event loop wrapper
 
 
+async def _stopper():
+    pass
+
+
+_stop_task = None
+
+
 class Loop:
     def create_task(coro):
         return create_task(coro)
 
     def run_forever():
-        run_until_complete()
+        global _stop_task
+        _stop_task = Task(_stopper(), globals())
+        run_until_complete(_stop_task)
         # TODO should keep running until .stop() is called, even if there're no tasks left
 
     def run_until_complete(aw):
         return run_until_complete(_promote_to_task(aw))
 
+    def stop():
+        global _stop_task
+        if _stop_task is not None:
+            _task_queue.push_head(_stop_task)
+            # If stop() is called again, do nothing
+            _stop_task = None
+
     def close():
         pass
 

tests/extmod/uasyncio_loop_stop.py

@@ -0,0 +1,45 @@
+# Test Loop.stop() to stop the event loop
+
+try:
+    import uasyncio as asyncio
+except ImportError:
+    try:
+        import asyncio
+    except ImportError:
+        print("SKIP")
+        raise SystemExit
+
+
+async def task():
+    print("task")
+
+
+async def main():
+    print("start")
+
+    # Stop the loop after next yield
+    loop.stop()
+
+    # Check that calling stop() again doesn't do/break anything
+    loop.stop()
+
+    # This await should stop
+    print("sleep")
+    await asyncio.sleep(0)
+
+    # Schedule stop, then create a new task, then yield
+    loop.stop()
+    asyncio.create_task(task())
+    await asyncio.sleep(0)
+
+    # Final stop
+    print("end")
+    loop.stop()
+
+
+loop = asyncio.get_event_loop()
+loop.create_task(main())
+
+for i in range(3):
+    print("run", i)
+    loop.run_forever()

tests/extmod/uasyncio_loop_stop.py.exp

@@ -0,0 +1,7 @@
+run 0
+start
+sleep
+run 1
+run 2
+task
+end