Added AsyncRunnablePlugin class.

This class handles runnable plugins that have their own asyncio event
loop, without the pain usually caused by the management of multiple
threads + asyncio loops.

platypush/plugins/__init__.py

@@ -1,7 +1,9 @@
+import asyncio
 import logging
 import threading
 import time
 
+from abc import ABC, abstractmethod
 from functools import wraps
 from typing import Optional
 
@@ -110,4 +112,74 @@ class RunnablePlugin(Plugin):
         self._thread = None
 
 
+class AsyncRunnablePlugin(RunnablePlugin, ABC):
+    """
+    Class for runnable plugins with an asynchronous event loop attached.
+    """
+
+    def __init__(self, *args, _stop_timeout: Optional[float] = 30.0, **kwargs):
+        super().__init__(*args, **kwargs)
+
+        self._stop_timeout = _stop_timeout
+        self._loop: Optional[asyncio.AbstractEventLoop] = None
+        self._loop_runner: Optional[threading.Thread] = None
+        self._task: Optional[asyncio.Task] = None
+
+    @property
+    def _should_start_runner(self):
+        return True
+
+    @abstractmethod
+    async def listen(self):
+        pass
+
+    async def _listen(self):
+        try:
+            await self.listen()
+        except KeyboardInterrupt:
+            pass
+        except RuntimeError as e:
+            if not (
+                str(e).startswith('Event loop stopped before ')
+                or str(e).startswith('no running event loop')
+            ):
+                raise e
+
+    def _start_listener(self):
+        set_thread_name(self.__class__.__name__ + ':listener')
+        self._loop = asyncio.new_event_loop()
+        asyncio.set_event_loop(self._loop)
+
+        self._task = self._loop.create_task(self._listen())
+        self._task.set_name(self.__class__.__name__ + '.listen')
+        self._loop.run_forever()
+
+    def main(self):
+        if self.should_stop() or (self._loop_runner and self._loop_runner.is_alive()):
+            self.logger.info('The main loop is already being run/stopped')
+            return
+
+        if self._should_start_runner:
+            self._loop_runner = threading.Thread(target=self._start_listener)
+            self._loop_runner.start()
+
+        self.wait_stop()
+
+    def stop(self):
+        if self._task and self._loop and not self._task.done():
+            self._loop.call_soon_threadsafe(self._task.cancel)
+
+        if self._loop and self._loop.is_running():
+            self._loop.call_soon_threadsafe(self._loop.stop)
+            self._loop = None
+
+        if self._loop_runner and self._loop_runner.is_alive():
+            try:
+                self._loop_runner.join(timeout=self._stop_timeout)
+            finally:
+                self._loop_runner = None
+
+        super().stop()
+
+
 # vim:sw=4:ts=4:et: