2.4. Services¶

Services is an abstraction to help organize lots of different tasks in one process. Each service must implement start() method and can implement stop() method.

Service instance should be passed to the entrypoint, and will be started after the event loop has been created.

Note

Current event-loop will be set before start() method called. The event loop will be set as current for this thread.

Please avoid using asyncio.get_event_loop() explicitly inside start() method. Use self.loop instead:

import asyncio
from threading import Event
from aiomisc import entrypoint, Service

event = Event()

class MyService(Service):
  async def start(self):
      # Send signal to entrypoint for continue running
      self.start_event.set()

      event.set()
      # Start service task
      await asyncio.sleep(3600)


with entrypoint(MyService()) as loop:
    assert event.is_set()

Method start() creates as a separate task that can run forever. But in this case self.start_event.set() should be called for notifying entrypoint.

If one service fails during startup, pending starts from the same group and their readiness waiters are cancelled and joined before the original error is propagated. POST_START runs after this cleanup, including on failure. Tasks unrelated to the entrypoint’s startup group are left running.

During graceful shutdown, long-lived start() tasks are cancelled before the services’ stop() methods are called. Applications that need coordinated draining or other work while service loops are active should quiesce that work before exiting the entrypoint. When calling __aenter__() directly, call __aexit__() after a failed startup as well, to stop already-created services and release their resources.

This package contains some useful base classes for simple services writing.