Refactor web server shutdown procedure

[asvetlov]

Now we should use complicated code for graceful shutdown:

loop = asyncio.get_event_loop()
handler = app.make_handler()
f = loop.create_server(handler, '0.0.0.0', 8080)
srv = loop.run_until_complete(f)
print('serving on', srv.sockets[0].getsockname())
try:
    loop.run_forever()
except KeyboardInterrupt:
    pass
finally:
    loop.run_until_complete(handler.finish_connections(1.0))
    srv.close()
    loop.run_until_complete(srv.wait_closed())
    loop.run_until_complete(app.finish())
loop.close()

The problem is:

1. finally block is very complex
2. It doesn't prevent establishing new connections by client on handler.finish_connections() call.

I guess add new API like:

finalizer = yield from app.create_server(...)
try:
    loop.run_forever()
finally:
    yield from finalizer 

[ludovic-gasc]

+2

[asvetlov]

Well, finalizer api should be more complex:

finalizer.close(3.0)
yield from finalizer.wait_closed()

[asvetlov]

Or even

app.close(3.0)
yield from app.wait_closed()

to mimic asyncio server protocol and to avoid inventing new Finalizer class.

[fafhrd91]

-10, "establishing new connections" is not a concern of application. you want to copy whole create_server api from asyncio?

[asvetlov]

Fixed by #734

[lock]

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