[Core] Call wait_for_alert in a thread

This spawns a thread in alertmanager to call wait_for_alert in a thread.
This reduces latency to deluge responding to events.
And removes all `hasattr` checks in Component

Closes: https://github.com/deluge-torrent/deluge/pull/221

4 files changed, 85 insertions, 10 deletions

diff --git a/deluge/component.py b/deluge/component.py
index fec510903..421f49a7b 100644
--- a/deluge/component.py
+++ b/deluge/component.py
@@ -64,9 +64,9 @@ class Component:
                    paused by instructing the :class:`ComponentRegistry` to pause
                    this Component.
 
-        **pause()** - This method is called when the component is being paused.
+       **pause()** - This method is called when the component is being paused.
 
-        **resume()** - This method is called when the component resumes from a Paused
+       **resume()** - This method is called when the component resumes from a Paused
                     state.
 
         **shutdown()** - This method is called when the client is exiting.  If the
@@ -85,7 +85,7 @@ class Component:
 
         **Stopped** - The Component has either been stopped or has yet to be started.
 
-        **Stopping** - The Component has had it's stop method called, but it hasn't
+        **Stopping** - The Component has had its stop method called, but it hasn't
                     fully stopped yet.
 
         **Paused** - The Component has had its update timer stopped, but will
diff --git a/deluge/conftest.py b/deluge/conftest.py
index d394a271e..ca25cce8e 100644
--- a/deluge/conftest.py
+++ b/deluge/conftest.py
@@ -42,11 +42,13 @@ def mock_callback():
     The returned Mock instance will have a `deferred` attribute which will complete when the callback has been called.
     """
 
-    def reset():
+    def reset(timeout=0.5, *args, **kwargs):
         if mock.called:
-            original_reset_mock()
-        deferred = Deferred()
-        deferred.addTimeout(0.5, reactor)
+            original_reset_mock(*args, **kwargs)
+        if mock.deferred:
+            mock.deferred.cancel()
+        deferred = Deferred(canceller=lambda x: deferred.callback(None))
+        deferred.addTimeout(timeout, reactor)
         mock.side_effect = lambda *args, **kw: deferred.callback((args, kw))
         mock.deferred = deferred
 
diff --git a/deluge/core/alertmanager.py b/deluge/core/alertmanager.py
index 51a7f2993..452c159bf 100644
--- a/deluge/core/alertmanager.py
+++ b/deluge/core/alertmanager.py
@@ -16,11 +16,12 @@ This should typically only be used by the Core. Plugins should utilize the
 """
 import contextlib
 import logging
+import threading
 from collections import defaultdict
 from types import SimpleNamespace
 from typing import Any, Callable
 
-from twisted.internet import reactor
+from twisted.internet import reactor, threads
 
 import deluge.component as component
 from deluge._libtorrent import lt
@@ -34,7 +35,7 @@ class AlertManager(component.Component):
 
     def __init__(self):
         log.debug('AlertManager init...')
-        component.Component.__init__(self, 'AlertManager', interval=0.3)
+        component.Component.__init__(self, 'AlertManager')
         self.session = component.get('Core').session
 
         # Increase the alert queue size so that alerts don't get lost.
@@ -57,10 +58,17 @@ class AlertManager(component.Component):
         # handlers is a dictionary of lists {"alert_type": [handler1,h2,..]}
         self.handlers = defaultdict(list)
         self.delayed_calls = []
+        self._event = threading.Event()
 
     def update(self):
         self.delayed_calls = [dc for dc in self.delayed_calls if dc.active()]
-        self.handle_alerts()
+
+    def start(self):
+        thread = threading.Thread(
+            target=self.wait_for_alert_in_thread, name='alert-poller', daemon=True
+        )
+        thread.start()
+        self._event.set()
 
     def stop(self):
         for delayed_call in self.delayed_calls:
@@ -68,6 +76,23 @@ class AlertManager(component.Component):
                 delayed_call.cancel()
         self.delayed_calls = []
 
+    def pause(self):
+        self._event.clear()
+
+    def resume(self):
+        self._event.set()
+
+    def wait_for_alert_in_thread(self):
+        while self._component_state not in ('Stopping', 'Stopped'):
+            if self.session.wait_for_alert(1000) is None:
+                continue
+            if self._event.wait():
+                threads.blockingCallFromThread(reactor, self.maybe_handle_alerts)
+
+    def maybe_handle_alerts(self):
+        if self._component_state == 'Started':
+            self.handle_alerts()
+
     def register_handler(self, alert_type: str, handler: Callable[[Any], None]) -> None:
         """
         Registers a function that will be called when 'alert_type' is pop'd
diff --git a/deluge/tests/test_alertmanager.py b/deluge/tests/test_alertmanager.py
index 683b011b4..576e76693 100644
--- a/deluge/tests/test_alertmanager.py
+++ b/deluge/tests/test_alertmanager.py
@@ -3,17 +3,47 @@
 # the additional special exception to link portions of this program with the OpenSSL library.
 # See LICENSE for more details.
 #
+from types import SimpleNamespace
+
+import pytest_twisted
 
 import deluge.component as component
 from deluge.conftest import BaseTestCase
 from deluge.core.core import Core
 
 
+class DummyAlert1:
+    def __init__(self):
+        self.message = '1'
+
+
+class DummyAlert2:
+    def __init__(self):
+        self.message = '2'
+
+
+class SessionMock:
+    def __init__(self):
+        self.alerts = []
+
+    def set_alerts(self):
+        self.alerts = [DummyAlert1(), DummyAlert2()]
+
+    def wait_for_alert(self, timeout):
+        return self.alerts[0] if len(self.alerts) > 0 else None
+
+    def pop_alerts(self):
+        alerts = self.alerts
+        self.alerts = []
+        return alerts
+
+
 class TestAlertManager(BaseTestCase):
     def set_up(self):
         self.core = Core()
         self.core.config.config['lsd'] = False
         self.am = component.get('AlertManager')
+        self.am.session = SessionMock()
         return component.start(['AlertManager'])
 
     def tear_down(self):
@@ -28,6 +58,24 @@ class TestAlertManager(BaseTestCase):
         assert self.am.handlers['dummy1'] == [handler]
         assert self.am.handlers['dummy2'] == [handler]
 
+    @pytest_twisted.ensureDeferred
+    async def test_pop_alert(self, mock_callback):
+        mock_callback.reset_mock()
+        self.am.register_handler('DummyAlert1', mock_callback)
+        self.am.session.set_alerts()
+        await mock_callback.deferred
+        mock_callback.assert_called_once_with(SimpleNamespace(message='1'))
+
+    @pytest_twisted.ensureDeferred
+    async def test_pause_not_pop_alert(self, mock_callback):
+        await component.pause(['AlertManager'])
+        self.am.register_handler('DummyAlert1', mock_callback)
+        self.am.session.set_alerts()
+        await mock_callback.deferred
+        mock_callback.assert_not_called()
+        assert not self.am._event.isSet()
+        assert len(self.am.session.alerts) == 2
+
     def test_deregister_handler(self):
         def handler(alert):
             ...