Merge pull request tornadoweb#2179 from pitrou/periodic_callback_iolo…

…op_compat Fetch IOLoop in PeriodicCallback.start(), not __init__()
sjtuldl · Oct 28, 2017 · 5bc4924 · 5bc4924
2 parents 5ee7f45 + b1a7390
commit 5bc4924
Show file tree

Hide file tree

Showing 2 changed files with 19 additions and 1 deletion.
diff --git a/tornado/ioloop.py b/tornado/ioloop.py
@@ -1086,12 +1086,15 @@ def __init__(self, callback, callback_time):
         if callback_time <= 0:
             raise ValueError("Periodic callback must have a positive callback_time")
         self.callback_time = callback_time
-        self.io_loop = IOLoop.current()
         self._running = False
         self._timeout = None
 
     def start(self):
         """Starts the timer."""
+        # Looking up the IOLoop here allows to first instantiate the
+        # PeriodicCallback in another thread, then start it using
+        # IOLoop.add_callback().
+        self.io_loop = IOLoop.current()
         self._running = True
         self._next_timeout = self.io_loop.time()
         self._schedule_next()

diff --git a/tornado/test/ioloop_test.py b/tornado/test/ioloop_test.py
@@ -761,6 +761,21 @@ def cb():
         self.io_loop.start()
         self.assertEqual(calls, expected)
 
+    def test_io_loop_set_at_start(self):
+        # Check PeriodicCallback uses the current IOLoop at start() time,
+        # not at instantiation time.
+        calls = []
+        io_loop = FakeTimeIOLoop()
+
+        def cb():
+            calls.append(io_loop.time())
+        pc = PeriodicCallback(cb, 10000)
+        io_loop.make_current()
+        pc.start()
+        io_loop.call_later(50, io_loop.stop)
+        io_loop.start()
+        self.assertEqual(calls, [1010, 1020, 1030, 1040, 1050])
+
 
 class TestIOLoopConfiguration(unittest.TestCase):
     def run_python(self, *statements):