If IOLoop.stop is called before the loop is running, make the next

call to IOLoop.start return immediately, so that one call each to start
and stop will result in the loop not running rather than running
infinitely, even if the call to stop happens first.

diff --git a/tornado/ioloop.py b/tornado/ioloop.py
index 11ea4469efc647175e152d1566ddd00010358299..ec7450a9e36c0c1ef29450a4bd3520a9a4600597 100644 (file)
--- a/tornado/ioloop.py
+++ b/tornado/ioloop.py
@@ -86,6 +86,7 @@ class IOLoop(object):
         self._callbacks = set()
         self._timeouts = []
         self._running = False
+        self._stopped = False
 
         # Create a pipe that we send bogus data to when we want to wake
         # the I/O loop when it is idle
@@ -144,6 +145,9 @@ class IOLoop(object):
         The loop will run until one of the I/O handlers calls stop(), which
         will make the loop stop after the current event iteration completes.
         """
+        if self._stopped:
+            self._stopped = False
+            return
         self._running = True
         while True:
             # Never use an infinite timeout here - it can stall epoll
@@ -203,10 +207,24 @@ class IOLoop(object):
                 except:
                     logging.error("Exception in I/O handler for fd %d",
                                   fd, exc_info=True)
+        # reset the stopped flag so another start/stop pair can be issued
+        self._stopped = False
 
     def stop(self):
-        """Stop the loop after the current event loop iteration is complete."""
+        """Stop the loop after the current event loop iteration is complete.
+        If the event loop is not currently running, the next call to start()
+        will return immediately.
+
+        To use asynchronous methods from otherwise-synchronous code (such as
+        unit tests), you can start and stop the event loop like this:
+          ioloop = IOLoop()
+          async_method(ioloop=ioloop, callback=ioloop.stop)
+          ioloop.start()
+        ioloop.start() will return after async_method has run its callback,
+        whether that callback was invoked before or after ioloop.start.
+        """
         self._running = False
+        self._stopped = True
         self._wake()
 
     def running(self):