asyncio: sync with Tulip

* Tulip issue #182: Improve logs of BaseEventLoop._run_once()

  - Don't log non-blocking poll
  - Only log polling with a timeout if it gets events or if it timed out after
    more than 1 second.

* Fix some pyflakes warnings: remove unused imports

Lib/asyncio/base_events.py

@@ -882,19 +882,26 @@ class BaseEventLoop(events.AbstractEventLoop):
             when = self._scheduled[0]._when
             timeout = max(0, when - self.time())
 
-        if self._debug:
+        if self._debug and timeout != 0:
             t0 = self.time()
             event_list = self._selector.select(timeout)
             dt = self.time() - t0
-            if dt >= 1:
+            if dt >= 1.0:
                 level = logging.INFO
             else:
                 level = logging.DEBUG
-            if timeout is not None:
-                logger.log(level, 'poll %.3f took %.3f seconds',
-                           timeout, dt)
-            else:
-                logger.log(level, 'poll took %.3f seconds', dt)
+            nevent = len(event_list)
+            if timeout is None:
+                logger.log(level, 'poll took %.3f ms: %s events',
+                           dt * 1e3, nevent)
+            elif nevent:
+                logger.log(level,
+                           'poll %.3f ms took %.3f ms: %s events',
+                           timeout * 1e3, dt * 1e3, nevent)
+            elif dt >= 1.0:
+                logger.log(level,
+                           'poll %.3f ms took %.3f ms: timeout',
+                           timeout * 1e3, dt * 1e3)
         else:
             event_list = self._selector.select(timeout)
         self._process_events(event_list)

Lib/asyncio/streams.py

@@ -14,7 +14,6 @@ from . import coroutines
 from . import events
 from . import futures
 from . import protocols
-from . import tasks
 from .coroutines import coroutine
 
 

Lib/asyncio/tasks.py

@@ -18,7 +18,6 @@ from . import coroutines
 from . import events
 from . import futures
 from .coroutines import coroutine
-from .log import logger
 
 _PY34 = (sys.version_info >= (3, 4))