Support only tornado>=5.0

- Drop support for all versions of tornado prior to 5.0. This negates
the need for version-aware conditionals that previous existed.
- Update tox to test Tornado 5.0 and the unpinned latest version.

requires/installation.txt

@@ -1 +1 @@
-tornado>=3.1,<6
+tornado>=5,<6

sprockets/http/app.py

@@ -1,12 +1,8 @@
+import asyncio
 import logging
 import sys
 
 from tornado import concurrent, web
-import tornado
-
-ASYNCIO_TORNADO = tornado.version_info[0] >= 5
-if ASYNCIO_TORNADO:
-    import asyncio
 
 
 class _ShutdownHandler(object):
@@ -45,18 +41,12 @@ class _ShutdownHandler(object):
 
     def _maybe_stop(self):
         now = self.io_loop.time()
-        if now < self.__deadline and self._ioloop_has_tasks():
+        if now < self.__deadline and asyncio.Task.all_tasks():
             self.io_loop.add_timeout(now + 1, self._maybe_stop)
         else:
             self.io_loop.stop()
             self.logger.info('stopped IOLoop')
 
-    def _ioloop_has_tasks(self):
-        if ASYNCIO_TORNADO:
-            return bool(asyncio.Task.all_tasks())
-        else:
-            return bool(self.io_loop._callbacks or self.io_loop._timeouts)
-
 
 class CallbackManager(object):
     """
@@ -131,8 +121,8 @@ class CallbackManager(object):
             try:
                 maybe_future = callback(self.tornado_application)
 
-                if ASYNCIO_TORNADO and asyncio.iscoroutine(maybe_future):
-                        maybe_future = asyncio.create_task(maybe_future)
+                if asyncio.iscoroutine(maybe_future):
+                    maybe_future = asyncio.create_task(maybe_future)
 
                 if concurrent.is_future(maybe_future):
                     shutdown.add_future(maybe_future)

sprockets/http/runner.py

@@ -12,7 +12,6 @@ import signal
 import sys
 
 from tornado import httpserver, ioloop
-import tornado
 
 import sprockets.http.app
 
@@ -91,12 +90,7 @@ class Runner(object):
             self.server.listen(port_number)
         else:
             self.logger.info('starting processes on port %d', port_number)
-            if tornado.version_info >= (4, 4):
-                self.server.bind(port_number, reuse_port=True)
-            else:
-                self.logger.warning('port reuse disabled, please upgrade to'
-                                    'at least Tornado 4.4')
-                self.server.bind(port_number)
+            self.server.bind(port_number, reuse_port=True)
             self.server.start(number_of_procs)
 
     def stop_server(self):

tests.py

@@ -15,7 +15,6 @@ except ImportError:
     open_name = '__builtin__.open'
 
 from tornado import concurrent, httpserver, httputil, ioloop, testing, web
-import tornado
 
 import sprockets.http.mixins
 import sprockets.http.runner
@@ -410,8 +409,6 @@ class RunnerTests(MockHelper, unittest.TestCase):
 
         self.http_server.start.assert_called_once_with(0)
 
-    @unittest.skipUnless(tornado.version_info >= (4, 4),
-                         'port reuse requries newer tornado')
     def test_that_production_enables_reuse_port(self):
         runner = sprockets.http.runner.Runner(self.application)
         runner.run(8000)
@@ -448,34 +445,6 @@ class RunnerTests(MockHelper, unittest.TestCase):
             self.io_loop.add_callback_from_signal.assert_called_once_with(
                 runner._shutdown)
 
-    @unittest.skipUnless(tornado.version_info < (5,), '')
-    def test_that_shutdown_waits_for_callbacks(self):
-        def add_timeout(_, callback):
-            self.io_loop._callbacks.pop()
-            callback()
-        self.io_loop.add_timeout = mock.Mock(side_effect=add_timeout)
-
-        self.io_loop._callbacks = [mock.Mock(), mock.Mock()]
-        runner = sprockets.http.runner.Runner(self.application)
-        runner.run(8000)
-        runner._shutdown()
-        self.io_loop.stop.assert_called_once_with()
-        self.assertEqual(self.io_loop.add_timeout.call_count, 2)
-
-    @unittest.skipUnless(tornado.version_info < (5,), '')
-    def test_that_shutdown_waits_for_timeouts(self):
-        def add_timeout(_, callback):
-            self.io_loop._timeouts.pop()
-            callback()
-        self.io_loop.add_timeout = mock.Mock(side_effect=add_timeout)
-
-        self.io_loop._timeouts = [mock.Mock(), mock.Mock()]
-        runner = sprockets.http.runner.Runner(self.application)
-        runner.run(8000)
-        runner._shutdown()
-        self.io_loop.stop.assert_called_once_with()
-        self.assertEqual(self.io_loop.add_timeout.call_count, 2)
-
     def test_that_shutdown_stops_after_timelimit(self):
         def add_timeout(_, callback):
             time.sleep(0.1)

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py35,py36,py37,tornado42,tornado44,tornado45
+envlist = py35,py36,py37,tornado,tornado50
 indexserver =
 	default = https://pypi.python.org/simple
 toxworkdir = build/tox
@@ -13,22 +13,12 @@ commands =
 deps =
 	-rrequires/testing.txt
 
-[testenv:tornado42]
+[testenv:tornado]
 commands =
-	{envbindir}/pip install tornado>=4.2,<4.3
+	{envbindir}/pip install tornado
 	{[testenv]commands}
 
-[testenv:tornado43]
+[testenv:tornado50]
 commands =
-	{envbindir}/pip install tornado>=4.3,<4.4
-	{[testenv]commands}
-
-[testenv:tornado44]
-commands =
-	{envbindir}/pip install tornado>=4.4,<4.5
-	{[testenv]commands}
-
-[testenv:tornado45]
-commands =
-	{envbindir}/pip install tornado>=4.5,<4.6
+	{envbindir}/pip install tornado=5.0
 	{[testenv]commands}