Use a single Python Forwarder instance for each base test runner instance.

build/android/pylib/base/base_test_runner.py

 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Base class for running tests on a single device."""
 
 import contextlib
 import httplib
 import logging
 import os
@@ skipping 107 matching lines @@
     self._http_server = lighttpd_server.LighttpdServer(
         document_root, port=port, extra_config_contents=extra_config_contents)
     if self._http_server.StartupHttpServer():
       logging.info('http server started: http://localhost:%s',
                    self._http_server.port)
     else:
       logging.critical('Failed to start http server')
     self.StartForwarderForHttpServer()
     return (self._forwarder_device_port, self._http_server.port)
 
-  def _CreateAndRunForwarder(
-      self, adb, port_pairs, tool, host_name, build_type):
-    """Creates and run a forwarder."""
-    forwarder = Forwarder(adb, build_type)
-    forwarder.Run(port_pairs, tool, host_name)
-    return forwarder
+  def _ForwardPort(self, port_pairs):
+    """Creates a forwarder instance if needed and forward a port."""
+    if not self._forwarder:
+      self._forwarder = Forwarder(self.adb, self.build_type)
+    self._forwarder.Run(port_pairs, self.tool, '127.0.0.1')
 
   def StartForwarder(self, port_pairs):
     """Starts TCP traffic forwarding for the given |port_pairs|.
 
     Args:
       host_port_pairs: A list of (device_port, local_port) tuples to forward.
     """
-    if self._forwarder:
-      self._forwarder.Close()
-    self._forwarder = self._CreateAndRunForwarder(
-        self.adb, port_pairs, self.tool, '127.0.0.1', self.build_type)
+    self._ForwardPort(port_pairs)
 
   def StartForwarderForHttpServer(self):
     """Starts a forwarder for the HTTP server.
 
     The forwarder forwards HTTP requests and responses between host and device.
     """
-    self.StartForwarder([(self._forwarder_device_port, self._http_server.port)])
+    self._ForwardPort([(self._forwarder_device_port, self._http_server.port)])
 
   def RestartHttpServerForwarderIfNecessary(self):
     """Restarts the forwarder if it's not open."""
     # Checks to see if the http server port is being used.  If not forwards the
     # request.
     # TODO(dtrainor): This is not always reliable because sometimes the port
     # will be left open even after the forwarder has been killed.
     if not ports.IsDevicePortUsed(self.adb,
         self._forwarder_device_port):
       self.StartForwarderForHttpServer()
@@ skipping 18 matching lines @@
     If the spawning server is reused for multiple tests, this should be called
     after each test to prevent tests affecting each other.
     """
     if self._spawning_server:
       self._spawning_server.CleanupState()
 
   def LaunchChromeTestServerSpawner(self):
     """Launches test server spawner."""
     server_ready = False
     error_msgs = []
+    # TODO(pliard): deflake this function. The for loop should be removed as
+    # well as IsHttpServerConnectable(). spawning_server.Start() should also
+    # block until the server is ready.
     # Try 3 times to launch test spawner server.
     for i in xrange(0, 3):
-      # Do not allocate port for test server here. We will allocate
-      # different port for individual test in TestServerThread.
       self.test_server_spawner_port = ports.AllocateTestServerPort()
+      self._ForwardPort(
+          [(self.test_server_spawner_port, self.test_server_spawner_port)])
       self._spawning_server = SpawningServer(self.test_server_spawner_port,
                                              self.adb,
                                              self.tool,
+                                             self._forwarder,
                                              self.build_type)
       self._spawning_server.Start()
       server_ready, error_msg = ports.IsHttpServerConnectable(
           '127.0.0.1', self.test_server_spawner_port, path='/ping',
           expected_read='ready')
       if server_ready:
         break
       else:
         error_msgs.append(error_msg)
       self._spawning_server.Stop()
       # Wait for 2 seconds then restart.
       time.sleep(2)
     if not server_ready:
       logging.error(';'.join(error_msgs))
       raise Exception('Can not start the test spawner server.')
     self._PushTestServerPortInfoToDevice()
-    self._spawner_forwarder = self._CreateAndRunForwarder(
-        self.adb,
-        [(self.test_server_spawner_port, self.test_server_spawner_port)],
-        self.tool, '127.0.0.1', self.build_type)