Revert "Reland r212020: Move Python setup/tear down logic into Forwarder ..."

This reverts r212020 which caused some timeouts on the net_unittests every ~15
builds.

Conflicts:
	build/android/pylib/base/test_dispatcher.py
	build/android/pylib/instrumentation/test_runner.py
	chrome/test/chromedriver/run_py_tests.py

TBR=bulach@chromium.org
BUG=262573,242846

Review URL: https://codereview.chromium.org/19844006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@212888 0039d316-1c4b-4281-b951-d872f2087c98

8 files changed, 131 insertions, 245 deletions

diff --git a/build/android/adb_reverse_forwarder.py b/build/android/adb_reverse_forwarder.py
index ee38332..e465ea7 100755
--- a/build/android/adb_reverse_forwarder.py
+++ b/build/android/adb_reverse_forwarder.py
@@ -17,6 +17,7 @@ import time
 
 from pylib import android_commands, forwarder
 from pylib.utils import run_tests_helper
+from pylib.valgrind_tools import CreateTool
 
 
 def main(argv):
@@ -50,14 +51,17 @@ def main(argv):
     sys.exit(1)
 
   adb = android_commands.AndroidCommands(options.device)
+  tool = CreateTool(None, adb)
+  forwarder_instance = forwarder.Forwarder(adb, options.build_type)
   try:
-    forwarder.Forwarder.Map(port_pairs, adb, options.build_type)
+    forwarder_instance.Run(port_pairs, tool)
     while True:
       time.sleep(60)
   except KeyboardInterrupt:
     sys.exit(0)
   finally:
-    forwarder.Forwarder.UnmapAllDevicePorts(adb)
+    forwarder_instance.Close()
+
 
 if __name__ == '__main__':
   main(sys.argv)
diff --git a/build/android/bb_run_sharded_steps.py b/build/android/bb_run_sharded_steps.py
index 9b768a9..afd354a 100755
--- a/build/android/bb_run_sharded_steps.py
+++ b/build/android/bb_run_sharded_steps.py
@@ -165,6 +165,7 @@ def _PrintAllStepsOutput(steps):
 
 def _KillPendingServers():
   for retry in range(5):
+    forwarder.Forwarder.KillHost()
     for server in ['lighttpd', 'web-page-replay']:
       pids = cmd_helper.GetCmdOutput(['pgrep', '-f', server])
       pids = [pid.strip() for pid in pids.split('\n') if pid.strip()]
@@ -200,8 +201,6 @@ def main(argv):
   # previous runs.
   _KillPendingServers()
 
-  forwarder.Forwarder.UseMultiprocessing()
-
   # Reset the test port allocation. It's important to do it before starting
   # to dispatch any step.
   if not ports.ResetTestServerPortAllocation():
diff --git a/build/android/pylib/base/base_test_runner.py b/build/android/pylib/base/base_test_runner.py
index 9173b72..df04f9f 100644
--- a/build/android/pylib/base/base_test_runner.py
+++ b/build/android/pylib/base/base_test_runner.py
@@ -44,12 +44,14 @@ class BaseTestRunner(object):
     self.adb = android_commands.AndroidCommands(device=device)
     self.tool = CreateTool(tool, self.adb)
     self._http_server = None
+    self._forwarder = None
     self._forwarder_device_port = 8000
     self.forwarder_base_url = ('http://localhost:%d' %
         self._forwarder_device_port)
     self.flags = FlagChanger(self.adb)
     self.flags.AddFlags(['--disable-fre'])
     self._spawning_server = None
+    self._spawner_forwarder = None
     # We will allocate port for test server spawner when calling method
     # LaunchChromeTestServerSpawner and allocate port for test server when
     # starting it in TestServerThread.
@@ -88,6 +90,7 @@ class BaseTestRunner(object):
 
   def SetUp(self):
     """Run once before all tests are run."""
+    Forwarder.KillDevice(self.adb, self.tool)
     self.InstallTestPackage()
     push_size_before = self.adb.GetPushSizeInfo()
     if self._push_deps:
@@ -125,47 +128,49 @@ class BaseTestRunner(object):
                    self._http_server.port)
     else:
       logging.critical('Failed to start http server')
-    self._ForwardPortsForHttpServer()
+    self.StartForwarderForHttpServer()
     return (self._forwarder_device_port, self._http_server.port)
 
-  def _ForwardPorts(self, port_pairs):
-    """Forwards a port."""
-    Forwarder.Map(port_pairs, self.adb, self.build_type, self.tool)
+  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)
 
-  def _UnmapPorts(self, port_pairs):
-    """Unmap previously forwarded ports."""
-    for (device_port, _) in port_pairs:
-      Forwarder.UnmapDevicePort(device_port, self.adb)
-
-  # Deprecated: Use ForwardPorts instead.
   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.
     """
-    self._ForwardPorts(port_pairs)
+    self._ForwardPort(port_pairs)
 
-  def _ForwardPortsForHttpServer(self):
+  def StartForwarderForHttpServer(self):
     """Starts a forwarder for the HTTP server.
 
     The forwarder forwards HTTP requests and responses between host and device.
     """
-    self._ForwardPorts([(self._forwarder_device_port, self._http_server.port)])
+    self._ForwardPort([(self._forwarder_device_port, self._http_server.port)])
 
-  def _RestartHttpServerForwarderIfNecessary(self):
+  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._ForwardPortsForHttpServer()
+    if not ports.IsDevicePortUsed(self.adb,
+        self._forwarder_device_port):
+      self.StartForwarderForHttpServer()
 
   def ShutdownHelperToolsForTestSuite(self):
     """Shuts down the server and the forwarder."""
+    # Forwarders should be killed before the actual servers they're forwarding
+    # to as they are clients potentially with open connections and to allow for
+    # proper hand-shake/shutdown.
+    Forwarder.KillDevice(self.adb, self.tool)
+    if self._forwarder:
+      self._forwarder.Close()
     if self._http_server:
-      self._UnmapPorts([(self._forwarder_device_port, self._http_server.port)])
       self._http_server.ShutdownHttpServer()
     if self._spawning_server:
       self._spawning_server.Stop()
@@ -190,11 +195,12 @@ class BaseTestRunner(object):
     # Try 3 times to launch test spawner server.
     for i in xrange(0, 3):
       self.test_server_spawner_port = ports.AllocateTestServerPort()
-      self._ForwardPorts(
+      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(
diff --git a/build/android/pylib/base/test_dispatcher.py b/build/android/pylib/base/test_dispatcher.py
index 8e30c2e..03644ec 100644
--- a/build/android/pylib/base/test_dispatcher.py
+++ b/build/android/pylib/base/test_dispatcher.py
@@ -21,6 +21,7 @@ import threading
 
 from pylib import android_commands
 from pylib import constants
+from pylib import forwarder
 from pylib.utils import reraiser_thread
 from pylib.utils import watchdog_timer
 
@@ -380,7 +381,7 @@ def RunTests(tests, runner_factory, wait_for_debugger, test_device,
   devices = _GetAttachedDevices(wait_for_debugger, test_device)
 
   logging.info('Will run %d tests: %s', len(tests), str(tests))
-
+  forwarder.Forwarder.KillHost(build_type)
   runners = _CreateRunners(runner_factory, devices, setup_timeout)
   try:
     return _RunAllTests(runners, test_collection_factory,
@@ -390,3 +391,5 @@ def RunTests(tests, runner_factory, wait_for_debugger, test_device,
       _TearDownRunners(runners, setup_timeout)
     except android_commands.errors.DeviceUnresponsiveError as e:
       logging.warning('Device unresponsive during TearDown: [%s]', e)
+    finally:
+      forwarder.Forwarder.KillHost(build_type)
diff --git a/build/android/pylib/chrome_test_server_spawner.py b/build/android/pylib/chrome_test_server_spawner.py
index f9fcd30..4fea07a 100644
--- a/build/android/pylib/chrome_test_server_spawner.py
+++ b/build/android/pylib/chrome_test_server_spawner.py
@@ -23,7 +23,6 @@ import urlparse
 import constants
 import ports
 
-from pylib.forwarder import Forwarder
 
 # Path that are needed to import necessary modules when launching a testserver.
 os.environ['PYTHONPATH'] = os.environ.get('PYTHONPATH', '') + (':%s:%s:%s:%s:%s'
@@ -100,7 +99,7 @@ def _GetServerTypeCommandLine(server_type):
 class TestServerThread(threading.Thread):
   """A thread to run the test server in a separate process."""
 
-  def __init__(self, ready_event, arguments, adb, tool, build_type):
+  def __init__(self, ready_event, arguments, adb, tool, forwarder, build_type):
     """Initialize TestServerThread with the following argument.
 
     Args:
@@ -108,6 +107,7 @@ class TestServerThread(threading.Thread):
       arguments: dictionary of arguments to run the test server.
       adb: instance of AndroidCommands.
       tool: instance of runtime error detection tool.
+      forwarder: instance of Forwarder.
       build_type: 'Release' or 'Debug'.
     """
     threading.Thread.__init__(self)
@@ -122,6 +122,7 @@ class TestServerThread(threading.Thread):
     self.is_ready = False
     self.host_port = self.arguments['port']
     assert isinstance(self.host_port, int)
+    self._test_server_forwarder = forwarder
     # The forwarder device port now is dynamically allocated.
     self.forwarder_device_port = 0
     # Anonymous pipe in order to get port info from test server.
@@ -239,10 +240,11 @@ class TestServerThread(threading.Thread):
       else:
         self.is_ready = _CheckPortStatus(self.host_port, True)
     if self.is_ready:
-      Forwarder.Map([(0, self.host_port)], self.adb, self.build_type, self.tool)
+      self._test_server_forwarder.Run([(0, self.host_port)], self.tool)
       # Check whether the forwarder is ready on the device.
       self.is_ready = False
-      device_port = Forwarder.DevicePortForHostPort(self.host_port)
+      device_port = self._test_server_forwarder.DevicePortForHostPort(
+          self.host_port)
       if device_port and _CheckDevicePortStatus(self.adb, device_port):
         self.is_ready = True
         self.forwarder_device_port = device_port
@@ -252,7 +254,7 @@ class TestServerThread(threading.Thread):
     _WaitUntil(lambda: self.stop_flag, max_attempts=sys.maxint)
     if self.process.poll() is None:
       self.process.kill()
-    Forwarder.UnmapDevicePort(self.forwarder_device_port, self.adb)
+    self._test_server_forwarder.UnmapDevicePort(self.forwarder_device_port)
     self.process = None
     self.is_ready = False
     if self.pipe_out:
@@ -322,6 +324,7 @@ class SpawningServerRequestHandler(BaseHTTPServer.BaseHTTPRequestHandler):
         json.loads(test_server_argument_json),
         self.server.adb,
         self.server.tool,
+        self.server.forwarder,
         self.server.build_type)
     self.server.test_server_instance.setDaemon(True)
     self.server.test_server_instance.start()
@@ -389,12 +392,14 @@ class SpawningServerRequestHandler(BaseHTTPServer.BaseHTTPRequestHandler):
 class SpawningServer(object):
   """The class used to start/stop a http server."""
 
-  def __init__(self, test_server_spawner_port, adb, tool, build_type):
+  def __init__(self, test_server_spawner_port, adb, tool, forwarder,
+               build_type):
     logging.info('Creating new spawner on port: %d.', test_server_spawner_port)
     self.server = BaseHTTPServer.HTTPServer(('', test_server_spawner_port),
                                             SpawningServerRequestHandler)
     self.server.adb = adb
     self.server.tool = tool
+    self.server.forwarder = forwarder
     self.server.test_server_instance = None
     self.server.build_type = build_type
 
diff --git a/build/android/pylib/forwarder.py b/build/android/pylib/forwarder.py
index adf538c..5bdb1cd 100644
--- a/build/android/pylib/forwarder.py
+++ b/build/android/pylib/forwarder.py
@@ -2,49 +2,24 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import fcntl
 import logging
 import os
-import psutil
 import re
 import sys
+import threading
 import time
 
 import android_commands
 import cmd_helper
 import constants
 
-from pylib import valgrind_tools
+from pylib import pexpect
 
 
 def _MakeBinaryPath(build_type, binary_name):
   return os.path.join(cmd_helper.OutDirectory.get(), build_type, binary_name)
 
 
-def _GetProcessStartTime(pid):
-  return psutil.Process(pid).create_time
-
-
-class _FileLock(object):
-  """With statement-aware implementation of a file lock.
-
-  File locks are needed for cross-process synchronization when the
-  multiprocessing Python module is used.
-  """
-  def __init__(self, path):
-    self._path = path
-
-  def __enter__(self):
-    self._fd = os.open(self._path, os.O_RDONLY | os.O_CREAT)
-    if self._fd < 0:
-      raise Exception('Could not open file %s for reading' % self._path)
-    fcntl.flock(self._fd, fcntl.LOCK_EX)
-
-  def __exit__(self, type, value, traceback):
-    fcntl.flock(self._fd, fcntl.LOCK_UN)
-    os.close(self._fd)
-
-
 class Forwarder(object):
   """Thread-safe class to manage port forwards from the device to the host."""
 
@@ -53,18 +28,28 @@ class Forwarder(object):
   _DEVICE_FORWARDER_PATH = (constants.TEST_EXECUTABLE_DIR +
                             '/forwarder/device_forwarder')
   _LD_LIBRARY_PATH = 'LD_LIBRARY_PATH=%s' % _DEVICE_FORWARDER_FOLDER
-  _LOCK_PATH = '/tmp/chrome.forwarder.lock'
-  _MULTIPROCESSING_ENV_VAR = 'CHROME_FORWARDER_USE_MULTIPROCESSING'
 
-  _instance = None
+  def __init__(self, adb, build_type):
+    """Forwards TCP ports on the device back to the host.
 
-  @staticmethod
-  def UseMultiprocessing():
-    """Tells the forwarder that multiprocessing is used."""
-    os.environ[Forwarder._MULTIPROCESSING_ENV_VAR] = '1'
+    Works like adb forward, but in reverse.
 
-  @staticmethod
-  def Map(port_pairs, adb, build_type='Debug', tool=None):
+    Args:
+      adb: Instance of AndroidCommands for talking to the device.
+      build_type: 'Release' or 'Debug'.
+    """
+    assert build_type in ('Release', 'Debug')
+    self._adb = adb
+    self._device_to_host_port_map = dict()
+    self._host_to_device_port_map = dict()
+    self._device_initialized = False
+    self._host_adb_control_port = 0
+    self._lock = threading.Lock()
+    self._host_forwarder_path = _MakeBinaryPath(build_type, 'host_forwarder')
+    self._device_forwarder_path_on_host = os.path.join(
+        cmd_helper.OutDirectory.get(), build_type, 'forwarder_dist')
+
+  def Run(self, port_pairs, tool):
     """Runs the forwarder.
 
     Args:
@@ -73,29 +58,24 @@ class Forwarder(object):
                  port will by dynamically assigned on the device. You can
                  get the number of the assigned port using the
                  DevicePortForHostPort method.
-      adb: An AndroidCommands instance.
       tool: Tool class to use to get wrapper, if necessary, for executing the
             forwarder (see valgrind_tools.py).
 
     Raises:
       Exception on failure to forward the port.
     """
-    if not tool:
-      tool = valgrind_tools.CreateTool(None, adb)
-    with _FileLock(Forwarder._LOCK_PATH):
-      instance = Forwarder._GetInstanceLocked(build_type, tool)
-      instance._InitDeviceLocked(adb, tool)
-
-      device_serial = adb.Adb().GetSerialNumber()
+    with self._lock:
+      self._InitDeviceLocked(tool)
+      host_name = '127.0.0.1'
       redirection_commands = [
-          ['--serial-id=' + device_serial, '--map', str(device),
-           str(host)] for device, host in port_pairs]
+          ['--serial-id=' + self._adb.Adb().GetSerialNumber(), '--map',
+           str(device), str(host)] for device, host in port_pairs]
       logging.info('Forwarding using commands: %s', redirection_commands)
 
       for redirection_command in redirection_commands:
         try:
           (exit_code, output) = cmd_helper.GetCmdStatusAndOutput(
-              [instance._host_forwarder_path] + redirection_command)
+              [self._host_forwarder_path] + redirection_command)
         except OSError as e:
           if e.errno == 2:
             raise Exception('Unable to start host forwarder. Make sure you have'
@@ -103,203 +83,83 @@ class Forwarder(object):
           else: raise
         if exit_code != 0:
           raise Exception('%s exited with %d:\n%s' % (
-              instance._host_forwarder_path, exit_code, '\n'.join(output)))
+              self._host_forwarder_path, exit_code, '\n'.join(output)))
         tokens = output.split(':')
         if len(tokens) != 2:
           raise Exception(('Unexpected host forwarder output "%s", ' +
                           'expected "device_port:host_port"') % output)
         device_port = int(tokens[0])
         host_port = int(tokens[1])
-        serial_with_port = (device_serial, device_port)
-        instance._device_to_host_port_map[serial_with_port] = host_port
-        instance._host_to_device_port_map[host_port] = serial_with_port
+        self._device_to_host_port_map[device_port] = host_port
+        self._host_to_device_port_map[host_port] = device_port
         logging.info('Forwarding device port: %d to host port: %d.',
                      device_port, host_port)
 
-  @staticmethod
-  def UnmapDevicePort(device_port, adb):
-    """Unmaps a previously forwarded device port.
-
-    Args:
-      adb: An AndroidCommands instance.
-      device_port: A previously forwarded port (through Map()).
-    """
-    with _FileLock(Forwarder._LOCK_PATH):
-      Forwarder._UnmapDevicePortLocked(device_port, adb)
-
-  @staticmethod
-  def UnmapAllDevicePorts(adb):
-    """Unmaps all the previously forwarded ports for the provided device.
-
-    Args:
-      adb: An AndroidCommands instance.
-      port_pairs: A list of tuples (device_port, host_port) to unmap.
-    """
-    with _FileLock(Forwarder._LOCK_PATH):
-      port_map = Forwarder._GetInstanceLocked(
-          None, None)._device_to_host_port_map
-      adb_serial = adb.Adb().GetSerialNumber()
-      for ((device_serial, device_port), _) in port_map:
-        if adb_serial == device_serial:
-          Forwarder._UnmapDevicePortLocked(device_port, adb)
-
-  @staticmethod
-  def DevicePortForHostPort(host_port):
-    """Returns the device port that corresponds to a given host port."""
-    with _FileLock(Forwarder._LOCK_PATH):
-      (device_serial, device_port) = Forwarder._GetInstanceLocked(
-          None, None)._host_to_device_port_map.get(host_port)
-      return device_port
-
-  @staticmethod
-  def _GetInstanceLocked(build_type, tool):
-    """Returns the singleton instance.
-
-    Note that the global lock must be acquired before calling this method.
-
-    Args:
-      build_type: 'Release' or 'Debug'
-      tool: Tool class to use to get wrapper, if necessary, for executing the
-            forwarder (see valgrind_tools.py).
-    """
-    if not Forwarder._instance:
-      Forwarder._instance = Forwarder(build_type, tool)
-    return Forwarder._instance
-
-  def __init__(self, build_type, tool):
-    """Constructs a new instance of Forwarder.
+  def _InitDeviceLocked(self, tool):
+    """Initializes the device forwarder process (only once)."""
+    if self._device_initialized:
+      return
+    self._adb.PushIfNeeded(
+        self._device_forwarder_path_on_host,
+        Forwarder._DEVICE_FORWARDER_FOLDER)
+    (exit_code, output) = self._adb.GetShellCommandStatusAndOutput(
+        '%s %s %s' % (Forwarder._LD_LIBRARY_PATH, tool.GetUtilWrapper(),
+                      Forwarder._DEVICE_FORWARDER_PATH))
+    if exit_code != 0:
+      raise Exception(
+          'Failed to start device forwarder:\n%s' % '\n'.join(output))
+    self._device_initialized = True
 
-    Note that Forwarder is a singleton therefore this constructor should be
-    called only once.
+  def UnmapDevicePort(self, device_port):
+    """Unmaps a previously forwarded device port.
 
     Args:
-      build_type: 'Release' or 'Debug'
-      tool: Tool class to use to get wrapper, if necessary, for executing the
-            forwarder (see valgrind_tools.py).
+      device_port: A previously forwarded port (through Run()).
     """
-    assert not Forwarder._instance
-    self._build_type = build_type
-    self._tool = tool
-    self._initialized_devices = set()
-    self._device_to_host_port_map = dict()
-    self._host_to_device_port_map = dict()
-    self._host_forwarder_path = _MakeBinaryPath(
-        self._build_type, 'host_forwarder')
-    if not os.path.exists(self._host_forwarder_path):
-      self._build_type = 'Release' if self._build_type == 'Debug' else 'Debug'
-      self._host_forwarder_path = _MakeBinaryPath(
-          self._build_type, 'host_forwarder')
-      assert os.path.exists(
-          self._host_forwarder_path), 'Please build forwarder2'
-    self._device_forwarder_path_on_host = os.path.join(
-        cmd_helper.OutDirectory.get(), self._build_type, 'forwarder_dist')
-    self._InitHostLocked()
-
-  @staticmethod
-  def _UnmapDevicePortLocked(device_port, adb):
-    """Internal method used by UnmapDevicePort().
+    with self._lock:
+      self._UnmapDevicePortInternalLocked(device_port)
 
-    Note that the global lock must be acquired before calling this method.
-    """
-    instance = Forwarder._GetInstanceLocked(None, None)
-    serial = adb.Adb().GetSerialNumber()
-    serial_with_port = (serial, device_port)
-    if not serial_with_port in instance._device_to_host_port_map:
-      logging.error('Trying to unmap non-forwarded port %d' % device_port)
+  def _UnmapDevicePortInternalLocked(self, device_port):
+    if not device_port in self._device_to_host_port_map:
       return
-    redirection_command = ['--serial-id=' + serial, '--unmap', str(device_port)]
+    redirection_command = [
+        '--serial-id=' + self._adb.Adb().GetSerialNumber(), '--unmap',
+        str(device_port)]
     (exit_code, output) = cmd_helper.GetCmdStatusAndOutput(
-        [instance._host_forwarder_path] + redirection_command)
+        [self._host_forwarder_path] + redirection_command)
     if exit_code != 0:
       logging.error('%s exited with %d:\n%s' % (
-          instance._host_forwarder_path, exit_code, '\n'.join(output)))
-    host_port = instance._device_to_host_port_map[serial_with_port]
-    del instance._device_to_host_port_map[serial_with_port]
-    del instance._host_to_device_port_map[host_port]
+          self._host_forwarder_path, exit_code, '\n'.join(output)))
+    host_port = self._device_to_host_port_map[device_port]
+    del self._device_to_host_port_map[device_port]
+    del self._host_to_device_port_map[host_port]
 
   @staticmethod
-  def _GetPidForLock():
-    """Returns the PID used for host_forwarder initialization.
-
-    In case multi-process sharding is used, the PID of the "sharder" is used.
-    The "sharder" is the initial process that forks that is the parent process.
-    By default, multi-processing is not used. In that case the PID of the
-    current process is returned.
-    """
-    use_multiprocessing = Forwarder._MULTIPROCESSING_ENV_VAR in os.environ
-    return os.getppid() if use_multiprocessing else os.getpid()
-
-  def _InitHostLocked(self):
-    """Initializes the host forwarder daemon.
-
-    Note that the global lock must be acquired before calling this method. This
-    method kills any existing host_forwarder process that could be stale.
-    """
-    # See if the host_forwarder daemon was already initialized by a concurrent
-    # process or thread (in case multi-process sharding is not used).
-    pid_for_lock = Forwarder._GetPidForLock()
-    fd = os.open(Forwarder._LOCK_PATH, os.O_RDWR | os.O_CREAT)
-    with os.fdopen(fd, 'r+') as pid_file:
-      pid_with_start_time = pid_file.readline()
-      if pid_with_start_time:
-        (pid, process_start_time) = pid_with_start_time.split(':')
-        if pid == str(pid_for_lock):
-          if process_start_time == str(_GetProcessStartTime(pid_for_lock)):
-            return
-      self._KillHostLocked()
-      pid_file.seek(0)
-      pid_file.write(
-          '%s:%s' % (pid_for_lock, str(_GetProcessStartTime(pid_for_lock))))
-
-  def _InitDeviceLocked(self, adb, tool):
-    """Initializes the device_forwarder daemon for a specific device (once).
-
-    Note that the global lock must be acquired before calling this method. This
-    method kills any existing device_forwarder daemon on the device that could
-    be stale, pushes the latest version of the daemon (to the device) and starts
-    it.
-
-    Args:
-      adb: An AndroidCommands instance.
-      tool: Tool class to use to get wrapper, if necessary, for executing the
-            forwarder (see valgrind_tools.py).
-    """
-    device_serial = adb.Adb().GetSerialNumber()
-    if device_serial in self._initialized_devices:
-      return
-    Forwarder._KillDeviceLocked(adb, tool)
-    adb.PushIfNeeded(
-        self._device_forwarder_path_on_host,
-        Forwarder._DEVICE_FORWARDER_FOLDER)
-    (exit_code, output) = adb.GetShellCommandStatusAndOutput(
-        '%s %s %s' % (Forwarder._LD_LIBRARY_PATH, tool.GetUtilWrapper(),
-                      Forwarder._DEVICE_FORWARDER_PATH))
-    if exit_code != 0:
-      raise Exception(
-          'Failed to start device forwarder:\n%s' % '\n'.join(output))
-    self._initialized_devices.add(device_serial)
-
-  def _KillHostLocked(self):
+  def KillHost(build_type='Debug'):
     """Kills the forwarder process running on the host.
 
-    Note that the global lock must be acquired before calling this method.
+    Args:
+      build_type: 'Release' or 'Debug' (default='Debug')
     """
     logging.info('Killing host_forwarder.')
+    host_forwarder_path = _MakeBinaryPath(build_type, 'host_forwarder')
+    if not os.path.exists(host_forwarder_path):
+      host_forwarder_path = _MakeBinaryPath(
+          'Release' if build_type == 'Debug' else 'Debug', 'host_forwarder')
+    assert os.path.exists(host_forwarder_path), 'Please build forwarder2'
     (exit_code, output) = cmd_helper.GetCmdStatusAndOutput(
-        [self._host_forwarder_path, '--kill-server'])
+        [host_forwarder_path, '--kill-server'])
     if exit_code != 0:
       (exit_code, output) = cmd_helper.GetCmdStatusAndOutput(
-          ['pkill', '-9', 'host_forwarder'])
+          ['pkill', 'host_forwarder'])
       if exit_code != 0:
         raise Exception('%s exited with %d:\n%s' % (
-              self._host_forwarder_path, exit_code, '\n'.join(output)))
+              host_forwarder_path, exit_code, '\n'.join(output)))
 
   @staticmethod
-  def _KillDeviceLocked(adb, tool):
+  def KillDevice(adb, tool):
     """Kills the forwarder process running on the device.
 
-    Note that the global lock must be acquired before calling this method.
-
     Args:
       adb: Instance of AndroidCommands for talking to the device.
       tool: Wrapper tool (e.g. valgrind) that can be used to execute the device
@@ -320,3 +180,14 @@ class Forwarder(object):
       pids = adb.ExtractPid('device_forwarder')
       if pids:
         raise Exception('Timed out while killing device_forwarder')
+
+  def DevicePortForHostPort(self, host_port):
+    """Returns the device port that corresponds to a given host port."""
+    with self._lock:
+      return self._host_to_device_port_map.get(host_port)
+
+  def Close(self):
+    """Releases the previously forwarded ports."""
+    with self._lock:
+      for device_port in self._device_to_host_port_map.copy():
+        self._UnmapDevicePortInternalLocked(device_port)
diff --git a/build/android/pylib/host_driven/python_test_sharder.py b/build/android/pylib/host_driven/python_test_sharder.py
index 17539d1f..d6475fd 100644
--- a/build/android/pylib/host_driven/python_test_sharder.py
+++ b/build/android/pylib/host_driven/python_test_sharder.py
@@ -122,7 +122,7 @@ class PythonTestSharder(object):
     final_results = base_test_result.TestRunResults()
     tests_to_run = self.tests
 
-    Forwarder.UseMultiprocessing()
+    Forwarder.KillHost()
 
     for retry in xrange(self.retries):
       logging.warning('Try %d of %d', retry + 1, self.retries)
diff --git a/build/android/pylib/instrumentation/test_runner.py b/build/android/pylib/instrumentation/test_runner.py
index be46a1a..dcf3d20 100644
--- a/build/android/pylib/instrumentation/test_runner.py
+++ b/build/android/pylib/instrumentation/test_runner.py
@@ -154,13 +154,11 @@ class TestRunner(base_test_runner.BaseTestRunner):
     http_server_ports = self.LaunchTestHttpServer(
         os.path.join(constants.DIR_SOURCE_ROOT), self._lighttp_port)
     if self.ports_to_forward:
-      self.ForwardPorts([(port, port) for port in self.ports_to_forward])
+      self.StartForwarder([(port, port) for port in self.ports_to_forward])
     self.flags.AddFlags(['--enable-test-intents'])
 
   def TearDown(self):
     """Cleans up the test harness and saves outstanding data from test run."""
-    if self.ports_to_forward:
-      self._UnmapPorts([(port, port) for port in self.ports_to_forward])
     super(TestRunner, self).TearDown()
 
   def TestSetup(self, test):
@@ -174,7 +172,7 @@ class TestRunner(base_test_runner.BaseTestRunner):
     self.tool.SetupEnvironment()
 
     # Make sure the forwarder is still running.
-    self._RestartHttpServerForwarderIfNecessary()
+    self.RestartHttpServerForwarderIfNecessary()
 
   def _IsPerfTest(self, test):
     """Determines whether a test is a performance test.