[Telemetry] Terminate any dangling subprocesses

tools/telemetry/telemetry/util/global_hooks.py

 # Copyright 2014 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.
 
 """Hooks that apply globally to all scripts that import or use Telemetry."""
 
+import atexit
 import os
 import signal
 import sys
 
+from telemetry.core import platform
 from telemetry.core import util
 from telemetry.util import exception_formatter
 
 
 def InstallHooks():
   RemoveAllStalePycFiles(util.GetTelemetryDir())
   RemoveAllStalePycFiles(util.GetBaseDir())
   InstallUnhandledExceptionFormatter()
   InstallStackDumpOnSigusr1()
   InstallTerminationHook()
+  InstallAtExitHook()
 
 
 def RemoveAllStalePycFiles(base_dir):
   """Scan directories for old .pyc files without a .py file and delete them."""
   for dirname, _, filenames in os.walk(base_dir):
     if '.svn' in dirname or '.git' in dirname:
       continue
     for filename in filenames:
       root, ext = os.path.splitext(filename)
       if ext != '.pyc':
@@ skipping 33 matching lines @@
   signal.signal(signal.SIGUSR1, PrintDiagnostics)
 
 
 def InstallTerminationHook():
   """Catch SIGTERM, print a stack trace, and exit."""
   def PrintStackAndExit(sig, stack_frame):
     exception_string = 'Received signal %s, exiting' % sig
     exception_formatter.PrintFormattedFrame(stack_frame, exception_string)
     sys.exit(-1)
   signal.signal(signal.SIGTERM, PrintStackAndExit)
+
+
+def InstallAtExitHook():
+  """Ensure all subprocesses are killed.
+
+  Subprocesses should never outlive Telemetry. If they do, they can cause
+  hangs on the builbots.
+  """
+  # TODO(tonyg): Find a way to do something similar on Windows.
+  if platform.GetHostPlatform().GetOSName() == 'win':
+    return
+
+  # Create new process group and become its leader.
+  os.setpgrp()
+
+  # At exit, terminate everything in the group.
+  def KillGroup():
+    # Ignore the TERM we're about to get.
+    signal.signal(signal.SIGTERM, signal.SIG_IGN)
+    os.killpg(0, signal.SIGTERM)
+  atexit.register(KillGroup)