Temporary workaround to fix make_chroot --fast

parallel_emerge

 #!/usr/bin/python2.6
 # Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Program to run emerge in parallel, for significant speedup.
 
 Usage:
  ./parallel_emerge [--board=BOARD] [--workon=PKGS] [--no-workon-deps]
                    [emerge args] package"
@@ skipping 282 matching lines @@
       board_no_variant = self.board.split('_')[0]
       f = open(toolchain_path % (scripts_dir, board_no_variant))
       os.environ["CHOST"] = f.readline().strip()
       f.close()
 
       # Although CHROMEOS_ROOT isn't specific to boards, it's normally setup
       # inside emerge-${BOARD}, so we set it up here for compatibility. It
       # will be going away soon as we migrate to CROS_WORKON_SRCROOT.
       os.environ.setdefault("CHROMEOS_ROOT", os.environ["HOME"] + "/trunk")
 
-    # Modify the environment to disable locking.
-    os.environ["PORTAGE_LOCKS"] = "false"
+      # Modify the environment to disable locking by default.
+      # TODO(davidjames): This option can cause problems if packages muck
+      # with each other during the post-install step. There are a few host
+      # packages that do this, so we only do this environment modification for
+      # board builds.
+      os.environ.setdefault("PORTAGE_LOCKS", "false")
 
     # Turn off interactive delays
     os.environ["EBEEP_IGNORE"] = "1"
     os.environ["EPAUSE_IGNORE"] = "1"
     os.environ["UNMERGE_DELAY"] = "0"
 
     # Parse the emerge options.
     action, opts, cmdline_packages = parse_opts(emerge_args)
 
     # If we're installing to the board, we want the --root-deps option so that
@@ skipping 22 matching lines @@
     # strict, and less useful: it fails if it finds a conflicting file, even
     # if that file was created by an earlier ebuild that failed to install.
     #
     # We want to disable collision-protect here because we don't handle
     # failures during the merge step very well. Sometimes we leave old files
     # lying around and they cause problems, so for now we disable the flag.
     # TODO(davidjames): Look for a better solution.
     features = os.environ.get("FEATURES", "") + " -collision-protect"
 
     # If we're cross-compiling, updating the environment every time we install
-    # a package isn't necessary, and leads to race conditions. Do environment
-    # updates at the end, instead.
-    if self.board:
+    # a package isn't necessary, and leads to race conditions when
+    # PORTAGE_LOCKS is false. In this case, do environment updates at the end,
+    # instead.
+    if self.board and os.environ.get("PORTAGE_LOCKS") == "false":
       features = features + " no-env-update"
 
     os.environ["FEATURES"] = features
 
     # Now that we've setup the necessary environment variables, we can load the
     # emerge config from disk.
     settings, trees, mtimedb = load_emerge_config()
 
     # Check whether our portage tree is out of date. Typically, this happens
     # when you're setting up a new portage tree, such as in setup_board and
@@ skipping 1325 matching lines @@
   # If we already upgraded portage, we don't need to do so again. But we do
   # need to upgrade the rest of the packages. So we'll go ahead and do that.
   if portage_upgrade:
     args = sys.argv[1:] + ["--nomerge=sys-apps/portage"]
     os.execvp(os.path.realpath(sys.argv[0]), args)
 
   print "Done"
 
 if __name__ == "__main__":
   main()