Update parallel_emerge to use no-env-update feature which skips env_update.

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 309 matching lines @@
     # is quite useful: it checks to make sure that we don't have multiple
     # packages that own the same file. The collision-protect feature is more
     # 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:
+      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     # Check whether our portage tree is out of date.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
     # make_chroot. In that case, portage applies a bunch of global updates
     # here. Once the updates are finished, we need to commit any changes
@@ skipping 968 matching lines @@
     new_world_pkgs = []
     root = emerge.settings["ROOT"]
     final_db = emerge.depgraph._dynamic_config.mydbapi[root]
     for pkg in emerge.cmdline_packages:
       for db_pkg in final_db.match_pkgs(pkg):
         print "Adding %s to world" % db_pkg.cp
         new_world_pkgs.append(db_pkg.cp)
     if new_world_pkgs:
       world_set.update(new_world_pkgs)
 
+  # Update environment (library cache, symlinks, etc.)
+  if deps.board and "--pretend" not in emerge.opts:
+    portage.env_update()
+
   print "Done"
 
 if __name__ == "__main__":
   main()