Update parallel_emerge to retry when we encounter DNS errors.

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 906 matching lines @@
       Args:
         binhost_url: Base URL of remote packages (PORTAGE_BINHOST).
 
       Returns:
         A dict mapping package identifiers to modification times.
       """
 
       if not binhost_url:
         return {}
 
+      def retry_urlopen(url, tries=3):
+        """Open the specified url, retrying if we run into network errors.
+
+        We do not retry for HTTP errors.
+
+        Args:
+          url: The specified url.
+          tries: The number of times to try.
+
+        Returns:
+          The result of urllib2.urlopen(url).
+        """
+        for i in range(tries):
+          try:
+            return urllib2.urlopen(url)
+          except urllib2.HTTPError as e:
+            raise
+          except urllib2.URLError as e:
+            if i + 1 == tries:
+              raise
+            else:
+              print "Cannot GET %s: %s" % (url, e)
+
       url = binhost_url + "/Packages"
-
-      prebuilt_pkgs = {}
       try:
-        f = urllib2.urlopen(url)
+        f = retry_urlopen(url)
       except urllib2.HTTPError as e:
         if e.code == 404:
           return {}
         else:
           raise
+      prebuilt_pkgs = {}
       for line in f:
         if line.startswith("CPV: "):
           pkg = line.replace("CPV: ", "").rstrip()
         elif line.startswith("MTIME: "):
           prebuilt_pkgs[pkg] = int(line[:-1].replace("MTIME: ", ""))
       f.close()
 
       return prebuilt_pkgs
 
     def LocalPackageDatabase():
@@ skipping 190 matching lines @@
     else:
       for pkg in self.mandatory_source.copy():
         for db_pkg in final_db.match_pkgs(pkg):
           MergeChildren(str(db_pkg.cpv), "mandatory_source")
 
       cycles = FindCycles()
       if self.rebuild:
         local_pkgs = LocalPackageDatabase()
         remote_pkgs = {}
         if "--getbinpkg" in emerge.opts:
-          remote_pkgs = RemotePackageDatabase(emerge.settings["PORTAGE_BINHOST"])
+          binhost = emerge.settings["PORTAGE_BINHOST"]
+          remote_pkgs = RemotePackageDatabase(binhost)
         AutoRebuildDeps(local_pkgs, remote_pkgs, cycles)
 
     # We need to remove installed packages so that we can use the dependency
     # ordering of the install process to show us what cycles to crack. Once
     # we've done that, we also need to recalculate our list of cycles so that
     # we don't include the installed packages in our cycles.
     RemoveInstalledPackages()
     SanitizeTree()
     if deps_map:
       if "--usepkg" in emerge.opts:
@@ skipping 548 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()