build_scan: Raise ValueError on URL fetch error

scripts/slave/build_scan.py

Index: scripts/slave/build_scan.py
diff --git a/scripts/slave/build_scan.py b/scripts/slave/build_scan.py
index b73c995e079b699407edbf18129903363a6438c4..e33b3bd0b3cc6cc48d4146ae91c1aa725899cda2 100755
--- a/scripts/slave/build_scan.py
+++ b/scripts/slave/build_scan.py
@@ -236,10 +236,19 @@ def get_options():
 
 
 def get_updated_builds(masters, build_db, parallelism):
-  new_builds, master_jsons = find_new_builds_per_master(masters, build_db)
-  build_jsons = get_build_jsons(new_builds, parallelism)
-  propagate_build_json_to_db(build_db, build_jsons)
-  return master_jsons, build_jsons
+  try:
+    new_builds, master_jsons = find_new_builds_per_master(masters, build_db)
+    build_jsons = get_build_jsons(new_builds, parallelism)
+    propagate_build_json_to_db(build_db, build_jsons)
+    return master_jsons, build_jsons
+
+  # Catch this and raise a ValueError because this can be called from
+  # mulitprocessing, which can't pickle SSLContext objects, which apparently are
+  # properties of urllib2.URLError (it seems).
+  except (urllib2.URLError, IOError) as f:
+    msg = "Error encountered during URL Fetch: %s" % f
+    logging.error(msg)
+    raise ValueError(msg)
 
 
 def main():