Stop choosing $TMPDIR as a safe place to create hardlinks on OSX.

client/run_isolated.py

 #!/usr/bin/env python
 # Copyright 2012 The LUCI Authors. All rights reserved.
 # Use of this source code is governed by the Apache v2.0 license that can be
 # found in the LICENSE file.
 
 """Reads a .isolated, creates a tree of hardlinks and runs the test.
 
 To improve performance, it keeps a local cache. The local cache can safely be
 deleted.
 
@@ skipping 70 matching lines @@
   package.add_directory(os.path.join(BASE_DIR, 'third_party'))
   package.add_directory(os.path.join(BASE_DIR, 'utils'))
   return package
 
 
 def make_temp_dir(prefix, root_dir=None):
   """Returns a temporary directory.
 
   If root_dir is given and /tmp is on same file system as root_dir, uses /tmp.
   Otherwise makes a new temp directory under root_dir.
+
+  Except on OSX, because it's dangerous to create hardlinks in $TMPDIR on OSX!
+  /System/Library/LaunchDaemons/com.apple.bsd.dirhelper.plist runs every day at
+  3:35am and deletes all files older than 3 days in $TMPDIR, but hardlinks do
+  not have the inode modification time updated, so they tend to be old, thus
+  they get deleted.
   """
   base_temp_dir = None
-  if (root_dir and
-      not file_path.is_same_filesystem(
-        root_dir, unicode(tempfile.gettempdir()))):
+  real_temp_dir = unicode(tempfile.gettempdir())
+  if sys.platform == 'darwin':
+    # Nope! Nope! Nope!
+    assert root_dir, 'It is unsafe to create hardlinks in $TMPDIR'
+    base_temp_dir = root_dir
+  elif root_dir and not file_path.is_same_filesystem(root_dir, real_temp_dir):
     base_temp_dir = root_dir
   return unicode(tempfile.mkdtemp(prefix=prefix, dir=base_temp_dir))
 
 
 def change_tree_read_only(rootdir, read_only):
   """Changes the tree read-only bits according to the read_only specification.
 
   The flag can be 0, 1 or 2, which will affect the possibility to modify files
   and create or delete files.
   """
@@ skipping 428 matching lines @@
     assert storage.hash_algo == cache.hash_algo
     return run_tha_test(
         options.isolated, storage, cache, options.leak_temp_dir, options.json,
         options.root_dir, options.hard_timeout, options.grace_period, args)
 
 
 if __name__ == '__main__':
   # Ensure that we are always running with the correct encoding.
   fix_encoding.fix_encoding()
   sys.exit(main(sys.argv[1:]))