1# Copyright 2015 The Chromium Authors. All rights reserved.
2# Use of this source code is governed by a BSD-style license that can be
3# found in the LICENSE file.
4
5import threading
6
7
8class WeakConstant(object):
9  """A thread-safe, lazily initialized object.
10
11  This does not support modification after initialization. The intended
12  constant nature of the object is not enforced, though, hence the "weak".
13  """
14
15  def __init__(self, initializer):
16    self._initialized = False
17    self._initializer = initializer
18    self._lock = threading.Lock()
19    self._val = None
20
21  def read(self):
22    """Get the object, creating it if necessary."""
23    if self._initialized:
24      return self._val
25    with self._lock:
26      if not self._initialized:
27        self._val = self._initializer()
28        self._initialized = True
29    return self._val
30