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