| # Copyright 2015 The Chromium Authors. All rights reserved. |
| # Use of this source code is governed by a BSD-style license that can be |
| # found in the LICENSE file. |
| |
| import threading |
| |
| |
| class WeakConstant(object): |
| """A thread-safe, lazily initialized object. |
| |
| This does not support modification after initialization. The intended |
| constant nature of the object is not enforced, though, hence the "weak". |
| """ |
| |
| def __init__(self, initializer): |
| self._initialized = False |
| self._initializer = initializer |
| self._lock = threading.Lock() |
| self._val = None |
| |
| def read(self): |
| """Get the object, creating it if necessary.""" |
| if self._initialized: |
| return self._val |
| with self._lock: |
| if not self._initialized: |
| self._val = self._initializer() |
| self._initialized = True |
| return self._val |
