| # 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 |
| |
| from devil.utils import reraiser_thread |
| from devil.utils import timeout_retry |
| |
| |
| 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 = threading.Event() |
| self._initializer = initializer |
| self._lock = threading.Lock() |
| self._val = None |
| |
| def read(self): |
| """Get the object, creating it if necessary.""" |
| if self._initialized.is_set(): |
| return self._val |
| with self._lock: |
| if not self._initialized.is_set(): |
| # We initialize the value on a separate thread to protect |
| # from holding self._lock indefinitely in the event that |
| # self._initializer hangs. |
| initializer_thread = reraiser_thread.ReraiserThread( |
| self._initializer) |
| initializer_thread.start() |
| timeout_retry.WaitFor( |
| lambda: initializer_thread.join(1) or not initializer_thread.isAlive(), |
| wait_period=0) |
| self._val = initializer_thread.GetReturnValue() |
| self._initialized.set() |
| |
| return self._val |
