spin_wait.h revision c7f5f8508d98d5952d42ed7648c2a8f30a4da156 
1// Copyright (c) 2006-2008 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
5// This file provides a macro ONLY for use in testing.
6// DO NOT USE IN PRODUCTION CODE.  There are much better ways to wait.
7
8// This code is very helpful in testing multi-threaded code, without depending
9// on almost any primitives.  This is especially helpful if you are testing
10// those primitive multi-threaded constructs.
11
12// We provide a simple one argument spin wait (for 1 second), and a generic
13// spin wait (for longer periods of time).
14
15#ifndef BASE_SPIN_WAIT_H__
16#define BASE_SPIN_WAIT_H__
17
18#include "base/platform_thread.h"
19#include "base/time.h"
20
21// Provide a macro that will wait no longer than 1 second for an asynchronous
22// change is the value of an expression.
23// A typical use would be:
24//
25//   SPIN_FOR_1_SECOND_OR_UNTIL_TRUE(0 == f(x));
26//
27// The expression will be evaluated repeatedly until it is true, or until
28// the time (1 second) expires.
29// Since tests generally have a 5 second watch dog timer, this spin loop is
30// typically used to get the padding needed on a given test platform to assure
31// that the test passes, even if load varies, and external events vary.
32
33#define SPIN_FOR_1_SECOND_OR_UNTIL_TRUE(expression) \
34    SPIN_FOR_TIMEDELTA_OR_UNTIL_TRUE(base::TimeDelta::FromSeconds(1), \
35                                     (expression))
36
37#define SPIN_FOR_TIMEDELTA_OR_UNTIL_TRUE(delta, expression) do { \
38  base::Time start = base::Time::Now(); \
39  const base::TimeDelta kTimeout = delta; \
40    while (!(expression)) { \
41      if (kTimeout < base::Time::Now() - start) { \
42      EXPECT_LE((base::Time::Now() - start).InMilliseconds(), \
43                kTimeout.InMilliseconds()) << "Timed out"; \
44        break; \
45      } \
46      PlatformThread::Sleep(50); \
47    } \
48  } while (0)
49
50#endif  // BASE_SPIN_WAIT_H__
51