spin_wait.h revision 3345a6884c488ff3a535c2c9acdd33d74b37e311 
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#pragma once
18
19#include "base/platform_thread.h"
20#include "base/time.h"
21
22// Provide a macro that will wait no longer than 1 second for an asynchronous
23// change is the value of an expression.
24// A typical use would be:
25//
26//   SPIN_FOR_1_SECOND_OR_UNTIL_TRUE(0 == f(x));
27//
28// The expression will be evaluated repeatedly until it is true, or until
29// the time (1 second) expires.
30// Since tests generally have a 5 second watch dog timer, this spin loop is
31// typically used to get the padding needed on a given test platform to assure
32// that the test passes, even if load varies, and external events vary.
33
34#define SPIN_FOR_1_SECOND_OR_UNTIL_TRUE(expression) \
35    SPIN_FOR_TIMEDELTA_OR_UNTIL_TRUE(base::TimeDelta::FromSeconds(1), \
36                                     (expression))
37
38#define SPIN_FOR_TIMEDELTA_OR_UNTIL_TRUE(delta, expression) do { \
39  base::TimeTicks start = base::TimeTicks::Now(); \
40  const base::TimeDelta kTimeout = delta; \
41    while (!(expression)) { \
42      if (kTimeout < base::TimeTicks::Now() - start) { \
43      EXPECT_LE((base::TimeTicks::Now() - start).InMilliseconds(), \
44                kTimeout.InMilliseconds()) << "Timed out"; \
45        break; \
46      } \
47      PlatformThread::Sleep(50); \
48    } \
49  } while (0)
50
51#endif  // BASE_SPIN_WAIT_H__
52