base/spin_wait.h

   1 // Copyright (c) 2011 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/threading/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       base::PlatformThread::Sleep(base::TimeDelta::FromMilliseconds(50)); \
  48     } \
  49   } while (0)
  50
  51 #endif  // BASE_SPIN_WAIT_H_