base/spin_wait.h

// Copyright 2008, Google Inc.
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//
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// This file provides a macro ONLY for use in testing.
// DO NOT USE IN PRODUCTION CODE.  There are much better ways to wait.

// This code is very helpful in testing multi-threaded code, without depending
// on almost any primitives.  This is especially helpful if you are testing
// those primitive multi-threaded constructs.

// We provide a simple one argument spin wait (for 1 second), and a generic
// spin wait (for longer periods of time).

#ifndef BASE_SPIN_WAIT_H__
#define BASE_SPIN_WAIT_H__

#include "base/platform_thread.h"
#include "base/time.h"

// Provide a macro that will wait no longer than 1 second for an asynchronous
// change is the value of an expression.
// A typical use would be:
//
//   SPIN_FOR_1_SECOND_OR_UNTIL_TRUE(0 == f(x));
//
// The expression will be evaluated repeatedly until it is true, or until
// the time (1 second) expires.
// Since tests generally have a 5 second watch dog timer, this spin loop is
// typically used to get the padding needed on a given test platform to assure
// that the test passes, even if load varies, and external events vary.

#define SPIN_FOR_1_SECOND_OR_UNTIL_TRUE(expression) \
    SPIN_FOR_TIMEDELTA_OR_UNTIL_TRUE(TimeDelta::FromSeconds(1), (expression))

#define SPIN_FOR_TIMEDELTA_OR_UNTIL_TRUE(delta, expression) do { \
  Time start = Time::Now(); \
  const TimeDelta kTimeout = delta; \
    while(!(expression)) { \
      if (kTimeout < Time::Now() - start) { \
      EXPECT_LE((Time::Now() - start).InMilliseconds(), \
                kTimeout.InMilliseconds()) << "Timed out"; \
        break; \
      } \
      PlatformThread::Sleep(50); \
    } \
  } \
  while(0)

#endif  // BASE_SPIN_WAIT_H__