mfbt/ChaosMode.h
author Timothy Nikkel <tnikkel@gmail.com>
Sat, 02 Apr 2016 13:53:12 -0500
changeset 329300 9adc763aae7608252bb3e9df1ef7888da4f9f2ba
parent 284762 fe2800b80350314ab5cdab826f69f2837a4c3fd6
child 482768 44b62ee96921df348dff53cc505db58132eeba03
permissions -rw-r--r--
Bug 1260247. In chaos mode randomly decide to start a new image load even if the image is in the image cache when allowed by spec. r=seth If the image load is from the same document that cached the image we are required to use the cached version. Otherwise we should be free to ignore the cached version.

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef mozilla_ChaosMode_h
#define mozilla_ChaosMode_h

#include "mozilla/Atomics.h"
#include "mozilla/EnumSet.h"

#include <stdint.h>
#include <stdlib.h>

namespace mozilla {

enum ChaosFeature {
  None = 0x0,
  // Altering thread scheduling.
  ThreadScheduling = 0x1,
  // Altering network request scheduling.
  NetworkScheduling = 0x2,
  // Altering timer scheduling.
  TimerScheduling = 0x4,
  // Read and write less-than-requested amounts.
  IOAmounts = 0x8,
  // Iterate over hash tables in random order.
  HashTableIteration = 0x10,
  // Randomly refuse to use cached version of image (when allowed by spec).
  ImageCache = 0x20,
  Any = 0xffffffff,
};

namespace detail {
extern MFBT_DATA Atomic<uint32_t> gChaosModeCounter;
extern MFBT_DATA ChaosFeature gChaosFeatures;
} // namespace detail

/**
 * When "chaos mode" is activated, code that makes implicitly nondeterministic
 * choices is encouraged to make random and extreme choices, to test more
 * code paths and uncover bugs.
 */
class ChaosMode
{
public:
  static void SetChaosFeature(ChaosFeature aChaosFeature)
  {
    detail::gChaosFeatures = aChaosFeature;
  }

  static bool isActive(ChaosFeature aFeature)
  {
    if (detail::gChaosModeCounter > 0) {
      return true;
    }
    return detail::gChaosFeatures & aFeature;
  }

  /**
   * Increase the chaos mode activation level. An equivalent number of
   * calls to leaveChaosMode must be made in order to restore the original
   * chaos mode state. If the activation level is nonzero all chaos mode
   * features are activated.
   */
  static void enterChaosMode()
  {
    detail::gChaosModeCounter++;
  }

  /**
   * Decrease the chaos mode activation level. See enterChaosMode().
   */
  static void leaveChaosMode()
  {
    MOZ_ASSERT(detail::gChaosModeCounter > 0);
    detail::gChaosModeCounter--;
  }

  /**
   * Returns a somewhat (but not uniformly) random uint32_t < aBound.
   * Not to be used for anything except ChaosMode, since it's not very random.
   */
  static uint32_t randomUint32LessThan(uint32_t aBound)
  {
    MOZ_ASSERT(aBound != 0);
    return uint32_t(rand()) % aBound;
  }
};

} /* namespace mozilla */

#endif /* mozilla_ChaosMode_h */