mfbt/ChaosMode.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef mozilla_ChaosMode_h
   8 #define mozilla_ChaosMode_h
   9
  10 #include "mozilla/Atomics.h"
  11 #include "mozilla/EnumSet.h"
  12
  13 #include <stdint.h>
  14 #include <stdlib.h>
  15
  16 namespace mozilla {
  17
  18 enum ChaosFeature {
  19   None = 0x0,
  20   // Altering thread scheduling.
  21   ThreadScheduling = 0x1,
  22   // Altering network request scheduling.
  23   NetworkScheduling = 0x2,
  24   // Altering timer scheduling.
  25   TimerScheduling = 0x4,
  26   // Read and write less-than-requested amounts.
  27   IOAmounts = 0x8,
  28   // Iterate over hash tables in random order.
  29   HashTableIteration = 0x10,
  30   // Randomly refuse to use cached version of image (when allowed by spec).
  31   ImageCache = 0x20,
  32   // Delay dispatching threads to encourage dispatched tasks to run.
  33   TaskDispatching = 0x40,
  34   // Delay task running to encourage sending threads to run.
  35   TaskRunning = 0x80,
  36   Any = 0xffffffff,
  37 };
  38
  39 namespace detail {
  40 extern MFBT_DATA Atomic<uint32_t, SequentiallyConsistent> gChaosModeCounter;
  41 extern MFBT_DATA ChaosFeature gChaosFeatures;
  42 }  // namespace detail
  43
  44 /**
  45  * When "chaos mode" is activated, code that makes implicitly nondeterministic
  46  * choices is encouraged to make random and extreme choices, to test more
  47  * code paths and uncover bugs.
  48  */
  49 class ChaosMode {
  50  public:
  51   static void SetChaosFeature(ChaosFeature aChaosFeature) {
  52     detail::gChaosFeatures = aChaosFeature;
  53   }
  54
  55   static bool isActive(ChaosFeature aFeature) {
  56     if (detail::gChaosModeCounter > 0) {
  57       return true;
  58     }
  59     return detail::gChaosFeatures & aFeature;
  60   }
  61
  62   /**
  63    * Increase the chaos mode activation level. An equivalent number of
  64    * calls to leaveChaosMode must be made in order to restore the original
  65    * chaos mode state. If the activation level is nonzero all chaos mode
  66    * features are activated.
  67    */
  68   static void enterChaosMode() { detail::gChaosModeCounter++; }
  69
  70   /**
  71    * Decrease the chaos mode activation level. See enterChaosMode().
  72    */
  73   static void leaveChaosMode() {
  74     MOZ_ASSERT(detail::gChaosModeCounter > 0);
  75     detail::gChaosModeCounter--;
  76   }
  77
  78   /**
  79    * Returns a somewhat (but not uniformly) random uint32_t < aBound.
  80    * Not to be used for anything except ChaosMode, since it's not very random.
  81    */
  82   static uint32_t randomUint32LessThan(uint32_t aBound) {
  83     MOZ_ASSERT(aBound != 0);
  84     return uint32_t(rand()) % aBound;
  85   }
  86 };
  87
  88 } /* namespace mozilla */
  89
  90 #endif /* mozilla_ChaosMode_h */