1 files changed, 94 insertions, 0 deletions
diff --git a/mfbt/ChaosMode.h b/mfbt/ChaosMode.h
new file mode 100644
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+++ b/mfbt/ChaosMode.h
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+/* -*- 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 */