Bug 955888. Part 1: Add ChaosMode.h base functionality. r=waldo

--HG--
extra : rebase_source : e892a951a3d3951e70e00f0b51046b744140eeee

mfbt/ChaosMode.h

@@ -0,0 +1,41 @@
+/* -*- 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 <stdint.h>
+#include <stdlib.h>
+
+namespace mozilla {
+
+/**
+ * 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 bool isActive()
+    {
+      // Flip this to true to activate chaos mode
+      return false;
+    }
+
+    /**
+     * 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)
+    {
+      return uint32_t(rand()) % aBound;
+    }
+};
+
+} /* namespace mozilla */
+
+#endif /* mozilla_ChaosMode_h */

mfbt/moz.build

@@ -18,6 +18,7 @@ EXPORTS.mozilla = [
     'Attributes.h',
     'BloomFilter.h',
     'Casting.h',
+    'ChaosMode.h',
     'Char16.h',
     'CheckedInt.h',
     'Compiler.h',