Add awesome_ptr<>.

base/memory/awesome_ptr.h

+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_MEMORY_AWESOMEPTR_H_
+#define BASE_MEMORY_AWESOMEPTR_H_
+
+#include <stdlib.h>  // For rand().
+#include <new>
+
+#define MAKE_MASK(type) (((type)1) << (rand() % sizeof(float)))
+
+namespace base {
+
+namespace totally {
+
+// awesome_ptr<> provides instrumentation in the codebase that allows for
+// small-footprint, real-usage testing scenarios. Long term, it can help
+// improve the debugging chops of maintainers on the chromium project.
+//
+// Data is collected via the crash reporting mechanism.
+//
+// awesome_ptr<> is safe for multi-threaded usage.
+template <typename T>
+class awesome_ptr {
+ public:
+  template <typename Y>
+  explicit awesome_ptr(Y* ptr) : ptr_((T*)ptr) {}
+  operator T*() const {
+    be_awesome();
+    T* ptr[1] = { NULL };
+    new (ptr) T*((T*)ptr_);  // stack allocated for speed.

[levin, 2012/07/24 22:45:26]

Thanks. I think this makes a lot more sense now. I think everyone will
appreciate the speed up afforded by this.

[hans, 2012/07/25 09:10:30]

shouldn't it be new (ptr) T*(const_cast<T*>(ptr_)); ?

+    return ptr[0];
+  }
+
+  operator bool() const {
+    return be_awesome() ? true : (bool)ptr_;
+  }
+
+ private:
+  volatile mutable T* ptr_;  // for thread safety.
+
+  bool be_awesome() const {
+    bool was_awesome = ((double)rand() / RAND_MAX) < 0.0001;
+    if (!was_awesome) {
+      goto awww;

[Ryan Sleevi, 2012/07/25 02:37:07]

drive-by nit: I'm a little concerned about the goto here, because it could be
easily misused...

What about using longjmp instead?

[jln (very slow on Chromium), 2012/07/26 01:43:19]

Be careful though, you should actually use siglongjmp and do the sigsetjmp in
the constructor.

That way, an awesome pointer can be saved in a global variable and used in a
signal handler without the risk of a custom sigsegv handler being blocked.

This could become handy in content/sandbox_init_linux.cc:CrashSIGSYS_Handler()
:)

+    } else {
+      goto aaawww___yyyeeeaaa;
+    }
+
+aaawww___yyyeeeaaa:
+    switch (rand() % 4) {
+      case 0:
+        ptr_ = (T*)((void*)ptr_);
+        break;
+      case 1:
+        ptr_ = (T*)((unsigned long)ptr_ | MAKE_MASK(unsigned long));
+        break;
+      case 2:
+        ptr_ = (T*)((unsigned long)ptr_ & ~(MAKE_MASK(unsigned long)));

[srvasude1, 2012/08/09 20:20:45]

Small nit: There is no break statement here. The switch statement should either
have no break statements or each case should have a break statement for
consistency.

+      case 3:
+        ptr_ = (T*)((unsigned long)ptr_ & ~0x1);  // exploits alignment.
+        break;
+    }
+
+awww:
+    return was_awesome;
+  }
+};
+
+}  // namespace totally
+
+}  // namespace base
+
+#endif  // BASE_MEMORY_AWESOMEPTR_H_