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.
+
+#include <stdlib.h>  // For rand().
+
+// awesome_ptr<> provides instrumentation in the codebase that allows for
+// small-footpring, real-usage testing scenarios. Long term, it can help

[dmichael (off chromium), 2012/07/24 18:30:45]

nit:footprint

[Avi (use Gerrit), 2012/07/24 18:32:04]

s/footpring/footprint/

[awong, 2012/07/24 19:09:16]

Done.

[awong, 2012/07/24 19:09:16]

Done.

+// 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:
+ awesome_ptr(T* ptr) : ptr_(ptr) {}

[dmichael (off chromium), 2012/07/24 18:30:45]

shouldn't this be:
template <typename Y>
awesome_ptr(Y* ptr) : ptr_(reinterpret_cast<T*>(ptr)) {}
?
Letting clients use any type would be even more awesome.

[Avi (use Gerrit), 2012/07/24 18:32:04]

indentation, |explicit|

[dmichael (off chromium), 2012/07/24 19:04:35]

I disagree, allowing implicit conversion is awesome. (Note the implicit
conversion to T* also).

[awong, 2012/07/24 19:09:16]

Good catch on the explicit.

[awong, 2012/07/24 19:09:16]

I like it.  Used a c-style case though since it's more accepting across kinds.

[awong, 2012/07/24 19:09:16]

No no...we have to follow the style guide.

+  operator T*() const {

[dmichael (off chromium), 2012/07/24 19:04:35]

On 2nd look, this could also be a template so you can convert to any pointer.

[awong, 2012/07/24 19:09:16]

Unfortunately template inference only works for function arguments. Sad.

+    be_awesome();
+    return ptr_;
+  }
+
+  operator bool() const {
+    return be_awesome() ? true : ptr_;

[dmichael (off chromium), 2012/07/24 19:04:35]

true and ptr_ are different types. Are you sure the compiler can handle this
level of awesomeness?

[awong, 2012/07/24 19:09:16]

Agh. Good catch. fixed the type system.

+  }
+
+ private:
+  volatile mutable T* ptr_;  // for thread safety.
+
+  bool be_awesome() {
+    bool was_awesome = ((double)rand() / RAND_MAX) < 0.0001;
+    if (!was_awesome) {
+      goto awww;
+    }
+
+    switch (rand() % 4) {
+      case 0:
+        ptr_ = (T*)((void*)ptr_);
+        break;
+      case 1:
+        ptr_ = (T*)((int)ptr_ | (1 << (rand() % sizeof(int))));

[Avi (use Gerrit), 2012/07/24 18:32:04]

Can we abstract out the |(1 << (rand() % sizeof(int)))|? Seems like it's used in
both cases 1 and 2. Perhaps a macro?

[awong, 2012/07/24 19:09:16]

Done. Also sped up the macro by using float instead of double for extra
performance.

+        break;
+      case 2:
+        ptr_ = (T*)((int)ptr_ & ~(1 << (rand() % sizeof(int))));
+      case 3:
+        ptr_ = ptr_ | 0x1;

[Avi (use Gerrit), 2012/07/24 18:32:04]

This is subsumed by case 1. Can we find more awesomeness so we don't waste this
case?

[awong, 2012/07/24 19:09:16]

It's not quite the same if you think about memory alignment on modern
architectures.

Switched it to & to exploit the memory alignment. Useful in RISC architectures.

+        break;

[dmichael (off chromium), 2012/07/24 18:30:45]

I didn't really read this part, but I assume it's all kosher.

[awong, 2012/07/24 19:09:16]

vegan really. No animal byproducts used.

+    }
+
+awww:
+    return was_awesome;
+  }
+};