Mojo: Armed Watchers

mojo/public/cpp/bindings/lib/destruction_tracker.h

Index: mojo/public/cpp/bindings/lib/destruction_tracker.h
diff --git a/mojo/public/cpp/bindings/lib/destruction_tracker.h b/mojo/public/cpp/bindings/lib/destruction_tracker.h
new file mode 100644
index 0000000000000000000000000000000000000000..7508487faf005dddfdb4e92d4eba2af58d9bb8ac
--- /dev/null
+++ b/mojo/public/cpp/bindings/lib/destruction_tracker.h
@@ -0,0 +1,61 @@
+// Copyright 2017 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 MOJO_PUBLIC_CPP_BINDINGS_LIB_DELETION_TRACKER_H_

[yzshen1, 2017/03/03 00:03:50]

Please make it consistent with the file name.

[Ken Rockot(use gerrit already), 2017/03/03 00:37:05]

N/A - delete this code and used WeakPtrs instead per
https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/lTXF4ejhbnQ

+#define MOJO_PUBLIC_CPP_BINDINGS_LIB_DELETION_TRACKER_H_
+
+#include "base/macros.h"
+
+namespace mojo {
+
+// A helper which can be used to detect object deletion from within the object's
+// own methods.
+//
+// To use this, a class should declare a DestructionTracker as a data member
+// and guard any operation which might delete the owning object with a
+// stack-local instance of DestructionTracker::Flag, like so:
+//
+//   DestructionTracker::Flag was_destroyed(&destruction_tracker_);
+//   DoSomethingWhichMightDestroyThis();
+//   if (was_destroyed)
+//     return;  // Escape safely
+//   // Continue doing stuff to |this|.
+//
+// This mechanism supports multiple DestructionTracker::Flag instances nested
+// within the call stack so that methods which use it can be reentrant.
+class DestructionTracker {
+ public:
+  class Flag {
+   public:
+    explicit Flag(DestructionTracker* tracker);
+    ~Flag();
+
+    explicit operator bool() const { return was_destroyed_; }

[yzshen1, 2017/03/03 00:03:50]

can we use !tracker_ to indicate destructed?

[Ken Rockot(use gerrit already), 2017/03/03 00:37:05]

N/A

+
+   private:
+    friend class DestructionTracker;
+
+    void NotifyDestroyed();
+
+    DestructionTracker* tracker_;
+    Flag* const outer_flag_;
+    bool was_destroyed_ = false;
+
+    DISALLOW_COPY_AND_ASSIGN(Flag);
+  };
+
+  DestructionTracker();
+  ~DestructionTracker();
+
+ private:
+  void SetFlag(Flag* flag);
+
+  Flag* flag_ = nullptr;
+
+  DISALLOW_COPY_AND_ASSIGN(DestructionTracker);
+};
+
+}  // namespace mojo
+
+#endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_DELETION_TRACKER_H_