Rename/re-comment tests and added new death tests for WeakPtr

base/memory/weak_ptr.h

Index: base/memory/weak_ptr.h
===================================================================
--- base/memory/weak_ptr.h	(revision 145398)
+++ base/memory/weak_ptr.h	(working copy)
@@ -8,14 +8,17 @@
 // reference counting is not a good fit.
 //
 // Thread-safety notes:
-// When you get a WeakPtr (from a WeakPtrFactory or SupportsWeakPtr),
-// the WeakPtr becomes bound to the current thread. You may only
-// dereference the WeakPtr on that thread. However, it is safe to
-// destroy the WeakPtr object on another thread.
-// Since a WeakPtr object may be destroyed on a background thread,
-// querying WeakPtrFactory's HasWeakPtrs() method can be racy.
+// When you get a WeakPtr (from a WeakPtrFactory or SupportsWeakPtr), the
+// WeakPtr becomes bound to the current thread. You may only dereference the
+// WeakPtr on that thread. However, it is safe to destroy the WeakPtr object
+// on another thread. Since a WeakPtr object may be destroyed on a background
+// thread, querying WeakPtrFactory's HasWeakPtrs() method can be racy.
+// On the other hand, the object that supports WeakPtr (extends
+// SupportsWeakPtr) will be bound to the first thread that creates a WeakPtr
+// pointing to it, and can not be deleted from other threads unless all
+// WeakPtrs are deleted. To work around of this, call

[Ryan Sleevi, 2012/07/10 00:06:44]

nit: To work around this

[kaiwang, 2012/07/10 22:21:19]

Done.

+// SupportsWeakPtr::DetachFromThread().

[Ryan Sleevi, 2012/07/10 00:06:44]

I'm not sure we should encourage calling DetachFromThread().

The behaviour being displayed is very much intentional - the WeakPtrFactory
should only disappear on the thread that is associated with all of the WeakPtrs.
The ThreadChecker that exists (and is used by DetachFromThread) is meant to
guard that.

Doing

Thread 1:
WeakPtr<Foo> foo = controller->AsWeakPtr();
controller->DetachFromThread();
thread_2->DeleteSoon(FROM_HERE, controller)

Is inherently dangerous, and it seems to be what the comment is suggesting.

[kaiwang, 2012/07/10 22:21:19]

Changed the wording.

 //
-//
 // A common alternative to weak pointers is to have the shared object hold a
 // list of all referrers, and then when the shared object is destroyed, it
 // calls a method on the referrers to tell them to drop their references.  This
@@ -225,7 +228,8 @@
   friend class WeakPtrFactory<T>;
 
   WeakPtr(const internal::WeakReference& ref, T* ptr)
-      : WeakPtrBase(ref), ptr_(ptr) {
+      : WeakPtrBase(ref),
+        ptr_(ptr) {
   }
 
   // This pointer is only valid when ref_.is_valid() is true.  Otherwise, its