Revert 114494 - Remove BindStateHolder and have Bind() return a Callback<> object directly.

base/callback.h

Index: base/callback.h
===================================================================
--- base/callback.h	(revision 114494)
+++ base/callback.h	(working copy)
@@ -129,28 +129,29 @@
 // The Callback classes represent a generic function pointer. Internally,
 // it stores a refcounted piece of state that represents the target function
 // and all its bound parameters.  Each Callback specialization has a templated
-// constructor that takes an BindState<>*.  In the context of the constructor,
-// the static type of this BindState<> pointer uniquely identifies the
-// function it is representing, all its bound parameters, and a Run() method
-// that is capable of invoking the target.
+// constructor that takes an BindStateHolder<> object.  In the context of
+// the constructor, the static type of this BindStateHolder<> object
+// uniquely identifies the function it is representing, all its bound
+// parameters, and a DoInvoke() that is capable of invoking the target.
 //
-// Callback's constructor takes the BindState<>* that has the full static type
-// and erases the target function type as well as the types of the bound
-// parameters.  It does this by storing a pointer to the specific Run()
-// function, and upcasting the state of BindState<>* to a
-// BindStateBase*. This is safe as long as this BindStateBase pointer
-// is only used with the stored Run() pointer.
+// Callback's constructor is takes the BindStateHolder<> that has the
+// full static type and erases the target function type, and the bound
+// parameters.  It does this by storing a pointer to the specific DoInvoke()
+// function, and upcasting the state of BindStateHolder<> to a
+// BindStateBase. This is safe as long as this BindStateBase pointer
+// is only used with the stored DoInvoke() pointer.
 //
-// To BindState<> objects are created inside the Bind() functions.
-// These functions, along with a set of internal templates, are responsible for
+// To create BindStateHolder<> objects, we use the Bind() functions.
+// These functions, along with a set of internal templates, are reponsible for
 //
 //  - Unwrapping the function signature into return type, and parameters
 //  - Determining the number of parameters that are bound
-//  - Creating the BindState storing the bound parameters
+//  - Creating the storage for the bound parameters
 //  - Performing compile-time asserts to avoid error-prone behavior
-//  - Returning an Callback<> with an arity matching the number of unbound
-//    parameters and that knows the correct refcounting semantics for the
-//    target object if we are binding a method.
+//  - Returning an BindStateHolder<> with an DoInvoke() that has an arity
+//    matching the number of unbound parameters, and knows the correct
+//    refcounting semantics for the target object if we are binding a class
+//    method.
 //
 // The Bind functions do the above using type-inference, and template
 // specializations.
@@ -238,30 +239,27 @@
 template <typename Sig>
 class Callback;
 
-namespace internal {
-template <typename Runnable, typename RunType, typename BoundArgsType>
-struct BindState;
-}  // namespace internal
-
 template <typename R>
 class Callback<R(void)> : public internal::CallbackBase {
  public:
   typedef R(RunType)();
 
-  Callback() : CallbackBase(NULL) { }
+  Callback() : CallbackBase(NULL, NULL) { }
 
+  // We pass BindStateHolder by const ref to avoid incurring an
+  // unnecessary AddRef/Unref pair even though we will modify the object.
+  // We cannot use a normal reference because the compiler will warn
+  // since this is often used on a return value, which is a temporary.
+  //
   // Note that this constructor CANNOT be explicit, and that Bind() CANNOT
   // return the exact Callback<> type.  See base/bind.h for details.
-  template <typename Runnable, typename RunType, typename BoundArgsType>
-  Callback(internal::BindState<Runnable, RunType, BoundArgsType>* bind_state)
-      : CallbackBase(bind_state) {
-
-    // Force the assignment to a local variable of PolymorphicInvoke
+  template <typename T>
+  Callback(const internal::BindStateHolder<T>& bind_state_holder)
+      : CallbackBase(NULL, &bind_state_holder.bind_state_) {
+    // Force the assignment to a location variable of PolymorphicInvoke
     // so the compiler will typecheck that the passed in Run() method has
     // the correct type.
-    PolymorphicInvoke invoke_func =
-        &internal::BindState<Runnable, RunType, BoundArgsType>
-            ::InvokerType::Run;
+    PolymorphicInvoke invoke_func = &T::InvokerType::Run;
     polymorphic_invoke_ = reinterpret_cast<InvokeFuncStorage>(invoke_func);
   }
 
@@ -287,20 +285,22 @@
  public:
   typedef R(RunType)(A1);
 
-  Callback() : CallbackBase(NULL) { }
+  Callback() : CallbackBase(NULL, NULL) { }
 
+  // We pass BindStateHolder by const ref to avoid incurring an
+  // unnecessary AddRef/Unref pair even though we will modify the object.
+  // We cannot use a normal reference because the compiler will warn
+  // since this is often used on a return value, which is a temporary.
+  //
   // Note that this constructor CANNOT be explicit, and that Bind() CANNOT
   // return the exact Callback<> type.  See base/bind.h for details.
-  template <typename Runnable, typename RunType, typename BoundArgsType>
-  Callback(internal::BindState<Runnable, RunType, BoundArgsType>* bind_state)
-      : CallbackBase(bind_state) {
-
-    // Force the assignment to a local variable of PolymorphicInvoke
+  template <typename T>
+  Callback(const internal::BindStateHolder<T>& bind_state_holder)
+      : CallbackBase(NULL, &bind_state_holder.bind_state_) {
+    // Force the assignment to a location variable of PolymorphicInvoke
     // so the compiler will typecheck that the passed in Run() method has
     // the correct type.
-    PolymorphicInvoke invoke_func =
-        &internal::BindState<Runnable, RunType, BoundArgsType>
-            ::InvokerType::Run;
+    PolymorphicInvoke invoke_func = &T::InvokerType::Run;
     polymorphic_invoke_ = reinterpret_cast<InvokeFuncStorage>(invoke_func);
   }
 
@@ -327,20 +327,22 @@
  public:
   typedef R(RunType)(A1, A2);
 
-  Callback() : CallbackBase(NULL) { }
+  Callback() : CallbackBase(NULL, NULL) { }
 
+  // We pass BindStateHolder by const ref to avoid incurring an
+  // unnecessary AddRef/Unref pair even though we will modify the object.
+  // We cannot use a normal reference because the compiler will warn
+  // since this is often used on a return value, which is a temporary.
+  //
   // Note that this constructor CANNOT be explicit, and that Bind() CANNOT
   // return the exact Callback<> type.  See base/bind.h for details.
-  template <typename Runnable, typename RunType, typename BoundArgsType>
-  Callback(internal::BindState<Runnable, RunType, BoundArgsType>* bind_state)
-      : CallbackBase(bind_state) {
-
-    // Force the assignment to a local variable of PolymorphicInvoke
+  template <typename T>
+  Callback(const internal::BindStateHolder<T>& bind_state_holder)
+      : CallbackBase(NULL, &bind_state_holder.bind_state_) {
+    // Force the assignment to a location variable of PolymorphicInvoke
     // so the compiler will typecheck that the passed in Run() method has
     // the correct type.
-    PolymorphicInvoke invoke_func =
-        &internal::BindState<Runnable, RunType, BoundArgsType>
-            ::InvokerType::Run;
+    PolymorphicInvoke invoke_func = &T::InvokerType::Run;
     polymorphic_invoke_ = reinterpret_cast<InvokeFuncStorage>(invoke_func);
   }
 
@@ -370,20 +372,22 @@
  public:
   typedef R(RunType)(A1, A2, A3);
 
-  Callback() : CallbackBase(NULL) { }
+  Callback() : CallbackBase(NULL, NULL) { }
 
+  // We pass BindStateHolder by const ref to avoid incurring an
+  // unnecessary AddRef/Unref pair even though we will modify the object.
+  // We cannot use a normal reference because the compiler will warn
+  // since this is often used on a return value, which is a temporary.
+  //
   // Note that this constructor CANNOT be explicit, and that Bind() CANNOT
   // return the exact Callback<> type.  See base/bind.h for details.
-  template <typename Runnable, typename RunType, typename BoundArgsType>
-  Callback(internal::BindState<Runnable, RunType, BoundArgsType>* bind_state)
-      : CallbackBase(bind_state) {
-
-    // Force the assignment to a local variable of PolymorphicInvoke
+  template <typename T>
+  Callback(const internal::BindStateHolder<T>& bind_state_holder)
+      : CallbackBase(NULL, &bind_state_holder.bind_state_) {
+    // Force the assignment to a location variable of PolymorphicInvoke
     // so the compiler will typecheck that the passed in Run() method has
     // the correct type.
-    PolymorphicInvoke invoke_func =
-        &internal::BindState<Runnable, RunType, BoundArgsType>
-            ::InvokerType::Run;
+    PolymorphicInvoke invoke_func = &T::InvokerType::Run;
     polymorphic_invoke_ = reinterpret_cast<InvokeFuncStorage>(invoke_func);
   }
 
@@ -416,20 +420,22 @@
  public:
   typedef R(RunType)(A1, A2, A3, A4);
 
-  Callback() : CallbackBase(NULL) { }
+  Callback() : CallbackBase(NULL, NULL) { }
 
+  // We pass BindStateHolder by const ref to avoid incurring an
+  // unnecessary AddRef/Unref pair even though we will modify the object.
+  // We cannot use a normal reference because the compiler will warn
+  // since this is often used on a return value, which is a temporary.
+  //
   // Note that this constructor CANNOT be explicit, and that Bind() CANNOT
   // return the exact Callback<> type.  See base/bind.h for details.
-  template <typename Runnable, typename RunType, typename BoundArgsType>
-  Callback(internal::BindState<Runnable, RunType, BoundArgsType>* bind_state)
-      : CallbackBase(bind_state) {
-
-    // Force the assignment to a local variable of PolymorphicInvoke
+  template <typename T>
+  Callback(const internal::BindStateHolder<T>& bind_state_holder)
+      : CallbackBase(NULL, &bind_state_holder.bind_state_) {
+    // Force the assignment to a location variable of PolymorphicInvoke
     // so the compiler will typecheck that the passed in Run() method has
     // the correct type.
-    PolymorphicInvoke invoke_func =
-        &internal::BindState<Runnable, RunType, BoundArgsType>
-            ::InvokerType::Run;
+    PolymorphicInvoke invoke_func = &T::InvokerType::Run;
     polymorphic_invoke_ = reinterpret_cast<InvokeFuncStorage>(invoke_func);
   }
 
@@ -466,20 +472,22 @@
  public:
   typedef R(RunType)(A1, A2, A3, A4, A5);
 
-  Callback() : CallbackBase(NULL) { }
+  Callback() : CallbackBase(NULL, NULL) { }
 
+  // We pass BindStateHolder by const ref to avoid incurring an
+  // unnecessary AddRef/Unref pair even though we will modify the object.
+  // We cannot use a normal reference because the compiler will warn
+  // since this is often used on a return value, which is a temporary.
+  //
   // Note that this constructor CANNOT be explicit, and that Bind() CANNOT
   // return the exact Callback<> type.  See base/bind.h for details.
-  template <typename Runnable, typename RunType, typename BoundArgsType>
-  Callback(internal::BindState<Runnable, RunType, BoundArgsType>* bind_state)
-      : CallbackBase(bind_state) {
-
-    // Force the assignment to a local variable of PolymorphicInvoke
+  template <typename T>
+  Callback(const internal::BindStateHolder<T>& bind_state_holder)
+      : CallbackBase(NULL, &bind_state_holder.bind_state_) {
+    // Force the assignment to a location variable of PolymorphicInvoke
     // so the compiler will typecheck that the passed in Run() method has
     // the correct type.
-    PolymorphicInvoke invoke_func =
-        &internal::BindState<Runnable, RunType, BoundArgsType>
-            ::InvokerType::Run;
+    PolymorphicInvoke invoke_func = &T::InvokerType::Run;
     polymorphic_invoke_ = reinterpret_cast<InvokeFuncStorage>(invoke_func);
   }
 
@@ -519,20 +527,22 @@
  public:
   typedef R(RunType)(A1, A2, A3, A4, A5, A6);
 
-  Callback() : CallbackBase(NULL) { }
+  Callback() : CallbackBase(NULL, NULL) { }
 
+  // We pass BindStateHolder by const ref to avoid incurring an
+  // unnecessary AddRef/Unref pair even though we will modify the object.
+  // We cannot use a normal reference because the compiler will warn
+  // since this is often used on a return value, which is a temporary.
+  //
   // Note that this constructor CANNOT be explicit, and that Bind() CANNOT
   // return the exact Callback<> type.  See base/bind.h for details.
-  template <typename Runnable, typename RunType, typename BoundArgsType>
-  Callback(internal::BindState<Runnable, RunType, BoundArgsType>* bind_state)
-      : CallbackBase(bind_state) {
-
-    // Force the assignment to a local variable of PolymorphicInvoke
+  template <typename T>
+  Callback(const internal::BindStateHolder<T>& bind_state_holder)
+      : CallbackBase(NULL, &bind_state_holder.bind_state_) {
+    // Force the assignment to a location variable of PolymorphicInvoke
     // so the compiler will typecheck that the passed in Run() method has
     // the correct type.
-    PolymorphicInvoke invoke_func =
-        &internal::BindState<Runnable, RunType, BoundArgsType>
-            ::InvokerType::Run;
+    PolymorphicInvoke invoke_func = &T::InvokerType::Run;
     polymorphic_invoke_ = reinterpret_cast<InvokeFuncStorage>(invoke_func);
   }
 
@@ -575,20 +585,22 @@
  public:
   typedef R(RunType)(A1, A2, A3, A4, A5, A6, A7);
 
-  Callback() : CallbackBase(NULL) { }
+  Callback() : CallbackBase(NULL, NULL) { }
 
+  // We pass BindStateHolder by const ref to avoid incurring an
+  // unnecessary AddRef/Unref pair even though we will modify the object.
+  // We cannot use a normal reference because the compiler will warn
+  // since this is often used on a return value, which is a temporary.
+  //
   // Note that this constructor CANNOT be explicit, and that Bind() CANNOT
   // return the exact Callback<> type.  See base/bind.h for details.
-  template <typename Runnable, typename RunType, typename BoundArgsType>
-  Callback(internal::BindState<Runnable, RunType, BoundArgsType>* bind_state)
-      : CallbackBase(bind_state) {
-
-    // Force the assignment to a local variable of PolymorphicInvoke
+  template <typename T>
+  Callback(const internal::BindStateHolder<T>& bind_state_holder)
+      : CallbackBase(NULL, &bind_state_holder.bind_state_) {
+    // Force the assignment to a location variable of PolymorphicInvoke
     // so the compiler will typecheck that the passed in Run() method has
     // the correct type.
-    PolymorphicInvoke invoke_func =
-        &internal::BindState<Runnable, RunType, BoundArgsType>
-            ::InvokerType::Run;
+    PolymorphicInvoke invoke_func = &T::InvokerType::Run;
     polymorphic_invoke_ = reinterpret_cast<InvokeFuncStorage>(invoke_func);
   }