Merge 237541 "Revert of https://codereview.chromium.org/71013004/"

base/win/scoped_handle.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_WIN_SCOPED_HANDLE_H_
 #define BASE_WIN_SCOPED_HANDLE_H_
 
 #include <windows.h>
 
 #include "base/base_export.h"
@@ skipping 21 matching lines @@
 //     and INVALID_HANDLE_VALUE (-1) for Win32 handles.
 //   - Receive() method allows to receive a handle value from a function that
 //     takes a raw handle pointer only.
 template <class Traits, class Verifier>
 class GenericScopedHandle {
   MOVE_ONLY_TYPE_FOR_CPP_03(GenericScopedHandle, RValue)
 
  public:
   typedef typename Traits::Handle Handle;
 
+  // Helper object to contain the effect of Receive() to the function that needs
+  // a pointer, and allow proper tracking of the handle.
+  class Receiver {
+   public:
+    explicit Receiver(GenericScopedHandle* owner)
+        : handle_(Traits::NullHandle()),
+          owner_(owner) {}
+    ~Receiver() { owner_->Set(handle_); }
+
+    operator Handle*() { return &handle_; }
+
+   private:
+    Handle handle_;
+    GenericScopedHandle* owner_;
+  };
+
   GenericScopedHandle() : handle_(Traits::NullHandle()) {}
 
   explicit GenericScopedHandle(Handle handle) : handle_(Traits::NullHandle()) {
     Set(handle);
   }
 
   // Move constructor for C++03 move emulation of this type.
   GenericScopedHandle(RValue other) : handle_(Traits::NullHandle()) {
     Set(other.object->Take());
   }
@@ skipping 27 matching lines @@
   }
 
   Handle Get() const {
     return handle_;
   }
 
   operator Handle() const {
     return handle_;
   }
 
+  // This method is intended to be used with functions that require a pointer to
+  // a destination handle, like so:
+  //    void CreateRequiredHandle(Handle* out_handle);
+  //    ScopedHandle a;
+  //    CreateRequiredHandle(a.Receive());
+  Receiver Receive() {
+    DCHECK(!Traits::IsHandleValid(handle_)) << "Handle must be NULL";
+    return Receiver(this);
+  }
+
   // Transfers ownership away from this object.
   Handle Take() {
     Handle temp = handle_;
     handle_ = Traits::NullHandle();
     if (Traits::IsHandleValid(temp)) {
       Verifier::StopTracking(temp, this, BASE_WIN_GET_CALLER,
                              tracked_objects::GetProgramCounter());
     }
     return temp;
   }
@@ skipping 68 matching lines @@
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(VerifierTraits);
 };
 
 typedef GenericScopedHandle<HandleTraits, VerifierTraits> ScopedHandle;
 
 }  // namespace win
 }  // namespace base
 
 #endif  // BASE_SCOPED_HANDLE_WIN_H_