RefCounted types should not have public destructors, base/ edition

base/files/file_path_watcher.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.
 
 // This module provides a way to monitor a file or directory for changes.
 
 #ifndef BASE_FILES_FILE_PATH_WATCHER_H_
 #define BASE_FILES_FILE_PATH_WATCHER_H_
 #pragma once
 
@@ skipping 15 matching lines @@
 // detect the creation and deletion of files in a watched directory, but will
 // not detect modifications to those files. See file_path_watcher_mac.cc for
 // details.
 class BASE_EXPORT FilePathWatcher {
  public:
   // Declares the callback client code implements to receive notifications. Note
   // that implementations of this interface should not keep a reference to the
   // corresponding FileWatcher object to prevent a reference cycle.
   class Delegate : public base::RefCountedThreadSafe<Delegate> {
    public:
-    virtual ~Delegate() {}
     virtual void OnFilePathChanged(const FilePath& path) = 0;
     // Called when platform specific code detected an error. The watcher will
     // not call OnFilePathChanged for future changes.
     virtual void OnFilePathError(const FilePath& path) {}
+
+   protected:
+    friend class base::RefCountedThreadSafe<Delegate>;
+    virtual ~Delegate() {}
   };
 
   // Used internally to encapsulate different members on different platforms.
   // TODO(jhawkins): Move this into its own file. Also fix the confusing naming
   // wrt Delegate vs PlatformDelegate.
   class PlatformDelegate : public base::RefCountedThreadSafe<PlatformDelegate> {
    public:
     PlatformDelegate();
 
     // Start watching for the given |path| and notify |delegate| about changes.
     virtual bool Watch(const FilePath& path,
                        Delegate* delegate) WARN_UNUSED_RESULT = 0;
 
     // Stop watching. This is called from FilePathWatcher's dtor in order to
     // allow to shut down properly while the object is still alive.
     // It can be called from any thread.
     virtual void Cancel() = 0;
 
    protected:
+    friend class base::RefCountedThreadSafe<PlatformDelegate>;
     friend class FilePathWatcher;
 
     virtual ~PlatformDelegate();
 
     // Stop watching. This is only called on the thread of the appropriate
     // message loop. Since it can also be called more than once, it should
     // check |is_cancelled()| to avoid duplicate work.
     virtual void CancelOnMessageLoopThread() = 0;
 
     scoped_refptr<base::MessageLoopProxy> message_loop() const {
       return message_loop_;
     }
 
     void set_message_loop(base::MessageLoopProxy* loop) {
       message_loop_ = loop;
     }
 
     // Must be called before the PlatformDelegate is deleted.
     void set_cancelled() {
       cancelled_ = true;
     }
 
     bool is_cancelled() const {
       return cancelled_;
     }
 
    private:
-    friend class base::RefCountedThreadSafe<PlatformDelegate>;
-
     scoped_refptr<base::MessageLoopProxy> message_loop_;
     bool cancelled_;
   };
 
   FilePathWatcher();
   virtual ~FilePathWatcher();
 
   // A callback that always cleans up the PlatformDelegate, either when executed
   // or when deleted without having been executed at all, as can happen during
   // shutdown.
   static void CancelWatch(const scoped_refptr<PlatformDelegate>& delegate);
 
   // Register interest in any changes on |path|. OnPathChanged will be called
   // back for each change. Returns true on success.
   // OnFilePathChanged() will be called on the same thread as Watch() is called,
   // which should have a MessageLoop of TYPE_IO.
   virtual bool Watch(const FilePath& path, Delegate* delegate)
       WARN_UNUSED_RESULT;
 
  private:
   scoped_refptr<PlatformDelegate> impl_;
 
   DISALLOW_COPY_AND_ASSIGN(FilePathWatcher);
 };
 
 }  // namespace files
 }  // namespace base
 
 #endif  // BASE_FILES_FILE_PATH_WATCHER_H_