Merge "libbinder: document attach/find/detach object" am: 9a55e4a1

    typedef void (*object_cleanup_func)(const void* id, void* obj, void* cleanupCookie);

    /**

     * This object is attached for the lifetime of this binder object. When

     * this binder object is destructed, the cleanup function of all attached

     * objects are invoked with their respective objectID, object, and

     * cleanupCookie. Access to these APIs can be made from multiple threads,

     * but calls from different threads are allowed to be interleaved.

     */

    virtual void            attachObject(   const void* objectID,

                                            void* object,

                                            void* cleanupCookie,

                                            object_cleanup_func func) = 0;

    /**

     * Returns object attached with attachObject.

     */

    virtual void*           findObject(const void* objectID) const = 0;

    /**

     * WARNING: this API does not call the cleanup function for legacy reasons.

     * It also does not return void* for legacy reasons. If you need to detach

     * an object and destroy it, there are two options:

     * - if you can, don't call detachObject and instead wait for the destructor

     *   to clean it up.

     * - manually retrieve and destruct the object (if multiple of your threads

     *   are accessing these APIs, you must guarantee that attachObject isn't

     *   called after findObject and before detachObject is called).

     */

    virtual void            detachObject(const void* objectID) = 0;

    virtual BBinder*        localBinder();