c# - Google drive api, wont upload async -

i using google.apis.drive.v3 manage files. problem can upload files sync way. async upload wont upload file:

    var service = getservice(i_user_credential, i_application_name);      var filemetadata = new google.apis.drive.v3.data.file();     filemetadata.name = i_file_name;     filemetadata.parents = new list<string> { i_folder_id };      filesresource.createmediaupload request;     cancellationtoken ctsupload = new cancellationtoken();       using (var stream = new system.io.filestream(i_file_path, system.io.filemode.open))     {         request = service.files.create(             filemetadata, stream, i_file_type);         request.fields = "id";         request.uploadasync(ctsupload);     }