How to create a folder with read and write permission in joomla?

In many modules, example module jvheadline, jvnews, or some module for slide show, it is usually need a written permission for thumbnail image folder. Some you can change write permission by fpt, but some time image folder is created by command for example:   JFolder::create($thumbImgFolder); .
We should change this command into:     JFolder::create($thumbImgParentFolder,0777);
This will set written permission for this folder right after it is created.