http://stackoverflow.com/questions/2819548/autorelease-for-cgmutablepathref
Autorelease pools exist in the Foundation layer and above (AppKit/UIKit, etc).
They don‘t exist for CoreFoundation/CoreGraphics objects.
IOS - Autorelease for CGMutablePathRef?
原文：http://www.cnblogs.com/tx8899/p/3969303.html