Quartz PDF-context based function fails (occasionally) with BAD_ACCESS

Im Getting a Frequent enough BAD_ACCESS when i call this Quartz function:

CGContextDrawPDFPage ((CGContextRef)context, (CGPDFPageRef)pageRef);

Here is how i call it:

CGContextRef context = UIGraphicsGetCurrentContext();
//trans开发者_如何学运维late, scale
CGPDFPageRef myPageRef = CGPDFDocumentGetPage ([PDFDocument sharedPDFDocument].documentData, pageNumber);
CGContextDrawPDFPage (context, myPageRef);//BAD_ACCESS HERE
return UIGraphicsGetImageFromCurrentImageContext();//autoreleased- saved on return
//close context

Neither variable is Nil, or have been released/auto released.

Here is the Stack trace, from the debugger:

Can anyone shed any light on this? Even some pointers on how i might investigate this better. it might not even be function specific. I probobly should mention this function is performed on a separate thread.

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Check the documentation for that returns your myPageRef and see if you have to retain it.

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At the time of writing the question, UIGraphicsGetImageFromCurrentImageContext and such functions where not thread safe, this was my issue. As of iOs 4.1+ many UI function are now thread safe.