Open Radar

 
Summary:
Every time a PDF page is drawn in a CGContextRef, a copy of its resources (images in the PDF etc) are created and retained (probably by the context).

In our app we use a CATiledLayer to draw PDFs, which seems to trigger this bug, probably because CATiledLayer uses a pool of CGContextRefs that it reuses when needed. I tried to find a workaround but couldn't find a way to drain that pool.

Steps to Reproduce:
Profile the attached project using the Allocations Instrument
Watch memory usage go up

(see ViewController.m for relevant code)

Expected Results:
Memory usage should only go up during CGContextDrawPDFPage, but then go down immediately, or at least after CGPDFDocumentRelease

Actual Results:
Memory usage goes up with every iteration
Multiple copies of a 7.77MB image are kept in memory

Version:
iOS 10 

Notes:


Configuration:
iPad Mini 2, iPhone SE, iOS Simulator

Attachments:
'DrawPDFPage.zip' was successfully uploaded.


Relevant code:

UIGraphicsBeginImageContext(CGSizeMake(1024, 768));
    
CGContextRef context = UIGraphicsGetCurrentContext();

for (int i = 0; i < 100; ++i)
{
    CGPDFDocumentRef document = CGPDFDocumentCreateWithURL((__bridge CFURLRef)url);
    if (document)
    {
        CGPDFPageRef page = CGPDFDocumentGetPage(document, 1);
        if (page)
        {
            CGContextDrawPDFPage(context, page);
        }
        
        CGPDFDocumentRelease(document);
    }
    
    [NSThread sleepForTimeInterval:1.0];
}

UIGraphicsEndImageContext();