Open Radar

 
Display link remembers the pthread_t from last display link thread but does not clean it in CVDisplayLinkStop. When next thread has identical pthread id display link will fail to start.

Code to reproduce:

#import <Foundation/Foundation.h>
#import <CoreVideo/CoreVideo.h>

int main(int argc, const char * argv[]) {
    CVDisplayLinkRef link;
    CVDisplayLinkCreateWithActiveCGDisplays(&link);
    CVDisplayLinkSetOutputHandler(link, ^(CVDisplayLinkRef displayLink, const CVTimeStamp* inNow, const CVTimeStamp* inOutputTime,
                                          CVOptionFlags flagsIn, CVOptionFlags* flagsOut) {
        return 0;
    });
    CVReturn res = CVDisplayLinkStart(link);
    assert(res == kCVReturnSuccess);
    CVDisplayLinkStop(link);
    [NSThread detachNewThreadWithBlock:^{
        CVReturn res = CVDisplayLinkStart(link);
        assert(res == kCVReturnSuccess);
    }];
    return 0;
}