A Boolean value that determines whether Photos processes the image request synchronously.
- iOS 8.0+
- macOS 10.13+
- tvOS 10.0+
false (the default), the
request method returns immediately. Depending on the
delivery property, Photos may call your
result block before the method returns, at some later time, or both.
request method blocks the calling thread until image data is ready or an error occurs. Photos calls your result handler block exactly once.