CGContextDrawImage thread safe?

Question

I have a context that needs to be around for the life of my app because it is a buffer that I continuously render images into. It is created using CGBitmapContextCreate on my main thread when the app launches.

Is it safe to later call the following code from a background thread in an NSOperation?

CGImageRef imageRef = [[UIImage imageWithContentsOfFile:[fileURL path]] CGImage];
if (imageRef)
{
    //  Draw the base image to the bitmap context
    CGContextDrawImage(myContext, myRect, imageRef);
}