title: Null Graphics Context
body: <p>Here is a code excerpt I am using:</p>
  
  <pre><code>dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0), ^
  {
  
      UIGraphicsBeginImageContextWithOptions(irect.size, YES, 0.0 );
      CGContextRef context = UIGraphicsGetCurrentContext();
      if (context == 0)
          NSLog (@"Null Graphics Context") ;
      else
          NSLog (@"OK") ;
  
      . . . .
      // Various drawing functions
  
      UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
      UIGraphicsEndImageContext();
    }) ;
  </code></pre>
  
  <p>I am finding that every other call to UIGraphicsGetCurrentContext is returning NULL. I get this message on the console.</p>
  
  <p>CGContextRestoreGState: invalid context 0x0. This is a serious error. This application, or a library it uses, is using an invalid context  and is thereby contributing to an overall degradation of system stability and reliability. This notice is a courtesy: please fix this problem. It will become a fatal error in an upcoming update.</p>
  
  <p>What would cause UIGraphicsGetCurrentContext to return an invalid graphic context?</p>