title: NSThread with _NSAutoreleaseNoPool error
body: <p>I have an method which save files to the internet, it works but just slow. Then I'd like to make the user interface more smooth, so I create an NSThread to handle the slow task. </p>
  
  <p>I am seeing a list of errors like:</p>
  
  <pre><code>_NSAutoreleaseNoPool(): Object 0x18a140 of class NSCFString autoreleased with no pool in place - just leaking
  </code></pre>
  
  <p>Without NSThread, I call the method like:</p>
  
  <pre><code>[self save:self.savedImg];
  </code></pre>
  
  <p>And I used the following to use NSThread to call the method:</p>
  
  <pre><code>NSThread* thread1 = [[NSThread alloc] initWithTarget:self
                                          selector:@selector(save:)
                                                object:self.savedImg];
  [thread1 start];
  </code></pre>
  
  <p>Thanks. </p>