title: Wait for multiple events in iOS?
body: <p>What is equivalent of Win32's WaitForMultipleObjects function in iOS?</p>
  
  <p>This is roughly what I want:</p>
  
  <pre><code>NSCondition *condition1;
  NSCondition *condition2;
  NSCondition *condition3;
  
  wait_for_conditions([NSArray arrayWithObjects: condition1, condition2, condition3, nil], 
  ^{
      // Some code which must be executed when all conditions were fired
  });
  
  // in some other places of program:
  [condition1 signal];
  
  // ...
  [condition2 signal];
  
  // ...
  [condition3 signal];
  </code></pre>
  
  <p>What are the ways to accomplish this in iOS?</p>
  
  <p>Edit: I'm not bound to usage of NSCondition, any other synchronization things will be ok (I've just googled and found NSCondition).</p>