title: How to block until an event occurs in an RX stream?
body: <p>With Microsoft Reavtive Extensions (RX), I'm wondering if its possible to block until an event occurs?</p>
  
  <p>Somthing like this:</p>
  
  <pre><code>observableStream.BlockUntilTrue(o =&gt; o.MyProperty == true);
  </code></pre>
  
  <p><strong>What I have tried</strong></p>
  
  <p>I have tried <code>observableStream.TakeUntil(o =&gt; o.MyProperty == true);</code>, but this exits immediately.</p>