title: Using await SemaphoreSlim.WaitAsync in .NET 4
body: <p>My application is using .NET 4. I am using await async using <a href="https://www.nuget.org/packages/Microsoft.Bcl.Async/" rel="noreferrer">nuget package</a></p>
  
  <p>In my application I want to do an await on sempahore WaitAsync call as follows.</p>
  
  <pre><code>SemaphoreSlim semphore = new SemaphoreSlim(100);
  await semphore.WaitAsync();
  </code></pre>
  
  <p>However I am getting following compilation error.</p>
  
  <blockquote>
    <blockquote>
      <p>'System.Threading.SemaphoreSlim' does not contain a definition for 'WaitAsync' and no extension method 'WaitAsync' accepting a first argument of type 'System.Threading.SemaphoreSlim' could be found (are you missing a using directive or an assembly reference?)   </p>
    </blockquote>
  </blockquote>
  
  <p>Could there be anyway of uisng WaitAsync in .NET 4.0?</p>