title: is the initial value of a threadgroup atomic_uint zero?
body: <p>Is the initial value of a <code>threadgroup atomic_uint</code> zero? I didn't see anything in the MSL spec. Or do I need to do something like the following to initialize it to zero?</p>
  
  <pre><code>threadgroup atomic_uint flags;
  if(localIndex == 0) {
      atomic_store_explicit(&amp;flags, 0, memory_order_relaxed);
  }
  
  threadgroup_barrier(mem_flags::mem_threadgroup);
  </code></pre>