title: Google Maps Utility: how to get all markers from ClusterManager<?>?
body: <p><em>Sorry for my English</em></p>
  
  <p>I tried the <code>ClusterManager&lt;?&gt;.getMarkerCollection().getMarkers()</code> method but it returns empty collection.</p>
  
  <p>I use in my app <code>Google Maps Utility Library</code>. Every time after a <em>screen rotation</em> I create <code>AsynkTask</code> and in background thread read data from DB and add items to <code>ClusterManager</code>:</p>
  
  <pre><code>cursor.moveToFirst();
  while (!cursor.isAfterLast()) {
      SomeData row = readSomeDataRow(cursor);
      clusterManager.addItem(new ClusterItemImpl(row));
      cursor.moveToNext();
  }
  </code></pre>
  
  <p>When the <code>AsyncTask</code> finished its work (i.e. in main thread) I tried to get all markers from the <code>ClusterManager</code>:</p>
  
  <pre><code>clusterManager.cluster();
  // cluster manager returns empty collection  \|/
  markers = clusterManager.getMarkerCollection().getMarkers(); 
  </code></pre>
  
  <p>but the <code>ClusterManager</code> returns empty collection.</p>
  
  <p>May be at the moment when I call <code>getMarkers()</code> the <code>ClusterManager</code> yet doesn't place markers on map and will do it a bit later (may be in background thread). If so, then how can I catch that moment?</p>