title: What is a "Sync Block" and tips for reducing the count
body: <p>We have a Windows Forms application that uses a (third party) ActiveX control, and are noticing in the .NET performance objects under ".NET CLR Memory" that the number of "Sync Blocks" in use is constantly increasing (along with increasing memory usage), even though our application is sitting there idle. </p>
  
  <p>The built-in explanation for the sink block count states:</p>
  
  <blockquote>
    <p>This counter displays the current number of sync blocks in use. Sync blocks are per-object data structures allocated for storing synchronization information. Sync blocks hold weak references to managed objects and need to be scanned by the Garbage Collector. Sync blocks are not limited to storing synchronization information and can also store COM interop metadata. This counter was designed to indicate performance problems with heavy use of synchronization primitives.</p>
  </blockquote>
  
  <p>The sync block count does seem to get reset when we switch to a different application though. What exactly causes these to get created, and are there any tips for reducing the number of these?</p>
  
  <p>(BTW, it really is spelled "sink block" in the list of performance counters. I'm not sure if its a typo or a plumbing joke)</p>