title: Why boost::shared_mutex cannot block more than 128 threads?
body: <p>Why boost::shared_mutex cannot block more than 128 threads? Is this a well-known issue?</p>
  <p>boost1.67+mscv2015</p>
  <pre><code>    boost::shared_mutex mutex; 
      for (int i = 0; i &lt; 256; i++)
      {
          std::thread([&amp;]() {
                  printf(&quot;begin\n&quot;);
                  {    //crash after 128 times
                      boost::unique_lock&lt;boost::shared_mutex&gt; lock(mutex);
                      Sleep(5000);
                  }
                  printf(&quot;end\n&quot;);
              }).detach();
      }
      Sleep(5000);
  </code></pre>