title: segmentation fault on pthread_mutex_lock
body: <p>I'm getting a segmentation fault when I try to do</p>
  
  <pre><code>pthread_mutex_lock(&amp;_mutex).
  </code></pre>
  
  <p>This is really odd, I'm not sure what might have caused it. I have initialized _mutex in the constructor with</p>
  
  <pre><code>pthread_mutex_init(&amp;_mutex,NULL).
  </code></pre>
  
  <p>anything I can do?</p>