title: Some questions about linux signals
body: <ol>
  <li><p>Is (<code>SIGRTMIN + 1</code>) safe for inter-process communication? Will it change in different processes?</p></li>
  <li><p>Are there any differences to use <code>sigqueue(2)</code> or <code>kill(2)</code> to send standard signals and real time signals?<br>
  If I use <code>sigqueue(2)</code> to send a series of <code>SIGUSR1</code>(standard signals) and handle them slowly, are there mutiple instances of <code>SIGUSR1</code> in the queue?<br>
  What about using <code>kill(2)</code> to send <code>SIGRTMIN</code>(real time signals)? Will they be queued?</p></li>
  </ol>