 given timeout (in milliseconds), the message handler is invoked with a <code>NULL</code> message.<br  />
 You can then destroy the subscription in the callback, or simply return, in which case, the message handler will fire again when a message is received or the subscription times-out again.</p>
<dl class="section note"><dt>Note</dt><dd>Receiving a message reset the timeout. Until all pending messages are processed, no timeout will occur. The timeout starts when the message handler for the last pending me