title: Cancel a single Webworker event
body: <p>Is it possible to cancel the handling of a single action invoked by <code>worker.postMessage(..)</code> ?
  There is the <code>worker.terminate()</code> method, but it cancels any waiting event. Also it seems to render the whole worker dead, as it doesn't react to further <code>postMessage</code> calls. </p>
  
  <p>On the other hand, it seems useless to create a new <code>Worker</code> for every task, if they operate on a large amount of common data, that have to be traversed from <code>Worker</code> to <code>Worker</code> via the main script, cloning the whole data everytime.</p>