What exactly does domain.dispose() do in nodejs? Are there any hooks?

Question

Reading the documentation at http://nodejs.org/api/domain.html makes it a little vague: "makes a best effort attempt to clean up any and all IO that is associated with the domain". It mentions that timers are shutdown, which isn't exactly IO. It would be very nice to know the comprehensive list of things domain.dispose does. Does anyone have that list?

Also, is there any way to hook into that functionality - ie allow some custom clean up code to be called when domain.dispose() is run?

Answer 1

The dispose function calls the exit and dispose functions, removes all listeners, removes all error handlers, and attempts to kill all members of the domain. The function the checks if the domain has a parent, and if it does, then it is removed from the domain. The domain is then set for garbage collection, and the marked as disposed.

From the Node documentation:

Once the domain is disposed the dispose event will emit.

I would go more in-depth on the topic, but the Node source is already nicely annotated.

The timer you are talking about would be here, where the members of the domain are being iterated through.

this.members.forEach(function(m) {
  // if it's a timeout or interval, cancel it.
  clearTimeout(m);
});

Here's from the Node source:

Domain.prototype.dispose = function() {
  if (this._disposed) return;

  // if we're the active domain, then get out now.
  this.exit();

  this.emit('dispose');

  // remove error handlers.
  this.removeAllListeners();
  this.on('error', function() {});

  // try to kill all the members.
  // XXX There should be more consistent ways
  // to shut down things!
  this.members.forEach(function(m) {
    // if it's a timeout or interval, cancel it.
    clearTimeout(m);

    // drop all event listeners.
    if (m instanceof EventEmitter) {
      m.removeAllListeners();
      // swallow errors
      m.on('error', function() {});
    }

    // Be careful!
    // By definition, we're likely in error-ridden territory here,
    // so it's quite possible that calling some of these methods
    // might cause additional exceptions to be thrown.
    endMethods.forEach(function(method) {
      if (typeof m[method] === 'function') {
        try {
          m[method]();
        } catch (er) {}
      }
    });

  });

  // remove from parent domain, if there is one.
  if (this.domain) this.domain.remove(this);

  // kill the references so that they can be properly gc'ed.
  this.members.length = 0;

  // finally, mark this domain as 'no longer relevant'
  // so that it can't be entered or activated.
  this._disposed = true;
};