* emit 'worker close' in master process when a worker closes

* delay execution of process.exit with a callback when listening on 'worker close'

Closes LearnBoost#167

lib/worker.js

@@ -139,14 +139,30 @@ Worker.prototype.connect = function(id, options){
 };
 
 /**
- * Immediate shutdown.
+ * Shutdown the process (using process.nextTick to put it at the end of
+ * event queue).
+ *
+ * If the master is listening on the 'worker close' event, a callback
+ * is passed. The callback *must* be called to shutdown the worker.
  *
  * @api private
  */
 
-Worker.prototype.destroy = function(){
-  this.emit('close');
-  process.nextTick(process.exit);
+Worker.prototype.destroy = function() {
+  var eventName = 'worker close'
+    , listeners = this.master.listeners(eventName);
+
+  var exit = function() {
+    process.nextTick(process.exit());
+  };
+
+  if (listeners.length > 0) {
+    this.master.emit(eventName, function() {
+      exit();
+    });
+  } else {
+    exit();
+  }
 };
 
 /**