Assign priority to nodejs tasks in a event loop

Question

Is there any way by which one can apply priority to Node.js task's in a event loop. I want to assign priority to task which are present in a event loop of nodejs.
Suppose in a event loop there are 5 jobs A,B,C,D,E which having same priority and then next job is received whose priority is higher than last five jobs. Then event loop starts executing that higher priority job.

Answer 1

The event loop in node.js does not support priorities. See some documentation:

• http://nodejs.org/api/events.html
• http://strongloop.com/strongblog/node-js-event-loop/

Short of rewriting it, I don't think there is much you can do about that.

Answer 2

You should use a priority queue, something like priorityqueuejs

In this way you can dequeue an item with the max priority and execute it.

Some code:

'use strict';

var PriorityQueue = require('priorityqueuejs');

var queue = new PriorityQueue(function(a, b) {
  return a.value - b.value;
});

queue.enq({ value: 10, func: function() { console.log("PRIORITY: 10"); } });
queue.enq({ value: 500, func: function() { console.log("PRIORITY: 500"); } });
queue.enq({ value: 300, func: function() { console.log("PRIORITY: 300"); } });
queue.enq({ value: 100, func: function() { console.log("PRIORITY: 100"); } });

(function executeNext() {
  if(queue.size()) {
    var next = queue.deq();
    next.func();
    if(queue.size()) {
      setTimeout(executeNext, 0);
    }
  }
})();

And the output is:

PRIORITY: 500
PRIORITY: 300
PRIORITY: 100
PRIORITY: 10

Here is the executeNext function extracts the next top-priority item and executes it.