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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.

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.

• javascript
• node.js
• event-loop

Share Improve this question Follow edited Oct 7, 2014 at 19:30 Paul Sweatte 24.6k77 gold badges131131 silver badges268268 bronze badges asked Sep 30, 2014 at 7:07 SanketSanket 98511 gold badge1111 silver badges2424 bronze badges 9

• A code example would help. – tikider Commented Sep 30, 2014 at 8:46
• Added example please check it. – Sanket Commented Sep 30, 2014 at 11:14
• Why would you need to do this? – neelsg Commented Sep 30, 2014 at 11:33
• @neelsg: en.wikipedia/wiki/Dynamic_priority_scheduling is a well-known problem with lots of applications – Bergi Commented Sep 30, 2014 at 12:13
• Actually in my application multiple functions' are executing parallelly i.e in a event loop. So if there are some important high priority functions are there so I want these functions to be executed first and then other. – Sanket Commented Sep 30, 2014 at 12:34

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2 Answers 2

Sorted by: Reset to default 3

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

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

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

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.

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