hals

hals

hals (is German for throat) is a concurrency limiter that has a maximum capacity for queued-up functions. When the capacity is reached newly added tasks will be dropped. New tasks will be accepted once it has capacity again.

Unlike a queue, hals does not have a worker function that takes queued payloads but instead takes functions and executes them.

The analogy goes as follows:

• Only concurrency things can go down the throat at the same time.
• But the mouth and throat can only hold capacity things. Everything else drops on the floor.

Install

npm install hals --save

Usage

var hals = require('hals');

function drain () {
  console.log('drained');
}

function drop (usedCapacity, fn) {
  console.log('dropped', fn.name, 'used capacity:', usedCapacity);
}

var feed = hals({
  capacity: 3,    // optional; default: null (null = unlimited capacity)
  concurrency: 1, // optional; default: 1
  drain: drain,   // optional; default null; function to be called when queue is empty
  drop: drop      // optional; default null; function to be called when a function is dropped. Receives task as first argument
});

var foods = [  
  'broccoli',
  'tomato',
  'beans',
  'pork'
];

// add some tasks to hals
foods.forEach(function (food) {
  feed(function (next) {
    console.log('ate', food);
    next();
  });
});

// after a while add another task
setTimeout(function () {
	feed(function (next) {
	  console.log('ate zucchini');
	  next();
	});
}, 100);

prints:

dropped task used capacity: 3
ate broccoli
ate tomato
ate beans
drained

// didn't eat pork

ate zucchini
drained

License

MIT