state-trooper

Version:
Application State Manager
83 lines (71 loc) • 1.88 kB
JavaScript
"use strict";

// TODO: Use process.nextTick if it's available since it's more
// efficient
// http://howtonode.org/understanding-process-next-tick
// Maybe we don't even need to queue ourselves in that case?

// XXX: But http://blog.nodejs.org/2013/03/11/node-v0-10-0-stable/
// Looks like it will blow up the stack (or is that just about
// pre-empting IO (but that's already bad enough IMO)?)

// Looks like
// http://nodejs.org/api/process.html#process_process_nexttick_callback
// is the equivalent of our TASK_BATCH_SIZE

var buffers = require("./buffers");

var TASK_BATCH_SIZE = 1024;

var tasks = buffers.ring(32);
var running = false;
var queued = false;

var queue_dispatcher;

function process_messages() {
  running = true;
  queued = false;
  var count = 0;
  while (true) {
    var task = tasks.pop();
    if (task === buffers.EMPTY) {
      break;
    }
    // TODO: Don't we need a try/finally here?
    task();
    if (count >= TASK_BATCH_SIZE) {
      break;
    }
    count ++;
  }
  running = false;
  if (tasks.length > 0) {
    queue_dispatcher();
  }
}

if (typeof MessageChannel !== "undefined") {
  var message_channel = new MessageChannel();
  message_channel.port1.onmessage = function(_) {
    process_messages();
  };
  queue_dispatcher = function()  {
    if (!(queued && running)) {
      queued = true;
      message_channel.port2.postMessage(0);
    }
  };
} else if (typeof setImmediate !== "undefined") {
  queue_dispatcher = function() {
    if (!(queued && running)) {
      queued = true;
      setImmediate(process_messages);
    }
  };
} else {
  queue_dispatcher = function() {
    if (!(queued && running)) {
      queued = true;
      setTimeout(process_messages, 0);
    }
  };
}

exports.run = function (f) {
  tasks.unbounded_unshift(f);
  queue_dispatcher();
};

exports.queue_delay = function(f, delay) {
  setTimeout(f, delay);
};