nedb/lib/executor.js

/**
 * Responsible for sequentially executing actions on the database
 */

var async = require('async')
  ;

function Executor () {
  this.buffer = [];
  this.ready = false;

  // This queue will execute all commands, one-by-one in order
  this.queue = async.queue(function (task, cb) {
    var newArguments = [];

    // task.arguments is an array-like object on which adding a new field doesn't work, so we transform it into a real array
    for (var i = 0; i < task.arguments.length; i += 1) { newArguments.push(task.arguments[i]); }
    var lastArg = task.arguments[task.arguments.length - 1];

    // Always tell the queue task is complete. Execute callback if any was given.
    if (typeof lastArg === 'function') {
      // Callback was supplied
      newArguments[newArguments.length - 1] = function () {
        if (typeof setImmediate === 'function') {
           setImmediate(cb);
        } else {
          process.nextTick(cb);
        }
        lastArg.apply(null, arguments);
      };
    } else if (!lastArg && task.arguments.length) {
      // false/undefined/null supplied as callbback
      newArguments[newArguments.length - 1] = function () { cb(); };
    } else {
      // Nothing supplied as callback
      newArguments.push(function () { cb(); });
    }


    task.fn.apply(task.this, newArguments);
  }, 1);
}


/**
 * If executor is ready, queue task (and process it immediately if executor was idle)
 * If not, buffer task for later processing
 * @param {Object} task
 *                 task.this - Object to use as this
 *                 task.fn - Function to execute
 *                 task.arguments - Array of arguments, IMPORTANT: only the last argument may be a function (the callback)
 *                                                                 and the last argument cannot be false/undefined/null
 * @param {Boolean} forceQueuing Optional (defaults to false) force executor to queue task even if it is not ready
 */
Executor.prototype.push = function (task, forceQueuing) {
  if (this.ready || forceQueuing) {
    this.queue.push(task);
  } else {
    this.buffer.push(task);
  }
};


/**
 * Queue all tasks in buffer (in the same order they came in)
 * Automatically sets executor as ready
 */
Executor.prototype.processBuffer = function () {
  var i;
  this.ready = true;
  for (i = 0; i < this.buffer.length; i += 1) { this.queue.push(this.buffer[i]); }
  this.buffer = [];
};



// Interface
module.exports = Executor;