Node.js Fully Concurrent Execution of an Async Function without Rate Limiting

control-flow-2.js

/* Control Flow 2 - Fully Concurrent Executions of a Function (not rate limited)
 *
 * Based on:
 *   - http://book.mixu.net/node/ch7.html
 *   - https://github.com/mixu
 *
 * Characteristics:
 *
 *  - Runs a number of operations concurrently
 *  - Starts all async operations near simultaneously (full concurrency)
 *  - No guarantee of order, only that all the operations have been completed
 *
 * Variations:
 *
 *  - The way in which the result is collected (manual or via a
 *    “stashing” callback)
 *  - How error handling is done (via the first argument of the final function,
 *    manually in each subfunction, or via a dedicated, additional function)
 *  - Whether a final callback can be specified
 *
 * Tags: parallel, full-concurrency, no-concurrency-control
 */

/*
 * A Simulated Asynchronous Function
 */

function async(arg, callback) {
    var delay = Math.floor(1000 * Math.random());
    console.log('Do something with "' + arg + '", and return ' + delay + 'ms later');
    setTimeout(function() {
        result = arg; // keep the result the same as the argument so async impact can be easily observed
        callback(result);
    }, delay);
}

/*
 * A Simulated Completion Function
 */

function final(results) {
    console.log('Done', results);
    console.log(process.hrtime(start)[0] + "." + (process.hrtime(start)[1] / 1000000).toFixed(0) + " sec(s) total time");
}

/*
 * 'Parallel' Flow Control Construct
 */

function parallel(remaining_items, results) {
    items.forEach(function(item) {
        async(item, function(result) {
            results.push(result);
            console.log('Results so far: ', results);
            if (results.length == items.length) {
                final(results);
            }
        });
    });
}

/*
 * Main
 */

var items   = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]; // Work array
var results = [];                              // Results array
var start   = process.hrtime();                // Start a timer

parallel(items, results);