#async-rollback

A plugin for caolan's async module that adds additional async methods with improved integrity. For example, async.parallel normally executes the callback immediately if any task returns an error, but this is not always desired. async-rollback contains a parallelRollback method which can undo parallel tasks that succeeded if one of the tasks fails.

Documentation

Control Flow

• parallelAll
• parallelRollback

Control Flow

Run an array of functions in parallel, without waiting until the previous function has completed. If any of the functions pass an error to its callback, the error is cached until all tasks complete. Once the tasks have completed, the results are passed to the final callback as an array. If any functions passed errors, the main callbacks error argument will be an array, corresponding to the input functions.

It is also possible to use an object instead of an array. Each property will be run as a function and the results will be passed to the final callback as an object instead of an array. If any tasks result in an error, the final callbacks error argument will also be an object.

Arguments

• tasks - An array or object containing functions to run, each function is passed a callback(err, result) it must call on completion with an error (which can be null) and an optional result value.
• callback(errs, results) - An optional callback to run once all the functions have completed. This function gets a results array (or object) containing all the result arguments passed to the task callbacks. It also receives an error array (or object) if any errors occurred (null otherwise).

Example

async.parallelAll([
    function(callback){
        setTimeout(function(){
            callback(null, 'one');
        }, 200);
    },
    function(callback){
        setTimeout(function(){
            callback('error2');
        }, 100);
    }
],
// optional callback
function(errs, results){
    // errs = [null, 'error2']
    // results = ['one', null]
    if (errs)
        console.log('Errors occurred');
});


// an example using an object instead of an array
async.parallel({
    one: function(callback){
        setTimeout(function(){
            callback(null, 1);
        }, 200);
    },
    two: function(callback){
        setTimeout(function(){
            callback(2, null);
        }, 100);
    }
},
function(errs, results) {
    // errs = {one: null, two: 2}
    // results = {one: 1, two: null}
    if (errs)
        console.log('Errors occurred');
});