Deprecation Notice

As of this notice, the node-sync project has been archived and will no longer receive maintenance or updates. I want to express my gratitude to the entire community for your usage and contributions.

Introduction

node-sync is a simple library that allows you to call any asynchronous function in synchronous way. The main benefit is that it uses javascript-native design - Function.prototype.sync function, instead of heavy APIs which you'll need to learn. Also, asynchronous function which was called synchronously through node-sync doesn't blocks the whole process - it blocks only current thread!

It built on node-fibers library as a multithreading solution.

Examples

Simply call asynchronous function synchronously:

var Sync = require('sync');

function asyncFunction(a, b, callback) {
    process.nextTick(function(){
        callback(null, a + b);
    })
}

// Run in a fiber
Sync(function(){

    // Function.prototype.sync() interface is same as Function.prototype.call() - first argument is 'this' context
    var result = asyncFunction.sync(null, 2, 3);
    console.log(result); // 5

    // Read file synchronously without blocking whole process? no problem
    var source = require('fs').readFile.sync(null, __filename);
    console.log(String(source)); // prints the source of this example itself
})

It throws exceptions!

var Sync = require('sync');

function asyncFunction(a, b, callback) {
    process.nextTick(function(){
        callback('something went wrong');
    })
}

// Run in a fiber
Sync(function(){

    try {
        var result = asyncFunction.sync(null, 2, 3);
    }
    catch (e) {
        console.error(e); // something went wrong
    }
})

// Or simply specify callback function for Sync fiber
// handy when you use Sync in asynchronous environment
Sync(function(){

    // The result will be passed to a Sync callback
    var result = asyncFunction.sync(null, 2, 3);
    return result;

}, function(err, result){ // <-- standard callback

    if (err) console.error(err); // something went wrong

    // The result which was returned from Sync body function
    console.log(result);
})

Transparent integration

var Sync = require('sync');

var MyNewFunctionThatUsesFibers = function(a, b) { // <-- no callback here

    // we can use yield here
    // yield();

    // or throw an exception!
    // throw new Error('something went wrong');

    // or even sleep
    // Sync.sleep(200);

    // or turn fs.readFile to non-blocking synchronous function
    // var source = require('fs').readFile.sync(null, __filename)

    return a + b; // just return a value

}.async() // <-- here we make this function friendly with async environment

// Classic asynchronous nodejs environment
var MyOldFashoinAppFunction = function() {

    // We just use our MyNewFunctionThatUsesFibers normally, in a callback-driven way
    MyNewFunctionThatUsesFibers(2, 3, function(err, result){

        // If MyNewFunctionThatUsesFibers will throw an exception, it will go here
        if (err) return console.error(err);

        // 'return' value of MyNewFunctionThatUsesFibers
        console.log(result); // 5
    })
}

// From fiber environment
Sync(function(){

    // Run MyNewFunctionThatUsesFibers synchronously
    var result = MyNewFunctionThatUsesFibers(2, 3);
    console.log(result); // 5

    // Or use sync() for it (same behavior)
    var result = MyNewFunctionThatUsesFibers.sync(null, 2, 3);
    console.log(result); // 5
})

Parallel execution:

var Sync = require('sync'),
    Future = Sync.Future();

// Run in a fiber
Sync(function(){
    try {
        // Three function calls in parallel
        var foo = asyncFunction.future(null, 2, 3);
        var bar = asyncFunction.future(null, 5, 5);
        var baz = asyncFunction.future(null, 10, 10);

        // We are immediately here, no blocking

        // foo, bar, baz - our tickets to the future!
        console.log(foo); // { [Function: Future] result: [Getter], error: [Getter] }

        // Get the results
        // (when you touch 'result' getter, it blocks until result would be returned)
        console.log(foo.result, bar.result, baz.result); // 5 10 20

        // Or you can straightly use Sync.Future without wrapper
        // This call doesn't blocks
        asyncFunction(2, 3, foo = Future());

        // foo is a ticket
        console.log(foo); // { [Function: Future] result: [Getter], error: [Getter] }

        // Wait for the result
        console.log(foo.result); // 5
    }
    catch (e) {
        // If some of async functions returned an error to a callback
        // it will be thrown as exception
        console.error(e);
    }
})

Timeouts support

var Sync = require('sync'),
    Future = Sync.Future;

function asyncFunction(a, b, callback) {
    setTimeout(function(){
        callback(null, a + b);
    }, 1000)
}

// Run in a fiber
Sync(function(){

    // asyncFunction returns the result after 1000 ms
    var foo = asyncFunction.future(null, 2, 3);
    // but we can wait only 500ms!
    foo.timeout = 500;

    try {
        var result = foo.result;
    }
    catch (e) {
        console.error(e); // Future function timed out at 500 ms
    }

    // Same example with straight future function
    asyncFunction(2, 3, foo = new Future(500));

    try {
        var result = foo.result;
    }
    catch (e) {
        console.error(e); // Future function timed out at 500 ms
    }
})

How to address non-uniform callbacks

Sometimes third-party libraries are not following convention and passing multiple result parameters to the callback, e.g. callback(err, recordsets, returnValue). In this situation, node-sync will simply return array of values instead of value.

// Asynchronous which returns multiple arguments to a callback and returning a value synchronously
function asyncFunctionReturningMultipleArguments(callback) {
    process.nextTick(function(){
        callback(null, 2, 3);
    })
}

Sync(function(){
    var result = asyncFunctionReturningMultipleArguments.sync();
    assert.equal(result, [2, 3]);
})

See more examples in examples directory.

Installation

install

$ npm install sync

and then

$ node your_file_using_sync.js