Auto create Fiber when calling sync() on a function

[fzaninotto]

At the moment, if not run inside a Sync() with a callback, calling sync() on a Function throws the following error:

/path/to/node_modules/sync/lib/sync.js:58
        if (yielded) fiber.run();
                           ^
TypeError: Cannot call method 'run' of undefined
    at Function.sync.syncCallback (/path/to/node_modules/sync/lib/sync.js:58:28)
    at Object.oncomplete (fs.js:297:15)

It would be very convenient to allow each Function to run in its own Fiber, i.e. create one if it doesn't exist yet, so that on could call:

fs.readdir.sync(null, './');

instead of:

Sync(function() {
  fs.readdir.sync(null, './');
});

Is there a limitation in the Fiber lib that prevents it from working?

[ybogdanov]

Yep, there's a limitation. Fiber should wrap the code you want to be "synced". It should be outside. Running fiber inside of Function.prototype.sync will not work.

[fzaninotto]

OK. From reading the Fiber documentation, I thought this was possible. Here is one example they give:

var Fiber = require('fibers');

// Generator function. Returns a function which returns incrementing
// Fibonacci numbers with each call.
function Fibonacci() {
    // Create a new fiber which yields sequential Fibonacci numbers
    var fiber = Fiber(function() {
        Fiber.yield(0); // F(0) -> 0
        var prev = 0, curr = 1;
        while (true) {
            Fiber.yield(curr);
            var tmp = prev + curr;
            prev = curr;
            curr = tmp;
        }
    });
    // Return a bound handle to `run` on this fiber
    return fiber.run.bind(fiber);
}

// Initialize a new Fibonacci sequence and iterate up to 1597
var seq = Fibonacci();
for (var ii = seq(); ii <= 1597; ii = seq()) {
    console.log(ii);
}

So you say you can't create a Fiber on the fly and run it as in this example?

[ybogdanov]

Really. Now it works, seems that something was changed to fibers & node recently. I will think about how I can adopt node-sync to this.

Thanks for your request!

[fzaninotto]

If you can implement it, it will change the life of generations of Node.js developers stuck in callback spaghetti... Looking forward to using your module !

[ybogdanov]

Ah, got it. It can't be asynchronous. Fibonacci example is fully synchronous. If you'll try to add setTimeout or process.nextTick there - it will fail.

With express you can wrap each request with fiber automatically by using Function.prototype.asyncMiddleware mixin. I've added an example for you: https://github.com/0ctave/node-sync/blob/1d567bac8ae5bc9982372ab89ab9a1b1021ab923/examples/express.js

[fzaninotto]

Ok, thanks for taking a look at this anyway.