illustration of timer-related event loop problem in Node.js 0.6

toosoon.js

var i = 0;

// complain loudly if node exits before this handler is removed
var onExit = function() {
    console.log('Exiting prematurely! (after %s iterations)', i);
};
process.on('exit', onExit);


function doIteration() {
    if (i < 100) {
        i++;

        // set a timeout
        var to = setTimeout(function() {
            console.log('timed out');

            // set another timeout.
            // (IMPORTANT! without this second setTimeout the problem goes away)
            to = setTimeout(function() {
                to = null;
                console.log('timed out again');
            }, 2);
        }, 2);

        // for each iteration, wait 5ms, clear the timeout if it is still active,
        // then call doIteration again
        setTimeout(function() {
            if (to) {
                // without this clearTimeout the problem goes away
                console.log('clearing timeout');
                clearTimeout(to);
            }
            doIteration();
        }, 5);

    }
    else {
        process.removeListener('exit', onExit);
        console.log('exiting properly after %s iterations', i);
    }
}

doIteration();