how to apply a timelimit to series of callback functions - node.js

Question

How would you go about applying a time limit to a series of callbacks in node.js?
Would this be easier using the async library?
Thankyou, as you can see I'm struggling with asynchronous javascript.

Answer 1

Instead of calling the next step directly, call the below function with
doNext : your actual next step
stepData : your parameters plus an execution time limit in miliseconds
unDoThis : the function to run if the work just done ever must be undone
function nextStep(doNext, stepData, unDoThis) {
The first time, set the time out
if (!stepData.expireAt) {
var currentDate = new Date();
stepData.expireAt = currentDate.setMilliseconds(currentDate.getMilliseconds() + stepData.runMiliseconds);
console.log(new Date().toISOString() +" We will expire at "
+ new Date(stepData.expireAt).toISOString());
};
Remember how to undo the last completed step
if (!stepData.unDoAll) stepData.unDoAll = [];
if (unDoThis) stepData.unDoAll.push(unDoThis);
If time is expired, undo all completed steps
if (new Date(stepData.expireAt) < new Date().getTime()) {
while (stepData.unDoAll.length) {
var unDoOne = stepData.unDoAll.pop();
unDoOne();
}
console.log(new Date().toISOString() +' That was it!');
else perform the next step
} else {
doNext(stepData, Array.prototype.slice.call(arguments, 2));
}
}
From the below worker functions we will build the chain that we will interupt
function sleep(milliseconds) {
var start = new Date().getTime();
for (var i = 0; i < 1e7; i++) {
if ((new Date().getTime() - start) > milliseconds){
break;
}
}
}
function oneStep(stepData) {
console.log (new Date().toISOString() +' ('+ stepData.nrIterations +') I do some stuff ');
sleep(100);
var myIteration = stepData.nrIterations--;
if (stepData.nrIterations) {
nextStep(otherStep, stepData);
}
}
function otherStep(stepData) {
console.log (new Date().toISOString() +' ('+ stepData.nrIterations +') I do more stuff, leaving a trace');
sleep(100);
var myIteration = stepData.nrIterations--;
if (stepData.nrIterations) {
nextStep(oneStep, stepData, function () {
console.log(new Date().toISOString() +' ('+ myIteration +') I clean some trace ');
});
}
}
And now we use it.
Play around with runMiliseconds and nrIterations to see the effect
console.log (new Date().toISOString() + ' About to start ');
var currentDate = new Date();
nextStep(oneStep, {
runMiliseconds : 250,
nrIterations: 22
});