Create a gist now

Instantly share code, notes, and snippets.

What would you like to do?
Event loop
/**
* Event loop.
*
* Read details here:
* http://dmitrysoshnikov.com/ecmascript/javascript-the-core-2nd-edition/#job
*
* by Dmitry Soshnikov <dmitry.soshnikov@gmail.com>
*/
/**
* Call-stack.
*/
const stack = [];
/**
* Jobs queue.
*/
const jobs = [];
/**
* Event loop spins, and checks whether something was enqueued.
* If the execution stack is empty, it picks a job, and executes it.
* A job can enqueue other jobs.
*/
setInterval(function eventLoop() {
console.log(
`\n Analyzing jobs queue:`,
`[${jobs.map(job => job.name).join(', ')}]\n`
);
// Something is on the stack, can't run jobs yet.
if (stack.length) {
return;
}
// Nothing to run.
if (!jobs.length) {
return;
}
// Pick up the next job, and put it onto the stack.
const job = jobs.shift();
run(job);
}, /* Spin! */ 1000);
/**
* Executes the code.
*/
function run(activation) {
// Emulate stack "push-pop".
stack.push(activation);
console.log(
`Running "${activation.name}", stack:`,
`[${stack.map(context => context.name).join(', ')}]`
);
// Run the code.
activation();
stack.pop(activation);
}
/**
* The `postponeCall` waits for the ms, and then
* enqueues the activation as a job.
*/
function postponeCall(runnable, ms) {
setTimeout(() => jobs.push(runnable), ms);
}
// -----------------------------------------------------------------------------
// Tests.
function one() {
run(two);
}
function two() {
postponeCall(three, 10);
}
function three() {
postponeCall(four, 10);
postponeCall(five, 20);
run(six);
}
function four() {
return;
}
function five() {
return;
}
function six() {
return;
}
// Go!
(function start() {
// Enqueue the first call, which will run other functions,
// and enqueue other postponed calls.
postponeCall(one, 100);
})();
// -----------------------------------------------------------------------------
// Results:
/*
Analyzing jobs queue: [one]
Running "one", stack: [one]
Running "two", stack: [one, two]
Analyzing jobs queue: [three]
Running "three", stack: [three]
Running "six", stack: [three, six]
Analyzing jobs queue: [four, five]
Running "four", stack: [four]
Analyzing jobs queue: [five]
Running "five", stack: [five]
Analyzing jobs queue: []
Analyzing jobs queue: []
Analyzing jobs queue: []
...
*/

👍

IegorT commented Dec 7, 2017

Clear example
image

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment