I have a very expensive task running on a Worker, similar as this
for(var i = 0; i < 1000000000; i++)
//operations using i...
How can I make is so that, in that loop, I can check if a message was received from the Worker owner asking it to stop? I would like to have something like this
for(var i = 0; i < 1000000000; i++)
if(windowDidNotAskToStop())
//operations using i...
Right now I have a onmessage function registered so I can start listen to message coming from the owner, but it is blocked while my loop is running (obviously).
I imagine that the postMessage calls from the owner are queued somewhere, so I would simply have to access that in order to process the calls from inside my loop.
You’ll have to handle the events as usual and set a flag, but make sure to leave time for the event to be received in your loop, probably using setTimeout:
var exitLoop = false;
(function loop(i) {
if (exitLoop || i >= 1000000000) {
return;
}
// …
setTimeout(function () {
loop(i + 1);
}, 0);
})(0);
onmessage = function (e) {
if (e.data === 'stop') {
exitLoop = true;
}
};
Or, as a general utility function:
function asyncIterateRange(start, end, callback) {
var exitLoop = false;
var doneCallbacks = [];
(function loop(i) {
if (exitLoop) {
return;
}
if (i >= end) {
doneCallbacks.forEach(function (callback) {
callback();
});
return;
}
callback(function () {
setTimeout(function () {
loop(i + 1);
}, 0);
});
})(start);
return {
abort: function abort() {
exitLoop = true;
},
done: function addDoneCallback(callback) {
doneCallbacks.push(callback);
}
};
}
Use it like so:
var innerIterator;
var outerIterator = asyncIterateRange(0, 1000000, function outerLoop(next) {
innerIterator = asyncIterateRange(0, 1000, function innerLoop(next) {
// …
next();
}).done(next);
});
// To stop:
if (innerIterator) {
innerIterator.abort();
}
outerIterator.abort();
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