Hi, I need to create a infinite (but breakable) cycle where I can slow down the cycle by awaiting promises inside. While cycle should be able to do this, but as you can see in the image, the duration is all over the place.

Why is this happening? Is there a way to make it close to the original sleep duration?

  • pe1uca@lemmy.pe1uca.dev
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    1 year ago

    JS is a single threaded language, so there’s just one long line of instructions, there’s no actual background tasks.
    A promise just runs at the next available slot the event loop provides so it’s just as soon as it can run.

    In this case I’m guessing other part of the code running in your JS engine is blocking the event loop preventing your code to run just after one second.

    Where are you running it? Browser or server?
    Are you using a framework? If so, have you tried just this piece of code without any other imported code?

  • JaddedFauceet@lemmy.world
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    1 year ago

    Here is the code for anyone else who want to try

    async function slowLoop() {
        while (true) {
            console.time('sleepDuration')
            await new Promise(resolve => setTimeout(resolve, 1000))
            console.timeEnd('sleepDuration')
        }
    }
    

    It is not suppose to deviate too much. setTimeout will execute whenever possible at / after the given timeout duration. I am getting between 1006 to 1023 on my sysyem

    Is your device performance starved during this test?

    • iFarmGolems@lemmy.worldOP
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      1 year ago

      It’s not. I am running process lasso tough but doubt that’s the issue.

      I have Ryzen 5800x3D and tried the code on latest Ms edge (chromium) browser.

      Which browser did you try it on? Or did you try to run it in node?

      The browser tab was active and focused also.

      • JaddedFauceet@lemmy.world
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        1 year ago

        I have tested the code in both Chrome and MS Edge.

        Is anything else running on the same page that you are testing?

        You can test this in an empty environment like this: Enter this in your URL, “about:blank” and test the code in the console.

        • iFarmGolems@lemmy.worldOP
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          1 year ago

          I tried it in about:blank but it does the same. Maybe there is some extension in my browser that slows it down (somehow). Im running tampermonkey but it’s not active on any pages I tried this on.

          I ran the script in nodejs and everything works perfectly, the sleep time is very close to the original value so it’s definitely something inside browser that causes it to lag.

  • Windex007@lemmy.world
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    1 year ago

    I don’t know anything about JS, but those timings are suspiciously close to integer multiples of your sleep duration, after the first.

    Based on what you’ve shown, “All over place” is not what I’d call it. It either fires “on time” or takes “exactly-ish” twice as long.

    • iFarmGolems@lemmy.worldOP
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      1 year ago

      I said all over the place because I’ve seen numbers like 1.7 seconds, 2.8 seconds and so on. But it does mostly land on integer multiples.

      Anyway, tried to run this in nodejs and it works as expected - so the conclusion is that it’s somehow a limitation in browser engine (V8 in this case)

  • masnun@lemmy.world
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    1 year ago

    It’s the while loop that may be blocking the event loop and slowing the execution.

    • iFarmGolems@lemmy.worldOP
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      1 year ago

      This also happens when I create recursive asynchronous function that awaits the sleep and then itself. I have no clue what the problem is in that case.