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waterfall much slower than series #621

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elad opened this issue Sep 11, 2014 · 4 comments
Closed

waterfall much slower than series #621

elad opened this issue Sep 11, 2014 · 4 comments
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performance

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@elad
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elad commented Sep 11, 2014

Hello,

I've put the following in a file called async.html and opened it in Chrome:

<html>
    <head>
        <script type="text/javascript" src="http://cdnjs.cloudflare.com/ajax/libs/async/0.9.0/async.js"></script>
        <script type="text/javascript">
            function log(msg) {
                console.log((new Date).toISOString(), msg);
            }

            log('waterfall: start');
            async.waterfall([
                function(callback) {
                    log('waterfall: function');
                    callback();
                }
            ], function(err) {
                log('waterfall: finish');
            });

            log('series: start');
            async.series([
                function(callback) {
                    log('series: function');
                    callback();
                }
            ], function(err) {
                log('series: finish');
            });
        </script>
    </head>
</html>

The output in the console looks like:

2014-09-11T14:16:41.136Z waterfall: start async.html:6
2014-09-11T14:16:41.141Z series: start async.html:6
2014-09-11T14:16:41.141Z series: function async.html:6
2014-09-11T14:16:41.142Z series: finish async.html:6
2014-09-11T14:16:41.150Z waterfall: function async.html:6
2014-09-11T14:16:41.151Z waterfall: finish async.html:6

Note the delay between waterfall's "start" and "function" (14ms) vs. series' (0ms). In a real-world web app I have the waterfall delay is usually around 600ms. (!)

Is this a known issue, or even an issue at all? is there a reason for such a delay?
@aearly
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aearly commented Sep 11, 2014

waterfall has a async.nextTick at each stage of its iteration to prevent stack overflows. In the browser, this is implemented as setTimeout(iterate, 0), which can actually take as long as 8 ms in certain cases.

If your functions are not actually asynchronous, i would not recommend using waterfall, bust something like _.compose instead.

@elad
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elad commented Sep 11, 2014

Good call. I was under the impression it was something like that since it could not be reproduced in jsfiddle or node.js.

My functions are async but this suggests I should work around control flow (passing values) and use series if I don't want to suffer a performance impact.

I would suggest making this distinction clearer in the documentation, but I'll accept if this is something too obvious/esoteric. Feel free to close this issue.

Thanks! :)

@aearly
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aearly commented Sep 11, 2014

I actually would be a fan of removing the nextTick and just add the caveat that you could have a stack overflow if your functions aren't async. But that's something for @caolan to decide.

@BrandonZacharie
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It is important to use process.nextTick in asynchronous APIs. This is fully explained in the Node.js documentation.

@aearly aearly mentioned this issue Jan 11, 2015
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@aearly aearly closed this as completed May 19, 2015
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@BrandonZacharie @aearly @elad