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    <p>setTimeout does not have a minimal delay of <code>0ms</code>. The minimal delay is anywhere in the range of 5ms-20ms dependent on browsers.</p> <p>My own personal testing shows that <code>setTimeout</code> doesn't place your back on the event stack immediately</p> <p><a href="http://jsfiddle.net/km5tY/63/">Live Example</a></p> <p>It has an arbitary minimal time delay before it gets called again</p> <pre><code>var s = new Date(), count = 10000, cb = after(count, function() { console.log(new Date() - s); }); doo(count, function() { test(10, undefined, cb); }); </code></pre> <ul> <li>Running 10000 of these in parallel counting to 10 takes 500ms. </li> <li>Running 100 counting to 10 takes 60ms.</li> <li>Running 1 counting to 10 takes 40ms. </li> <li>Running 1 counting to 100 takes 400ms.</li> </ul> <p>Cleary it seems that each individual <code>setTimeout</code> has to wait at least 4ms to be called again. But that's the bottle neck. The individual delay on <code>setTimeout</code>.</p> <p>If you schedule a 100 or more of these in parallel then it will just work. </p> <p>How do we optimise this?</p> <pre><code>var s = new Date(), count = 100, cb = after(count, function() { console.log(new Date() - s); }), array = []; doo(count, function() { test(10, array, cb); }); </code></pre> <p>Set up 100 running in parallel on the same array. This will avoid the main bottleneck which is the setTimeout delay.</p> <p>The above completes in 2ms.</p> <pre><code>var s = new Date(), count = 1000, cb = after(count, function() { console.log(new Date() - s); }), array = []; doo(count, function() { test(1000, array, cb); }); </code></pre> <p>Completes in 7 milliseconds</p> <pre><code>var s = new Date(), count = 1000, cb = after(1, function() { console.log(new Date() - s); }), array = []; doo(count, function() { test(1000000, array, cb); }); </code></pre> <p>Running a 1000 jobs in parallel is roughly optimum. But you will start hitting bottlenecks. Counting to 1 million still takes 4500ms.</p>
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    1. COI did think that perhaps a solution similar to this could be used as a work around. I'm not to sure that this is the absolute best approach. I have not tested it fully yet but it's interesting about the 4ms min delay on setTimeout. I will have a deeper play, do you know if setInterval has the same min delay?
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    2. CO@ashmokhberi all of them do. None of the timeouts are actually 0.
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    3. CO"Running a 1000 "threads" in parallel is roughly optimum", this is completely incorrect. For one, setTimeout does NOT spawn threads; it schedules timer events to be processed. Secondly, IF setTimeout DID spawn threads then having 1000 threads is totally NOT optimal, the memory overhead and CPU scheduling overhead would be atrocious. But, besides semantics the answer is 'technically' correct.
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