Only by reducing the number of iterations from 10⁷ to 10⁵, it completed after 2:23 minutes! (If you wonder, passing 1, instead of 0, as the delay parameter to setTimeout makes no difference - more on this later) Unfortunately, the cost of this solution is too high: we can see that the CPU is at about ~10%, so it seems it doesn’t work hard enough on the computation, which practically takes forever to complete (didn’t have enough patience to see it happen). So let’s start with a simple Express server:įinally, the server remains responsive during the heavy computation. You can play with the code bellow by cloning
First, let’s block the Node.js Event-Loop!Įxamples below use Node 10.9.0 on an Ubuntu 18.04 VM with 4 cores, running on a MacBook Pro 2017 I’ll do my best to share the various questions I had, and share the answers I’ve found in various great articles, some fun experimentation and digging. Plenty of valuable information already exists about the Node.js Event-Loop, but it took me time find the answers for the specific questions I wanted to ask. I believe it’s important that as many Node developers will have this knowledge too - which led me to writing this article. When I tried to fix the situation, I realized how little I actually knew about the event-loop behavior and gained some realizations that at first surprised me and some fellow developers I shared this with. I recently stumbled upon a real event-loop blocking scenario here at Snyk.
This is a known and challenging limitation of Node and is also nicely explained in the docs. There is a single main thread (a.k.a the Event-Loop) that executes all these callbacks, and thus the callbacks should be quick to complete as all other pending callbacks are waiting for their turn. But in the second model, even with few nurses, you might be able to serve many patients.A typical Node.js app is basically a collection of callbacks that are executed in reaction to various events: an incoming connection, I/O completion, timeout expiry, Promise resolution, etc. To ask each nurse to check each patient, and during the interval till next check, go on and check other patients.Either to ask each nurse (thread) to watch one, and only one patient (a job, a task to be done), even if between each check she waits for an hour ( Sleep() method).If we compare operating system to a hospital, and compare the threads to nurses in that hospital, the supervisor (programmer) can choose a policy: This way, during that 100 ms, your program can do other tasks.
You can schedule a task to check that third API every 100 ms. Update: I don't know about the infrastructure of Timer class in C#. For example, node.js is a non-blocking language. Recent efforts is to make blocking as least as possible. One reason is that Thread.Sleep() is blocking your code from doing anything else.
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