No different than having a dedicated threadpool for asynchronous programming on the JVM.
Yes blocking the event loop is easy. No it's not THAT easy. I've never done it because you think about it while writing code. It's part of the environment. I have had to fix lots of reports etc that try to load up the world and iterate through it in a loop that doesn't yield to the event loop. It's possible to never make that mistake by understanding your environment (just like how managing pointers in C is "hard").
To be pedantic, all JavaScript functions block the event loop. It's just that the vast majority of functions execute so quickly that the amount of time your function blocks is very short.
I once had a loop that processed tons of data and would block the event loop for 1-3 seconds. I ended up solving it by writing an asynchronous loop which used promises and process.nextTick() to make each iteration a separate execution block on the event loop. But I've only had to do something weird like that once in 10 years of node development.
At one company I built API middleware that calculated time spent in the event loop vs waiting on dependencies (other apis, Redis, etc) by managing a couple counters per request. It was very helpful.
However, running multiple containers for parallelism sounds a little bit crazy. In the worst case, each container may be running on its own server, but even assuming multiple containers per host, I'm guessing they were running an insignificant number of instances, which is probably why they were able to save $300k in server costs.
> We were running 4,000 Node containers (or "workers") for our bank integration service.
All I'm saying is that the choice of language is (usually) not the issue. Poor architecture design causes a lot more problems than whether you choose python/java/ruby/node for your webapp.
As someone not well-versed in js, could you describe one such case? Concurrent access to a global from two threads? Mutexes? My background is more with systems languages and I have done very little js for the browser, so I do not see that big red button.
If your function blocks, for example, by performing a wait on something without yielding, then nothing else gets computed because of the wait, but the event queue is occupied since the function has not yielded. This breaks the cooperative part of the cooperative multithreading mechanism of Node.
If the event loop is part of the Node language/runtime, I can see the case for making it preemptive.
All this has happened before. All this will happen again.
In Javascript world I guess you could do the same by replacing time.sleep with some CPU bound code. eg a big calculation or an infinite for loop.
I'm working on a project now that's very CPU bound and using limited workers behind an MQ as a distributed RPC behind a fronting API interface so that I can handle scaling... though it's also a Windows-only library involved. There's definitely an art to scaling certain types of workloads and many different options. Sometimes the simplest solution you can come up with really is the best option.
The first Node.js service I wrote and maintained, processed thousands of requests in parallel and was successfully in production until the company it was developed for ran out of money.
Some features would become unusable, like Promises and async/await, but those would be worthless in such a design anyway.
As much as I'd like to see it, your JS without an event loop is a purely theoretical construct so far.
I wouldn't implement it for the HTTP server/backend use case, because I find the blocking/share nothing architecture of PHP limiting.
The point is the language doesn't prevent this kind of architecture.
There is a massive deadlocking design mistake in the centre of the language - literally a huge red button with DO NOT PRESS printed on it. Thousands of programmers pass it by every single day, or hour, or minute, and the creators of the runtime insist that it is impossible to fix that button whatsoever; instead, all users need to work around it by ensuring that their code in no way presses that red button on purpose or even by accident.
These people insist that it is impossible to program normally and in a language that is actually sane and does not advertise obvious and gaping design mistakes as "features of the language". These people advertise the analogue of Python's Global Interpreter Lock as the core foundation of their language.
These people advertise Node and the language it implements as practical for implementing multithreaded applications. Posts such as this show what sort of bullshit it is; it is only practical to use Node for parallelism if each single Node instance is only ever run single-threaded. You don't parallelize by running multiple threads, you parallelize by running multiple Node runtimes.
This is no longer an act against productivity or usability. This is simply insane and shows one of the most basic things that are wrong about Node's language and approach. It is impossible to write a multithreaded program if your language of choice makes it trivial, and practically unavoidable, to globally lock your whole runtime with every single line of code you write and import as your dependencies.