UV_THREADPOOL_SIZE undefined in Windows

[rhernandog]

• Node.js Version: 8.11.2
• OS: Windows 7 64
• Scope (install, code, runtime, meta, other?): startup
• Module (and version) (if relevant): none

Hi,

I'm not completely sure if this should be here or on the libuv repo, so correct me if I'm in the wrong place asking the wrong question.

I was running some benchmarks with apache benchmark on an express server and I tried to modify the number of threads in the thread pool through my index.js file with no success:
process.env.UV_THREADPOOL_SIZE=1;

I ran it through the command line and it worked, then I wanted to check the amount of threads by doing a console.log(process.env.UV_THREADPOOL_SIZE) call. The thing is that I forgot to remove that line of code and when I restarted my laptop I got undefined from the console call.

So in fact when you start a fresh boot of the machine the UV_THREADPOOL_SIZE property is not set in the process.env object. Why is that?, Why the property is not added with it's default size (4 as I understand from the libuv docs) at startup?.

On Start Up

console.log(process.env.UV_THREADPOOL_SIZE); // -> undefined

[gireeshpunathil]

#cat 1429.js
process.env.UV_THREADPOOL_SIZE=1;
console.log(process.env.UV_THREADPOOL_SIZE)
#node 1429.js
1
#

it does not happen to me. Just to be sure that we are on the same page: index.js is the only code you are having, or do you spawn other processes? I guess the settings in the index.js do not propagate to child processes, can you please check?

[rhernandog]

@gireeshpunathil Thanks for the answer.

Yep just one file. Here's an extremely simplified set up to reproduce the issue:

index.js

console.log( process.env.UV_THREADPOOL_SIZE ); // -> undefined

const express = require("express");

// EXPRESS
const app = express();

app.get("/", (req, res) => {
  res.send("Hi didly ho!!!");
});

app.get("/fast", (req, res) => {
  res.send("FAST FAST FAST!!!!");
});

app.listen(3000, null, () => {
  console.log("express working on port 3000!!!");
})

This in a folder with just express 4.16.3 installed. Run node index and this is the result:

As I mentioned this happens on Windows 7 64b (I believe most windows OS as well, haven't tested in 8 or 10 yet).

Also is worth mentioning that if I set the thread pool size via command line it is defined and set and after that I can change it through the index.js file or any other file. So doing this first:

$ SET UV_THREADPOOL_SIZE=1

Then running the index file gives this result:

$ node index
1
express working on port 3000!!!

[gireeshpunathil]

where are you doing:
process.env.UV_THREADPOOL_SIZE=1; in index.js ? I don't see it in your code (previous comment)

setting the value in the command line is the right behavior, and the right way to use it - so that different runs can use different values, if need be, without changing the source.

[rhernandog]

Yep, in that file is not there, it is just the most reduced code sample to reproduce that.

A simple solution is to create an NPM script:

SET UV_THREADPOOL_SIZE=1 && node index

But I was trying to actually avoid that. At the end I was just curious about why process.env.UV_THREADPOOL_SIZE returns undefined in Windows OS' before setting the value via CLI and not on OSX, because in OSX you can set the number of threads through a file. I just want to know if it's by design or not, if it's because how the specific OS works, etc. Just looking for an answer of why 😄

[gireeshpunathil]

#uname
Darwin
#node
> console.log( process.env.UV_THREADPOOL_SIZE );
undefined
undefined
> 

I don't see anything special with macos. If UV_THREADPOOL_SIZE is not defined in the command line (export UV_THREADPOOL_SIZE ... ) or in the source (process.env.UV_THREADPOOL_SIZE ...) it is always going to be undefined.

I fear there is a disconnect between us. Am I missing something from your explanation?

[rhernandog]

No you're getting everything right, It was just I wanted to know why is undefined in one OS and not in another, just that.

[gireeshpunathil]

ok, let us resolve this confusion.

1. Can you run:
   console.log( process.env.UV_THREADPOOL_SIZE ); in both win and mac to see if it differs?

2. Can you run:

process.env.UV_THREADPOOL_SIZE = 1;
console.log( process.env.UV_THREADPOOL_SIZE ); 

in both and see if it dffers?

3. Can you run:

$ export UV_THREADPOOL_SIZE=1
and
console.log( process.env.UV_THREADPOOL_SIZE );

in UNIX and
> set UV_THREADPOOL_SIZE=1
and
console.log( process.env.UV_THREADPOOL_SIZE );

in windows and see if they differ?

In all cases I would expect they don't.

[gireeshpunathil]

ping @rhernandog

[gireeshpunathil]

inactive, closing; pls reopen if the the issue is still relevant

[Polyhistor]

@gireeshpunathil the issue exists on windows. I'm currently running on windows 10 and Node v12. I've logged process.env, it's got no UV_THREADPOOL_SIZE property on it...

The exact same behaviour exists on Ubuntu 10 and Node V10

[lorand-horvath]

Having the exact same problem on Win 7 and Node 12.22.12. By default, process.env.UV_THREADPOOL_SIZE is undefined, unless I set it from CMD with set UV_THREADPOOL_SIZE=1, for example.

The other very strange issue that I must mention is that setting process.env.UV_THREADPOOL_SIZE = 1; in the js file doesn't have any effect on the actual number of threads. It only does if I set it via the command line, BEFORE running node index.js
A similar report can be found here: https://stackoverflow.com/questions/68691702/process-uv-threadpool-size-size-is-not-working-in-windows

[gireeshpunathil]

re-opening, as there are at least 2 affected parties

@nodejs/libuv - is there anything special with UV_THREADPOOL_SIZE on windows? I couldn't find anything either in the code or in docs; yet the reports say that the value is not honoured.

[saghul]

AFAIS Node calls uv_os_setenv here: https://github.com/nodejs/node/blob/5fad0b93667ffc6e4def52996b9529ac99b26319/src/node_env_var.cc#L149

But it does not check for the return value, and that function might fail: https://github.com/libuv/libuv/blob/97dcdb1926f6aca43171e1614338bcef067abd59/src/win/util.c#L1543