Node: Process V8 profiler output not working (new v8.10.0)

Created on 7 Mar 2018 · 20Comments · Source: nodejs/node

Version: v8.10.0
Platform: linux x64
Subsystem: Ubuntu 17.10 artful

After generate log statistical profiling information (node --prof), process V8 profiler output generated (node --prof-process isolate-0xnnnnnnnnnnnn-v8.log) doesn't output anything to standard ouput. It seems it consumes almost all CPU available.

I've been testing with example from Easy profiling for Node.js Applications.

It works fine with previous v8.9.4 version. You can use Simple profiling repository to test it.

help wanted

Source

antoniobusrod

👍9

Most helpful comment

It looks like the .log files produced by node v8.9.4 have a newline at the end, and the ones produced by v8.10.0 don't.

I built a debug build of v8.10.0 and interrupted it in the debugger while it was hanging. It seems to be calling filesystem read in an infinite loop. I guess something expects a newline at the end of the file.

None of the log files I can generate to cause the hanging end with 0xa and all of the ones that work end with 0xa.

Not sure where that expectation is happening though, also not sure whether the v8 profiler output changed or if node itself writes the file.

psmarshall on 29 Mar 2018

👍23 🎉3 ❤1

All 20 comments

I guess that makes the V8 6.2 update a prime candidate for causing this … /cc @nodejs/v8

addaleax on 7 Mar 2018

/cc @gibfahn

MylesBorins on 13 Mar 2018

It works fine with previous v8.9.4 version. You can use Simple profiling repository to test it.

Can you explain more about how to reproduce with that repository?

This is what I get when I run the steps from the readme on a vagrant box (on a macOS machine):

Node v8.10.0

Node v8.9.4

I set up the VM with:

vagrant init ubuntu/artful64
vagrant up
vagrant ssh

And then used nvm to install node 8.10.0.

gibfahn on 14 Mar 2018

One observation that might help:

The issue happens when I use node --prof with v8.10.0 to record the profiling information and then --prof-process gets stuck with either v8.10.0 or v8.9.4.

However, when I use v8.9.4 to create the profiler file, both versions succeed with --prof-process...

guymguym on 15 Mar 2018

any idea how to push this forward?
more info needed?

guymguym on 22 Mar 2018

I think we need someone from the V8 team to take a look at it (cc/ @nodejs/v8 again).

gibfahn on 22 Mar 2018

It looks like the .log files produced by node v8.9.4 have a newline at the end, and the ones produced by v8.10.0 don't.

None of the log files I can generate to cause the hanging end with 0xa and all of the ones that work end with 0xa.

Not sure where that expectation is happening though, also not sure whether the v8 profiler output changed or if node itself writes the file.

psmarshall on 29 Mar 2018

👍23 🎉3 ❤1

Hi @psmarshall is right, I've repeated the test using v8.11.1 and it failed as I described in this issue. However, If I manually add an empty line at the end of isolate-0xnnnnnnnnnnnn-v8.log, it works.

antoniobusrod on 2 Apr 2018

👍1

@psmarshall thanks a lot!

charlesdarkwind on 8 Apr 2018

Ran into the same issue, checked the isolate-0xnnnnnnnnnnnn-v8.log file for a missing newline. Interestingly, mine already had a newline... So I added another and it worked fine after! Strange, but thought I'd share.

archcorsair on 1 May 2018

👍13 🚀1

@davidmarkclements FYI

psmarshall on 4 May 2018

Hi, I've just tested with new v8.11.2, and I reproduced same results than previous comment https://github.com/nodejs/node/issues/19199#issuecomment-377943343

Version: v8.11.2
Platform: linux x64
Subsystem: Ubuntu 18.04 LTS bionic

antoniobusrod on 16 May 2018

👍1

@archcorsair weird your solution worked for me

DaAwesomeRazor on 20 May 2018

👍3

@archcorsair thanks! That's the fix for Node v8.x

karliky on 7 Jun 2018

I think this issue needs some investigation on what code has changed (v8 vs. node) that causes the newline to be missing. Adding the 'help wanted' label.

ofrobots on 25 Jun 2018

I just tried to reproduce this on mac and I couldn't, it seems people commenting here who reproduced it did so on linux. Not sure why that's the case but I can take a look next week when I have access to my linux machine again.

psmarshall on 29 Jun 2018

@psmarshall I have reproduced it on my mac.
macOS: 10.13.5
node: v8.11.3

The newline fixed the issue for me as well.

michaeltarleton on 1 Jul 2018

👍4

It's not just a simple missing newline for me. The last line in the log file is actually incomplete after CTRL-C'ing.
Likely meaning the process is abruptly terminating instead of flushing the rest of the line and a newline.

os: Ubuntu 16.04, node: v8.11.3

s-stark on 24 Jul 2018

I have reproduced it on my linux.
ubuntu version: 16.04
node: v8.11.4

gtzinos on 3 Oct 2018

Node.js v8.x has reached the end-of-life and won't receive any fixes anymore. I am closing this since this issue seems to only apply to Node.js v8.x. If it does apply to newer versions as well, please leave a comment so that this can be reopened. No matter if you run into this issue or not, please update to a newer Node.js version in case you still use v8.x.