Main Thread hangs w/ glitch+debugger open in background

[digitarald]

STR:

• Start a new html-webpage based glitch project
• Open the Show Live page in a new tab and open the Debugger on it
• Switch back to tab with Glitch editor
• Open the script.js file
• Type away and edit the file (adding a console.log, etc)

ER: Blissful editing with usual performance behaviour
AR: Glitch updating the JS file in the background causes 1s+ hangs (on a high end MBP) from getSourcesByUrlInSources

https://perfht.ml/2R6Cn7i

[jasonLaster]

It looks like there are two big issues:

• checkPendingBreakpoints which uses an expensive check -- perf
• newSources which calls updateSource -- perf

[jasonLaster]

@digitarald i could not reproduce with this example https://glitch.com/edit/#!/workable-worm

Also the profile has a lot of checkPendingBreakpoints did you have any breakpoints set?

[digitarald]

Just tried again in Nightly: http://bit.ly/2Wiw58G

I am using https://glitch.com/edit/#!/seed-swamp?path=script.js:8:27 with some async functions and console.trace statements.

[jasonLaster]

@digitarald the perf link isn't opening for me...

[digitarald]

@digitarald the perf link isn't opening for me...

Try a hard refresh, this fixed it for me.

[julienw]

Hard refresh should never be necessary, especially now that we have this nifty reload notification. Moreover we (should) reload automatically if we see this error and there's an update.

Basically a hard refresh avoids the service worker, so it may seem to work when the service worker hasn't downloaded an update yet, but this is never a good fix for perf-html :)

I believe this happened because @digitarald doesn't use perf-html.io to capture, but maybe another URL (like master.perf-html.io?)

[julienw]

Or the update wasn't finished yet :)

[digitarald]

Updated link that works for me: http://bit.ly/2Wiw58G

[jasonLaster]

thanks. I'm still not reproducing the slowdown, which makes sense given i don't see checkPendingBreakpoints in my profile either. http://bit.ly/2TlZHjs

mind checking how many bps you have saved?

1. browser toolbox
2. select debugger.html
3. await dbg.asyncStore.pendingBreakpoints in the console

[digitarald]

Closing for now as we don't have a working STR; will re-open if I see this again.