warning: <x> FS.syncfs operations in flight at once, probably just doing extra work

Aurigan · Dec 21, 2016

I'm getting an old game running on webGL for the first time ever, using Unity 5.5p1. So far I have everything working but the (chrome) console every 8 seconds is spitting out 3 warnings:

warning: 2 FS.syncfs operations in flight at once, probably just doing extra work
warning: 3 FS.syncfs operations in flight at once, probably just doing extra work
warning: 4 FS.syncfs operations in flight at once, probably just doing extra work

From a quick google search FS.syncfs appears to be something to do with the javascript / indexed db filesystem so presumably *something* is doing a file op 4x at the same time ... I have no idea what that might be though, still happens after disabling save games (which use player prefs).

Has anyone seen this / have a solution for it?

Arsinx · Jan 23, 2017

I recently built a game for webgl using 5.5 and i am getting the same warnings as soon as the unity logo appears after which it gets stuck there, if any one knows how to solve this issue it will be really appreciated.

DSL-TailorIt · Jan 25, 2017

This warning also appears in my builds, although it doesn't prevent me from actually using my application.

In my case I think it might have something to do with loading AssetBundles, but I haven't verified it yet.

I worry more about warnings than actual errors, so if anyone knows something about this, I would be also be thankful to get some possible solution.

Thanks in advance

Aurigan · Mar 16, 2017

bump! getting this in a completely new game also

Schubkraft · Mar 17, 2017

This seems to be harmless, we'll look into it though.

Aurigan · Mar 17, 2017

Thank you - it DOES appear to be harmless in practice but vexing to have unneeded log spam.

AzureByte · May 3, 2017

For me I think this is a symptom of another problem. I am getting random fps drops throughout the game while running a WebGL build in browser. No performance issues on mobile/PC builds

3DNewsman · Jul 5, 2017

Bumping this. We've had it on our app for a long time, and seems like it would be helpful to get to the bottom of it.

therealao · Jul 27, 2017

Bump, I've a feeling this is causing some performance issues. I'm only getting about 25% of the framerate of a native x86-64 build in WebGL, for a much smaller scene.. Any insight would be greatly appreciated

Marco-Trivellato · Aug 1, 2017

therealao said: ↑

Bump, I've a feeling this is causing some performance issues. I'm only getting about 25% of the framerate of a native x86-64 build in WebGL, for a much smaller scene.. Any insight would be greatly appreciated
Click to expand...

how many "FS.syncfs operations..." warnings are you seeing? just a few or a continuous flow?

The gap in performance might be simply be caused by the fact that Unity WebGL is single-threaded at the moment.

hromoyDron · Jan 24, 2018

I have the same message (unity 2017.3)

When I start using AssetBundleManager I see much more warnings

What to do?

Marco-Trivellato · Jan 24, 2018

hromoyDron said: ↑

I have the same message (unity 2017.3)

When I start using AssetBundleManager I see much more warnings

What to do?
Click to expand...

If everything works well, do nothing

keeves_test14 · Feb 28, 2018

Hi, I'm using unity 5.6.3f3 and when I run webgl build I'm getting the following warning.

warning: 2 FS.syncfs operations in flight at once, probably just doing extra work.

I've AI player in my game,when AI turn occurs, the warning is occured and ai player can't take its move for this.Please help me to solve the issue.

ProgrammingWhileSleeping · Jun 12, 2018

Hi, I have found a solution but I'm not sure I could say this is a great one, it would disable all the logging and it would only work for WebGL. Just add these lines of code before the game is instantiated.

var DEBUG = false;
if(!DEBUG){
if(!window.console) window.console = {};
var methods = ["log", "debug", "warn", "info"];
for(var i=0;i<methods.length;i++){
console[methods] = function(){};
}
}

Source: https://stackoverflow.com/questions...disable-all-console-log-statements-in-my-code

WARNING: This will completely remove all console logs, so if you have any intended clues for the game in the logs, then it would not be recommended.

ProgrammingWhileSleeping · Jun 12, 2018

Full code in case anyone gets confused with my answer, just replace your index.html code with this:

<!DOCTYPE html>
<html lang="en-us">
<head>
<meta charset="utf-8">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Unity WebGL Player | Your Title</title>
<link rel="shortcut icon" href="TemplateData/favicon.ico">
<link rel="stylesheet" href="TemplateData/style.css">
<script src="TemplateData/UnityProgress.js"></script>
<script src="Build/UnityLoader.js"></script>
<script>
var DEBUG = false;
if(!DEBUG){
if(!window.console) window.console = {};
var methods = ["log", "debug", "warn", "info"];
for(var i=0;i<methods.length;i++){
console[methods] = function(){};
}
}
var gameInstance = UnityLoader.instantiate("gameContainer", "Build/Your Title.json", {onProgress: UnityProgress});
</script>
</head>
<body>
<div class="webgl-content">
<div id="gameContainer" style="width: 960px; height: 600px"></div>
<div class="footer">
<div class="webgl-logo"></div>
<div class="fullscreen" onclick="gameInstance.SetFullscreen(1)"></div>
<div class="title">Your Title</div>
</div>
</div>
</body>
</html>

twobob · Jul 16, 2018

Hmmm.. this seems like a nothing error all in. that said. Roll-on threading

EDIT: and yes, I have it too

VMS_Lab · Aug 6, 2018

I think this error is related to my game crashing in WebGL. When I do a build with No Exceptions enabled my the game crashes in the browser. When I do a build with Full Exceptions enabled this error is the first pop up and and the game loads fine. No other exceptions are thrown. Could this error cause a game to crash?

emirkoskenli · Dec 1, 2018

Looks like this error causing high CPU usage and my game getting slower in time. It is continuous flow at console.
"warning: 65 FS.syncfs operations in flight at once, probably just doing extra work"
Spammed this error like 60-100 times in a minute. Searched google but no luck.

hsallander · Oct 10, 2019

Hi all, we're seeing this issue as well in our WebGL game, using Unity 2019.2. Any progress on this issue, or a workaround we can use, @Marco-Trivellato or @Schubkraft ?

jukka_j · Oct 10, 2019

FS.syncfs() is triggered by a call that either saves or loads persistent content to IndexedDB. I am not sure exactly which all Unity APIs can trigger this, but look for a connection with PlayerPrefs, writing to disk/filesystem or asset bundles.

The warning itself is not about anything bad/incorrect happening, but it is a performance warning of redundant work that occurs - a previous save/load operation has not yet finished, but a new save/load operation is already being attempted.

TheJimz · Nov 21, 2019

jukka_j said: ↑

FS.syncfs() is triggered by a call that either saves or loads persistent content to IndexedDB. I am not sure exactly which all Unity APIs can trigger this, but look for a connection with PlayerPrefs, writing to disk/filesystem or asset bundles.

The warning itself is not about anything bad/incorrect happening, but it is a performance warning of redundant work that occurs - a previous save/load operation has not yet finished, but a new save/load operation is already being attempted.
Click to expand...

Sounds like this warning itself is causing a lot more slowdown than what it's warning about. Can we please disable it?

jukka_j · Nov 27, 2019

You can disable the warning by editing C:\Program Files\Unity\Hub\Editor\<unity_version>\Editor\Data\PlaybackEngines\WebGLSupport\BuildTools\Emscripten\src\library_fs.js around line ~496, delete line

console.log('warning: ' + FS.syncFSRequests + ' FS.syncfs operations in flight at once, probably just doing extra work');

forzabo · Jan 12, 2020

For any one on macOS (like me) wondering where this file is:

/Applications/Unity/PlaybackEngines/WebGLSupport/BuildTools/Emscripten/src/library_fs.js

Commenting out lines 495-497 does the trick.

dblaw · Nov 30, 2020

As a potential help to others who may be googling this:

I had the same problem. Things fine in the editor, crash in WebGL, when turning on the warnings things worked fine with the error "FS.syncfs operations" as described here.

I had been using a .Find on a game object (I know I know). But, that game object was not there because I had moved things around and renamed stuff. Getting rid of my bad .Find fixed things right up. Really wish there would have been some kind of error telling me what I had done.

salqadri · Sep 8, 2021

I see this warning as well. If this should not be a warning, how about not use the word 'warning' in the log, or better yet, how about Unity get rid of that message unless you can give concrete documentation on why this message is something we should act on and how.

twobob · Sep 9, 2021

salqadri said: ↑

I see this warning as well. If this should not be a warning, how about not use the word 'warning' in the log, or better yet, how about Unity get rid of that message unless you can give concrete documentation on why this message is something we should act on and how.
Click to expand...

HOW ABOUT YOU READ UP - ABOUT 3 MESSAGES.
since we all so keen to be shoutily telling other what to do.

jukka_j

Unity Technologies

States very clearly what it is - why it is - and what you can do.

mickfcna · Mar 31, 2022

Got the same error on Unity 2019.4, any update ?

sebj · May 31, 2022

In our game, the number of FS.syncFSRequests increases continuously (up to the thousands over an hour or so). Is that also expected or are we leaking something?

EduTech_dev · Nov 18, 2022

I solved the issue by just limiting the FPS to 30p/second.

Application.targetFrameRate = targetFrameRate;

ExNinja · Feb 12, 2023

Be wary of setting Application.targetFrameRate on WebGL, as it causes other issues:
https://forum.unity.com/threads/ren...questanimationframe-for-the-main-loop.373331/

kenorbik · Feb 15, 2023

Same warning, and nothing loads, stuck on the black screen.

Code (Boo):

Initialize engine version: 2021.3.16f1 (4016570cf34f)

[UnityCache] 'http://localhost:8000/Build/WebGL.data' successfully revalidated and served from the indexedDB cache

WebGL.loader.js:80

warning: 2 FS.syncfs operations in flight at once, probably just doing extra work

printErr @ WebGL.loader.js:80

syncfs @ WebGL.framework.js:5329

sync @ WebGL.framework.js:1641

(anonymous) @ WebGL.framework.js:1650

setInterval (async)

setInterval @ WebGL.loader.js:66

_JS_FileSystem_Initialize @ WebGL.framework.js:1649

$main @ WebGL.wasm:0x22d13c5

(anonymous) @ WebGL.framework.js:1060

callMain @ WebGL.framework.js:18515

doRun @ WebGL.framework.js:18558

run @ WebGL.framework.js:18570

runCaller @ WebGL.framework.js:18498

removeRunDependency @ WebGL.framework.js:1015

(anonymous) @ WebGL.loader.js:1104

keli_laerdal · May 15, 2023

I've been hit by this bug as well and tracked the problem down to the sync(onlyPendingSync) method inside .../WebGLSupport/BuildToos/lib/FileSystem.js

The problem is when the onlyPendingSync parameter is true, the method is supposed to only run if there were syncRequests pending while a previous sync was running. The solution is to ensure that in addition to having pending syncs, it should also ensure that the ongoing fsync is not running. Here's a patch that should fix the problem:

Code (JavaScript):

--- old/FileSystem.js 2023-04-18 15:23:34.885222700 +0200

+++ new/FileSystem.js 2023-04-18 15:24:12.256876100 +0200

@@ -7,7 +7,7 @@

sync : function(onlyPendingSync)

{

if (onlyPendingSync) {

- if (fs.numPendingSync == 0)

+ if (fs.syncInProgress || fs.numPendingSync == 0)

return;

}

else if (fs.syncInProgress) {

Edit: Regarding whether this bug is harmless, it seems that it could be serious, as the original pending/inProgress hack is to work around a potential memory leak inside indexedDB, according to a comment in that file:

Code (JavaScript):

else if (fs.syncInProgress) {

// this is to avoid indexedDB memory leak when FS.syncfs is executed before the previous one completed.

fs.numPendingSync++;

return;

}

Update 05.15 I submitted a bug report with this patch, which got rejected without consideration due to not being "reprducible" I replied with a link to this thread.

JanetGilbertPraxis · Jun 8, 2023

It happens on all our WebGL builds, a lot. Very reproducible.

JanetGilbertPraxis · Jun 8, 2023

jukka_j said: ↑

You can disable the warning by editing C:\Program Files\Unity\Hub\Editor\<unity_version>\Editor\Data\PlaybackEngines\WebGLSupport\BuildTools\Emscripten\src\library_fs.js around line ~496, delete line

console.log('warning: ' + FS.syncFSRequests + ' FS.syncfs operations in flight at once, probably just doing extra work');
Click to expand...

We can't edit this file as we use Cloud build.

Leonova0 · Aug 2, 2023

Seems like no body is working on this....

AritaDev · Aug 30, 2023

I also encountered the same problem. I solved it by turning off parallel download tasks.
I guess if Unity WebGL has multiple tasks in IO or IndexDB processing at the same time, this log will be issued. Such as downloading files in parallel, resulting in parallel writing to IndexDB.
I changed the parallel download to serial and there is no such log

jukka_j · Aug 30, 2023

I audited the code path in question in detail today, and even though there was an old comment about a memory leak, that comment was stale from nearly a decade ago.

The message can be safely ignored, or if you would like to remove it, the earlier post helps to do that.

The root source of the "X FS.syncfs operations in flight at once, probably just doing extra work" message comes from an external codebase that is not authored by Unity ( https://github.com/emscripten-core/...a0fc0eeb91f60c5b6682cb/src/library_fs.js#L504 ), which is why controlling it in-house has had such friction for a long time.

However you all do bring up good points that the message should not be posted in the first place if it does not mean anything, since it will then be just a red herring to diagnosing some other more important issues. I have now authored a fix PR that will clean the warning away altogether, that should help resolve this topic for good. Thanks for persisting with the comments!

legoesbenr · Sep 5, 2023

jukka_j said: ↑

I audited the code path in question in detail today, and even though there was an old comment about a memory leak, that comment was stale from nearly a decade ago.

The message can be safely ignored, or if you would like to remove it, the earlier post helps to do that.

The root source of the "X FS.syncfs operations in flight at once, probably just doing extra work" message comes from an external codebase that is not authored by Unity ( https://github.com/emscripten-core/...a0fc0eeb91f60c5b6682cb/src/library_fs.js#L504 ), which is why controlling it in-house has had such friction for a long time.

However you all do bring up good points that the message should not be posted in the first place if it does not mean anything, since it will then be just a red herring to diagnosing some other more important issues. I have now authored a fix PR that will clean the warning away altogether, that should help resolve this topic for good. Thanks for persisting with the comments!
Click to expand...

Running LTS 2021.3.16f1 and this is till a problem. As a developer I don't understand how hiding the error can ever be considered a fix.
Just because the error is in a 3rd party library, does not remove the responsibility of the consumer (Unity), distributing it.
This bug is so old and there is even a fix for it posted. But us using Cloud Build can't leverage from that.
I strongly suggest that Unity pick this up and resolve it, either by addressing to the vendor of the third party library, contributing or deploying the above fix to Unity distributions.

We get this error massively. The console is spammed heavily, so it is a "biggy".

legoesbenr · Sep 5, 2023

AritaDev said: ↑

I also encountered the same problem. I solved it by turning off parallel download tasks.
I guess if Unity WebGL has multiple tasks in IO or IndexDB processing at the same time, this log will be issued. Such as downloading files in parallel, resulting in parallel writing to IndexDB.
I changed the parallel download to serial and there is no such log
Click to expand...

Where do you configure parallel vs. serial download?

kaluga1 · Nov 6, 2023

legoesbenr said: ↑

Where do you configure parallel vs. serial download?
Click to expand...

Please someone answer, i've been searching in google for this parallel download tasks or parallel download to serial and nothing appears...

I found this: https://docs.unity3d.com/Manual/JobSystemParallelForJobs.html
But doesnt show how to disable, just to create

AritaDev · Nov 27, 2023 at 8:38 AM

kaluga1 said: ↑

Please someone answer, i've been searching in google for this parallel download tasks or parallel download to serial and nothing appears...

I found this: https://docs.unity3d.com/Manual/JobSystemParallelForJobs.html
But doesnt show how to disable, just to create
Click to expand...

Sorry for confusion, I mean in my case I have called UnityWebRequest.Download multiple times within a short time and it will start parallel download tasks. So I ensure to call UnityWebRequest.Download one by one in order to keep only one download task is excuted at the same time.

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