FS.trackingDelegate[callback name] with -sFS_DEBUG will impact performance or not?

[aisnote]

hi, just curiously -sFS_DEBUG will impact the performance or not?

FS.trackingDelegate[callback name] Users can specify callbacks to receive different filesystem events. This is useful for tracking changes in the filesystem. This requires -sFS_DEBUG.

thanks.

[tlively]

Besides the overhead of looking up and running the user callbacks, I wouldn't expect there to be any additional overhead. Note that this feature doesn't have complete coverage of all the file system calls and might go away in the future, so I wouldn't use it for anything more than debugging.

[sbc100]

But I imagine -sFS_DEBUG could also add other debugging things.. such as tracing. I would not advise using that setting in production (or any of the XX_DEBUG macros).

I'm not sure what your use case it but perhaps we could find some other way to achieve it, or we could add yet another settings such as a FS_ENABLE_TRACKING_DELEGATE (but I very much like to avoid that if possible).

[sbc100]

I wonder if you could inject your own interceptors at runtime, using custom JS? What are you using the tracking callbacks for?

[aisnote]

I used to monitor there is new file generated in MEMFS so that I can read that file and post to JS main UI. the scenario is like using FFmpeg.js to generate the TS file continually in MEMFS.

[sbc100]

I think it would be great if we could find a way to give you the callback you need without requiring FS.trackingDelegate.

Can you modify the ffmpeg sources, or do you want a solution that works purely on the JS side?

[aisnote]

I can not modify the FFMpeg source code. Hope EMS can do something on this file operations hook. I know Go lang has this functional to hook FS

[sbc100]

I think you should be able to so something like this in your post-js file:

// Intercept calls to rename() so we know when the application
// renames a file.
var old_rename = FS.rename;
FS.rename = function(old, new) {
  var rtn = old_rename(old, new);
  callMeOnFileRename(new);
  return rtn;
}

[aisnote]

let me have a try and very appreciate your help.

[aisnote]

thanks a lot @sbc100 . I made it as this.