[3.x] Repeatedly calling JavaScript->Godot callback causes infinite memory consumption increases.

[SysError99]

Godot version

3.5.2-stable

System information

Linux 6.1.44-1-MANJARO

Issue description

Calling Godot Callback from JavaScript causes memory consumption to go higher than expected, even with empty project that does nothing but keep calling Godot's callback via JavaScript or Godot's JavaScript interface.

Steps to reproduce

1. On the game's script. create Godot Callback for JavaScript.
2. Bind the callback to reachable JavaScript interface (window in particular)
3. Call the callback by either using native JavaScript code on browser, or from Godot's JavaScript interface in high amount of times per second (in the reproduce, ~300 times per second).
4. Memory consumption in JavaScript's heap keeps increasing.

This happens on both Firefox and Chromium-based browsers, WebKit is untested.

Minimal reproduction project

Archive.zip

[SysError99]

I left it for awhile and it still keeps increasing, on an empty project.

[SysError99]

Further testing on bleeding edge 3.x branch found out that after disabling internal call line from JavaScriptObjectImpl::_callback, its memory footprint grows much less, however it's still growing. Suggesting that something is wrong in some sort of memory reserving mechanism in this function.

Since my experience with C++ and manual memory management is still very limited, I cannot analyse the problem any further, but I will try my test to figure out the culprit.

[SysError99]

Looks like the problem sits down somewhere at the callback function, since repeatedly calling it even with zero arguments still pile the array up. GodotJsWrapper seemed to not free the arg passing array on callback for some reason.

[SysError99]

As for heads up, I found a culprit that GodotJsWrapper never frees up freshy-created and 'proxied' array in the callback. I wrapped the array with GodotJSWrapper.MyProxy instead of GodotJSWrapper.get_proixed and then free out the proxy manually after callback execution.

Still, I can't be too sure if this is the 'right' solution since JS GC can be wonky to deal with especially when interfacing with WASM. However, as for my test bench code it doesn't ruin anything and value still gets copied and referenced properly.

This message is mirrored from Godot Contributors Chat.

[akien-mga]

Fixed by #81090.