`WGPUSync.instanceRequestAdapter` returns a broken `WGPUAdapter`

[ShadelessFox]

On Windows 11, Temurin 24.0.1+9, the following snippet fails against 0.4.3:

import club.doki7.ffm.library.ILibraryLoader;
import club.doki7.webgpu.WGPU;
import club.doki7.webgpu.WGPUSync;

public class Demo {
    public static void main(String[] args) {
        var wgpu = new WGPU(ILibraryLoader.platformLoader().loadLibrary("..."));
        var instance = wgpu.createInstance(null);
        var adapter = WGPUSync.instanceRequestAdapter(wgpu, instance, null).adapter;
        var device = WGPUSync.adapterRequestDevice(wgpu, adapter, null).device;
    }
}

Exception in thread "main" java.lang.RuntimeException: java.lang.IllegalStateException: Already closed
	at club.doki7.webgpu.WGPU.adapterRequestDevice(WGPU.java:538)
	at club.doki7.webgpu.WGPUSync.adapterRequestDevice(WGPUSync.java:93)
	at sh.adelessfox.demo.Demo.main(Demo.java:12)
Caused by: java.lang.IllegalStateException: Already closed
	at java.base/jdk.internal.foreign.MemorySessionImpl.alreadyClosed(MemorySessionImpl.java:318)
	at java.base/jdk.internal.misc.ScopedMemoryAccess$ScopedAccessError.newRuntimeException(ScopedMemoryAccess.java:114)
	at java.base/jdk.internal.foreign.MemorySessionImpl.checkValidState(MemorySessionImpl.java:217)
	at java.base/jdk.internal.foreign.ConfinedSession.acquire0(ConfinedSession.java:53)
	at club.doki7.webgpu.WGPU.adapterRequestDevice(WGPU.java:531)
	... 2 more

Which is interesting because I didn't encounter the same issue on Linux.

I have discovered that FFM upcalls on Windows use a confined arena for allocating their arguments. When an upcall returns, its arena is closed, and all its MemorySegment arguments become invalid. I haven't investigated why it doesn't happen on Linux, though.

The workaround is to use the raw address of a segment:

MemorySegment.ofAddress(segment.address())

An example patch for WGPUSync#onRequestDeviceFinished (please note that WGPUSync#adapterRequestDevice is affected as well):

    private static void onRequestDeviceFinished(
            ...
    ) {
        @Nullable WGPUDevice deviceHandle = device == MemorySegment.NULL
                ? null
-               : new WGPUDevice(device);
+               : new WGPUDevice(MemorySegment.ofAddress(device.address()));
        @Nullable String messageString = WGPUUtil.readStringView(message);
        saveSlot.value = new RequestDeviceResult(status, deviceHandle, messageString);
    }

[chuigda]

Hi, I've reproduced the issue.

I have discovered that FFM upcalls on Windows use a confined arena for allocating their arguments. When an upcall returns, its arena is closed, and all its MemorySegment arguments become invalid.

Do you have any link to relevant posts/questions/answers/issues? If this is true, I'm afraid that this is rather an issue of Java FFM itself: such "FFI-returned" MemorySegment should theoretically not be considered allocated at all.

I'll still make a patch from my side. And before the release of next patch version (v0.4.5), you can temporarily live with your own fork of WGPUSync. Also feel free to request more utility functions.