Support Device fence sharing with dx12 on Windows (#4900)

Co-authored-by: Sotaro Ikeda <you@example.com>

wgpu-core/src/resource.rs

@@ -854,6 +854,23 @@ impl<G: GlobalIdentityHandlerFactory> Global<G> {
         hal_device_callback(hal_device)
     }
 
+    /// # Safety
+    ///
+    /// - The raw fence handle must not be manually destroyed
+    pub unsafe fn device_fence_as_hal<A: HalApi, F: FnOnce(Option<&A::Fence>) -> R, R>(
+        &self,
+        id: DeviceId,
+        hal_fence_callback: F,
+    ) -> R {
+        profiling::scope!("Device::fence_as_hal");
+
+        let hub = A::hub(self);
+        let device = hub.devices.try_get(id).ok().flatten();
+        let hal_fence = device.as_ref().map(|device| device.fence.read());
+
+        hal_fence_callback(hal_fence.as_deref().unwrap().as_ref())
+    }
+
     /// # Safety
     /// - The raw surface handle must not be manually destroyed
     pub unsafe fn surface_as_hal<A: HalApi, F: FnOnce(Option<&A::Surface>) -> R, R>(

wgpu-hal/src/dx12/device.rs

@@ -1514,7 +1514,7 @@ impl crate::Device<super::Api> for super::Device {
         let hr = unsafe {
             self.raw.CreateFence(
                 0,
-                d3d12_ty::D3D12_FENCE_FLAG_NONE,
+                d3d12_ty::D3D12_FENCE_FLAG_SHARED,
                 &d3d12_ty::ID3D12Fence::uuidof(),
                 raw.mut_void(),
             )

wgpu-hal/src/dx12/mod.rs

@@ -493,6 +493,12 @@ pub struct Fence {
 unsafe impl Send for Fence {}
 unsafe impl Sync for Fence {}
 
+impl Fence {
+    pub fn raw_fence(&self) -> &d3d12::Fence {
+        &self.raw
+    }
+}
+
 #[derive(Debug)]
 pub struct BindGroupLayout {
     /// Sorted list of entries.