Allow disabling waiting for latency waitable object (#7400)

Author: marcpabst

CHANGELOG.md

@@ -73,7 +73,7 @@ By @Vecvec in [#7913](https://github.com/gfx-rs/wgpu/pull/7913).
 
 #### DX12
 
-- Fixed a bug where access to matrices with 2 rows would not work in some cases. By @andyleiserson in [#7438](https://github.com/gfx-rs/wgpu/pull/7438).
+- Allow disabling waiting for latency waitable object. By @marcpabst in [#7400](https://github.com/gfx-rs/wgpu/pull/7400)
 
 ### Bug Fixes
 
@@ -85,6 +85,11 @@ By @Vecvec in [#7913](https://github.com/gfx-rs/wgpu/pull/7913).
 
 - Fix `STATUS_HEAP_CORRUPTION` crash when concurrently calling `create_sampler`. By @atlv24 in [#8043](https://github.com/gfx-rs/wgpu/pull/8043).
 
+##### DX12
+
+- Fixed a bug where access to matrices with 2 rows would not work in some cases. By @andyleiserson in [#7438](https://github.com/gfx-rs/wgpu/pull/7438).
+
+
 ## v26.0.2 (2025-07-23)
 
 ### Bug Fixes

deno_webgpu/lib.rs

@@ -158,6 +158,7 @@ impl GPU {
                     backend_options: wgpu_types::BackendOptions {
                         dx12: wgpu_types::Dx12BackendOptions {
                             shader_compiler: wgpu_types::Dx12Compiler::Fxc,
+                            ..Default::default()
                         },
                         gl: wgpu_types::GlBackendOptions::default(),
                         noop: wgpu_types::NoopBackendOptions::default(),

tests/src/init.rs

@@ -50,6 +50,7 @@ pub fn initialize_instance(backends: wgpu::Backends, params: &TestParameters) ->
         backend_options: wgpu::BackendOptions {
             dx12: wgpu::Dx12BackendOptions {
                 shader_compiler: dx12_shader_compiler,
+                ..Default::default()
             },
             gl: wgpu::GlBackendOptions {
                 fence_behavior: if cfg!(target_family = "wasm") {

wgpu-hal/examples/ray-traced-triangle/main.rs

@@ -242,6 +242,7 @@ impl<A: hal::Api> Example<A> {
             backend_options: wgpu_types::BackendOptions {
                 dx12: Dx12BackendOptions {
                     shader_compiler: wgpu_types::Dx12Compiler::default_dynamic_dxc(),
+                    ..Default::default()
                 },
                 ..Default::default()
             },

wgpu-hal/src/dx12/adapter.rs

@@ -58,6 +58,7 @@ impl super::Adapter {
         instance_flags: wgt::InstanceFlags,
         memory_budget_thresholds: wgt::MemoryBudgetThresholds,
         compiler_container: Arc<shader_compilation::CompilerContainer>,
+        backend_options: wgt::Dx12BackendOptions,
     ) -> Option<crate::ExposedAdapter<super::Api>> {
         // Create the device so that we can get the capabilities.
         let device = {
@@ -534,6 +535,7 @@ impl super::Adapter {
                 workarounds,
                 memory_budget_thresholds,
                 compiler_container,
+                options: backend_options,
             },
             info,
             features,
@@ -697,6 +699,7 @@ impl crate::Adapter for super::Adapter {
             &self.library,
             self.memory_budget_thresholds,
             self.compiler_container.clone(),
+            self.options.clone(),
         )?;
         Ok(crate::OpenDevice {
             device,

wgpu-hal/src/dx12/device.rs

@@ -48,6 +48,7 @@ impl super::Device {
         library: &Arc<D3D12Lib>,
         memory_budget_thresholds: wgt::MemoryBudgetThresholds,
         compiler_container: Arc<shader_compilation::CompilerContainer>,
+        backend_options: wgt::Dx12BackendOptions,
     ) -> Result<Self, crate::DeviceError> {
         if private_caps
             .instance_flags
@@ -198,6 +199,7 @@ impl super::Device {
                 raw.clone(),
                 Direct3D12::D3D12_DESCRIPTOR_HEAP_TYPE_CBV_SRV_UAV,
             )),
+            options: backend_options,
             library: Arc::clone(library),
             #[cfg(feature = "renderdoc")]
             render_doc: Default::default(),

wgpu-hal/src/dx12/instance.rs

@@ -109,6 +109,7 @@ impl crate::Instance for super::Instance {
             flags: desc.flags,
             memory_budget_thresholds: desc.memory_budget_thresholds,
             compiler_container: Arc::new(compiler_container),
+            options: desc.backend_options.dx12.clone(),
         })
     }
 
@@ -125,6 +126,7 @@ impl crate::Instance for super::Instance {
                 target: SurfaceTarget::WndHandle(Foundation::HWND(handle.hwnd.get() as *mut _)),
                 supports_allow_tearing: self.supports_allow_tearing,
                 swap_chain: RwLock::new(None),
+                options: self.options.clone(),
             }),
             _ => Err(crate::InstanceError::new(format!(
                 "window handle {window_handle:?} is not a Win32 handle"
@@ -147,6 +149,7 @@ impl crate::Instance for super::Instance {
                     self.flags,
                     self.memory_budget_thresholds,
                     self.compiler_container.clone(),
+                    self.options.clone(),
                 )
             })
             .collect()

wgpu-hal/src/dx12/mod.rs

@@ -464,6 +464,7 @@ pub struct Instance {
     flags: wgt::InstanceFlags,
     memory_budget_thresholds: wgt::MemoryBudgetThresholds,
     compiler_container: Arc<shader_compilation::CompilerContainer>,
+    options: wgt::Dx12BackendOptions,
 }
 
 impl Instance {
@@ -481,6 +482,7 @@ impl Instance {
             target: SurfaceTarget::Visual(visual.to_owned()),
             supports_allow_tearing: self.supports_allow_tearing,
             swap_chain: RwLock::new(None),
+            options: self.options.clone(),
         }
     }
 
@@ -498,6 +500,7 @@ impl Instance {
             target: SurfaceTarget::SurfaceHandle(surface_handle),
             supports_allow_tearing: self.supports_allow_tearing,
             swap_chain: RwLock::new(None),
+            options: self.options.clone(),
         }
     }
 
@@ -514,6 +517,7 @@ impl Instance {
             target: SurfaceTarget::SwapChainPanel(swap_chain_panel.to_owned()),
             supports_allow_tearing: self.supports_allow_tearing,
             swap_chain: RwLock::new(None),
+            options: self.options.clone(),
         }
     }
 }
@@ -528,7 +532,7 @@ struct SwapChain {
     // when the swapchain is destroyed
     resources: Vec<Direct3D12::ID3D12Resource>,
     /// Handle is freed in [`Self::release_resources()`]
-    waitable: Foundation::HANDLE,
+    waitable: Option<Foundation::HANDLE>,
     acquired_count: usize,
     present_mode: wgt::PresentMode,
     format: wgt::TextureFormat,
@@ -550,6 +554,7 @@ pub struct Surface {
     target: SurfaceTarget,
     supports_allow_tearing: bool,
     swap_chain: RwLock<Option<SwapChain>>,
+    options: wgt::Dx12BackendOptions,
 }
 
 unsafe impl Send for Surface {}
@@ -559,6 +564,12 @@ impl Surface {
     pub fn swap_chain(&self) -> Option<Dxgi::IDXGISwapChain3> {
         Some(self.swap_chain.read().as_ref()?.raw.clone())
     }
+
+    /// Returns the waitable handle associated with this swap chain, if any.
+    /// Handle is only valid while the swap chain is alive.
+    pub unsafe fn waitable_handle(&self) -> Option<Foundation::HANDLE> {
+        self.swap_chain.read().as_ref()?.waitable
+    }
 }
 
 #[derive(Debug, Clone, Copy)]
@@ -601,6 +612,7 @@ pub struct Adapter {
     workarounds: Workarounds,
     memory_budget_thresholds: wgt::MemoryBudgetThresholds,
     compiler_container: Arc<shader_compilation::CompilerContainer>,
+    options: wgt::Dx12BackendOptions,
 }
 
 unsafe impl Send for Adapter {}
@@ -659,6 +671,7 @@ pub struct Device {
     idler: Idler,
     features: wgt::Features,
     shared: Arc<DeviceShared>,
+    options: wgt::Dx12BackendOptions,
     // CPU only pools
     rtv_pool: Arc<Mutex<descriptor::CpuPool>>,
     dsv_pool: Mutex<descriptor::CpuPool>,
@@ -1178,7 +1191,9 @@ impl crate::DynAccelerationStructure for AccelerationStructure {}
 
 impl SwapChain {
     unsafe fn release_resources(mut self) -> Dxgi::IDXGISwapChain3 {
-        unsafe { Foundation::HANDLE::free(&mut self.waitable) };
+        if let Some(mut waitable) = self.waitable.take() {
+            unsafe { Foundation::HANDLE::free(&mut waitable) };
+        }
         self.raw
     }
 
@@ -1190,14 +1205,21 @@ impl SwapChain {
             Some(duration) => duration.as_millis() as u32,
             None => Threading::INFINITE,
         };
-        match unsafe { Threading::WaitForSingleObject(self.waitable, timeout_ms) } {
-            Foundation::WAIT_ABANDONED | Foundation::WAIT_FAILED => Err(crate::SurfaceError::Lost),
-            Foundation::WAIT_OBJECT_0 => Ok(true),
-            Foundation::WAIT_TIMEOUT => Ok(false),
-            other => {
-                log::error!("Unexpected wait status: 0x{other:x?}");
-                Err(crate::SurfaceError::Lost)
+
+        if let Some(waitable) = self.waitable {
+            match unsafe { Threading::WaitForSingleObject(waitable, timeout_ms) } {
+                Foundation::WAIT_ABANDONED | Foundation::WAIT_FAILED => {
+                    Err(crate::SurfaceError::Lost)
+                }
+                Foundation::WAIT_OBJECT_0 => Ok(true),
+                Foundation::WAIT_TIMEOUT => Ok(false),
+                other => {
+                    log::error!("Unexpected wait status: 0x{other:x?}");
+                    Err(crate::SurfaceError::Lost)
+                }
             }
+        } else {
+            Ok(true)
         }
     }
 }
@@ -1365,7 +1387,14 @@ impl crate::Surface for Surface {
 
         unsafe { swap_chain.SetMaximumFrameLatency(config.maximum_frame_latency) }
             .into_device_result("SetMaximumFrameLatency")?;
-        let waitable = unsafe { swap_chain.GetFrameLatencyWaitableObject() };
+
+        let waitable = match device.options.latency_waitable_object {
+            wgt::Dx12UseFrameLatencyWaitableObject::None => None,
+            wgt::Dx12UseFrameLatencyWaitableObject::Wait
+            | wgt::Dx12UseFrameLatencyWaitableObject::DontWait => {
+                Some(unsafe { swap_chain.GetFrameLatencyWaitableObject() })
+            }
+        };
 
         let mut resources = Vec::with_capacity(swap_chain_buffer as usize);
         for i in 0..swap_chain_buffer {
@@ -1412,7 +1441,13 @@ impl crate::Surface for Surface {
         let mut swapchain = self.swap_chain.write();
         let sc = swapchain.as_mut().unwrap();
 
-        unsafe { sc.wait(timeout) }?;
+        match self.options.latency_waitable_object {
+            wgt::Dx12UseFrameLatencyWaitableObject::None
+            | wgt::Dx12UseFrameLatencyWaitableObject::DontWait => {}
+            wgt::Dx12UseFrameLatencyWaitableObject::Wait => {
+                unsafe { sc.wait(timeout) }?;
+            }
+        }
 
         let base_index = unsafe { sc.raw.GetCurrentBackBufferIndex() } as usize;
         let index = (base_index + sc.acquired_count) % sc.resources.len();

wgpu-types/src/instance.rs

@@ -359,6 +359,8 @@ impl GlBackendOptions {
 pub struct Dx12BackendOptions {
     /// Which DX12 shader compiler to use.
     pub shader_compiler: Dx12Compiler,
+    /// Whether to wait for the latency waitable object before acquiring the next swapchain image.
+    pub latency_waitable_object: Dx12UseFrameLatencyWaitableObject,
 }
 
 impl Dx12BackendOptions {
@@ -368,8 +370,11 @@ impl Dx12BackendOptions {
     #[must_use]
     pub fn from_env_or_default() -> Self {
         let compiler = Dx12Compiler::from_env().unwrap_or_default();
+        let latency_waitable_object =
+            Dx12UseFrameLatencyWaitableObject::from_env().unwrap_or_default();
         Self {
             shader_compiler: compiler,
+            latency_waitable_object,
         }
     }
 
@@ -379,7 +384,12 @@ impl Dx12BackendOptions {
     #[must_use]
     pub fn with_env(self) -> Self {
         let shader_compiler = self.shader_compiler.with_env();
-        Self { shader_compiler }
+        let latency_waitable_object = self.latency_waitable_object.with_env();
+
+        Self {
+            shader_compiler,
+            latency_waitable_object,
+        }
     }
 }
 
@@ -515,6 +525,54 @@ impl Dx12Compiler {
     }
 }
 
+/// Whether and how to use a waitable handle obtained from `GetFrameLatencyWaitableObject`.
+#[derive(Clone, Debug, Default)]
+pub enum Dx12UseFrameLatencyWaitableObject {
+    /// Do not obtain a waitable handle and do not wait for it. The swapchain will
+    /// be created without the `DXGI_SWAP_CHAIN_FLAG_FRAME_LATENCY_WAITABLE_OBJECT` flag.
+    None,
+    /// Obtain a waitable handle and wait for it before acquiring the next swapchain image.
+    #[default]
+    Wait,
+    /// Create the swapchain with the `DXGI_SWAP_CHAIN_FLAG_FRAME_LATENCY_WAITABLE_OBJECT` flag and
+    /// obtain a waitable handle, but do not wait for it before acquiring the next swapchain image.
+    /// This is useful if the application wants to wait for the waitable object itself.
+    DontWait,
+}
+
+impl Dx12UseFrameLatencyWaitableObject {
+    /// Choose whether to use a frame latency waitable object from the environment variable `WGPU_DX12_USE_FRAME_LATENCY_WAITABLE_OBJECT`.
+    ///
+    /// Valid values, case insensitive:
+    /// - `None`
+    /// - `Wait`
+    /// - `DontWait`
+    #[must_use]
+    pub fn from_env() -> Option<Self> {
+        let value = crate::env::var("WGPU_DX12_USE_FRAME_LATENCY_WAITABLE_OBJECT")
+            .as_deref()?
+            .to_lowercase();
+        match value.as_str() {
+            "none" => Some(Self::None),
+            "wait" => Some(Self::Wait),
+            "dontwait" => Some(Self::DontWait),
+            _ => None,
+        }
+    }
+
+    /// Takes the given setting, modifies it based on the `WGPU_DX12_USE_FRAME_LATENCY_WAITABLE_OBJECT` environment variable, and returns the result.
+    ///
+    /// See `from_env` for more information.
+    #[must_use]
+    pub fn with_env(self) -> Self {
+        if let Some(compiler) = Self::from_env() {
+            compiler
+        } else {
+            self
+        }
+    }
+}
+
 /// Selects which OpenGL ES 3 minor version to request.
 ///
 /// When using ANGLE as an OpenGL ES/EGL implementation, explicitly requesting `Version1` can provide a non-conformant ES 3.1 on APIs like D3D11.