use 2 destination buffers for indirect dispatch validation

This removes the required barrier prior to the validation dispatch.

tests/tests/dispatch_workgroups_indirect.rs

@@ -212,6 +212,9 @@ async fn run_test(
             if !forget_to_set_bind_group {
                 compute_pass.set_bind_group(0, &bind_group, &[]);
             }
+            // Issue multiple dispatches to test the internal destination buffer switching
+            compute_pass.dispatch_workgroups_indirect(&indirect_buffer, indirect_offset);
+            compute_pass.dispatch_workgroups_indirect(&indirect_buffer, indirect_offset);
             compute_pass.dispatch_workgroups_indirect(&indirect_buffer, indirect_offset);
         }
 

wgpu-core/src/command/compute.rs

@@ -979,15 +979,6 @@ fn dispatch_indirect<A: HalApi>(
                 .transition_buffers(src_barrier.into_iter());
         }
 
-        unsafe {
-            state
-                .raw_encoder
-                .transition_buffers(std::iter::once(hal::BufferBarrier {
-                    buffer: params.dst_buffer,
-                    usage: hal::BufferUses::INDIRECT..hal::BufferUses::STORAGE_READ_WRITE,
-                }));
-        }
-
         unsafe {
             state.raw_encoder.dispatch([1, 1, 1]);
         }
@@ -1026,12 +1017,19 @@ fn dispatch_indirect<A: HalApi>(
         }
 
         unsafe {
-            state
-                .raw_encoder
-                .transition_buffers(std::iter::once(hal::BufferBarrier {
-                    buffer: params.dst_buffer,
-                    usage: hal::BufferUses::STORAGE_READ_WRITE..hal::BufferUses::INDIRECT,
-                }));
+            state.raw_encoder.transition_buffers(
+                [
+                    hal::BufferBarrier {
+                        buffer: params.dst_buffer,
+                        usage: hal::BufferUses::STORAGE_READ_WRITE..hal::BufferUses::INDIRECT,
+                    },
+                    hal::BufferBarrier {
+                        buffer: params.other_dst_buffer,
+                        usage: hal::BufferUses::INDIRECT..hal::BufferUses::STORAGE_READ_WRITE,
+                    },
+                ]
+                .into_iter(),
+            );
         }
 
         state.flush_states(None)?;

wgpu-core/src/indirect_validation.rs

@@ -1,3 +1,5 @@
+use std::sync::atomic::AtomicBool;
+
 use thiserror::Error;
 
 use crate::{
@@ -35,14 +37,18 @@ pub struct IndirectValidation<A: HalApi> {
     src_bind_group_layout: A::BindGroupLayout,
     pipeline_layout: A::PipelineLayout,
     pipeline: A::ComputePipeline,
-    dst_buffer: A::Buffer,
-    dst_bind_group: A::BindGroup,
+    dst_buffer_0: A::Buffer,
+    dst_buffer_1: A::Buffer,
+    dst_bind_group_0: A::BindGroup,
+    dst_bind_group_1: A::BindGroup,
+    is_next_dst_0: AtomicBool,
 }
 
 pub struct Params<'a, A: HalApi> {
     pub pipeline_layout: &'a A::PipelineLayout,
     pub pipeline: &'a A::ComputePipeline,
     pub dst_buffer: &'a A::Buffer,
+    pub other_dst_buffer: &'a A::Buffer,
     pub dst_bind_group: &'a A::BindGroup,
     pub aligned_offset: u64,
     pub offset_remainder: u64,
@@ -202,10 +208,12 @@ impl<A: HalApi> IndirectValidation<A> {
             usage: hal::BufferUses::INDIRECT | hal::BufferUses::STORAGE_READ_WRITE,
             memory_flags: hal::MemoryFlags::empty(),
         };
-        let dst_buffer =
+        let dst_buffer_0 =
+            unsafe { device.create_buffer(&dst_buffer_desc) }.map_err(DeviceError::from)?;
+        let dst_buffer_1 =
             unsafe { device.create_buffer(&dst_buffer_desc) }.map_err(DeviceError::from)?;
 
-        let dst_bind_group_desc = hal::BindGroupDescriptor {
+        let dst_bind_group_desc_0 = hal::BindGroupDescriptor {
             label: None,
             layout: &dst_bind_group_layout,
             entries: &[hal::BindGroupEntry {
@@ -214,17 +222,40 @@ impl<A: HalApi> IndirectValidation<A> {
                 count: 1,
             }],
             buffers: &[hal::BufferBinding {
-                buffer: &dst_buffer,
+                buffer: &dst_buffer_0,
                 offset: 0,
                 size: Some(std::num::NonZeroU64::new(4 * 3).unwrap()),
             }],
             samplers: &[],
             textures: &[],
             acceleration_structures: &[],
         };
-        let dst_bind_group = unsafe {
+        let dst_bind_group_0 = unsafe {
             device
-                .create_bind_group(&dst_bind_group_desc)
+                .create_bind_group(&dst_bind_group_desc_0)
+                .map_err(DeviceError::from)
+        }?;
+
+        let dst_bind_group_desc_1 = hal::BindGroupDescriptor {
+            label: None,
+            layout: &dst_bind_group_layout,
+            entries: &[hal::BindGroupEntry {
+                binding: 0,
+                resource_index: 0,
+                count: 1,
+            }],
+            buffers: &[hal::BufferBinding {
+                buffer: &dst_buffer_1,
+                offset: 0,
+                size: Some(std::num::NonZeroU64::new(4 * 3).unwrap()),
+            }],
+            samplers: &[],
+            textures: &[],
+            acceleration_structures: &[],
+        };
+        let dst_bind_group_1 = unsafe {
+            device
+                .create_bind_group(&dst_bind_group_desc_1)
                 .map_err(DeviceError::from)
         }?;
 
@@ -234,8 +265,11 @@ impl<A: HalApi> IndirectValidation<A> {
             src_bind_group_layout,
             pipeline_layout,
             pipeline,
-            dst_buffer,
-            dst_bind_group,
+            dst_buffer_0,
+            dst_buffer_1,
+            dst_bind_group_0,
+            dst_bind_group_1,
+            is_next_dst_0: AtomicBool::new(false),
         })
     }
 
@@ -299,11 +333,29 @@ impl<A: HalApi> IndirectValidation<A> {
         let aligned_offset = aligned_offset.min(max_aligned_offset);
         let offset_remainder = offset - aligned_offset;
 
+        let (dst_buffer, other_dst_buffer, dst_bind_group) = if self
+            .is_next_dst_0
+            .fetch_xor(true, core::sync::atomic::Ordering::AcqRel)
+        {
+            (
+                &self.dst_buffer_0,
+                &self.dst_buffer_1,
+                &self.dst_bind_group_0,
+            )
+        } else {
+            (
+                &self.dst_buffer_1,
+                &self.dst_buffer_0,
+                &self.dst_bind_group_1,
+            )
+        };
+
         Params {
             pipeline_layout: &self.pipeline_layout,
             pipeline: &self.pipeline,
-            dst_buffer: &self.dst_buffer,
-            dst_bind_group: &self.dst_bind_group,
+            dst_buffer,
+            other_dst_buffer,
+            dst_bind_group,
             aligned_offset,
             offset_remainder,
         }
@@ -316,14 +368,19 @@ impl<A: HalApi> IndirectValidation<A> {
             src_bind_group_layout,
             pipeline_layout,
             pipeline,
-            dst_buffer,
-            dst_bind_group,
+            dst_buffer_0,
+            dst_buffer_1,
+            dst_bind_group_0,
+            dst_bind_group_1,
+            is_next_dst_0: _,
         } = self;
 
         use hal::Device;
         unsafe {
-            device.destroy_bind_group(dst_bind_group);
-            device.destroy_buffer(dst_buffer);
+            device.destroy_bind_group(dst_bind_group_0);
+            device.destroy_bind_group(dst_bind_group_1);
+            device.destroy_buffer(dst_buffer_0);
+            device.destroy_buffer(dst_buffer_1);
             device.destroy_compute_pipeline(pipeline);
             device.destroy_pipeline_layout(pipeline_layout);
             device.destroy_bind_group_layout(src_bind_group_layout);