From 089294fc5145299c1f9f5d537ce9fdd019c4063c Mon Sep 17 00:00:00 2001
From: Dzmitry Malyshau <kvarkus@gmail.com>
Date: Sat, 25 Sep 2021 15:22:50 -0400
Subject: [PATCH] Skip mismatched epochs in the remove_abandoned check

---
 wgpu-core/src/device/life.rs | 22 +++++++++++-----------
 wgpu-core/src/track/mod.rs   | 13 ++++++++++---
 2 files changed, 21 insertions(+), 14 deletions(-)

diff --git a/wgpu-core/src/device/life.rs b/wgpu-core/src/device/life.rs
index 8971e4940..ae8069233 100644
--- a/wgpu-core/src/device/life.rs
+++ b/wgpu-core/src/device/life.rs
@@ -22,17 +22,17 @@ use std::mem;
 /// A struct that keeps lists of resources that are no longer needed by the user.
 #[derive(Debug, Default)]
 pub(super) struct SuspectedResources {
-    pub(crate) buffers: Vec<id::Valid<id::BufferId>>,
-    pub(crate) textures: Vec<id::Valid<id::TextureId>>,
-    pub(crate) texture_views: Vec<id::Valid<id::TextureViewId>>,
-    pub(crate) samplers: Vec<id::Valid<id::SamplerId>>,
-    pub(crate) bind_groups: Vec<id::Valid<id::BindGroupId>>,
-    pub(crate) compute_pipelines: Vec<id::Valid<id::ComputePipelineId>>,
-    pub(crate) render_pipelines: Vec<id::Valid<id::RenderPipelineId>>,
-    pub(crate) bind_group_layouts: Vec<id::Valid<id::BindGroupLayoutId>>,
-    pub(crate) pipeline_layouts: Vec<Stored<id::PipelineLayoutId>>,
-    pub(crate) render_bundles: Vec<id::Valid<id::RenderBundleId>>,
-    pub(crate) query_sets: Vec<id::Valid<id::QuerySetId>>,
+    pub(super) buffers: Vec<id::Valid<id::BufferId>>,
+    pub(super) textures: Vec<id::Valid<id::TextureId>>,
+    pub(super) texture_views: Vec<id::Valid<id::TextureViewId>>,
+    pub(super) samplers: Vec<id::Valid<id::SamplerId>>,
+    pub(super) bind_groups: Vec<id::Valid<id::BindGroupId>>,
+    pub(super) compute_pipelines: Vec<id::Valid<id::ComputePipelineId>>,
+    pub(super) render_pipelines: Vec<id::Valid<id::RenderPipelineId>>,
+    pub(super) bind_group_layouts: Vec<id::Valid<id::BindGroupLayoutId>>,
+    pub(super) pipeline_layouts: Vec<Stored<id::PipelineLayoutId>>,
+    pub(super) render_bundles: Vec<id::Valid<id::RenderBundleId>>,
+    pub(super) query_sets: Vec<id::Valid<id::QuerySetId>>,
 }
 
 impl SuspectedResources {
diff --git a/wgpu-core/src/track/mod.rs b/wgpu-core/src/track/mod.rs
index 0d0453a66..120ce3873 100644
--- a/wgpu-core/src/track/mod.rs
+++ b/wgpu-core/src/track/mod.rs
@@ -235,10 +235,17 @@ impl<S: ResourceState> ResourceTracker<S> {
         let (index, epoch, backend) = id.0.unzip();
         debug_assert_eq!(backend, self.backend);
         match self.map.entry(index) {
+            // This code explicitly ignores requests for IDs that are no longer valid,
+            // i.e. corresponding to removed entries, or entries that got re-filled
+            // with new elements (having different epochs).
+            // This is needed because of the asynchronous nature of the device internals.
+            // As such, by the time a resource is added to the suspected list, it may
+            // already be fully removed from all the trackers (and be a stale ID).
+            // see https://github.com/gfx-rs/wgpu/issues/1996
             Entry::Occupied(e) => {
-                if e.get().ref_count.load() == 1 {
-                    let res = e.remove();
-                    assert_eq!(res.epoch, epoch, "Epoch mismatch for {:?}", id);
+                // see https://github.com/gfx-rs/wgpu/issues/1996
+                if e.get().epoch == epoch && e.get().ref_count.load() == 1 {
+                    e.remove();
                     true
                 } else {
                     false