From c82a3a77d2b60401e5c2570fcc54c3e32c09560a Mon Sep 17 00:00:00 2001
From: Imbris <imbrisf@gmail.com>
Date: Sat, 27 Feb 2021 17:38:53 -0500
Subject: [PATCH] Avoid panic when requesting to unmap a buffer that is pending
 mapping

---
 wgpu-core/src/device/life.rs |  2 ++
 wgpu-core/src/device/mod.rs  | 19 +++++++++++++++----
 wgpu-core/src/resource.rs    |  1 +
 3 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/wgpu-core/src/device/life.rs b/wgpu-core/src/device/life.rs
index e54911c3a6..c4694b2c3b 100644
--- a/wgpu-core/src/device/life.rs
+++ b/wgpu-core/src/device/life.rs
@@ -698,6 +698,8 @@ impl<B: GfxBackend> LifetimeTracker<B> {
                     resource::BufferMapState::Idle,
                 ) {
                     resource::BufferMapState::Waiting(pending_mapping) => pending_mapping,
+                    // Mapping cancelled
+                    resource::BufferMapState::Idle => continue,
                     _ => panic!("No pending mapping."),
                 };
                 let status = if mapping.range.start != mapping.range.end {
diff --git a/wgpu-core/src/device/mod.rs b/wgpu-core/src/device/mod.rs
index 1a292e992e..3fdd512d32 100644
--- a/wgpu-core/src/device/mod.rs
+++ b/wgpu-core/src/device/mod.rs
@@ -4560,10 +4560,10 @@ impl<G: GlobalIdentityHandlerFactory> Global<G> {
         }
     }
 
-    pub fn buffer_unmap<B: GfxBackend>(
+    fn buffer_unmap_inner<B: GfxBackend>(
         &self,
         buffer_id: id::BufferId,
-    ) -> Result<(), resource::BufferAccessError> {
+    ) -> Result<Option<BufferMapPendingCallback>, resource::BufferAccessError> {
         span!(_guard, INFO, "Device::buffer_unmap");
 
         let hub = B::hub(self);
@@ -4645,7 +4645,9 @@ impl<G: GlobalIdentityHandlerFactory> Global<G> {
             resource::BufferMapState::Idle => {
                 return Err(resource::BufferAccessError::NotMapped);
             }
-            resource::BufferMapState::Waiting(_) => {}
+            resource::BufferMapState::Waiting(pending) => {
+                return Ok(Some((pending.op, resource::BufferMapAsyncStatus::Aborted)));
+            }
             resource::BufferMapState::Active {
                 ptr,
                 sub_range,
@@ -4671,6 +4673,15 @@ impl<G: GlobalIdentityHandlerFactory> Global<G> {
                 unmap_buffer(&device.raw, buffer)?;
             }
         }
-        Ok(())
+        Ok(None)
+    }
+
+    pub fn buffer_unmap<B: GfxBackend>(
+        &self,
+        buffer_id: id::BufferId,
+    ) -> Result<(), resource::BufferAccessError> {
+        self.buffer_unmap_inner::<B>(buffer_id)
+            //Note: outside inner function so no locks are held when calling the callback
+            .map(|pending_callback| fire_map_callbacks(pending_callback.into_iter()))
     }
 }
diff --git a/wgpu-core/src/resource.rs b/wgpu-core/src/resource.rs
index 045f2ec65f..36c276be43 100644
--- a/wgpu-core/src/resource.rs
+++ b/wgpu-core/src/resource.rs
@@ -76,6 +76,7 @@ bitflags::bitflags! {
 pub enum BufferMapAsyncStatus {
     Success,
     Error,
+    Aborted,
     Unknown,
     ContextLost,
 }