Use `Mutex` instead of a `RefCell` to acquire/release instance buffers (#7291)

Antonio Scandurra created 2 years ago

This fixes a panic happening when releasing an instance buffer.
Releasing the buffer happens on a different thread but the borrow
checker was not catching it because the metal buffer completion handler
API doesn't have a `Send` marker on it.

Release Notes:

- N/A

Change summary

crates/gpui/src/platform/mac/metal_renderer.rs | 18 +++++++-----------
1 file changed, 7 insertions(+), 11 deletions(-)

Detailed changes

crates/gpui/src/platform/mac/metal_renderer.rs

@@ -15,14 +15,9 @@ use foreign_types::ForeignType;
 use media::core_video::CVMetalTextureCache;
 use metal::{CommandQueue, MTLPixelFormat, MTLResourceOptions, NSRange};
 use objc::{self, msg_send, sel, sel_impl};
+use parking_lot::Mutex;
 use smallvec::SmallVec;
-use std::{
-    cell::{Cell, RefCell},
-    ffi::c_void,
-    mem, ptr,
-    rc::Rc,
-    sync::Arc,
-};
+use std::{cell::Cell, ffi::c_void, mem, ptr, sync::Arc};
 
 #[cfg(not(feature = "runtime_shaders"))]
 const SHADERS_METALLIB: &[u8] = include_bytes!(concat!(env!("OUT_DIR"), "/shaders.metallib"));
@@ -44,7 +39,8 @@ pub(crate) struct MetalRenderer {
     polychrome_sprites_pipeline_state: metal::RenderPipelineState,
     surfaces_pipeline_state: metal::RenderPipelineState,
     unit_vertices: metal::Buffer,
-    instance_buffers: Rc<RefCell<Vec<metal::Buffer>>>,
+    #[allow(clippy::arc_with_non_send_sync)]
+    instance_buffers: Arc<Mutex<Vec<metal::Buffer>>>,
     sprite_atlas: Arc<MetalAtlas>,
     core_video_texture_cache: CVMetalTextureCache,
 }
@@ -185,7 +181,7 @@ impl MetalRenderer {
             polychrome_sprites_pipeline_state,
             surfaces_pipeline_state,
             unit_vertices,
-            instance_buffers: Rc::default(),
+            instance_buffers: Arc::default(),
             sprite_atlas,
             core_video_texture_cache,
         }
@@ -215,7 +211,7 @@ impl MetalRenderer {
             );
             return;
         };
-        let mut instance_buffer = self.instance_buffers.borrow_mut().pop().unwrap_or_else(|| {
+        let mut instance_buffer = self.instance_buffers.lock().pop().unwrap_or_else(|| {
             self.device.new_buffer(
                 INSTANCE_BUFFER_SIZE as u64,
                 MTLResourceOptions::StorageModeManaged,
@@ -341,7 +337,7 @@ impl MetalRenderer {
         let instance_buffer = Cell::new(Some(instance_buffer));
         let block = ConcreteBlock::new(move |_| {
             if let Some(instance_buffer) = instance_buffer.take() {
-                instance_buffers.borrow_mut().push(instance_buffer);
+                instance_buffers.lock().push(instance_buffer);
             }
         });
         let block = block.copy();