Small improvements to cache (#130)

* Remove `Arc` around `RenderPipeline`

It is not necessary anymore in last `wgpu` version.

* Replace `RwLock` with `Mutex`

It was only used for writing.

src/cache.rs

@@ -1,5 +1,4 @@
 use crate::{GlyphToRender, Params};
-
 use wgpu::{
     BindGroup, BindGroupDescriptor, BindGroupEntry, BindGroupLayout, BindGroupLayoutEntry,
     BindingResource, BindingType, BlendState, Buffer, BufferBindingType, ColorTargetState,
@@ -14,7 +13,7 @@ use std::borrow::Cow;
 use std::mem;
 use std::num::NonZeroU64;
 use std::ops::Deref;
-use std::sync::{Arc, RwLock};
+use std::sync::{Arc, Mutex};
 
 #[derive(Debug, Clone)]
 pub struct Cache(Arc<Inner>);
@@ -27,12 +26,12 @@ struct Inner {
     atlas_layout: BindGroupLayout,
     uniforms_layout: BindGroupLayout,
     pipeline_layout: PipelineLayout,
-    cache: RwLock<
+    cache: Mutex<
         Vec<(
             TextureFormat,
             MultisampleState,
             Option<DepthStencilState>,
-            Arc<RenderPipeline>,
+            RenderPipeline,
         )>,
     >,
 }
@@ -150,7 +149,7 @@ impl Cache {
             uniforms_layout,
             atlas_layout,
             pipeline_layout,
-            cache: RwLock::new(Vec::new()),
+            cache: Mutex::new(Vec::new()),
         }))
     }
 
@@ -197,7 +196,7 @@ impl Cache {
         format: TextureFormat,
         multisample: MultisampleState,
         depth_stencil: Option<DepthStencilState>,
-    ) -> Arc<RenderPipeline> {
+    ) -> RenderPipeline {
         let Inner {
             cache,
             pipeline_layout,
@@ -206,14 +205,14 @@ impl Cache {
             ..
         } = self.0.deref();
 
-        let mut cache = cache.write().expect("Write pipeline cache");
+        let mut cache = cache.lock().expect("Write pipeline cache");
 
         cache
             .iter()
             .find(|(fmt, ms, ds, _)| fmt == &format && ms == &multisample && ds == &depth_stencil)
-            .map(|(_, _, _, p)| Arc::clone(p))
+            .map(|(_, _, _, p)| p.clone())
             .unwrap_or_else(|| {
-                let pipeline = Arc::new(device.create_render_pipeline(&RenderPipelineDescriptor {
+                let pipeline = device.create_render_pipeline(&RenderPipelineDescriptor {
                     label: Some("glyphon pipeline"),
                     layout: Some(pipeline_layout),
                     vertex: VertexState {
@@ -240,7 +239,7 @@ impl Cache {
                     multisample,
                     multiview: None,
                     cache: None,
-                }));
+                });
 
                 cache.push((format, multisample, depth_stencil, pipeline.clone()));