internal/atlas: bug fix: use the global lock for shaders

Closes #2129

internal/atlas/shader.go

@@ -26,6 +26,9 @@ type Shader struct {
 }
 
 func NewShader(ir *shaderir.Program) *Shader {
+	backendsM.Lock()
+	defer backendsM.Unlock()
+
 	s := &Shader{
 		shader: restorable.NewShader(ir),
 	}
@@ -39,6 +42,9 @@ func NewShader(ir *shaderir.Program) *Shader {
 // A function from finalizer must not be blocked, but disposing operation can be blocked.
 // Defer this operation until it becomes safe. (#913)
 func (s *Shader) MarkDisposed() {
+	backendsM.Lock()
+	defer backendsM.Unlock()
+
 	deferredM.Lock()
 	deferred = append(deferred, func() {
 		s.dispose()

internal/processtest/testdata/issue2129.go

@@ -0,0 +1,70 @@
+// Copyright 2022 The Ebiten Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build ignore
+// +build ignore
+
+package main
+
+import (
+	"errors"
+
+	"github.com/hajimehoshi/ebiten/v2"
+)
+
+var regularTermination = errors.New("regular termination")
+
+type Game struct {
+	count int
+}
+
+func (g *Game) Update() error {
+	const shaderData = `
+package main
+
+func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
+	return vec4(1)
+}
+`
+	g.count++
+	if g.count == 16 {
+		return regularTermination
+	}
+
+	if g.count < 8 {
+		go func() {
+			s, err := ebiten.NewShader([]byte(shaderData))
+			if err != nil {
+				panic(err)
+			}
+			s.Dispose()
+		}()
+		return nil
+	}
+
+	return nil
+}
+
+func (g *Game) Draw(screen *ebiten.Image) {
+}
+
+func (g *Game) Layout(width, height int) (int, int) {
+	return width, height
+}
+
+func main() {
+	if err := ebiten.RunGame(&Game{}); err != nil && err != regularTermination {
+		panic(err)
+	}
+}