internal/atlas: add TestGCShader

Updates #2897

internal/atlas/shader.go

@@ -38,18 +38,20 @@ func NewShader(ir *shaderir.Program) *Shader {
 	}
 }
 
+func (s *Shader) finalize() {
+	// A function from finalizer must not be blocked, but disposing operation can be blocked.
+	// Defer this operation until it becomes safe. (#913)
+	appendDeferred(func() {
+		s.deallocate()
+	})
+}
+
 func (s *Shader) ensureShader() *graphicscommand.Shader {
 	if s.shader != nil {
 		return s.shader
 	}
 	s.shader = graphicscommand.NewShader(s.ir)
-	runtime.SetFinalizer(s, func(shader *Shader) {
-		// A function from finalizer must not be blocked, but disposing operation can be blocked.
-		// Defer this operation until it becomes safe. (#913)
-		appendDeferred(func() {
-			shader.deallocate()
-		})
-	})
+	runtime.SetFinalizer(s, (*Shader).finalize)
 	return s.shader
 }
 

internal/atlas/shader_test.go

@@ -17,6 +17,7 @@ package atlas_test
 import (
 	"image"
 	"image/color"
+	"runtime"
 	"testing"
 
 	"github.com/hajimehoshi/ebiten/v2/internal/atlas"
@@ -78,3 +79,28 @@ func TestImageDrawTwice(t *testing.T) {
 		t.Errorf("got: %v, want: %v", got, want)
 	}
 }
+
+func TestGCShader(t *testing.T) {
+	s := atlas.NewShader(etesting.ShaderProgramFill(0xff, 0xff, 0xff, 0xff))
+
+	// Use the shader to initialize it.
+	const w, h = 1, 1
+	dst := atlas.NewImage(w, h, atlas.ImageTypeRegular)
+	vs := quadVertices(w, h, 0, 0, 1)
+	is := graphics.QuadIndices()
+	dr := image.Rect(0, 0, w, h)
+	dst.DrawTriangles([graphics.ShaderImageCount]*atlas.Image{}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderImageCount]image.Rectangle{}, s, nil, graphicsdriver.FillAll)
+
+	// Ensure other objects are GCed, as GC appends deferred functions for collected objects.
+	runtime.GC()
+
+	// Get the difference of the number of deferred functions before and after s is GCed.
+	c := atlas.DeferredFuncCountForTesting()
+	runtime.KeepAlive(s)
+	runtime.GC()
+	diff := atlas.DeferredFuncCountForTesting() - c
+
+	if got, want := diff, 1; got != want {
+		t.Errorf("got: %d, want: %d", got, want)
+	}
+}