From b9aa9e59f7e74ccbbdf6fb222b20422625932218 Mon Sep 17 00:00:00 2001
From: Joe Julian <me@joejulian.name>
Date: Mon, 20 Apr 2026 16:51:31 -0700
Subject: [PATCH] app: lock explicitly before refreshing contexts

Signed-off-by: Joe Julian <me@joejulian.name>
---
 app/gl_ios.go      |  3 --
 app/os.go          |  1 +
 app/window.go      | 12 +++----
 app/window_test.go | 85 ++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 92 insertions(+), 9 deletions(-)
 create mode 100644 app/window_test.go

diff --git a/app/gl_ios.go b/app/gl_ios.go
index 31db2541..34d85d1c 100644
--- a/app/gl_ios.go
+++ b/app/gl_ios.go
@@ -115,9 +115,6 @@ func (c *context) Unlock() {
 }
 
 func (c *context) Refresh() error {
-	if C.gio_makeCurrent(c.ctx) == 0 {
-		return errors.New("[EAGLContext setCurrentContext] failed")
-	}
 	if !c.init {
 		c.init = true
 		c.frameBuffer = c.c.CreateFramebuffer()
diff --git a/app/os.go b/app/os.go
index 6da6d34b..78ffa4cf 100644
--- a/app/os.go
+++ b/app/os.go
@@ -169,6 +169,7 @@ type context interface {
 	API() gpu.API
 	RenderTarget() (gpu.RenderTarget, error)
 	Present() error
+	// Refresh assumes the context is already locked and current.
 	Refresh() error
 	Release()
 	Lock() error
diff --git a/app/window.go b/app/window.go
index 977ab6a1..0e5d04d2 100644
--- a/app/window.go
+++ b/app/window.go
@@ -149,6 +149,12 @@ func (w *Window) validateAndProcess(size image.Point, sync bool, frame *op.Ops,
 				sync = true
 			}
 		}
+		if w.ctx != nil {
+			if err := w.ctx.Lock(); err != nil {
+				w.destroyGPU()
+				return err
+			}
+		}
 		if sync && w.ctx != nil {
 			if err := w.ctx.Refresh(); err != nil {
 				if errors.Is(err, errOutOfDate) {
@@ -163,12 +169,6 @@ func (w *Window) validateAndProcess(size image.Point, sync bool, frame *op.Ops,
 				return err
 			}
 		}
-		if w.ctx != nil {
-			if err := w.ctx.Lock(); err != nil {
-				w.destroyGPU()
-				return err
-			}
-		}
 		if w.gpu == nil && !w.nocontext {
 			gpu, err := gpu.New(w.ctx.API())
 			if err != nil {
diff --git a/app/window_test.go b/app/window_test.go
new file mode 100644
index 00000000..ca049d6c
--- /dev/null
+++ b/app/window_test.go
@@ -0,0 +1,85 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+package app
+
+import (
+	"image"
+	"image/color"
+	"testing"
+
+	"gioui.org/gpu"
+	"gioui.org/op"
+)
+
+func TestValidateAndProcessLocksBeforeRefresh(t *testing.T) {
+	ctx := &testContext{}
+	w := &Window{
+		ctx: ctx,
+		gpu: &testGPU{},
+	}
+
+	if err := w.validateAndProcess(image.Pt(320, 240), true, new(op.Ops), nil); err != nil {
+		t.Fatalf("validateAndProcess returned error: %v", err)
+	}
+
+	want := []string{"lock", "refresh", "render-target", "present", "unlock"}
+	if got := ctx.ops; !equalStringSlices(got, want) {
+		t.Fatalf("unexpected call order:\n got  %v\n want %v", got, want)
+	}
+}
+
+type testContext struct {
+	ops []string
+}
+
+func (c *testContext) API() gpu.API {
+	return nil
+}
+
+func (c *testContext) RenderTarget() (gpu.RenderTarget, error) {
+	c.ops = append(c.ops, "render-target")
+	return gpu.OpenGLRenderTarget{}, nil
+}
+
+func (c *testContext) Present() error {
+	c.ops = append(c.ops, "present")
+	return nil
+}
+
+func (c *testContext) Refresh() error {
+	c.ops = append(c.ops, "refresh")
+	return nil
+}
+
+func (c *testContext) Release() {}
+
+func (c *testContext) Lock() error {
+	c.ops = append(c.ops, "lock")
+	return nil
+}
+
+func (c *testContext) Unlock() {
+	c.ops = append(c.ops, "unlock")
+}
+
+type testGPU struct{}
+
+func (g *testGPU) Release() {}
+
+func (g *testGPU) Clear(color.NRGBA) {}
+
+func (g *testGPU) Frame(*op.Ops, gpu.RenderTarget, image.Point) error {
+	return nil
+}
+
+func equalStringSlices(a, b []string) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for i := range a {
+		if a[i] != b[i] {
+			return false
+		}
+	}
+	return true
+}