diff --git a/content/assets/zero-alloc-call-sched/app/window.go b/content/assets/zero-alloc-call-sched/app/window.go
index c2da39d..47d4ebf 100644
--- a/content/assets/zero-alloc-call-sched/app/window.go
+++ b/content/assets/zero-alloc-call-sched/app/window.go
@@ -32,6 +32,7 @@ func NewWindow() (*Win, error) {
 		if err != nil {
 			return
 		}
+		w.win.MakeContextCurrent()
 	})
 	return w, nil
 }
@@ -44,24 +45,21 @@ func Terminate() {
 }
 
 // Closed asserts if the given window is closed.
+// This function can be called from any thread.
 func (w *Win) Closed() (stop bool) {
-	return mainthread.CallV(func() interface{} {
-		return w.win.ShouldClose()
-	}).(bool)
+	return w.win.ShouldClose()
 }
 
 // Update updates the frame buffer of the given window.
+// This function can be called from any thread.
 func (w *Win) Update() {
-	mainthread.Call(func() {
-		w.win.SwapBuffers()
-		// glfw.WaitEventsTimeout(1.0 / 30)
-		glfw.PollEvents()
-	})
+	w.win.SwapBuffers()
+	// glfw.WaitEventsTimeout(1.0 / 30)
+	glfw.PollEvents()
 }
 
 // Stop stops the given window.
+// This function can be called from any thread.
 func (w *Win) Stop() {
-	mainthread.Call(func() {
-		w.win.SetShouldClose(true)
-	})
+	w.win.SetShouldClose(true)
 }
diff --git a/content/assets/zero-alloc-call-sched/app/window_test.go b/content/assets/zero-alloc-call-sched/app/window_test.go
new file mode 100644
index 0000000..a07cd65
--- /dev/null
+++ b/content/assets/zero-alloc-call-sched/app/window_test.go
@@ -0,0 +1,32 @@
+package app
+
+import (
+	"testing"
+	"x/mainthread"
+	"x/thread"
+
+	"github.com/go-gl/gl/v3.3-core/gl"
+)
+
+// This test will crash!
+func TestApp(t *testing.T) {
+	mainthread.Init(func() {
+		w, _ := NewWindow()
+		defer Terminate()
+
+		renderThread := thread.New()
+		renderThread.Call(func() {
+			// Initialize gl from a different thread
+			gl.Init()
+			// gl.MakeContextCurrent()
+			gl.GoStr(gl.GetString(gl.VERSION))
+		})
+		mainthread.Call(func() {
+			// Initialize gl from the main thread can
+			// prevent crash from the GetVersion crash.
+			// gl.Init()
+			gl.GoStr(gl.GetString(gl.VERSION))
+		})
+		w.Stop()
+	})
+}
diff --git a/content/assets/zero-alloc-call-sched/go.mod b/content/assets/zero-alloc-call-sched/go.mod
index 95858f5..794fc0e 100644
--- a/content/assets/zero-alloc-call-sched/go.mod
+++ b/content/assets/zero-alloc-call-sched/go.mod
@@ -3,6 +3,7 @@ module x
 go 1.16
 
 require (
+	github.com/go-gl/gl v0.0.0-20190320180904-bf2b1f2f34d7
 	github.com/go-gl/glfw/v3.3/glfw v0.0.0-20201108214237-06ea97f0c265
 	golang.org/x/sys v0.0.0-20210119212857-b64e53b001e4
 )
diff --git a/content/assets/zero-alloc-call-sched/go.sum b/content/assets/zero-alloc-call-sched/go.sum
index 177a0fd..1b7e9ac 100644
--- a/content/assets/zero-alloc-call-sched/go.sum
+++ b/content/assets/zero-alloc-call-sched/go.sum
@@ -1,3 +1,5 @@
+github.com/go-gl/gl v0.0.0-20190320180904-bf2b1f2f34d7 h1:SCYMcCJ89LjRGwEa0tRluNRiMjZHalQZrVrvTbPh+qw=
+github.com/go-gl/gl v0.0.0-20190320180904-bf2b1f2f34d7/go.mod h1:482civXOzJJCPzJ4ZOX/pwvXBWSnzD4OKMdH4ClKGbk=
 github.com/go-gl/glfw/v3.3/glfw v0.0.0-20201108214237-06ea97f0c265 h1:BcbKYUZo/TKPsiSh7LymK3p+TNAJJW3OfGO/21sBbiA=
 github.com/go-gl/glfw/v3.3/glfw v0.0.0-20201108214237-06ea97f0c265/go.mod h1:tQ2UAYgL5IevRw8kRxooKSPJfGvJ9fJQFa0TUsXzTg8=
 golang.org/x/sys v0.0.0-20210119212857-b64e53b001e4 h1:myAQVi0cGEoqQVR5POX+8RR2mrocKqNN1hmeMqhX27k=