func goCallback(p unsafe.Pointer) {
	i := *(*int)(p)

	callbackMutex.Lock()
	f := callbackFuncs[i]
	callbackMutex.Unlock()

	if f == nil {
		panic("missing callback function")
	}
	f()
}

func testCallback(t *testing.T) {
	var x = false
	nestedCall(func() { x = true })
	if !x {
		t.Fatal("nestedCall did not call func")
	}
}

func testCallbackGC(t *testing.T) {
	nestedCall(runtime.GC)
}