cutil: add test for PtrGuard

Signed-off-by: Sven Anderson <sven@redhat.com>

internal/cutil/ptrguard_test.go

@@ -0,0 +1,75 @@
+package cutil
+
+import (
+	"math/rand"
+	"testing"
+	"unsafe"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestPtrGuard(t *testing.T) {
+	t.Run("storeAndRelease", func(t *testing.T) {
+		s := "string"
+		goPtr := (unsafe.Pointer)(&s)
+		cPtr := Malloc(PtrSize)
+		defer Free(cPtr)
+		pg := NewPtrGuard(cPtr, goPtr)
+		assert.Equal(t, *(*unsafe.Pointer)(cPtr), goPtr)
+		pg.Release()
+		assert.Zero(t, *(*unsafe.Pointer)(cPtr))
+	})
+
+	t.Run("multiRelease", func(t *testing.T) {
+		s := "string"
+		goPtr := (unsafe.Pointer)(&s)
+		cPtr := Malloc(PtrSize)
+		defer Free(cPtr)
+		pg := NewPtrGuard(cPtr, goPtr)
+		assert.Equal(t, *(*unsafe.Pointer)(cPtr), goPtr)
+		pg.Release()
+		pg.Release()
+		pg.Release()
+		pg.Release()
+		assert.Zero(t, *(*unsafe.Pointer)(cPtr))
+	})
+
+	t.Run("stressTest", func(t *testing.T) {
+		// Because the default thread limit of the Go runtime is 10000, creating
+		// 20000 parallel PtrGuards asserts, that Go routines of PtrGuards don't
+		// create threads.
+		const N = 20000  // Number of parallel PtrGuards
+		const M = 100000 // Number of loops
+		var ptrGuards [N]*PtrGuard
+		cPtrArr := (*[N]CPtr)(unsafe.Pointer(Malloc(N * PtrSize)))
+		defer Free(CPtr(&cPtrArr[0]))
+		toggle := func(i int) {
+			if ptrGuards[i] == nil {
+				goPtr := unsafe.Pointer(&(struct{ byte }{42}))
+				cPtrPtr := CPtr(&cPtrArr[i])
+				ptrGuards[i] = NewPtrGuard(cPtrPtr, goPtr)
+				assert.Equal(t, (unsafe.Pointer)(cPtrArr[i]), goPtr)
+			} else {
+				ptrGuards[i].Release()
+				ptrGuards[i] = nil
+				assert.Zero(t, cPtrArr[i])
+			}
+		}
+		for i := range ptrGuards {
+			toggle(i)
+		}
+		for n := 0; n < M; n++ {
+			i := rand.Intn(N)
+			toggle(i)
+		}
+		for i := range ptrGuards {
+			if ptrGuards[i] != nil {
+				ptrGuards[i].Release()
+				ptrGuards[i] = nil
+			}
+		}
+		for i := uintptr(0); i < N; i++ {
+			assert.Zero(t, cPtrArr[i])
+		}
+	})
+}