feat: add empty slice overhead for arrayObject

array.go

@@ -615,6 +615,13 @@ func (a *arrayObject) MemUsage(ctx *MemUsageContext) (memUsage uint64, newMemUsa
 	if ctx.ArrayLenExceedsThreshold == nil {
 		return memUsage, newMemUsage, errArrayLenExceedsThresholdNil
 	}
+
+	// slice overhead from a.values
+	if a.values != nil {
+		memUsage += 0
+		newMemUsage += SizeEmptySlice
+	}
+
 	if ctx.ArrayLenExceedsThreshold(len(a.values)) {
 		inc, newInc, err := a.estimateMemUsage(ctx)
 		memUsage += inc

array_test.go

@@ -144,7 +144,7 @@ func TestArrayObjectMemUsage(t *testing.T) {
 		errExpected    error
 	}{
 		{
-			name: "mem below threshold",
+			name: "mem below threshold given a nil slice of values",
 			mu:   NewMemUsageContext(vm, 88, 5000, 50, 50, TestNativeMemUsageChecker{}),
 			ao:   &arrayObject{},
 			// array overhead + array baseObject
@@ -153,6 +153,16 @@ func TestArrayObjectMemUsage(t *testing.T) {
 			expectedNewMem: SizeEmptyStruct + SizeEmptyStruct,
 			errExpected:    nil,
 		},
+		{
+			name: "mem below threshold given empty slice of values",
+			mu:   NewMemUsageContext(vm, 88, 5000, 50, 50, TestNativeMemUsageChecker{}),
+			ao:   &arrayObject{values: []Value{}},
+			// array overhead + array baseObject
+			expectedMem: SizeEmptyStruct + SizeEmptyStruct,
+			// array overhead + array baseObject + values slice overhead
+			expectedNewMem: SizeEmptyStruct + SizeEmptyStruct + SizeEmptySlice,
+			errExpected:    nil,
+		},
 		{
 			name: "mem way above threshold returns first crossing of threshold",
 			mu:   NewMemUsageContext(vm, 88, 100, 50, 50, TestNativeMemUsageChecker{}),
@@ -172,8 +182,8 @@ func TestArrayObjectMemUsage(t *testing.T) {
 				(SizeEmptyStruct+SizeEmptyStruct+6)*4 +
 				// len("keyN") * entries (at 4 we reach the limit)
 				4*4,
-			// array overhead + array baseObject
-			expectedNewMem: SizeEmptyStruct + SizeEmptyStruct +
+			// array overhead + array baseObject + values slice overhead
+			expectedNewMem: SizeEmptyStruct + SizeEmptyStruct + SizeEmptySlice +
 				// (stringObject + baseObject + prop "length" with string overhead) * entries (at 4 we reach the limit)
 				(SizeEmptyStruct+SizeEmptyStruct+(6+SizeString))*4 +
 				// len("keyN") with string overhead * entries (at 4 we reach the limit)

value.go

@@ -126,6 +126,7 @@ const (
 	SizeInt32       = uint64(unsafe.Sizeof(int32(0)))
 	SizeInt         = uint64(unsafe.Sizeof(int(0)))
 	SizeEmptyStruct = uint64(unsafe.Sizeof((*baseObject)(nil)))
+	SizeEmptySlice  = uint64(unsafe.Sizeof([]Value{}))
 	// SizeString allows us to take into account the 16 additional bytes
 	// for any string type in go including the pointer to the start of
 	// the string data and the length of the string