fix immediate evict in cache

pkg/util/cache/cache.go

@@ -27,6 +27,9 @@ const (
 type Cache []*cacheShard
 
 func NewCache(maxSize int) Cache {
+	if maxSize < shardsCount {
+		maxSize = shardsCount
+	}
 	cache := make(Cache, shardsCount)
 	for i := 0; i < shardsCount; i++ {
 		cache[i] = &cacheShard{
@@ -61,14 +64,14 @@ func (s *cacheShard) add(index uint64, obj interface{}) bool {
 	s.Lock()
 	defer s.Unlock()
 	_, isOverwrite := s.items[index]
-	s.items[index] = obj
-	if len(s.items) > s.maxSize {
+	if !isOverwrite && len(s.items) >= s.maxSize {
 		var randomKey uint64
 		for randomKey = range s.items {
 			break
 		}
 		delete(s.items, randomKey)
 	}
+	s.items[index] = obj
 	return isOverwrite
 }
 

pkg/util/cache/cache_test.go

@@ -24,13 +24,16 @@ const (
 	maxTestCacheSize int = shardsCount * 2
 )
 
-func ExpectEntry(t *testing.T, cache Cache, index uint64, expectedValue interface{}) {
+func ExpectEntry(t *testing.T, cache Cache, index uint64, expectedValue interface{}) bool {
 	elem, found := cache.Get(index)
 	if !found {
-		t.Error("Expected to find entry with key 1")
+		t.Errorf("Expected to find entry with key %d", index)
+		return false
 	} else if elem != expectedValue {
 		t.Errorf("Expected to find %v, got %v", expectedValue, elem)
+		return false
 	}
+	return true
 }
 
 func TestBasic(t *testing.T) {
@@ -63,3 +66,25 @@ func TestOverwrite(t *testing.T) {
 	cache.Add(1, "yyy")
 	ExpectEntry(t, cache, 1, "yyy")
 }
+
+// TestEvict this test will fail sporatically depending on what add()
+// selects for the randomKey to be evicted.  Ensure that randomKey
+// is never the key we most recently added.  Since the chance of failure
+// on each evict is 50%, if we do it 7 times, it should catch the problem
+// if it exists >99% of the time.
+func TestEvict(t *testing.T) {
+	cache := NewCache(shardsCount)
+	var found bool
+	for retry := 0; retry < 7; retry++ {
+		cache.Add(uint64(shardsCount), "xxx")
+		found = ExpectEntry(t, cache, uint64(shardsCount), "xxx")
+		if !found {
+			break
+		}
+		cache.Add(0, "xxx")
+		found = ExpectEntry(t, cache, 0, "xxx")
+		if !found {
+			break
+		}
+	}
+}