lib/bytesutil: make sure that the cleanup code is performed only by a…

… single goroutine out of many concurrently running goroutines

Updates #3466

lib/bytesutil/fast_string_matcher.go

@@ -62,10 +62,8 @@ func (fsm *FastStringMatcher) Match(s string) bool {
 	s = strings.Clone(s)
 	fsm.m.Store(s, e)
 
-	if atomic.LoadUint64(&fsm.lastCleanupTime)+61 < ct {
-		// Perform a global cleanup for fsm.m by removing items, which weren't accessed
-		// during the last 5 minutes.
-		atomic.StoreUint64(&fsm.lastCleanupTime, ct)
+	if needCleanup(&fsm.lastCleanupTime, ct) {
+		// Perform a global cleanup for fsm.m by removing items, which weren't accessed during the last 5 minutes.
 		m := &fsm.m
 		m.Range(func(k, v interface{}) bool {
 			e := v.(*fsmEntry)
@@ -78,3 +76,14 @@ func (fsm *FastStringMatcher) Match(s string) bool {
 
 	return b
 }
+
+func needCleanup(lastCleanupTime *uint64, currentTime uint64) bool {
+	lct := atomic.LoadUint64(lastCleanupTime)
+	if lct+61 >= currentTime {
+		return false
+	}
+	// Atomically compare and swap the current time with the lastCleanupTime
+	// in order to guarantee that only a single goroutine out of multiple
+	// concurrently executing goroutines gets true from the call.
+	return atomic.CompareAndSwapUint64(lastCleanupTime, lct, currentTime)
+}

lib/bytesutil/fast_string_matcher_test.go

@@ -23,3 +23,27 @@ func TestFastStringMatcher(t *testing.T) {
 	f("a_b-C", false)
 	f("foobar", true)
 }
+
+func TestNeedCleanup(t *testing.T) {
+	f := func(lastCleanupTime, currentTime uint64, resultExpected bool) {
+		t.Helper()
+		lct := lastCleanupTime
+		result := needCleanup(&lct, currentTime)
+		if result != resultExpected {
+			t.Fatalf("unexpected result for needCleanup(%d, %d); got %v; want %v", lastCleanupTime, currentTime, result, resultExpected)
+		}
+		if result {
+			if lct != currentTime {
+				t.Fatalf("unexpected value for lct; got %d; want currentTime=%d", lct, currentTime)
+			}
+		} else {
+			if lct != lastCleanupTime {
+				t.Fatalf("unexpected value for lct; got %d; want lastCleanupTime=%d", lct, lastCleanupTime)
+			}
+		}
+	}
+	f(0, 0, false)
+	f(0, 61, false)
+	f(0, 62, true)
+	f(10, 100, true)
+}

lib/bytesutil/fast_string_transformer.go

@@ -67,10 +67,8 @@ func (fst *FastStringTransformer) Transform(s string) string {
 	}
 	fst.m.Store(s, e)
 
-	if atomic.LoadUint64(&fst.lastCleanupTime)+61 < ct {
-		// Perform a global cleanup for fst.m by removing items, which weren't accessed
-		// during the last 5 minutes.
-		atomic.StoreUint64(&fst.lastCleanupTime, ct)
+	if needCleanup(&fst.lastCleanupTime, ct) {
+		// Perform a global cleanup for fst.m by removing items, which weren't accessed during the last 5 minutes.
 		m := &fst.m
 		m.Range(func(k, v interface{}) bool {
 			e := v.(*fstEntry)

lib/bytesutil/internstring.go

@@ -30,10 +30,8 @@ func InternString(s string) string {
 	}
 	internStringsMap.Store(sCopy, e)
 
-	if atomic.LoadUint64(&internStringsMapLastCleanupTime)+61 < ct {
-		// Perform a global cleanup for internStringsMap by removing items, which weren't accessed
-		// during the last 5 minutes.
-		atomic.StoreUint64(&internStringsMapLastCleanupTime, ct)
+	if needCleanup(&internStringsMapLastCleanupTime, ct) {
+		// Perform a global cleanup for internStringsMap by removing items, which weren't accessed during the last 5 minutes.
 		m := &internStringsMap
 		m.Range(func(k, v interface{}) bool {
 			e := v.(*ismEntry)