lib/workingsetcache: move the cleaner for the prev cache into a separate goroutine

This makes the code more clear after d906d8573e

lib/workingsetcache/cache.go

@@ -42,7 +42,7 @@ type Cache struct {
 	maxBytes int
 
 	// mu serializes access to curr, prev and mode
-	// in expirationWatcher and cacheSizeWatcher.
+	// in expirationWatcher, prevCacheWatcher and cacheSizeWatcher.
 	mu sync.Mutex
 
 	wg     sync.WaitGroup
@@ -122,6 +122,11 @@ func (c *Cache) runWatchers(expireDuration time.Duration) {
 		c.expirationWatcher(expireDuration)
 	}()
 	c.wg.Add(1)
+	go func() {
+		defer c.wg.Done()
+		c.prevCacheWatcher()
+	}()
+	c.wg.Add(1)
 	go func() {
 		defer c.wg.Done()
 		c.cacheSizeWatcher()
@@ -132,7 +137,6 @@ func (c *Cache) expirationWatcher(expireDuration time.Duration) {
 	expireDuration += timeJitter(expireDuration / 10)
 	t := time.NewTicker(expireDuration)
 	defer t.Stop()
-	var csCurr, csPrev fastcache.Stats
 	for {
 		select {
 		case <-c.stopCh:
@@ -148,52 +152,61 @@ func (c *Cache) expirationWatcher(expireDuration time.Duration) {
 		// Reset prev cache and swap it with the curr cache.
 		prev := c.prev.Load().(*fastcache.Cache)
 		curr := c.curr.Load().(*fastcache.Cache)
-		csCurr.Reset()
-		curr.UpdateStats(&csCurr)
-		csPrev.Reset()
-		prev.UpdateStats(&csPrev)
-
 		c.prev.Store(curr)
-
-		prevGetCalls := csCurr.GetCalls
-		updateCacheStatsHistory(&c.csHistory, &csPrev)
-
+		var cs fastcache.Stats
+		prev.UpdateStats(&cs)
+		updateCacheStatsHistory(&c.csHistory, &cs)
 		prev.Reset()
 		c.curr.Store(prev)
 		c.mu.Unlock()
+	}
+}
 
+func (c *Cache) prevCacheWatcher() {
 	// Watch for the usage of the prev cache and drop it whenever it receives
-		// less than 5% of get calls comparing to the curr cache.
-		// This allows saving memory.
-		prev, curr = curr, prev
+	// less than 5% of requests comparing to the curr cache during the last 10 seconds.
 	checkInterval := 10 * time.Second
-		checkerT := time.NewTicker(checkInterval)
-		checkerDeadline := time.Now().Add(expireDuration - checkInterval)
-		for time.Now().Before(checkerDeadline) {
+	checkInterval += timeJitter(checkInterval / 10)
+	t := time.NewTicker(checkInterval)
+	defer t.Stop()
+	prevGetCalls := uint64(0)
+	currGetCalls := uint64(0)
+	for {
 		select {
 		case <-c.stopCh:
-				break
-			case <-checkerT.C:
+			return
+		case <-t.C:
 		}
 		c.mu.Lock()
 		if atomic.LoadUint32(&c.mode) != split {
 			// Do nothing in non-split mode.
 			c.mu.Unlock()
-				break
+			return
 		}
-			csCurr.Reset()
+		prev := c.prev.Load().(*fastcache.Cache)
+		curr := c.curr.Load().(*fastcache.Cache)
+		var csCurr, csPrev fastcache.Stats
 		curr.UpdateStats(&csCurr)
-			csPrev.Reset()
 		prev.UpdateStats(&csPrev)
-			getCalls := csPrev.GetCalls - prevGetCalls
-			if float64(getCalls) < 0.05*float64(csCurr.GetCalls) {
+		currRequests := csCurr.GetCalls
+		if currRequests >= currGetCalls {
+			currRequests -= currGetCalls
+		}
+		prevRequests := csPrev.GetCalls
+		if prevRequests >= prevGetCalls {
+			prevRequests -= prevGetCalls
+		}
+		currGetCalls = csCurr.GetCalls
+		prevGetCalls = csPrev.GetCalls
+		if currRequests >= 20 && float64(prevRequests)/float64(currRequests) < 0.05 {
 			// The majority of requests are served from the curr cache,
-				// so the prev cache can be deleted.
+			// so the prev cache can be deleted in order to free up memory.
+			if csPrev.EntriesCount > 0 {
+				updateCacheStatsHistory(&c.csHistory, &csPrev)
 				prev.Reset()
-				break
 			}
 		}
-		checkerT.Stop()
+		c.mu.Unlock()
 	}
 }
 
@@ -239,11 +252,9 @@ func (c *Cache) cacheSizeWatcher() {
 	prev := c.prev.Load().(*fastcache.Cache)
 	curr := c.curr.Load().(*fastcache.Cache)
 	c.prev.Store(curr)
-
 	var cs fastcache.Stats
 	prev.UpdateStats(&cs)
 	updateCacheStatsHistory(&c.csHistory, &cs)
-
 	prev.Reset()
 	// use c.maxBytes instead of maxBytesSize*2 for creating new cache, since otherwise the created cache
 	// couldn't be loaded from file with c.maxBytes limit after saving with maxBytesSize*2 limit.
@@ -268,11 +279,9 @@ func (c *Cache) cacheSizeWatcher() {
 	c.setMode(whole)
 	prev = c.prev.Load().(*fastcache.Cache)
 	c.prev.Store(fastcache.New(1024))
-
 	cs.Reset()
 	prev.UpdateStats(&cs)
 	updateCacheStatsHistory(&c.csHistory, &cs)
-
 	prev.Reset()
 	c.mu.Unlock()
 }
@@ -296,9 +305,13 @@ func (c *Cache) Stop() {
 
 // Reset resets the cache.
 func (c *Cache) Reset() {
+	var cs fastcache.Stats
 	prev := c.prev.Load().(*fastcache.Cache)
+	prev.UpdateStats(&cs)
 	prev.Reset()
 	curr := c.curr.Load().(*fastcache.Cache)
+	curr.UpdateStats(&cs)
+	updateCacheStatsHistory(&c.csHistory, &cs)
 	curr.Reset()
 	// Reset the mode to `split` in the hope the working set size becomes smaller after the reset.
 	c.setMode(split)