.

go/neo/client/cache.go

@@ -35,11 +35,15 @@ type Cache struct {
 	// cache is fully synchronized with storage for transactions with tid < before.
 	before	zodb.Tid
 
-	entryMap map[zodb.Oid]*cacheEntry
+	oidDir map[zodb.Oid]*oidEntry
+
+	bytesUsed int64
+
+	lru revListHead
 }
 
-// cacheEntry maintains cached revisions for 1 oid
-type cacheEntry struct {
+// oidCacheEntry maintains cached revisions for 1 oid
+type oidCacheEntry struct {
 	sync.Mutex	// XXX -> rw ?
 
 	// cached revisions in ascending order
@@ -53,7 +57,10 @@ type cacheEntry struct {
 
 // revCacheEntry is information about 1 cached oid revision
 type revCacheEntry struct {
-	sync.Mutex	// XXX -> rw ?
+	inLRU  revListHead
+	parent *oidCacheEntry
+
+//	sync.Mutex	XXX not needed
 
 	// oid revision
 	// 0 if don't know yet - loadBefore(.before) is in progress and actual
@@ -76,15 +83,56 @@ type revCacheEntry struct {
 	// case when loadBefore with tid > cache.before was called.
 	before zodb.Tid
 
-
-	// object data
+	// object data or loading error
 	data []byte
+	err  error
+
+	ready chan struct{} // closed when loading finished
+}
 
+type revListHead struct {
+	// XXX needs to be created with .next = .prev = self
+	next, prev *revCacheEntry
+}
 
-	// XXX + lru
-	ready chan struct{} // closed when entry loaded; nil if evicted from cache
+// XXX -> to ctor?
+func (h *revListHead) init() {
+	h.next = h
+	h.prev = h
 }
 
+// Delete deletes h from list
+func (h *revListHead) Delete() {
+	h.next.prev = h.prev
+	h.prev.next = h.next
+}
+
+// MoveBefore moves a to be before b
+// XXX ok to move if a was not previously on the list?
+func (a *revListHead) MoveBefore(b *revListHead) {
+	a.Delete()
+
+	a.next = b
+	b.prev = a
+	a.prev = b.prev
+	a.prev.next = a
+}
+
+
+// cleaner is the process that cleans cache by evicting less-needed entries.
+func (c *cache) cleaner() {
+	for {
+		// cleaner is the only mutator/user of Cache.lru and revCacheEntry.inLRU
+		select {
+		case rce := <-c.used:
+			rce.inLRU.MoveBefore(&c.lru)
+
+		default:
+			for rce := c.lru.next; rce != &c.lru; rce = rce.next {
+			}
+		}
+	}
+}
 
 
 // lock order: Cache > cacheEntry > (?) revCacheEntry
@@ -95,8 +143,11 @@ func (c *cache) Load(xid zodb.Xid) (data []byte, tid Tid, err error) {
 	// oid -> cacheEntry  ; creating new empty if not yet there
 	// exit with cacheEntry locked and cache.before read consistently
 	c.mu.RLock()
+
 	entry := c.entryMap[xid.Oid]
 	cacheBefore := c.before
+	cacheMemUsed := c.memUsed
+
 	if entry != nil {
 		entry.Lock()
 		c.mu.RUnlock()
@@ -108,7 +159,7 @@ func (c *cache) Load(xid zodb.Xid) (data []byte, tid Tid, err error) {
 			entry = &cacheEntry{}
 			c.entryMap[xid.Oid] = entry
 		}
-		cacheBefore = c.before
+		cacheBefore = c.before // reload c.before for correctness
 		entry.Lock()
 		c.mu.Unlock()
 	}
@@ -136,7 +187,7 @@ func (c *cache) Load(xid zodb.Xid) (data []byte, tid Tid, err error) {
 				rce.before = zodb.TidMax	// XXX vs concurrent invalidations?
 			}
 			rceNew = true
-			entry.revv = append(entry.revv, &revCacheEntry{before: before}
+			entry.revv = append(entry.revv, rce)
 
 		// found:
 		// tid <= revv[i].before
@@ -158,36 +209,33 @@ func (c *cache) Load(xid zodb.Xid) (data []byte, tid Tid, err error) {
 		// TODO
 	}
 
-	entry.Unlock()	// XXX order ok?
-	rce.Lock()
-
-	// entry is not in cache - this goroutine becomes responsible for loading it
-	if rce.ready == nil {
-		ready := make(chan struct{})
-		rce.ready = ready
-		rce.Unlock()
-
-		data, serial, err := c.stor.Load(xid)
-		rce.Lock()
-		if rce.ready != nil { // could be evicted	XXX ok?
-			// XXX if err != nil -> ?
-			rce.serial = serial
-			rce.data = data
-		}
-		rce.Unlock()
-		close(ready)
-
-		entry.Lock()
-		// XXX merge with adjacent entries in revv
-		entry.Unlock()
-
-		return rce
+	if rceNew {
+		rce.ready = make(chan struct{})
 	}
 
-	// entry is already in cache - use it
-	if rce.ready != nil {
-		rce.Unlock()
+	entry.Unlock()
+
+	// entry was already in cache - use it
+	if !rceNew {
 		<-rce.ready
-		return rce
+		return rce.data, rce.serial, rce.err
 	}
+
+	// entry was not in cache - this goroutine becomes responsible for loading it
+	data, serial, err := c.stor.Load(xid)
+	rce.serial = serial
+	rce.data = data
+	rce.err = err
+	close(ready)
+
+	entry.Lock()
+	// XXX merge with adjacent entries in revv
+	entry.Unlock()
+
+	c.Lock()
+	c.memUsed += len(data)
+	// XXX GC if memUsed > threthold ?
+	c.Unlock()
+
+	return rce.data, rce.serial, rce.err
 }