Re-add bunched request caching with a lazy janitor

And this time, only one lock is held at a time during the response.

socketserver/internal/server/commands.go

@@ -379,12 +379,82 @@ type BunchSubscriberList struct {
 	Members []BunchSubscriber
 }
 
+type CacheStatus byte
+const (
+	CacheStatusNotFound = iota
+	CacheStatusFound
+	CacheStatusExpired
+)
+
 var PendingBunchedRequests map[BunchedRequest]*BunchSubscriberList = make(map[BunchedRequest]*BunchSubscriberList)
 var PendingBunchLock sync.Mutex
+var CachedBunchedRequests map[BunchedRequest]BunchedResponse = make(map[BunchedRequest]BunchedResponse)
+var CachedBunchLock sync.RWMutex
+var BunchCacheCleanupSignal *sync.Cond = sync.NewCond(&CachedBunchLock)
+var BunchCacheLastCleanup time.Time
+
+func bunchCacheJanitor() {
+	go func() {
+		for {
+			time.Sleep(30*time.Minute)
+			BunchCacheCleanupSignal.Signal()
+		}
+	}()
+
+	CachedBunchLock.Lock()
+	for {
+		// Unlocks CachedBunchLock, waits for signal, re-locks
+		BunchCacheCleanupSignal.Wait()
+
+		if BunchCacheLastCleanup.After(time.Now().Add(-1*time.Second)) {
+			// skip if it's been less than 1 second
+			continue
+		}
+
+		// CachedBunchLock is held here
+		keepIfAfter := time.Now().Add(-5*time.Minute)
+		for req, resp := range CachedBunchedRequests {
+			if !resp.Timestamp.After(keepIfAfter) {
+				delete(CachedBunchedRequests, req)
+			}
+		}
+		BunchCacheLastCleanup = time.Now()
+		// Loop and Wait(), which re-locks
+	}
+}
 
 func HandleBunchedRemoteCommand(conn *websocket.Conn, client *ClientInfo, msg ClientMessage) (rmsg ClientMessage, err error) {
 	br := BunchedRequestFromCM(&msg)
 
+	cacheStatus := func() byte {
+		CachedBunchLock.RLock()
+		defer CachedBunchLock.RUnlock()
+		bresp, ok := CachedBunchedRequests[br]
+		if ok && bresp.Timestamp.After(time.Now().Add(-5*time.Minute)) {
+			client.MsgChannelKeepalive.Add(1)
+			go func() {
+				var rmsg ClientMessage
+				rmsg.Command = SuccessCommand
+				rmsg.MessageID = msg.MessageID
+				rmsg.origArguments = bresp.Response
+				rmsg.parseOrigArguments()
+				client.MessageChannel <- rmsg
+				client.MsgChannelKeepalive.Done()
+			}()
+			return CacheStatusFound
+		} else if ok {
+			return CacheStatusExpired
+		}
+		return CacheStatusNotFound
+	}()
+
+	if cacheStatus == CacheStatusFound {
+		return ClientMessage{Command: AsyncResponseCommand}, nil
+	} else if cacheStatus == CacheStatusExpired {
+		// Wake up the lazy janitor
+		BunchCacheCleanupSignal.Signal()
+	}
+
 	PendingBunchLock.Lock()
 	defer PendingBunchLock.Unlock()
 	list, ok := PendingBunchedRequests[br]
@@ -399,18 +469,24 @@ func HandleBunchedRemoteCommand(conn *websocket.Conn, client *ClientInfo, msg Cl
 	PendingBunchedRequests[br] = &BunchSubscriberList{Members: []BunchSubscriber{{Client: client, MessageID: msg.MessageID}}}
 
 	go func(request BunchedRequest) {
-		resp, err := SendRemoteCommandCached(string(request.Command), request.Param, AuthInfo{})
+		respStr, err := SendRemoteCommandCached(string(request.Command), request.Param, AuthInfo{})
 
 		var msg ClientMessage
 		if err == nil {
 			msg.Command = SuccessCommand
-			msg.origArguments = resp
+			msg.origArguments = respStr
 			msg.parseOrigArguments()
 		} else {
 			msg.Command = ErrorCommand
 			msg.Arguments = err.Error()
 		}
 
+		if err == nil {
+			CachedBunchLock.Lock()
+			CachedBunchedRequests[request] = BunchedResponse{Response: respStr, Timestamp: time.Now()}
+			CachedBunchLock.Unlock()
+		}
+
 		PendingBunchLock.Lock()
 		bsl := PendingBunchedRequests[request]
 		delete(PendingBunchedRequests, request)