Improving backend use of room.InputsBufferLock.

battle_srv/models/ringbuf.go

@@ -1,10 +1,5 @@
 package models
 
-import (
-	. "battle_srv/protos"
-	"sync"
-)
-
 type RingBuffer struct {
 	Ed        int32 // write index, open index
 	St        int32 // read index, closed index
@@ -83,42 +78,3 @@ func (rb *RingBuffer) GetByFrameId(frameId int32) interface{} {
 	}
 	return rb.GetByOffset(frameId - rb.StFrameId)
 }
-
-func (rb *RingBuffer) cloneInputFrameDownsyncsByFrameIdRange(stFrameId, edFrameId int32, mux *sync.Mutex) (int32, []*InputFrameDownsync) {
-	dst := make([]*InputFrameDownsync, 0, rb.Cnt)
-	if nil != mux {
-		mux.Lock()
-
-		defer func() {
-			mux.Unlock()
-		}()
-	}
-
-	prevFrameFound := true
-	j := stFrameId
-	for j < edFrameId {
-		tmp := rb.GetByFrameId(j)
-		if nil == tmp {
-			if false == prevFrameFound {
-				// The "id"s are always consecutive
-				break
-			} else {
-				prevFrameFound = false
-				continue
-			}
-		}
-		foo := tmp.(*InputFrameDownsync)
-		bar := &InputFrameDownsync{
-			InputFrameId:  foo.InputFrameId,
-			InputList:     make([]uint64, len(foo.InputList)),
-			ConfirmedList: foo.ConfirmedList,
-		}
-		for i, input := range foo.InputList {
-			bar.InputList[i] = input
-		}
-		dst = append(dst, bar)
-		j++
-	}
-
-	return j, dst
-}

battle_srv/models/room.go

@@ -158,7 +158,7 @@ type Room struct {
 	Barriers                               map[int32]*Barrier
 	InputsBuffer                           *RingBuffer // Indices are STRICTLY consecutive
 	InputsBufferLock                       sync.Mutex
-	RenderFrameBuffer                      *RingBuffer
+	RenderFrameBuffer                      *RingBuffer // Indices are STRICTLY consecutive
 	LastAllConfirmedInputFrameId           int32
 	LastAllConfirmedInputFrameIdWithChange int32
 	LastAllConfirmedInputList              []uint64
@@ -342,7 +342,7 @@ func (pR *Room) ConvertToLastUsedRenderFrameId(inputFrameId int32, inputDelayFra
 }
 
 func (pR *Room) RenderFrameBufferString() string {
-	return fmt.Sprintf("{renderFrameId: %d, stRenderFrameId: %d, edRenderFrameId: %d, lastAllConfirmedRenderFrameId: %d}", pR.RenderFrameId, pR.RenderFrameBuffer.StFrameId, pR.RenderFrameBuffer.EdFrameId, pR.CurDynamicsRenderFrameId)
+	return fmt.Sprintf("{renderFrameId: %d, stRenderFrameId: %d, edRenderFrameId: %d, curDynamicsRenderFrameId: %d}", pR.RenderFrameId, pR.RenderFrameBuffer.StFrameId, pR.RenderFrameBuffer.EdFrameId, pR.CurDynamicsRenderFrameId)
 }
 
 func (pR *Room) InputsBufferString(allDetails bool) string {
@@ -350,7 +350,7 @@ func (pR *Room) InputsBufferString(allDetails bool) string {
 		// Appending of the array of strings can be very SLOW due to on-demand heap allocation! Use this printing with caution.
 		s := make([]string, 0)
 		s = append(s, fmt.Sprintf("{renderFrameId: %v, stInputFrameId: %v, edInputFrameId: %v, lastAllConfirmedInputFrameIdWithChange: %v, lastAllConfirmedInputFrameId: %v}", pR.RenderFrameId, pR.InputsBuffer.StFrameId, pR.InputsBuffer.EdFrameId, pR.LastAllConfirmedInputFrameIdWithChange, pR.LastAllConfirmedInputFrameId))
-		for playerId, player := range pR.Players {
+		for playerId, player := range pR.PlayersArr {
 			s = append(s, fmt.Sprintf("{playerId: %v, ackingFrameId: %v, ackingInputFrameId: %v, lastSentInputFrameId: %v}", playerId, player.AckingFrameId, player.AckingInputFrameId, player.LastSentInputFrameId))
 		}
 		for i := pR.InputsBuffer.StFrameId; i < pR.InputsBuffer.EdFrameId; i++ {
@@ -428,7 +428,8 @@ func (pR *Room) StartBattle() {
 			}
 
 			if 0 == pR.RenderFrameId {
-				for playerId, player := range pR.Players {
+				for _, player := range pR.PlayersArr {
+					playerId := player.Id
 					thatPlayerBattleState := atomic.LoadInt32(&(player.BattleState)) // Might be changed in "OnPlayerDisconnected/OnPlayerLost" from other threads
 					// [WARNING] DON'T try to send any message to an inactive player!
 					switch thatPlayerBattleState {
@@ -445,32 +446,14 @@ func (pR *Room) StartBattle() {
 			}
 
 			dynamicsDuration := int64(0)
-			unconfirmedMask := uint64(0)
 
 			// Prefab and buffer backend inputFrameDownsync
 			if pR.BackendDynamicsEnabled {
-				if pR.shouldPrefabInputFrameDownsync(pR.RenderFrameId) {
+				unconfirmedMask, inputsBufferSnapshot := pR.doBattleMainLoopPerTickBackendDynamicsWithProperLocking(&dynamicsDuration)
-					noDelayInputFrameId := pR.ConvertToInputFrameId(pR.RenderFrameId, 0)
-					if existingInputFrame := pR.InputsBuffer.GetByFrameId(noDelayInputFrameId); nil == existingInputFrame {
-						pR.prefabInputFrameDownsync(noDelayInputFrameId, true)
-					}
-				}
-
-				// Force setting all-confirmed of buffered inputFrames periodically, kindly note that if "pR.BackendDynamicsEnabled", what we want to achieve is "recovery upon reconnection", which certainly requires "forceConfirmationIfApplicable" to move "pR.LastAllConfirmedInputFrameId" forward as much as possible
-				unconfirmedMask = pR.forceConfirmationIfApplicable()
-
-				if 0 <= pR.LastAllConfirmedInputFrameId {
-					dynamicsStartedAt := utils.UnixtimeNano()
-					// Apply "all-confirmed inputFrames" to move forward "pR.CurDynamicsRenderFrameId"
-					nextDynamicsRenderFrameId := pR.ConvertToLastUsedRenderFrameId(pR.LastAllConfirmedInputFrameId, pR.InputDelayFrames)
-					Logger.Debug(fmt.Sprintf("roomId=%v, room.RenderFrameId=%v, room.CurDynamicsRenderFrameId=%v, LastAllConfirmedInputFrameId=%v, InputDelayFrames=%v, nextDynamicsRenderFrameId=%v", pR.Id, pR.RenderFrameId, pR.CurDynamicsRenderFrameId, pR.LastAllConfirmedInputFrameId, pR.InputDelayFrames, nextDynamicsRenderFrameId))
-					pR.applyInputFrameDownsyncDynamics(pR.CurDynamicsRenderFrameId, nextDynamicsRenderFrameId, pR.collisionSpaceOffsetX, pR.collisionSpaceOffsetY)
-					dynamicsDuration = utils.UnixtimeNano() - dynamicsStartedAt
-				}
 				if 0 < unconfirmedMask {
-					Logger.Debug(fmt.Sprintf("roomId=%v, room.RenderFrameId=%v, room.CurDynamicsRenderFrameId=%v, room.LastAllConfirmedInputFrameId=%v, unconfirmedMask=%v", pR.Id, pR.RenderFrameId, pR.CurDynamicsRenderFrameId, pR.LastAllConfirmedInputFrameId, unconfirmedMask))
 					// Otherwise no need to downsync immediately
-					pR.downsyncToAllPlayers(pR.LastAllConfirmedInputFrameId, unconfirmedMask, false)
+					Logger.Debug(fmt.Sprintf("roomId=%v, room.RenderFrameId=%v, room.CurDynamicsRenderFrameId=%v, room.LastAllConfirmedInputFrameId=%v, unconfirmedMask=%v", pR.Id, pR.RenderFrameId, pR.CurDynamicsRenderFrameId, pR.LastAllConfirmedInputFrameId, unconfirmedMask))
+					pR.downsyncToAllPlayers(pR.LastAllConfirmedInputFrameId, unconfirmedMask, inputsBufferSnapshot)
 				}
 			}
 
@@ -496,6 +479,7 @@ func (pR *Room) toDiscreteInputsBufferIndex(inputFrameId int32, joinIndex int32)
 
 func (pR *Room) OnBattleCmdReceived(pReq *WsReq) {
 	// [WARNING] This function "OnBattleCmdReceived" could be called by different ws sessions and thus from different threads!
+	// TODO: Put a rate limiter on this function!
 	if swapped := atomic.CompareAndSwapInt32(&pR.State, RoomBattleStateIns.IN_BATTLE, RoomBattleStateIns.IN_BATTLE); !swapped {
 		return
 	}
@@ -515,44 +499,16 @@ func (pR *Room) OnBattleCmdReceived(pReq *WsReq) {
 	atomic.StoreInt32(&(player.AckingFrameId), ackingFrameId)
 	atomic.StoreInt32(&(player.AckingInputFrameId), ackingInputFrameId)
 
-	Logger.Debug(fmt.Sprintf("InputsBufferLock about to lock: roomId=%v", pR.Id))
+	newAllConfirmedCount := pR.markConfirmationIfApplicable(inputFrameUpsyncBatch, playerId, player)
-	pR.InputsBufferLock.Lock()
+	// [WARNING] By now "pR.InputsBufferLock" is unlocked
-	Logger.Debug(fmt.Sprintf("InputsBufferLock locked: roomId=%v", pR.Id))
-	defer func() {
-		pR.InputsBufferLock.Unlock()
-		Logger.Debug(fmt.Sprintf("InputsBufferLock unlocked: roomId=%v", pR.Id))
-	}()
-	for _, inputFrameUpsync := range inputFrameUpsyncBatch {
-		clientInputFrameId := inputFrameUpsync.InputFrameId
-		if clientInputFrameId < pR.InputsBuffer.StFrameId {
-			// The updates to "pR.InputsBuffer.StFrameId" is monotonically increasing, thus if "clientInputFrameId < pR.InputsBuffer.StFrameId" at any moment of time, it is obsolete in the future.
-			Logger.Warn(fmt.Sprintf("Omitting obsolete inputFrameUpsync: roomId=%v, playerId=%v, clientInputFrameId=%v, InputsBuffer=%v", pR.Id, playerId, clientInputFrameId, pR.InputsBufferString(false)))
-			continue
-		}
-		if clientInputFrameId > pR.InputsBuffer.EdFrameId {
-			Logger.Warn(fmt.Sprintf("Dropping too advanced inputFrameUpsync: roomId=%v, playerId=%v, clientInputFrameId=%v, InputsBuffer=%v; is this player cheating?", pR.Id, playerId, clientInputFrameId, pR.InputsBufferString(false)))
-			continue
-		}
-		var targetInputFrameDownsync *InputFrameDownsync = nil
-		if clientInputFrameId == pR.InputsBuffer.EdFrameId {
-			targetInputFrameDownsync = pR.prefabInputFrameDownsync(clientInputFrameId, false)
-			Logger.Debug(fmt.Sprintf("OnBattleCmdReceived-Prefabbed new inputFrameDownsync from inputFrameUpsync: roomId=%v, playerId=%v, clientInputFrameId=%v, InputsBuffer=%v", pR.Id, playerId, clientInputFrameId, pR.InputsBufferString(false)))
-		} else {
-			targetInputFrameDownsync = pR.InputsBuffer.GetByFrameId(clientInputFrameId).(*InputFrameDownsync)
-			Logger.Debug(fmt.Sprintf("OnBattleCmdReceived-stuffing inputFrameDownsync from inputFrameUpsync: roomId=%v, playerId=%v, clientInputFrameId=%v, InputsBuffer=%v", pR.Id, playerId, clientInputFrameId, pR.InputsBufferString(false)))
-		}
-		targetInputFrameDownsync.InputList[player.JoinIndex-1] = inputFrameUpsync.Encoded
-		targetInputFrameDownsync.ConfirmedList |= uint64(1 << uint32(player.JoinIndex-1))
-	}
-	newAllConfirmedCount := pR.markConfirmationIfApplicable()
 	if 0 < newAllConfirmedCount {
 		// Downsync new all-confirmed inputFrames asap
-		unconfirmedMask := uint64(0)
+		pR.downsyncToAllPlayers(pR.LastAllConfirmedInputFrameId, uint64(0), pR.createInputsBufferSnapshot())
-		pR.downsyncToAllPlayers(pR.LastAllConfirmedInputFrameId, unconfirmedMask, true)
 	}
 }
 
 func (pR *Room) onInputFrameDownsyncAllConfirmed(inputFrameDownsync *InputFrameDownsync, playerId int32) {
+	// [WARNING] This function MUST BE called while "pR.InputsBufferLock" is locked!
 	inputFrameId := inputFrameDownsync.InputFrameId
 	if -1 == pR.LastAllConfirmedInputFrameIdWithChange || false == pR.equalInputLists(inputFrameDownsync.InputList, pR.LastAllConfirmedInputList) {
 		if -1 == playerId {
@@ -560,9 +516,9 @@ func (pR *Room) onInputFrameDownsyncAllConfirmed(inputFrameDownsync *InputFrameD
 		} else {
 			Logger.Debug(fmt.Sprintf("Key inputFrame change: roomId=%v, playerId=%v, newInputFrameId=%v, lastInputFrameId=%v, newInputList=%v, lastInputList=%v, InputsBuffer=%v", pR.Id, playerId, inputFrameId, pR.LastAllConfirmedInputFrameId, inputFrameDownsync.InputList, pR.LastAllConfirmedInputList, pR.InputsBufferString(false)))
 		}
-		atomic.StoreInt32(&(pR.LastAllConfirmedInputFrameIdWithChange), inputFrameId)
+		pR.LastAllConfirmedInputFrameIdWithChange = inputFrameId
 	}
-	atomic.StoreInt32(&(pR.LastAllConfirmedInputFrameId), inputFrameId) // [WARNING] It's IMPORTANT that "pR.LastAllConfirmedInputFrameId" is NOT NECESSARILY CONSECUTIVE, i.e. if one of the players disconnects and reconnects within a considerable amount of frame delays!
+	pR.LastAllConfirmedInputFrameId = inputFrameId
 	for i, v := range inputFrameDownsync.InputList {
 		// To avoid potential misuse of pointers
 		pR.LastAllConfirmedInputList[i] = v
@@ -717,8 +673,8 @@ func (pR *Room) OnDismissed() {
 	pR.ServerFps = 60
 	pR.RollbackEstimatedDtMillis = 16.667  // Use fixed-and-low-precision to mitigate the inconsistent floating-point-number issue between Golang and JavaScript
 	pR.RollbackEstimatedDtNanos = 16666666 // A little smaller than the actual per frame time, just for logging FAST FRAME
-	dilutedServerFps := int64(58)
+	dilutedServerFps := float64(59.5)
-	pR.dilutedRollbackEstimatedDtNanos = pR.RollbackEstimatedDtNanos * (int64(pR.ServerFps) / dilutedServerFps)
+	pR.dilutedRollbackEstimatedDtNanos = pR.RollbackEstimatedDtNanos * int64(float64(pR.ServerFps)/dilutedServerFps)
 	pR.BattleDurationFrames = 30 * pR.ServerFps
 	pR.BattleDurationNanos = int64(pR.BattleDurationFrames) * (pR.RollbackEstimatedDtNanos + 1)
 	pR.InputFrameUpsyncDelayTolerance = 2
@@ -941,7 +897,7 @@ func (pR *Room) OnPlayerBattleColliderAcked(playerId int32) bool {
 	case PlayerBattleStateIns.READDED_PENDING_BATTLE_COLLIDER_ACK:
 		// only send resync info to the targetPlayer
 		// i.e. implies that "targetPlayer.LastSentInputFrameId == MAGIC_LAST_SENT_INPUT_FRAME_ID_READDED"
-		pR.downsyncToSinglePlayer(playerId, targetPlayer, pR.LastAllConfirmedInputFrameId, uint64(0), false)
+		pR.downsyncToSinglePlayer(playerId, targetPlayer, pR.LastAllConfirmedInputFrameId, uint64(0), pR.createInputsBufferSnapshot())
 	default:
 	}
 
@@ -996,24 +952,13 @@ func (pR *Room) shouldPrefabInputFrameDownsync(renderFrameId int32) bool {
 	return ((renderFrameId & ((1 << pR.InputScaleFrames) - 1)) == 0)
 }
 
-func (pR *Room) prefabInputFrameDownsync(inputFrameId int32, lockInputsBuffer bool) *InputFrameDownsync {
+func (pR *Room) prefabInputFrameDownsync(inputFrameId int32) *InputFrameDownsync {
 	/*
 	   Kindly note that on backend the prefab is much simpler than its frontend counterpart, because frontend will upsync its latest command immediately if there's any change w.r.t. its own prev cmd, thus if no upsync received from a frontend,
 	   - EITHER it's due to local lag and bad network,
 	   - OR there's no change w.r.t. to its prev cmd.
 	*/
 
-	if lockInputsBuffer {
-		Logger.Debug(fmt.Sprintf("prefabInputFrameDownsync-InputsBufferLock to about lock: roomId=%v", pR.Id))
-		pR.InputsBufferLock.Lock()
-		Logger.Debug(fmt.Sprintf("prefabInputFrameDownsync-InputsBufferLock locked: roomId=%v", pR.Id))
-
-		defer func() {
-			pR.InputsBufferLock.Unlock()
-			Logger.Debug(fmt.Sprintf("prefabInputFrameDownsync-InputsBufferLock unlocked: roomId=%v", pR.Id))
-		}()
-	}
-
 	var currInputFrameDownsync *InputFrameDownsync = nil
 
 	if 0 == inputFrameId && 0 == pR.InputsBuffer.Cnt {
@@ -1043,7 +988,42 @@ func (pR *Room) prefabInputFrameDownsync(inputFrameId int32, lockInputsBuffer bo
 	return currInputFrameDownsync
 }
 
-func (pR *Room) markConfirmationIfApplicable() int {
+func (pR *Room) markConfirmationIfApplicable(inputFrameUpsyncBatch []*InputFrameUpsync, playerId int32, player *Player) int {
+	Logger.Debug(fmt.Sprintf("markConfirmationIfApplicable-InputsBufferLock about to lock: roomId=%v, fromPlayerId=%v", pR.Id, playerId))
+	pR.InputsBufferLock.Lock()
+	Logger.Debug(fmt.Sprintf("markConfirmationIfApplicable-InputsBufferLock locked: roomId=%v, fromPlayerId=%v", pR.Id, playerId))
+	defer func() {
+		pR.InputsBufferLock.Unlock()
+		Logger.Debug(fmt.Sprintf("markConfirmationIfApplicable-InputsBufferLock unlocked: roomId=%v, fromPlayerId=%v", pR.Id, playerId))
+	}()
+
+	for _, inputFrameUpsync := range inputFrameUpsyncBatch {
+		clientInputFrameId := inputFrameUpsync.InputFrameId
+		if clientInputFrameId < pR.InputsBuffer.StFrameId {
+			// The updates to "pR.InputsBuffer.StFrameId" is monotonically increasing, thus if "clientInputFrameId < pR.InputsBuffer.StFrameId" at any moment of time, it is obsolete in the future.
+			Logger.Debug(fmt.Sprintf("Omitting obsolete inputFrameUpsync#1: roomId=%v, playerId=%v, clientInputFrameId=%v, lastAllConfirmedInputFrameId=%v, InputsBuffer=%v", pR.Id, playerId, clientInputFrameId, pR.LastAllConfirmedInputFrameId, pR.InputsBufferString(false)))
+			continue
+		}
+		if clientInputFrameId < pR.LastAllConfirmedInputFrameId {
+			Logger.Info(fmt.Sprintf("Omitting obsolete inputFrameUpsync#2: roomId=%v, playerId=%v, clientInputFrameId=%v, lastAllConfirmedInputFrameId=%v, InputsBuffer=%v", pR.Id, playerId, clientInputFrameId, pR.LastAllConfirmedInputFrameId, pR.InputsBufferString(false)))
+			continue
+		}
+		if clientInputFrameId > pR.InputsBuffer.EdFrameId {
+			Logger.Warn(fmt.Sprintf("Dropping too advanced inputFrameUpsync: roomId=%v, playerId=%v, clientInputFrameId=%v, lastAllConfirmedInputFrameId=%v, InputsBuffer=%v; is this player cheating?", pR.Id, playerId, clientInputFrameId, pR.LastAllConfirmedInputFrameId, pR.InputsBufferString(false)))
+			continue
+		}
+		var targetInputFrameDownsync *InputFrameDownsync = nil
+		if clientInputFrameId == pR.InputsBuffer.EdFrameId {
+			targetInputFrameDownsync = pR.prefabInputFrameDownsync(clientInputFrameId)
+			Logger.Debug(fmt.Sprintf("OnBattleCmdReceived-Prefabbed new inputFrameDownsync from inputFrameUpsync: roomId=%v, playerId=%v, clientInputFrameId=%v, InputsBuffer=%v", pR.Id, playerId, clientInputFrameId, pR.InputsBufferString(false)))
+		} else {
+			targetInputFrameDownsync = pR.InputsBuffer.GetByFrameId(clientInputFrameId).(*InputFrameDownsync)
+			Logger.Debug(fmt.Sprintf("OnBattleCmdReceived-stuffing inputFrameDownsync from inputFrameUpsync: roomId=%v, playerId=%v, clientInputFrameId=%v, InputsBuffer=%v", pR.Id, playerId, clientInputFrameId, pR.InputsBufferString(false)))
+		}
+		targetInputFrameDownsync.InputList[player.JoinIndex-1] = inputFrameUpsync.Encoded
+		targetInputFrameDownsync.ConfirmedList |= uint64(1 << uint32(player.JoinIndex-1))
+	}
+
 	newAllConfirmedCount := 0
 	inputFrameId1 := pR.LastAllConfirmedInputFrameId + 1
 	totPlayerCnt := uint32(pR.Capacity)
@@ -1058,7 +1038,7 @@ func (pR *Room) markConfirmationIfApplicable() int {
 		inputFrameDownsync := tmp.(*InputFrameDownsync)
 
 		if allConfirmedMask != inputFrameDownsync.ConfirmedList {
-			for _, player := range pR.Players {
+			for _, player := range pR.PlayersArr {
 				thatPlayerBattleState := atomic.LoadInt32(&(player.BattleState))
 				thatPlayerJoinMask := uint64(1 << uint32(player.JoinIndex-1))
 				if 0 == (inputFrameDownsync.ConfirmedList & thatPlayerJoinMask) {
@@ -1085,6 +1065,7 @@ func (pR *Room) markConfirmationIfApplicable() int {
 }
 
 func (pR *Room) forceConfirmationIfApplicable() uint64 {
+	// [WARNING] This function MUST BE called while "pR.InputsBufferLock" is locked!
 	// Force confirmation of non-all-confirmed inputFrame EXACTLY ONE AT A TIME, returns the non-confirmed mask of players, e.g. in a 4-player-battle returning 1001 means that players with JoinIndex=1 and JoinIndex=4 are non-confirmed for inputFrameId2
 	renderFrameId1 := (pR.RenderFrameId - pR.NstDelayFrames) // the renderFrameId which should've been rendered on frontend
 	if 0 > renderFrameId1 || !pR.shouldPrefabInputFrameDownsync(renderFrameId1) {
@@ -1103,14 +1084,6 @@ func (pR *Room) forceConfirmationIfApplicable() uint64 {
 		return 0
 	}
 
-	Logger.Debug(fmt.Sprintf("forceConfirmation-InputsBufferLock about to lock: roomId=%v", pR.Id))
-	pR.InputsBufferLock.Lock()
-	Logger.Debug(fmt.Sprintf("forceConfirmation-InputsBufferLock locked: roomId=%v", pR.Id))
-
-	defer func() {
-		pR.InputsBufferLock.Unlock()
-		Logger.Debug(fmt.Sprintf("forceConfirmation-InputsBufferLock unlocked: roomId=%v", pR.Id))
-	}()
 	tmp := pR.InputsBuffer.GetByFrameId(inputFrameId2)
 	if nil == tmp {
 		panic(fmt.Sprintf("inputFrameId2=%v doesn't exist for roomId=%v, this is abnormal because the server should prefab inputFrameDownsync in a most advanced pace, check the prefab logic! InputsBuffer=%v", inputFrameId2, pR.Id, pR.InputsBufferString(false)))
@@ -1164,7 +1137,7 @@ func (pR *Room) applyInputFrameDownsyncDynamics(fromRenderFrameId int32, toRende
 			}
 			delayedInputFrame = tmp.(*InputFrameDownsync)
 			// [WARNING] It's possible that by now "allConfirmedMask != delayedInputFrame.ConfirmedList && delayedInputFrameId <= pR.LastAllConfirmedInputFrameId", we trust "pR.LastAllConfirmedInputFrameId" as the TOP AUTHORITY.
-			atomic.StoreUint64(&(delayedInputFrame.ConfirmedList), allConfirmedMask)
+			delayedInputFrame.ConfirmedList = allConfirmedMask
 		}
 
 		nextRenderFrame := pR.applyInputFrameDownsyncDynamicsOnSingleRenderFrame(delayedInputFrame, currRenderFrame, pR.CollisionSysMap)
@@ -1211,7 +1184,8 @@ func (pR *Room) applyInputFrameDownsyncDynamicsOnSingleRenderFrame(delayedInputF
 	effPushbacks := make([]Vec2D, pR.Capacity)    // Guaranteed determinism regardless of traversal order
 
 	// Reset playerCollider position from the "virtual grid position"
-	for playerId, player := range pR.Players {
+	for _, player := range pR.PlayersArr {
+		playerId := player.Id
 		joinIndex := player.JoinIndex
 		bulletPushbacks[joinIndex-1].X, bulletPushbacks[joinIndex-1].Y = float64(0), float64(0)
 		effPushbacks[joinIndex-1].X, effPushbacks[joinIndex-1].Y = float64(0), float64(0)
@@ -1306,7 +1280,8 @@ func (pR *Room) applyInputFrameDownsyncDynamicsOnSingleRenderFrame(delayedInputF
 		}
 		inputList := delayedInputFrame.InputList
 		// Process player inputs
-		for playerId, player := range pR.Players {
+		for _, player := range pR.PlayersArr {
+			playerId := player.Id
 			joinIndex := player.JoinIndex
 			collisionPlayerIndex := COLLISION_PLAYER_INDEX_PREFIX + joinIndex
 			playerCollider := collisionSysMap[collisionPlayerIndex]
@@ -1368,7 +1343,7 @@ func (pR *Room) applyInputFrameDownsyncDynamicsOnSingleRenderFrame(delayedInputF
 		}
 
 		// handle pushbacks upon collision after all movements treated as simultaneous
-		for _, player := range pR.Players {
+		for _, player := range pR.PlayersArr {
 			joinIndex := player.JoinIndex
 			collisionPlayerIndex := COLLISION_PLAYER_INDEX_PREFIX + joinIndex
 			playerCollider := collisionSysMap[collisionPlayerIndex]
@@ -1387,7 +1362,8 @@ func (pR *Room) applyInputFrameDownsyncDynamicsOnSingleRenderFrame(delayedInputF
 			}
 		}
 
-		for playerId, player := range pR.Players {
+		for _, player := range pR.PlayersArr {
+			playerId := player.Id
 			joinIndex := player.JoinIndex
 			collisionPlayerIndex := COLLISION_PLAYER_INDEX_PREFIX + joinIndex
 			playerCollider := collisionSysMap[collisionPlayerIndex]
@@ -1447,8 +1423,48 @@ func (pR *Room) printBarrier(barrierCollider *resolv.Object) {
 	Logger.Info(fmt.Sprintf("Barrier in roomId=%v: w=%v, h=%v, shape=%v", pR.Id, barrierCollider.W, barrierCollider.H, barrierCollider.Shape))
 }
 
-func (pR *Room) downsyncToAllPlayers(upperToSendInputFrameId int32, unconfirmedMask uint64, prohibitsInputsBufferLock bool) {
+func (pR *Room) doBattleMainLoopPerTickBackendDynamicsWithProperLocking(pDynamicsDuration *int64) (uint64, *RingBuffer) {
-	for playerId, player := range pR.Players {
+	Logger.Debug(fmt.Sprintf("doBattleMainLoopPerTickBackendDynamicsWithProperLocking-InputsBufferLock to about lock: roomId=%v", pR.Id))
+	pR.InputsBufferLock.Lock()
+	Logger.Debug(fmt.Sprintf("doBattleMainLoopPerTickBackendDynamicsWithProperLocking-InputsBufferLock locked: roomId=%v", pR.Id))
+
+	defer func() {
+		// [WARNING] Unlock before calling "downsyncToAllPlayers -> downsyncToSinglePlayer" to avoid unlocking lags due to blocking network I/O
+		pR.InputsBufferLock.Unlock()
+		Logger.Debug(fmt.Sprintf("doBattleMainLoopPerTickBackendDynamicsWithProperLocking-InputsBufferLock unlocked: roomId=%v", pR.Id))
+	}()
+
+	if pR.shouldPrefabInputFrameDownsync(pR.RenderFrameId) {
+		noDelayInputFrameId := pR.ConvertToInputFrameId(pR.RenderFrameId, 0)
+		if existingInputFrame := pR.InputsBuffer.GetByFrameId(noDelayInputFrameId); nil == existingInputFrame {
+			pR.prefabInputFrameDownsync(noDelayInputFrameId)
+		}
+	}
+
+	// Force setting all-confirmed of buffered inputFrames periodically, kindly note that if "pR.BackendDynamicsEnabled", what we want to achieve is "recovery upon reconnection", which certainly requires "forceConfirmationIfApplicable" to move "pR.LastAllConfirmedInputFrameId" forward as much as possible
+	unconfirmedMask := pR.forceConfirmationIfApplicable()
+
+	if 0 <= pR.LastAllConfirmedInputFrameId {
+		dynamicsStartedAt := utils.UnixtimeNano()
+		// Apply "all-confirmed inputFrames" to move forward "pR.CurDynamicsRenderFrameId"
+		nextDynamicsRenderFrameId := pR.ConvertToLastUsedRenderFrameId(pR.LastAllConfirmedInputFrameId, pR.InputDelayFrames)
+		Logger.Debug(fmt.Sprintf("roomId=%v, room.RenderFrameId=%v, room.CurDynamicsRenderFrameId=%v, LastAllConfirmedInputFrameId=%v, InputDelayFrames=%v, nextDynamicsRenderFrameId=%v", pR.Id, pR.RenderFrameId, pR.CurDynamicsRenderFrameId, pR.LastAllConfirmedInputFrameId, pR.InputDelayFrames, nextDynamicsRenderFrameId))
+		pR.applyInputFrameDownsyncDynamics(pR.CurDynamicsRenderFrameId, nextDynamicsRenderFrameId, pR.collisionSpaceOffsetX, pR.collisionSpaceOffsetY)
+		*pDynamicsDuration = utils.UnixtimeNano() - dynamicsStartedAt
+	}
+
+	var inputsBufferSnapshot *RingBuffer = nil
+	if 0 < unconfirmedMask {
+		// [WARNING] This condition should be rarely met!
+		// Otherwise there's no need to create the inputsBufferSnapshot
+		inputsBufferSnapshot = pR.createInputsBufferSnapshot()
+	}
+	return unconfirmedMask, inputsBufferSnapshot
+}
+
+func (pR *Room) downsyncToAllPlayers(upperToSendInputFrameId int32, unconfirmedMask uint64, inputsBufferSnapshot *RingBuffer) {
+	// [WARNING] This function MUST BE called while "pR.InputsBufferLock" is unlocked -- otherwise the blocking "sendSafely" might cause significant lag!
+	for _, player := range pR.PlayersArr {
 		thatPlayerBattleState := atomic.LoadInt32(&(player.BattleState))
 		switch thatPlayerBattleState {
 		case PlayerBattleStateIns.DISCONNECTED:
@@ -1458,12 +1474,12 @@ func (pR *Room) downsyncToAllPlayers(upperToSendInputFrameId int32, unconfirmedM
 		case PlayerBattleStateIns.READDED_PENDING_BATTLE_COLLIDER_ACK: // This is the reason why battleState filter is put at "downsyncToAllPlayers" instead of "downsyncToSinglePlayer"
 			continue
 		}
-		pR.downsyncToSinglePlayer(playerId, player, pR.LastAllConfirmedInputFrameId, unconfirmedMask, prohibitsInputsBufferLock)
+		pR.downsyncToSinglePlayer(player.Id, player, pR.LastAllConfirmedInputFrameId, unconfirmedMask, inputsBufferSnapshot)
 	}
 }
 
-func (pR *Room) downsyncToSinglePlayer(playerId int32, player *Player, upperToSendInputFrameId int32, unconfirmedMask uint64, prohibitsInputsBufferLock bool) {
+func (pR *Room) downsyncToSinglePlayer(playerId int32, player *Player, upperToSendInputFrameId int32, unconfirmedMask uint64, inputsBufferSnapshot *RingBuffer) {
-	// TODO: DON'T try to send any message to an inactive player! However, note that player.BattleState could be modified from different threads and needs to be synced!
+	// [WARNING] This function MUST BE called while "pR.InputsBufferLock" is unlocked -- otherwise the blocking "sendSafely" might cause significant lag!
 	// [WARNING] Websocket is TCP-based, thus no need to re-send a previously sent inputFrame to a same player!
 	lowerToSentInputFrameId := player.LastSentInputFrameId + 1
 	/*
@@ -1494,13 +1510,8 @@ func (pR *Room) downsyncToSinglePlayer(playerId int32, player *Player, upperToSe
 	}
 
 	// [WARNING] EDGE CASE HERE: Upon initialization, all of "lastAllConfirmedInputFrameId", "lastAllConfirmedInputFrameIdWithChange" and "anchorInputFrameId" are "-1", thus "j" starts with "0", however "inputFrameId: 0" might not have been all confirmed!
-	var theInputsBufferLockToUse *sync.Mutex = &pR.InputsBufferLock
-	if prohibitsInputsBufferLock {
-		// Already locked in caller function
-		theInputsBufferLockToUse = nil
-	}
 	// [WARNING] Clone to deliberately avoid holding "pR.InputsBufferLock" while using network I/O
-	j, toSendInputFrameDownsyncs := pR.InputsBuffer.cloneInputFrameDownsyncsByFrameIdRange(lowerToSentInputFrameId, upperToSendInputFrameId+1, theInputsBufferLockToUse)
+	j, toSendInputFrameDownsyncs := pR.cloneInputFrameDownsyncsByFrameIdRange(lowerToSentInputFrameId, upperToSendInputFrameId+1, inputsBufferSnapshot)
 
 	if 0 >= len(toSendInputFrameDownsyncs) {
 		Logger.Debug(fmt.Sprintf("Not sending due to actually empty toSendInputFrameDownsyncs: roomId=%v, playerId=%v, playerLastSentInputFrameId=%v, refRenderFrameId=%v, lowerToSentInputFrameId=%v, upperToSendInputFrameId=%v, j=%v, lastSentInputFrameId=%v, playerAckingInputFrameId=%v", pR.Id, playerId, player.LastSentInputFrameId, refRenderFrameId, lowerToSentInputFrameId, upperToSendInputFrameId, j, player.LastSentInputFrameId, player.AckingInputFrameId))
@@ -1519,8 +1530,8 @@ func (pR *Room) downsyncToSinglePlayer(playerId int32, player *Player, upperToSe
 		}
 
 		refRenderFrame := tmp.(*RoomDownsyncFrame)
-		for playerId, player := range pR.Players {
+		for _, player := range pR.PlayersArr {
-			refRenderFrame.Players[playerId].ColliderRadius = player.ColliderRadius // hardcoded for now
+			refRenderFrame.Players[player.Id].ColliderRadius = player.ColliderRadius // hardcoded for now
 		}
 		refRenderFrame.BackendUnconfirmedMask = unconfirmedMask
 		Logger.Warn(fmt.Sprintf("Sending refRenderFrameId=%v for roomId=%v, , playerId=%v, playerJoinIndex=%v, renderFrameId=%v, curDynamicsRenderFrameId=%v, playerLastSentInputFrameId=%v, lowerToSentInputFrameId=%v, upperToSendInputFrameId=%v, j=%v: InputsBuffer=%v", refRenderFrameId, pR.Id, playerId, player.JoinIndex, pR.RenderFrameId, pR.CurDynamicsRenderFrameId, player.LastSentInputFrameId, lowerToSentInputFrameId, upperToSendInputFrameId, j, pR.InputsBufferString(false)))
@@ -1530,3 +1541,45 @@ func (pR *Room) downsyncToSinglePlayer(playerId int32, player *Player, upperToSe
 	}
 	player.LastSentInputFrameId = j - 1
 }
+
+func (pR *Room) createInputsBufferSnapshot() *RingBuffer {
+	// [WARNING] This function MUST BE called while "pR.InputsBufferLock" is locked!
+	snapshot := NewRingBuffer(pR.InputsBuffer.N)
+	for j := pR.InputsBuffer.StFrameId; j < pR.InputsBuffer.Ed; j++ {
+		tmp := pR.InputsBuffer.GetByFrameId(j)
+		snapshot.Put(tmp)
+	}
+
+	return snapshot
+}
+
+func (pR *Room) cloneInputFrameDownsyncsByFrameIdRange(stFrameId, edFrameId int32, src *RingBuffer) (int32, []*InputFrameDownsync) {
+	dst := make([]*InputFrameDownsync, 0, src.Cnt)
+	prevFrameFound := true
+	j := stFrameId
+	for j < edFrameId {
+		tmp := src.GetByFrameId(j)
+		if nil == tmp {
+			if false == prevFrameFound {
+				// The "id"s are always consecutive
+				break
+			} else {
+				prevFrameFound = false
+				continue
+			}
+		}
+		foo := tmp.(*InputFrameDownsync)
+		bar := &InputFrameDownsync{
+			InputFrameId:  foo.InputFrameId,
+			InputList:     make([]uint64, len(foo.InputList)),
+			ConfirmedList: foo.ConfirmedList,
+		}
+		for i, input := range foo.InputList {
+			bar.InputList[i] = input
+		}
+		dst = append(dst, bar)
+		j++
+	}
+
+	return j, dst
+}