path: root/library/cpp/actors/interconnect/interconnect_tcp_session.h

#pragma once

#include <library/cpp/actors/core/hfunc.h>
#include <library/cpp/actors/core/event_pb.h>
#include <library/cpp/actors/core/events.h>
#include <library/cpp/actors/core/log.h>
#include <library/cpp/actors/protos/services_common.pb.h>
#include <library/cpp/actors/util/datetime.h>
#include <library/cpp/actors/util/rope.h>
#include <library/cpp/actors/util/funnel_queue.h>
#include <library/cpp/actors/util/recentwnd.h>
#include <library/cpp/monlib/dynamic_counters/counters.h>
#include <library/cpp/actors/core/actor_bootstrapped.h>

#define XXH_INLINE_ALL
#include <contrib/libs/xxhash/xxhash.h>

#include <util/generic/queue.h>
#include <util/generic/deque.h>
#include <util/datetime/cputimer.h>

#include "interconnect_impl.h"
#include "poller_tcp.h"
#include "poller_actor.h"
#include "interconnect_channel.h"
#include "logging.h"
#include "watchdog_timer.h"
#include "event_holder_pool.h"
#include "channel_scheduler.h"
#include "outgoing_stream.h"

#include <unordered_set>
#include <unordered_map>

namespace NActors {
    class TSlowPathChecker {
        using TTraceCallback = std::function<void(double)>;
        TTraceCallback Callback;
        const NHPTimer::STime Start;

    public:
        TSlowPathChecker(TTraceCallback&& callback)
            : Callback(std::move(callback))
            , Start(GetCycleCountFast())
        {
        }

        ~TSlowPathChecker() {
            const NHPTimer::STime end = GetCycleCountFast();
            const NHPTimer::STime elapsed = end - Start;
            if (elapsed > 1000000) {
                Callback(NHPTimer::GetSeconds(elapsed) * 1000);
            }
        }

        operator bool() const {
            return false;
        }
    };

#define LWPROBE_IF_TOO_LONG(...)                                               \
    if (auto __x = TSlowPathChecker{[&](double ms) { LWPROBE(__VA_ARGS__); }}) \
        ;                                                                      \
    else

    class TTimeLimit {
    public:
        TTimeLimit(ui64 limitInCycles)
            : UpperLimit(limitInCycles == 0 ? 0 : GetCycleCountFast() + limitInCycles)
        {
        }

        TTimeLimit(ui64 startTS, ui64 limitInCycles)
            : UpperLimit(limitInCycles == 0 ? 0 : startTS + limitInCycles)
        {
        }

        bool CheckExceeded() {
            return UpperLimit != 0 && GetCycleCountFast() > UpperLimit;
        }

        const ui64 UpperLimit;
    };

    static constexpr TDuration DEFAULT_DEADPEER_TIMEOUT = TDuration::Seconds(10);
    static constexpr TDuration DEFAULT_LOST_CONNECTION_TIMEOUT = TDuration::Seconds(10);
    static constexpr ui32 DEFAULT_MAX_INFLIGHT_DATA = 10240 * 1024;
    static constexpr ui32 DEFAULT_TOTAL_INFLIGHT_DATA = 4 * 10240 * 1024;

    class TInterconnectProxyTCP;

    enum class EUpdateState : ui8 {
        NONE,                 // no updates generated by input session yet
        INFLIGHT,             // one update is inflight, and no more pending
        INFLIGHT_AND_PENDING, // one update is inflight, and one is pending
        CONFIRMING,           // confirmation inflight
    };

    struct TReceiveContext: public TAtomicRefCount<TReceiveContext> {
        /* All invokations to these fields should be thread-safe */

        ui64 ControlPacketSendTimer = 0;
        ui64 ControlPacketId = 0;

        // last processed packet by input session
        std::atomic_uint64_t LastPacketSerialToConfirm = 0;
        static constexpr uint64_t LastPacketSerialToConfirmLockBit = uint64_t(1) << 63;

        // for hardened checks
        TAtomic NumInputSessions = 0;

        NHPTimer::STime StartTime;

        std::atomic<ui64> PingRTT_us = 0;
        std::atomic<i64> ClockSkew_us = 0;

        std::atomic<EUpdateState> UpdateState;
        static_assert(std::atomic<EUpdateState>::is_always_lock_free);

        bool MainWriteBlocked = false;
        bool XdcWriteBlocked = false;
        bool MainReadPending = false;
        bool XdcReadPending = false;

        struct TPerChannelContext {
            struct TPendingEvent {
                TEventSerializationInfo SerializationInfo;
                TRope InternalPayload;
                TRope ExternalPayload;
                std::optional<TEventData> EventData;

                // number of bytes remaining through XDC channel
                size_t XdcSizeLeft = 0;
            };

            std::deque<TPendingEvent> PendingEvents;
            std::deque<TMutableContiguousSpan> XdcBuffers; // receive queue for current channel
            size_t FetchIndex = 0;
            size_t FetchOffset = 0;

            ui64 XdcCatchBytesRead = 0; // number of bytes actually read into cyclic buffer
            TRcBuf XdcCatchBuffer;

            void PrepareCatchBuffer();
            void ApplyCatchBuffer();
            void FetchBuffers(ui16 channel, size_t numBytes, std::deque<std::tuple<ui16, TMutableContiguousSpan>>& outQ);
            void DropFront(TRope *from, size_t numBytes);
        };

        std::array<TPerChannelContext, 16> ChannelArray;
        std::unordered_map<ui16, TPerChannelContext> ChannelMap;
        ui64 LastProcessedSerial = 0;

        TReceiveContext() {
            GetTimeFast(&StartTime);
        }

        // returns false if sessions needs to be terminated
        bool AdvanceLastPacketSerialToConfirm(ui64 nextValue) {
            for (;;) {
                uint64_t value = LastPacketSerialToConfirm.load();
                if (value & LastPacketSerialToConfirmLockBit) {
                    return false;
                }
                Y_DEBUG_ABORT_UNLESS(value + 1 == nextValue);
                if (LastPacketSerialToConfirm.compare_exchange_weak(value, nextValue)) {
                    return true;
                }
            }
        }

        ui64 LockLastPacketSerialToConfirm() {
            for (;;) {
                uint64_t value = LastPacketSerialToConfirm.load();
                if (value & LastPacketSerialToConfirmLockBit) {
                    return value & ~LastPacketSerialToConfirmLockBit;
                }
                if (LastPacketSerialToConfirm.compare_exchange_strong(value, value | LastPacketSerialToConfirmLockBit)) {
                    return value;
                }
            }
        }

        void UnlockLastPacketSerialToConfirm() {
            LastPacketSerialToConfirm &= ~LastPacketSerialToConfirmLockBit;
        }

        ui64 GetLastPacketSerialToConfirm() {
            return LastPacketSerialToConfirm.load() & ~LastPacketSerialToConfirmLockBit;
        }
    };

    class TInputSessionTCP
       : public TActorBootstrapped<TInputSessionTCP>
       , public TInterconnectLoggingBase
    {
        enum {
            EvCheckDeadPeer = EventSpaceBegin(TEvents::ES_PRIVATE),
            EvResumeReceiveData,
        };

        struct TEvCheckDeadPeer : TEventLocal<TEvCheckDeadPeer, EvCheckDeadPeer> {};

    public:
        static constexpr EActivityType ActorActivityType() {
            return EActivityType::INTERCONNECT_SESSION_TCP;
        }

        TInputSessionTCP(const TActorId& sessionId,
                         TIntrusivePtr<NInterconnect::TStreamSocket> socket,
                         TIntrusivePtr<NInterconnect::TStreamSocket> xdcSocket,
                         TIntrusivePtr<TReceiveContext> context,
                         TInterconnectProxyCommon::TPtr common,
                         std::shared_ptr<IInterconnectMetrics> metrics,
                         ui32 nodeId,
                         ui64 lastConfirmed,
                         TDuration deadPeerTimeout,
                         TSessionParams params);

    private:
        friend class TActorBootstrapped<TInputSessionTCP>;

        void Bootstrap();

        struct TExReestablishConnection {
            TDisconnectReason Reason;
        };

        struct TExDestroySession {
            TDisconnectReason Reason;
        };

        STATEFN(WorkingState);

        STRICT_STFUNC(WorkingStateImpl,
            cFunc(TEvents::TSystem::PoisonPill, PassAway)
            hFunc(TEvPollerReady, Handle)
            hFunc(TEvPollerRegisterResult, Handle)
            cFunc(EvResumeReceiveData, ReceiveData)
            cFunc(TEvInterconnect::TEvCloseInputSession::EventType, CloseInputSession)
            cFunc(EvCheckDeadPeer, HandleCheckDeadPeer)
            cFunc(TEvConfirmUpdate::EventType, HandleConfirmUpdate)
            hFunc(NMon::TEvHttpInfoRes, GenerateHttpInfo)
        )

    private:
        TRope IncomingData;

        const TActorId SessionId;
        TIntrusivePtr<NInterconnect::TStreamSocket> Socket;
        TIntrusivePtr<NInterconnect::TStreamSocket> XdcSocket;
        TPollerToken::TPtr PollerToken;
        TPollerToken::TPtr XdcPollerToken;
        TIntrusivePtr<TReceiveContext> Context;
        TInterconnectProxyCommon::TPtr Common;
        const ui32 NodeId;
        const TSessionParams Params;
        XXH3_state_t XxhashState;
        XXH3_state_t XxhashXdcState;

        size_t PayloadSize;
        ui32 ChecksumExpected, Checksum;
        bool IgnorePayload;
        TRope Payload;
        enum class EState {
            HEADER,
            PAYLOAD,
        };
        EState State = EState::HEADER;
        ui64 CurrentSerial = 0;

        std::vector<char> XdcCommands;

        struct TInboundPacket {
            ui64 Serial;
            size_t XdcUnreadBytes; // number of unread bytes from XDC stream for this exact unprocessed packet
        };
        std::deque<TInboundPacket> InboundPacketQ;
        std::deque<std::tuple<ui16, TMutableContiguousSpan>> XdcInputQ; // target buffers for the XDC stream with channel reference
        std::deque<std::tuple<ui16, ui32>> XdcChecksumQ; // (size, expectedChecksum)
        ui32 XdcCurrentChecksum = 0;

        // catch stream -- used after TCP reconnect to match XDC stream with main packet stream
        struct TXdcCatchStream {
            TRcBuf Buffer;
            ui64 BytesPending = 0;
            ui64 BytesProcessed = 0;
            std::deque<std::tuple<ui16, bool, size_t>> Markup; // a queue of tuples (channel, apply, bytes)
            bool Ready = false;
            bool Applied = false;
        };
        TXdcCatchStream XdcCatchStream;

        THolder<TEvUpdateFromInputSession> UpdateFromInputSession;

        ui64 ConfirmedByInput;

        std::shared_ptr<IInterconnectMetrics> Metrics;
        std::array<ui32, 16> InputTrafficArray;
        THashMap<ui16, ui32> InputTrafficMap;

        bool CloseInputSessionRequested = false;

        void CloseInputSession();

        void Handle(TEvPollerReady::TPtr ev);
        void Handle(TEvPollerRegisterResult::TPtr ev);
        void HandleConfirmUpdate();
        void ReceiveData();
        void ProcessHeader();
        void ProcessPayload(ui64 *numDataBytes);
        void ProcessInboundPacketQ(ui64 numXdcBytesRead);
        void ProcessXdcCommand(ui16 channel, TReceiveContext::TPerChannelContext& context);
        void ProcessEvents(TReceiveContext::TPerChannelContext& context);
        ssize_t Read(NInterconnect::TStreamSocket& socket, const TPollerToken::TPtr& token, bool *readPending,
            const TIoVec *iov, size_t num);
        bool ReadMore();
        bool ReadXdcCatchStream(ui64 *numDataBytes);
        void ApplyXdcCatchStream();
        bool ReadXdc(ui64 *numDataBytes);
        void HandleXdcChecksum(TContiguousSpan span);

        TReceiveContext::TPerChannelContext& GetPerChannelContext(ui16 channel) const;

        void PassAway() override;

        TDeque<TRcBuf> Buffers;

        size_t CurrentBuffers = 1; // number of buffers currently required to allocate
        static constexpr size_t MaxBuffers = 72; // maximum buffers possible
        static constexpr int BitsPerUsageCount = 5;
        static constexpr size_t ItemsPerUsageCount = sizeof(ui64) * CHAR_BIT / BitsPerUsageCount;
        std::array<ui64, (MaxBuffers + ItemsPerUsageCount - 1) / ItemsPerUsageCount> UsageHisto; // read count histogram

        void PreallocateBuffers();

        inline ui64 GetMaxCyclesPerEvent() const {
            return DurationToCycles(TDuration::MicroSeconds(500));
        }

        const TDuration DeadPeerTimeout;
        TMonotonic LastReceiveTimestamp;
        void HandleCheckDeadPeer();

        ////////////////////////////////////////////////////////////////////////////////////////////////////////////////
        // pinger logic

        bool NewPingProtocol = false;
        TDeque<TDuration> PingQ; // last N ping samples
        TDeque<i64> SkewQ; // last N calculated clock skew samples

        void HandlePingResponse(TDuration passed);
        void HandleClock(TInstant clock);

        ////////////////////////////////////////////////////////////////////////////////////////////////////////////////
        // Stats

        ui64 BytesReadFromSocket = 0;
        ui64 PacketsReadFromSocket = 0;
        ui64 DataPacketsReadFromSocket = 0;
        ui64 IgnoredDataPacketsFromSocket = 0;

        ui64 BytesReadFromXdcSocket = 0;
        ui64 XdcSections = 0;
        ui64 XdcRefs = 0;

        ui64 CpuStarvationEvents = 0;

        void GenerateHttpInfo(NMon::TEvHttpInfoRes::TPtr ev);
    };

    class TInterconnectSessionTCP
       : public TActor<TInterconnectSessionTCP>
       , public TInterconnectLoggingBase
    {
        enum {
            EvCheckCloseOnIdle = EventSpaceBegin(TEvents::ES_PRIVATE),
            EvCheckLostConnection,
            EvRam,
            EvTerminate,
            EvFreeItems,
        };

        struct TEvCheckCloseOnIdle : TEventLocal<TEvCheckCloseOnIdle, EvCheckCloseOnIdle> {};
        struct TEvCheckLostConnection : TEventLocal<TEvCheckLostConnection, EvCheckLostConnection> {};

        struct TEvRam : TEventLocal<TEvRam, EvRam> {
            const bool Batching;
            TEvRam(bool batching) : Batching(batching) {}
        };

        struct TEvTerminate : TEventLocal<TEvTerminate, EvTerminate> {
            TDisconnectReason Reason;

            TEvTerminate(TDisconnectReason reason)
                : Reason(std::move(reason))
            {}
        };

        const TInstant Created;
        TInstant NewConnectionSet;
        ui64 MessagesGot = 0;
        ui64 MessagesWrittenToBuffer = 0;
        ui64 PacketsGenerated = 0;
        ui64 BytesWrittenToSocket = 0;
        ui64 PacketsConfirmed = 0;
        ui64 BytesAlignedForOutOfBand = 0;
        ui64 OutOfBandBytesSent = 0;
        ui64 CpuStarvationEvents = 0;
        ui64 CpuStarvationEventsOnWriteData = 0;

    public:
        static constexpr EActivityType ActorActivityType() {
            return EActivityType::INTERCONNECT_SESSION_TCP;
        }

        TInterconnectSessionTCP(TInterconnectProxyTCP* const proxy, TSessionParams params);
        ~TInterconnectSessionTCP();

        void Init();
        void CloseInputSession();

        static TEvTerminate* NewEvTerminate(TDisconnectReason reason) {
            return new TEvTerminate(std::move(reason));
        }

        TDuration GetPingRTT() const {
            return TDuration::MicroSeconds(ReceiveContext->PingRTT_us);
        }

        i64 GetClockSkew() const {
            return ReceiveContext->ClockSkew_us;
        }

    private:
        friend class TInterconnectProxyTCP;

        void Handle(TEvTerminate::TPtr& ev);
        void HandlePoison();
        void Terminate(TDisconnectReason reason);
        void PassAway() override;

        void Forward(STATEFN_SIG);
        void Subscribe(STATEFN_SIG);
        void Unsubscribe(STATEFN_SIG);

        ////////////////////////////////////////////////////////////////////////////////////////////////////////////////
        std::optional<TTimeLimit> TimeLimit;

        STATEFN(StateFunc) {
            TimeLimit.emplace(GetMaxCyclesPerEvent());
            STRICT_STFUNC_BODY(
                fFunc(TEvInterconnect::EvForward, Forward)
                cFunc(TEvents::TEvPoisonPill::EventType, HandlePoison)
                fFunc(TEvInterconnect::TEvConnectNode::EventType, Subscribe)
                fFunc(TEvents::TEvSubscribe::EventType, Subscribe)
                fFunc(TEvents::TEvUnsubscribe::EventType, Unsubscribe)
                cFunc(TEvFlush::EventType, HandleFlush)
                hFunc(TEvPollerReady, Handle)
                hFunc(TEvPollerRegisterResult, Handle)
                hFunc(TEvUpdateFromInputSession, Handle)
                hFunc(TEvRam, HandleRam)
                hFunc(TEvCheckCloseOnIdle, CloseOnIdleWatchdog)
                hFunc(TEvCheckLostConnection, LostConnectionWatchdog)
                cFunc(TEvents::TSystem::Wakeup, SendUpdateToWhiteboard)
                hFunc(TEvSocketDisconnect, OnDisconnect)
                hFunc(TEvTerminate, Handle)
                hFunc(TEvProcessPingRequest, Handle)
            )
        }

        void Handle(TEvUpdateFromInputSession::TPtr& ev);

        void OnDisconnect(TEvSocketDisconnect::TPtr& ev);

        THolder<TEvHandshakeAck> ProcessHandshakeRequest(TEvHandshakeAsk::TPtr& ev);
        void SetNewConnection(TEvHandshakeDone::TPtr& ev);

        TEvRam* RamInQueue = nullptr;
        ui64 RamStartedCycles = 0;
        void IssueRam(bool batching);
        void HandleRam(TEvRam::TPtr& ev);
        void GenerateTraffic();
        void ProducePackets();

        size_t GetUnsentSize() const {
            return OutgoingStream.CalculateUnsentSize() + OutOfBandStream.CalculateUnsentSize() +
                XdcStream.CalculateUnsentSize();
        }

        size_t GetUnsentLimit() const {
            return 128 * 1024;
        }

        void SendUpdateToWhiteboard(bool connected = true);
        ui32 CalculateQueueUtilization();

        void Handle(TEvPollerReady::TPtr& ev);
        void Handle(TEvPollerRegisterResult::TPtr ev);
        void WriteData();
        ssize_t Write(NInterconnect::TOutgoingStream& stream, NInterconnect::TStreamSocket& socket, size_t maxBytes);

        ui32 MakePacket(bool data, TMaybe<ui64> pingMask = {});
        void FillSendingBuffer(TTcpPacketOutTask& packet, ui64 serial);
        void DropConfirmed(ui64 confirm);
        void ShutdownSocket(TDisconnectReason reason);

        void StartHandshake();
        void ReestablishConnection(TEvHandshakeDone::TPtr&& ev, bool startHandshakeOnSessionClose,
                TDisconnectReason reason);
        void ReestablishConnectionWithHandshake(TDisconnectReason reason);
        void ReestablishConnectionExecute();

        TInterconnectProxyTCP* const Proxy;

        // various connection settings access
        TDuration GetDeadPeerTimeout() const;
        TDuration GetCloseOnIdleTimeout() const;
        TDuration GetLostConnectionTimeout() const;
        ui32 GetTotalInflightAmountOfData() const;
        ui64 GetMaxCyclesPerEvent() const;


        ////////////////////////////////////////////////////////////////////////////////////////////////////////////////
        // pinger

        TMonotonic LastPingTimestamp;
        static constexpr TDuration PingPeriodicity = TDuration::Seconds(1);
        void IssuePingRequest();
        void Handle(TEvProcessPingRequest::TPtr ev);

        ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

        TMonotonic LastInputActivityTimestamp;
        TMonotonic LastPayloadActivityTimestamp;
        TWatchdogTimer<TEvCheckCloseOnIdle> CloseOnIdleWatchdog;
        TWatchdogTimer<TEvCheckLostConnection> LostConnectionWatchdog;

        void OnCloseOnIdleTimerHit() {
            LOG_INFO_IC("ICS27", "CloseOnIdle timer hit, session terminated");
            Terminate(TDisconnectReason::CloseOnIdle());
        }

        void OnLostConnectionTimerHit() {
            LOG_ERROR_IC("ICS28", "LostConnection timer hit, session terminated");
            Terminate(TDisconnectReason::LostConnection());
        }

        void RearmCloseOnIdle() {
            if (!NumEventsInQueue && OutputCounter == LastConfirmed) {
                CloseOnIdleWatchdog.Rearm(SelfId());
            } else {
                CloseOnIdleWatchdog.Disarm();
            }
        }

        ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

        const TSessionParams Params;
        TMaybe<TEventHolderPool> Pool;
        TMaybe<TChannelScheduler> ChannelScheduler;
        ui64 TotalOutputQueueSize;
        bool OutputStuckFlag;
        TRecentWnd<std::pair<ui64, ui64>> OutputQueueUtilization;
        size_t NumEventsInQueue = 0;

        void SetOutputStuckFlag(bool state);
        void SwitchStuckPeriod();

        NInterconnect::TOutgoingStream OutgoingStream;
        NInterconnect::TOutgoingStream OutOfBandStream;
        NInterconnect::TOutgoingStream XdcStream;

        struct TOutgoingPacket {
            ui32 PacketSize; // including header
            ui32 ExternalSize;
        };
        std::deque<TOutgoingPacket> SendQueue; // packet boundaries
        size_t OutgoingOffset = 0;
        size_t XdcOffset = 0;
        size_t OutgoingIndex = 0; // index into current packet in SendQueue
        size_t ForcedWriteLength = 0;

        ui64 XdcBytesSent = 0;

        ui64 WriteBlockedCycles = 0; // start of current block period
        TDuration WriteBlockedTotal; // total incremental duration that session has been blocked
        bool WriteBlockedByFullSendBuffer = false;

        TDuration GetWriteBlockedTotal() const {
            return WriteBlockedTotal + (WriteBlockedByFullSendBuffer
                ? TDuration::Seconds(NHPTimer::GetSeconds(GetCycleCountFast() - WriteBlockedCycles))
                : TDuration::Zero());
        }

        ui64 OutputCounter;

        TInstant LastHandshakeDone;

        TIntrusivePtr<NInterconnect::TStreamSocket> Socket;
        TIntrusivePtr<NInterconnect::TStreamSocket> XdcSocket;
        TPollerToken::TPtr PollerToken;
        TPollerToken::TPtr XdcPollerToken;
        ui32 SendBufferSize;
        ui64 InflightDataAmount = 0;

        std::unordered_map<TActorId, ui64, TActorId::THash> Subscribers;

        // time at which we want to send confirmation packet even if there was no outgoing data
        ui64 UnconfirmedBytes = 0;
        TMonotonic ForcePacketTimestamp = TMonotonic::Max();
        TPriorityQueue<TMonotonic, TVector<TMonotonic>, std::greater<TMonotonic>> FlushSchedule;
        size_t MaxFlushSchedule = 0;
        ui64 FlushEventsScheduled = 0;
        ui64 FlushEventsProcessed = 0;

        void SetForcePacketTimestamp(TDuration period);
        void ScheduleFlush();
        void HandleFlush();
        void ResetFlushLogic();

        void GenerateHttpInfo(NMon::TEvHttpInfoRes::TPtr& ev);

        TIntrusivePtr<TReceiveContext> ReceiveContext;
        TActorId ReceiverId;
        TDuration Ping;

        ui64 ConfirmPacketsForcedBySize = 0;
        ui64 ConfirmPacketsForcedByTimeout = 0;

        ui64 LastConfirmed = 0;

        TEvHandshakeDone::TPtr PendingHandshakeDoneEvent;
        bool StartHandshakeOnSessionClose = false;

        ui64 EqualizeCounter = 0;
    };

    class TInterconnectSessionKiller
       : public TActorBootstrapped<TInterconnectSessionKiller> {
        ui32 RepliesReceived = 0;
        ui32 RepliesNumber = 0;
        TActorId LargestSession = TActorId();
        ui64 MaxBufferSize = 0;
        TInterconnectProxyCommon::TPtr Common;

    public:
        static constexpr EActivityType ActorActivityType() {
            return EActivityType::INTERCONNECT_SESSION_KILLER;
        }

        TInterconnectSessionKiller(TInterconnectProxyCommon::TPtr common)
            : Common(common)
        {
        }

        void Bootstrap() {
            auto sender = SelfId();
            const auto eventFabric = [&sender](const TActorId& recp) -> IEventHandle* {
                auto ev = new TEvSessionBufferSizeRequest();
                return new IEventHandle(recp, sender, ev, IEventHandle::FlagTrackDelivery);
            };
            RepliesNumber = TlsActivationContext->ExecutorThread.ActorSystem->BroadcastToProxies(eventFabric);
            Become(&TInterconnectSessionKiller::StateFunc);
        }

        STRICT_STFUNC(StateFunc,
            hFunc(TEvSessionBufferSizeResponse, ProcessResponse)
            cFunc(TEvents::TEvUndelivered::EventType, ProcessUndelivered)
        )

        void ProcessResponse(TEvSessionBufferSizeResponse::TPtr& ev) {
            RepliesReceived++;
            if (MaxBufferSize < ev->Get()->BufferSize) {
                MaxBufferSize = ev->Get()->BufferSize;
                LargestSession = ev->Get()->SessionID;
            }
            if (RepliesReceived == RepliesNumber) {
                Send(LargestSession, new TEvents::TEvPoisonPill);
                AtomicUnlock(&Common->StartedSessionKiller);
                PassAway();
            }
        }

        void ProcessUndelivered() {
            RepliesReceived++;
        }
    };

    void CreateSessionKillingActor(TInterconnectProxyCommon::TPtr common);

}