intermediate changes

ref:cde9a383711a11544ce7e107a78147fb96cc4029

6 files changed, 2161 insertions, 0 deletions

diff --git a/library/cpp/grpc/client/grpc_client_low.cpp b/library/cpp/grpc/client/grpc_client_low.cpp
new file mode 100644
index 00000000000..73cc908ef82
--- /dev/null
+++ b/library/cpp/grpc/client/grpc_client_low.cpp
@@ -0,0 +1,586 @@
+#include "grpc_client_low.h"
+#include <contrib/libs/grpc/src/core/lib/iomgr/socket_mutator.h>
+#include <contrib/libs/grpc/include/grpc/support/log.h>
+
+#include <library/cpp/containers/stack_vector/stack_vec.h>
+
+#include <util/string/printf.h>
+#include <util/system/thread.h>
+#include <util/random/random.h>
+
+#if !defined(_WIN32) && !defined(_WIN64)
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <netinet/tcp.h>
+#endif
+
+namespace NGrpc {
+
+void EnableGRpcTracing() {
+    grpc_tracer_set_enabled("tcp", true);
+    grpc_tracer_set_enabled("client_channel", true);
+    grpc_tracer_set_enabled("channel", true);
+    grpc_tracer_set_enabled("api", true);
+    grpc_tracer_set_enabled("connectivity_state", true);
+    grpc_tracer_set_enabled("handshaker", true);
+    grpc_tracer_set_enabled("http", true);
+    grpc_tracer_set_enabled("http2_stream_state", true);
+    grpc_tracer_set_enabled("op_failure", true);
+    grpc_tracer_set_enabled("timer", true);
+    gpr_set_log_verbosity(GPR_LOG_SEVERITY_DEBUG);
+}
+
+class TGRpcKeepAliveSocketMutator : public grpc_socket_mutator {
+public:
+    TGRpcKeepAliveSocketMutator(int idle, int count, int interval)
+        : Idle_(idle)
+        , Count_(count)
+        , Interval_(interval)
+    {
+        grpc_socket_mutator_init(this, &VTable);
+    }
+private:
+    static TGRpcKeepAliveSocketMutator* Cast(grpc_socket_mutator* mutator) {
+        return static_cast<TGRpcKeepAliveSocketMutator*>(mutator);
+    }
+
+    template<typename TVal>
+    bool SetOption(int fd, int level, int optname, const TVal& value) {
+        return setsockopt(fd, level, optname, reinterpret_cast<const char*>(&value), sizeof(value)) == 0;
+    }
+    bool SetOption(int fd) {
+        if (!SetOption(fd, SOL_SOCKET, SO_KEEPALIVE, 1)) {
+            Cerr << Sprintf("Failed to set SO_KEEPALIVE option: %s", strerror(errno)) << Endl;
+            return false;
+        }
+#ifdef _linux_
+        if (Idle_ && !SetOption(fd, IPPROTO_TCP, TCP_KEEPIDLE, Idle_)) {
+            Cerr << Sprintf("Failed to set TCP_KEEPIDLE option: %s", strerror(errno)) << Endl;
+            return false;
+        }
+        if (Count_ && !SetOption(fd, IPPROTO_TCP, TCP_KEEPCNT, Count_)) {
+            Cerr << Sprintf("Failed to set TCP_KEEPCNT option: %s", strerror(errno)) << Endl;
+            return false;
+        }
+        if (Interval_ && !SetOption(fd, IPPROTO_TCP, TCP_KEEPINTVL, Interval_)) {
+            Cerr << Sprintf("Failed to set TCP_KEEPINTVL option: %s", strerror(errno)) << Endl;
+            return false;
+        }
+#endif
+        return true;
+    }
+    static bool Mutate(int fd, grpc_socket_mutator* mutator) {
+        auto self = Cast(mutator);
+        return self->SetOption(fd);
+    }
+    static int Compare(grpc_socket_mutator* a, grpc_socket_mutator* b) {
+        const auto* selfA = Cast(a);
+        const auto* selfB = Cast(b);
+        auto tupleA = std::make_tuple(selfA->Idle_, selfA->Count_, selfA->Interval_);
+        auto tupleB = std::make_tuple(selfB->Idle_, selfB->Count_, selfB->Interval_);
+        return tupleA < tupleB ? -1 : tupleA > tupleB ? 1 : 0;
+    }
+    static void Destroy(grpc_socket_mutator* mutator) {
+        delete Cast(mutator);
+    }
+
+    static grpc_socket_mutator_vtable VTable;
+    const int Idle_;
+    const int Count_;
+    const int Interval_;
+};
+
+grpc_socket_mutator_vtable TGRpcKeepAliveSocketMutator::VTable =
+    {
+        &TGRpcKeepAliveSocketMutator::Mutate,
+        &TGRpcKeepAliveSocketMutator::Compare,
+        &TGRpcKeepAliveSocketMutator::Destroy
+    };
+
+TChannelPool::TChannelPool(const TTcpKeepAliveSettings& tcpKeepAliveSettings, const TDuration& expireTime)
+    : TcpKeepAliveSettings_(tcpKeepAliveSettings)
+    , ExpireTime_(expireTime)
+    , UpdateReUseTime_(ExpireTime_ * 0.3 < TDuration::Seconds(20) ? ExpireTime_ * 0.3 : TDuration::Seconds(20))
+{}
+
+void TChannelPool::GetStubsHolderLocked(
+    const TString& channelId,
+    const TGRpcClientConfig& config,
+    std::function<void(TStubsHolder&)> cb)
+{
+    {
+        std::shared_lock readGuard(RWMutex_);
+        const auto it = Pool_.find(channelId);
+        if (it != Pool_.end()) {
+            if (!it->second.IsChannelBroken() && !(Now() > it->second.GetLastUseTime() + UpdateReUseTime_)) {
+                return cb(it->second);
+            }
+        }
+    }
+    {
+        std::unique_lock writeGuard(RWMutex_);
+        {
+            auto it = Pool_.find(channelId);
+            if (it != Pool_.end()) {
+                if (!it->second.IsChannelBroken()) {
+                    EraseFromQueueByTime(it->second.GetLastUseTime(), channelId);
+                    auto now = Now();
+                    LastUsedQueue_.emplace(now, channelId);
+                    it->second.SetLastUseTime(now);
+                    return cb(it->second);
+                } else {
+                    // This channel can't be used. Remove from pool to create new one
+                    EraseFromQueueByTime(it->second.GetLastUseTime(), channelId);
+                    Pool_.erase(it);
+                }
+            }
+        }
+        TGRpcKeepAliveSocketMutator* mutator = nullptr;
+        // will be destroyed inside grpc
+        if (TcpKeepAliveSettings_.Enabled) {
+            mutator = new TGRpcKeepAliveSocketMutator(
+                TcpKeepAliveSettings_.Idle,
+                TcpKeepAliveSettings_.Count,
+                TcpKeepAliveSettings_.Interval
+            );
+        }
+        cb(Pool_.emplace(channelId, CreateChannelInterface(config, mutator)).first->second);
+        LastUsedQueue_.emplace(Pool_.at(channelId).GetLastUseTime(), channelId);
+    }
+}
+
+void TChannelPool::DeleteChannel(const TString& channelId) {
+    std::unique_lock writeLock(RWMutex_);
+    auto poolIt = Pool_.find(channelId);
+    if (poolIt != Pool_.end()) {
+        EraseFromQueueByTime(poolIt->second.GetLastUseTime(), channelId);
+        Pool_.erase(poolIt);
+    }
+}
+
+void TChannelPool::DeleteExpiredStubsHolders() {
+    std::unique_lock writeLock(RWMutex_);
+    auto lastExpired = LastUsedQueue_.lower_bound(Now() - ExpireTime_);
+    for (auto i = LastUsedQueue_.begin(); i != lastExpired; ++i){
+        Pool_.erase(i->second);
+    }
+    LastUsedQueue_.erase(LastUsedQueue_.begin(), lastExpired);
+}
+
+void TChannelPool::EraseFromQueueByTime(const TInstant& lastUseTime, const TString& channelId) {
+    auto [begin, end] = LastUsedQueue_.equal_range(lastUseTime);
+    auto pos = std::find_if(begin, end, [&](auto a){return a.second == channelId;});
+    Y_VERIFY(pos != LastUsedQueue_.end(), "data corruption at TChannelPool");
+    LastUsedQueue_.erase(pos);
+}
+
+static void PullEvents(grpc::CompletionQueue* cq) {
+    TThread::SetCurrentThreadName("grpc_client");
+    while (true) {
+        void* tag;
+        bool ok;
+
+        if (!cq->Next(&tag, &ok)) {
+            break;
+        }
+
+        if (auto* ev = static_cast<IQueueClientEvent*>(tag)) {
+            if (!ev->Execute(ok)) {
+                ev->Destroy();
+            }
+        }
+    }
+}
+
+class TGRpcClientLow::TContextImpl final
+    : public std::enable_shared_from_this<TContextImpl>
+    , public IQueueClientContext
+{
+    friend class TGRpcClientLow;
+
+    using TCallback = std::function<void()>;
+    using TContextPtr = std::shared_ptr<TContextImpl>;
+
+public:
+    ~TContextImpl() override {
+        Y_VERIFY(CountChildren() == 0,
+                "Destructor called with non-empty children");
+
+        if (Parent) {
+            Parent->ForgetContext(this);
+        } else if (Y_LIKELY(Owner)) {
+            Owner->ForgetContext(this);
+        }
+    }
+
+    /**
+     * Helper for locking child pointer from a parent container
+     */
+    static TContextPtr LockChildPtr(TContextImpl* ptr) {
+        if (ptr) {
+            // N.B. it is safe to do as long as it's done under a mutex and
+            // pointer is among valid children. When that's the case we
+            // know that TContextImpl destructor has not finished yet, so
+            // the object is valid. The lock() method may return nullptr
+            // though, if the object is being destructed right now.
+            return ptr->weak_from_this().lock();
+        } else {
+            return nullptr;
+        }
+    }
+
+    void ForgetContext(TContextImpl* child) {
+        std::unique_lock<std::mutex> guard(Mutex);
+
+        auto removed = RemoveChild(child);
+        Y_VERIFY(removed, "Unexpected ForgetContext(%p)", child);
+    }
+
+    IQueueClientContextPtr CreateContext() override {
+        auto self = shared_from_this();
+        auto child = std::make_shared<TContextImpl>();
+
+        {
+            std::unique_lock<std::mutex> guard(Mutex);
+
+            AddChild(child.get());
+
+            // It's now safe to initialize parent and owner
+            child->Parent = std::move(self);
+            child->Owner = Owner;
+            child->CQ = CQ;
+
+            // Propagate cancellation to a child context
+            if (Cancelled.load(std::memory_order_relaxed)) {
+                child->Cancelled.store(true, std::memory_order_relaxed);
+            }
+        }
+
+        return child;
+    }
+
+    grpc::CompletionQueue* CompletionQueue() override {
+        Y_VERIFY(Owner, "Uninitialized context");
+        return CQ;
+    }
+
+    bool IsCancelled() const override {
+        return Cancelled.load(std::memory_order_acquire);
+    }
+
+    bool Cancel() override {
+        TStackVec<TCallback, 1> callbacks;
+        TStackVec<TContextPtr, 2> children;
+
+        {
+            std::unique_lock<std::mutex> guard(Mutex);
+
+            if (Cancelled.load(std::memory_order_relaxed)) {
+                // Already cancelled in another thread
+                return false;
+            }
+
+            callbacks.reserve(Callbacks.size());
+            children.reserve(CountChildren());
+
+            for (auto& callback : Callbacks) {
+                callbacks.emplace_back().swap(callback);
+            }
+            Callbacks.clear();
+
+            // Collect all children we need to cancel
+            // N.B. we don't clear children links (cleared by destructors)
+            // N.B. some children may be stuck in destructors at the moment
+            for (TContextImpl* ptr : InlineChildren) {
+                if (auto child = LockChildPtr(ptr)) {
+                    children.emplace_back(std::move(child));
+                }
+            }
+            for (auto* ptr : Children) {
+                if (auto child = LockChildPtr(ptr)) {
+                    children.emplace_back(std::move(child));
+                }
+            }
+
+            Cancelled.store(true, std::memory_order_release);
+        }
+
+        // Call directly subscribed callbacks
+        if (callbacks) {
+            RunCallbacksNoExcept(callbacks);
+        }
+
+        // Cancel all children
+        for (auto& child : children) {
+            child->Cancel();
+            child.reset();
+        }
+
+        return true;
+    }
+
+    void SubscribeCancel(TCallback callback) override {
+        Y_VERIFY(callback, "SubscribeCancel called with an empty callback");
+
+        {
+            std::unique_lock<std::mutex> guard(Mutex);
+
+            if (!Cancelled.load(std::memory_order_relaxed)) {
+                Callbacks.emplace_back().swap(callback);
+                return;
+            }
+        }
+
+        // Already cancelled, run immediately
+        callback();
+    }
+
+private:
+    void AddChild(TContextImpl* child) {
+        for (TContextImpl*& slot : InlineChildren) {
+            if (!slot) {
+                slot = child;
+                return;
+            }
+        }
+
+        Children.insert(child);
+    }
+
+    bool RemoveChild(TContextImpl* child) {
+        for (TContextImpl*& slot : InlineChildren) {
+            if (slot == child) {
+                slot = nullptr;
+                return true;
+            }
+        }
+
+        return Children.erase(child);
+    }
+
+    size_t CountChildren() {
+        size_t count = 0;
+
+        for (TContextImpl* ptr : InlineChildren) {
+            if (ptr) {
+                ++count;
+            }
+        }
+
+        return count + Children.size();
+    }
+
+    template<class TCallbacks>
+    static void RunCallbacksNoExcept(TCallbacks& callbacks) noexcept {
+        for (auto& callback : callbacks) {
+            if (callback) {
+                callback();
+                callback = nullptr;
+            }
+        }
+    }
+
+private:
+    // We want a simple lock here, without extra memory allocations
+    std::mutex Mutex;
+
+    // These fields are initialized on successful registration
+    TContextPtr Parent;
+    TGRpcClientLow* Owner = nullptr;
+    grpc::CompletionQueue* CQ = nullptr;
+
+    // Some children are stored inline, others are in a set
+    std::array<TContextImpl*, 2> InlineChildren{ { nullptr, nullptr } };
+    std::unordered_set<TContextImpl*> Children;
+
+    // Single callback is stored without extra allocations
+    TStackVec<TCallback, 1> Callbacks;
+
+    // Atomic flag for a faster IsCancelled() implementation
+    std::atomic<bool> Cancelled;
+};
+
+TGRpcClientLow::TGRpcClientLow(size_t numWorkerThread, bool useCompletionQueuePerThread)
+    : UseCompletionQueuePerThread_(useCompletionQueuePerThread)
+{
+    Init(numWorkerThread);
+}
+
+void TGRpcClientLow::Init(size_t numWorkerThread) {
+    SetCqState(WORKING);
+    if (UseCompletionQueuePerThread_) {
+        for (size_t i = 0; i < numWorkerThread; i++) {
+            CQS_.push_back(std::make_unique<grpc::CompletionQueue>());
+            auto* cq = CQS_.back().get();
+            WorkerThreads_.emplace_back(SystemThreadFactory()->Run([cq]() {
+                PullEvents(cq);
+            }).Release());
+        }
+    } else {
+        CQS_.push_back(std::make_unique<grpc::CompletionQueue>());
+        auto* cq = CQS_.back().get();
+        for (size_t i = 0; i < numWorkerThread; i++) {
+            WorkerThreads_.emplace_back(SystemThreadFactory()->Run([cq]() {
+                PullEvents(cq);
+            }).Release());
+        }
+    }
+}
+
+void TGRpcClientLow::AddWorkerThreadForTest() {
+    if (UseCompletionQueuePerThread_) {
+        CQS_.push_back(std::make_unique<grpc::CompletionQueue>());
+        auto* cq = CQS_.back().get();
+        WorkerThreads_.emplace_back(SystemThreadFactory()->Run([cq]() {
+            PullEvents(cq);
+        }).Release());
+    } else {
+        auto* cq = CQS_.back().get();
+        WorkerThreads_.emplace_back(SystemThreadFactory()->Run([cq]() {
+            PullEvents(cq);
+        }).Release());
+    }
+}
+
+TGRpcClientLow::~TGRpcClientLow() {
+    StopInternal(true);
+    WaitInternal();
+}
+
+void TGRpcClientLow::Stop(bool wait) {
+    StopInternal(false);
+
+    if (wait) {
+        WaitInternal();
+    }
+}
+
+void TGRpcClientLow::StopInternal(bool silent) {
+    bool shutdown;
+
+    TVector<TContextImpl::TContextPtr> cancelQueue;
+
+    {
+        std::unique_lock<std::mutex> guard(Mtx_);
+
+        auto allowStateChange = [&]() {
+            switch (GetCqState()) {
+                case WORKING:
+                    return true;
+                case STOP_SILENT:
+                    return !silent;
+                case STOP_EXPLICIT:
+                    return false;
+            }
+
+            Y_UNREACHABLE();
+        };
+
+        if (!allowStateChange()) {
+            // Completion queue is already stopping
+            return;
+        }
+
+        SetCqState(silent ? STOP_SILENT : STOP_EXPLICIT);
+
+        if (!silent && !Contexts_.empty()) {
+            cancelQueue.reserve(Contexts_.size());
+            for (auto* ptr : Contexts_) {
+                // N.B. some contexts may be stuck in destructors
+                if (auto context = TContextImpl::LockChildPtr(ptr)) {
+                    cancelQueue.emplace_back(std::move(context));
+                }
+            }
+        }
+
+        shutdown = Contexts_.empty();
+    }
+
+    for (auto& context : cancelQueue) {
+        context->Cancel();
+        context.reset();
+    }
+
+    if (shutdown) {
+        for (auto& cq : CQS_) {
+            cq->Shutdown();
+        }
+    }
+}
+
+void TGRpcClientLow::WaitInternal() {
+    std::unique_lock<std::mutex> guard(JoinMutex_);
+
+    for (auto& ti : WorkerThreads_) {
+        ti->Join();
+    }
+}
+
+void TGRpcClientLow::WaitIdle() {
+    std::unique_lock<std::mutex> guard(Mtx_);
+
+    while (!Contexts_.empty()) {
+        ContextsEmpty_.wait(guard);
+    }
+}
+
+std::shared_ptr<IQueueClientContext> TGRpcClientLow::CreateContext() {
+    std::unique_lock<std::mutex> guard(Mtx_);
+
+    auto allowCreateContext = [&]() {
+        switch (GetCqState()) {
+            case WORKING:
+                return true;
+            case STOP_SILENT:
+            case STOP_EXPLICIT:
+                return false;
+        }
+
+        Y_UNREACHABLE();
+    };
+
+    if (!allowCreateContext()) {
+        // New context creation is forbidden
+        return nullptr;
+    }
+
+    auto context = std::make_shared<TContextImpl>();
+    Contexts_.insert(context.get());
+    context->Owner = this;
+    if (UseCompletionQueuePerThread_) {
+        context->CQ = CQS_[RandomNumber(CQS_.size())].get();
+    } else {
+        context->CQ = CQS_[0].get();
+    }
+    return context;
+}
+
+void TGRpcClientLow::ForgetContext(TContextImpl* context) {
+    bool shutdown = false;
+
+    {
+        std::unique_lock<std::mutex> guard(Mtx_);
+
+        if (!Contexts_.erase(context)) {
+            Y_FAIL("Unexpected ForgetContext(%p)", context);
+        }
+
+        if (Contexts_.empty()) {
+            if (IsStopping()) {
+                shutdown = true;
+            }
+
+            ContextsEmpty_.notify_all();
+        }
+    }
+
+    if (shutdown) {
+        // This was the last context, shutdown CQ
+        for (auto& cq : CQS_) {
+            cq->Shutdown();
+        }
+    }
+}
+
+} // namespace NGRpc
diff --git a/library/cpp/grpc/client/grpc_client_low.h b/library/cpp/grpc/client/grpc_client_low.h
new file mode 100644
index 00000000000..ab0a0627be0
--- /dev/null
+++ b/library/cpp/grpc/client/grpc_client_low.h
@@ -0,0 +1,1399 @@
+#pragma once
+
+#include "grpc_common.h"
+
+#include <util/thread/factory.h>
+#include <grpc++/grpc++.h>
+#include <grpc++/support/async_stream.h>
+#include <grpc++/support/async_unary_call.h>
+
+#include <deque>
+#include <typeindex>
+#include <typeinfo>
+#include <variant>
+#include <vector>
+#include <unordered_map>
+#include <unordered_set>
+#include <mutex>
+#include <shared_mutex>
+
+/*
+ * This file contains low level logic for grpc
+ * This file should not be used in high level code without special reason
+ */
+namespace NGrpc {
+
+const size_t DEFAULT_NUM_THREADS = 2;
+
+////////////////////////////////////////////////////////////////////////////////
+
+void EnableGRpcTracing();
+
+////////////////////////////////////////////////////////////////////////////////
+
+struct TTcpKeepAliveSettings {
+    bool Enabled;
+    size_t Idle;
+    size_t Count;
+    size_t Interval;
+};
+
+////////////////////////////////////////////////////////////////////////////////
+
+// Common interface used to execute action from grpc cq routine
+class IQueueClientEvent {
+public:
+    virtual ~IQueueClientEvent() = default;
+
+    //! Execute an action defined by implementation
+    virtual bool Execute(bool ok) = 0;
+
+    //! Finish and destroy event
+    virtual void Destroy() = 0;
+};
+
+// Implementation of IQueueClientEvent that reduces allocations
+template<class TSelf>
+class TQueueClientFixedEvent : private IQueueClientEvent {
+    using TCallback = void (TSelf::*)(bool);
+
+public:
+    TQueueClientFixedEvent(TSelf* self, TCallback callback)
+        : Self(self)
+        , Callback(callback)
+    { }
+
+    IQueueClientEvent* Prepare() {
+        Self->Ref();
+        return this;
+    }
+
+private:
+    bool Execute(bool ok) override {
+        ((*Self).*Callback)(ok);
+        return false;
+    }
+
+    void Destroy() override {
+        Self->UnRef();
+    }
+
+private:
+    TSelf* const Self;
+    TCallback const Callback;
+};
+
+class IQueueClientContext;
+using IQueueClientContextPtr = std::shared_ptr<IQueueClientContext>;
+
+// Provider of IQueueClientContext instances
+class IQueueClientContextProvider {
+public:
+    virtual ~IQueueClientContextProvider() = default;
+
+    virtual IQueueClientContextPtr CreateContext() = 0;
+};
+
+// Activity context for a low-level client
+class IQueueClientContext : public IQueueClientContextProvider {
+public:
+    virtual ~IQueueClientContext() = default;
+
+    //! Returns CompletionQueue associated with the client
+    virtual grpc::CompletionQueue* CompletionQueue() = 0;
+
+    //! Returns true if context has been cancelled
+    virtual bool IsCancelled() const = 0;
+
+    //! Tries to cancel context, calling all registered callbacks
+    virtual bool Cancel() = 0;
+
+    //! Subscribes callback to cancellation
+    //
+    // Note there's no way to unsubscribe, if subscription is temporary
+    // make sure you create a new context with CreateContext and release
+    // it as soon as it's no longer needed.
+    virtual void SubscribeCancel(std::function<void()> callback) = 0;
+
+    //! Subscribes callback to cancellation
+    //
+    // This alias is for compatibility with older code.
+    void SubscribeStop(std::function<void()> callback) {
+        SubscribeCancel(std::move(callback));
+    }
+};
+
+// Represents grpc status and error message string
+struct TGrpcStatus {
+    TString Msg;
+    TString Details;
+    int GRpcStatusCode;
+    bool InternalError;
+
+    TGrpcStatus()
+        : GRpcStatusCode(grpc::StatusCode::OK)
+        , InternalError(false)
+    { }
+
+    TGrpcStatus(TString msg, int statusCode, bool internalError)
+        : Msg(std::move(msg))
+        , GRpcStatusCode(statusCode)
+        , InternalError(internalError)
+    { }
+
+    TGrpcStatus(grpc::StatusCode status, TString msg, TString details = {})
+        : Msg(std::move(msg))
+        , Details(std::move(details))
+        , GRpcStatusCode(status)
+        , InternalError(false)
+    { }
+
+    TGrpcStatus(const grpc::Status& status)
+        : TGrpcStatus(status.error_code(), TString(status.error_message()), TString(status.error_details()))
+    { }
+
+    TGrpcStatus& operator=(const grpc::Status& status) {
+        Msg = TString(status.error_message());
+        Details = TString(status.error_details());
+        GRpcStatusCode = status.error_code();
+        InternalError = false;
+        return *this;
+    }
+
+    static TGrpcStatus Internal(TString msg) {
+        return { std::move(msg), -1, true };
+    }
+
+    bool Ok() const {
+        return !InternalError && GRpcStatusCode == grpc::StatusCode::OK;
+    }
+};
+
+bool inline IsGRpcStatusGood(const TGrpcStatus& status) {
+    return status.Ok();
+}
+
+// Response callback type - this callback will be called when request is finished
+//  (or after getting each chunk in case of streaming mode)
+template<typename TResponse>
+using TResponseCallback = std::function<void (TGrpcStatus&&, TResponse&&)>;
+
+template<typename TResponse>
+using TAdvancedResponseCallback = std::function<void (const grpc::ClientContext&, TGrpcStatus&&, TResponse&&)>;
+
+// Call associated metadata
+struct TCallMeta {
+    std::shared_ptr<grpc::CallCredentials> CallCredentials;
+    std::vector<std::pair<TString, TString>> Aux;
+    std::variant<TDuration, TInstant> Timeout; // timeout as duration from now or time point in future
+};
+
+class TGRpcRequestProcessorCommon {
+protected:
+    void ApplyMeta(const TCallMeta& meta) {
+        for (const auto& rec : meta.Aux) {
+            Context.AddMetadata(rec.first, rec.second);
+        }
+        if (meta.CallCredentials) {
+            Context.set_credentials(meta.CallCredentials);
+        }
+        if (const TDuration* timeout = std::get_if<TDuration>(&meta.Timeout)) {
+            if (*timeout) {
+                auto deadline = gpr_time_add(
+                        gpr_now(GPR_CLOCK_MONOTONIC),
+                        gpr_time_from_micros(timeout->MicroSeconds(), GPR_TIMESPAN));
+                Context.set_deadline(deadline);
+            }
+        } else if (const TInstant* deadline = std::get_if<TInstant>(&meta.Timeout)) {
+            if (*deadline) {
+                Context.set_deadline(gpr_time_from_micros(deadline->MicroSeconds(), GPR_CLOCK_MONOTONIC));
+            }
+        }
+    }
+
+    void GetInitialMetadata(std::unordered_multimap<TString, TString>* metadata) {
+        for (const auto& [key, value] : Context.GetServerInitialMetadata()) {
+            metadata->emplace(
+                TString(key.begin(), key.end()),
+                TString(value.begin(), value.end())
+            );
+        }
+    }
+
+    grpc::Status Status;
+    grpc::ClientContext Context;
+    std::shared_ptr<IQueueClientContext> LocalContext;
+};
+
+template<typename TStub, typename TRequest, typename TResponse>
+class TSimpleRequestProcessor
+    : public TThrRefBase
+    , public IQueueClientEvent
+    , public TGRpcRequestProcessorCommon {
+    using TAsyncReaderPtr = std::unique_ptr<grpc::ClientAsyncResponseReader<TResponse>>;
+    template<typename> friend class TServiceConnection;
+public:
+    using TPtr = TIntrusivePtr<TSimpleRequestProcessor>;
+    using TAsyncRequest = TAsyncReaderPtr (TStub::*)(grpc::ClientContext*, const TRequest&, grpc::CompletionQueue*);
+
+    explicit TSimpleRequestProcessor(TResponseCallback<TResponse>&& callback)
+        : Callback_(std::move(callback))
+    { }
+
+    ~TSimpleRequestProcessor() {
+        if (!Replied_ && Callback_) {
+            Callback_(TGrpcStatus::Internal("request left unhandled"), std::move(Reply_));
+            Callback_ = nullptr; // free resources as early as possible
+        }
+    }
+
+    bool Execute(bool ok) override {
+        {
+            std::unique_lock<std::mutex> guard(Mutex_);
+            LocalContext.reset();
+        }
+        TGrpcStatus status;
+        if (ok) {
+            status = Status;
+        } else {
+            status = TGrpcStatus::Internal("Unexpected error");
+        }
+        Replied_ = true;
+        Callback_(std::move(status), std::move(Reply_));
+        Callback_ = nullptr; // free resources as early as possible
+        return false;
+    }
+
+    void Destroy() override {
+        UnRef();
+    }
+
+private:
+    IQueueClientEvent* FinishedEvent() {
+        Ref();
+        return this;
+    }
+
+    void Start(TStub& stub, TAsyncRequest asyncRequest, const TRequest& request, IQueueClientContextProvider* provider) {
+        auto context = provider->CreateContext();
+        if (!context) {
+            Replied_ = true;
+            Callback_(TGrpcStatus(grpc::StatusCode::CANCELLED, "Client is shutting down"), std::move(Reply_));
+            Callback_ = nullptr;
+            return;
+        }
+        {
+            std::unique_lock<std::mutex> guard(Mutex_);
+            LocalContext = context;
+            Reader_ = (stub.*asyncRequest)(&Context, request, context->CompletionQueue());
+            Reader_->Finish(&Reply_, &Status, FinishedEvent());
+        }
+        context->SubscribeStop([self = TPtr(this)] {
+            self->Stop();
+        });
+    }
+
+    void Stop() {
+        Context.TryCancel();
+    }
+
+    TResponseCallback<TResponse> Callback_;
+    TResponse Reply_;
+    std::mutex Mutex_;
+    TAsyncReaderPtr Reader_;
+
+    bool Replied_ = false;
+};
+
+template<typename TStub, typename TRequest, typename TResponse>
+class TAdvancedRequestProcessor
+    : public TThrRefBase
+    , public IQueueClientEvent
+    , public TGRpcRequestProcessorCommon {
+    using TAsyncReaderPtr = std::unique_ptr<grpc::ClientAsyncResponseReader<TResponse>>;
+    template<typename> friend class TServiceConnection;
+public:
+    using TPtr = TIntrusivePtr<TAdvancedRequestProcessor>;
+    using TAsyncRequest = TAsyncReaderPtr (TStub::*)(grpc::ClientContext*, const TRequest&, grpc::CompletionQueue*);
+
+    explicit TAdvancedRequestProcessor(TAdvancedResponseCallback<TResponse>&& callback)
+        : Callback_(std::move(callback))
+    { }
+
+    ~TAdvancedRequestProcessor() {
+        if (!Replied_ && Callback_) {
+            Callback_(Context, TGrpcStatus::Internal("request left unhandled"), std::move(Reply_));
+            Callback_ = nullptr; // free resources as early as possible
+        }
+    }
+
+    bool Execute(bool ok) override {
+        {
+            std::unique_lock<std::mutex> guard(Mutex_);
+            LocalContext.reset();
+        }
+        TGrpcStatus status;
+        if (ok) {
+            status = Status;
+        } else {
+            status = TGrpcStatus::Internal("Unexpected error");
+        }
+        Replied_ = true;
+        Callback_(Context, std::move(status), std::move(Reply_));
+        Callback_ = nullptr; // free resources as early as possible
+        return false;
+    }
+
+    void Destroy() override {
+        UnRef();
+    }
+
+private:
+    IQueueClientEvent* FinishedEvent() {
+        Ref();
+        return this;
+    }
+
+    void Start(TStub& stub, TAsyncRequest asyncRequest, const TRequest& request, IQueueClientContextProvider* provider) {
+        auto context = provider->CreateContext();
+        if (!context) {
+            Replied_ = true;
+            Callback_(Context, TGrpcStatus(grpc::StatusCode::CANCELLED, "Client is shutting down"), std::move(Reply_));
+            Callback_ = nullptr;
+            return;
+        }
+        {
+            std::unique_lock<std::mutex> guard(Mutex_);
+            LocalContext = context;
+            Reader_ = (stub.*asyncRequest)(&Context, request, context->CompletionQueue());
+            Reader_->Finish(&Reply_, &Status, FinishedEvent());
+        }
+        context->SubscribeStop([self = TPtr(this)] {
+            self->Stop();
+        });
+    }
+
+    void Stop() {
+        Context.TryCancel();
+    }
+
+    TAdvancedResponseCallback<TResponse> Callback_;
+    TResponse Reply_;
+    std::mutex Mutex_;
+    TAsyncReaderPtr Reader_;
+
+    bool Replied_ = false;
+};
+
+template<class TResponse>
+class IStreamRequestReadProcessor : public TThrRefBase {
+public:
+    using TPtr = TIntrusivePtr<IStreamRequestReadProcessor>;
+    using TReadCallback = std::function<void(TGrpcStatus&&)>;
+
+    /**
+     * Asynchronously cancel the request
+     */
+    virtual void Cancel() = 0;
+
+    /**
+     * Scheduled initial server metadata read from the stream
+     */
+    virtual void ReadInitialMetadata(std::unordered_multimap<TString, TString>* metadata, TReadCallback callback) = 0;
+
+    /**
+     * Scheduled response read from the stream
+     * Callback will be called with the status if it failed
+     * Only one Read or Finish call may be active at a time
+     */
+    virtual void Read(TResponse* response, TReadCallback callback) = 0;
+
+    /**
+     * Stop reading and gracefully finish the stream
+     * Only one Read or Finish call may be active at a time
+     */
+    virtual void Finish(TReadCallback callback) = 0;
+
+    /**
+     * Additional callback to be called when stream has finished
+     */
+    virtual void AddFinishedCallback(TReadCallback callback) = 0;
+};
+
+template<class TRequest, class TResponse>
+class IStreamRequestReadWriteProcessor : public IStreamRequestReadProcessor<TResponse> {
+public:
+    using TPtr = TIntrusivePtr<IStreamRequestReadWriteProcessor>;
+    using TWriteCallback = std::function<void(TGrpcStatus&&)>;
+
+    /**
+     * Scheduled request write to the stream
+     */
+    virtual void Write(TRequest&& request, TWriteCallback callback = { }) = 0;
+};
+
+class TGRpcKeepAliveSocketMutator;
+
+// Class to hold stubs allocated on channel.
+// It is poor documented part of grpc. See KIKIMR-6109 and comment to this commit
+
+// Stub holds shared_ptr<ChannelInterface>, so we can destroy this holder even if
+// request processor using stub
+class TStubsHolder : public TNonCopyable {
+    using TypeInfoRef = std::reference_wrapper<const std::type_info>;
+
+    struct THasher {
+        std::size_t operator()(TypeInfoRef code) const {
+            return code.get().hash_code();
+        }
+    };
+
+    struct TEqualTo {
+        bool operator()(TypeInfoRef lhs, TypeInfoRef rhs) const {
+            return lhs.get() == rhs.get();
+        }
+    };
+public:
+    TStubsHolder(std::shared_ptr<grpc::ChannelInterface> channel)
+        : ChannelInterface_(channel)
+    {}
+
+    // Returns true if channel can't be used to perform request now
+    bool IsChannelBroken() const {
+        auto state = ChannelInterface_->GetState(false);
+        return state == GRPC_CHANNEL_SHUTDOWN ||
+            state == GRPC_CHANNEL_TRANSIENT_FAILURE;
+    }
+
+    template<typename TStub>
+    std::shared_ptr<TStub> GetOrCreateStub() {
+        const auto& stubId = typeid(TStub);
+        {
+            std::shared_lock readGuard(RWMutex_);
+            const auto it = Stubs_.find(stubId);
+            if (it != Stubs_.end()) {
+                return std::static_pointer_cast<TStub>(it->second);
+            }
+        }
+        {
+            std::unique_lock writeGuard(RWMutex_);
+            auto it = Stubs_.emplace(stubId, nullptr);
+            if (!it.second) {
+                return std::static_pointer_cast<TStub>(it.first->second);
+            } else {
+                it.first->second = std::make_shared<TStub>(ChannelInterface_);
+                return std::static_pointer_cast<TStub>(it.first->second);
+            }
+        }
+    }
+
+    const TInstant& GetLastUseTime() const {
+        return LastUsed_;
+    }
+
+    void SetLastUseTime(const TInstant& time) {
+        LastUsed_ = time;
+    }
+private:
+    TInstant LastUsed_ = Now();
+    std::shared_mutex RWMutex_;
+    std::unordered_map<TypeInfoRef, std::shared_ptr<void>, THasher, TEqualTo> Stubs_;
+    std::shared_ptr<grpc::ChannelInterface> ChannelInterface_;
+};
+
+class TChannelPool {
+public:
+    TChannelPool(const TTcpKeepAliveSettings& tcpKeepAliveSettings, const TDuration& expireTime = TDuration::Minutes(6));
+    //Allows to CreateStub from TStubsHolder under lock
+    //The callback will be called just during GetStubsHolderLocked call
+    void GetStubsHolderLocked(const TString& channelId, const TGRpcClientConfig& config, std::function<void(TStubsHolder&)> cb);
+    void DeleteChannel(const TString& channelId);
+    void DeleteExpiredStubsHolders();
+private:
+    std::shared_mutex RWMutex_;
+    std::unordered_map<TString, TStubsHolder> Pool_;
+    std::multimap<TInstant, TString> LastUsedQueue_;
+    TTcpKeepAliveSettings TcpKeepAliveSettings_;
+    TDuration ExpireTime_;
+    TDuration UpdateReUseTime_;
+    void EraseFromQueueByTime(const TInstant& lastUseTime, const TString& channelId);
+};
+
+template<class TResponse>
+using TStreamReaderCallback = std::function<void(TGrpcStatus&&, typename IStreamRequestReadProcessor<TResponse>::TPtr)>;
+
+template<typename TStub, typename TRequest, typename TResponse>
+class TStreamRequestReadProcessor
+    : public IStreamRequestReadProcessor<TResponse>
+    , public TGRpcRequestProcessorCommon {
+    template<typename> friend class TServiceConnection;
+public:
+    using TSelf = TStreamRequestReadProcessor;
+    using TAsyncReaderPtr = std::unique_ptr<grpc::ClientAsyncReader<TResponse>>;
+    using TAsyncRequest = TAsyncReaderPtr (TStub::*)(grpc::ClientContext*, const TRequest&, grpc::CompletionQueue*, void*);
+    using TReaderCallback = TStreamReaderCallback<TResponse>;
+    using TPtr = TIntrusivePtr<TSelf>;
+    using TBase = IStreamRequestReadProcessor<TResponse>;
+    using TReadCallback = typename TBase::TReadCallback;
+
+    explicit TStreamRequestReadProcessor(TReaderCallback&& callback)
+        : Callback(std::move(callback))
+    {
+        Y_VERIFY(Callback, "Missing connected callback");
+    }
+
+    void Cancel() override {
+        Context.TryCancel();
+
+        {
+            std::unique_lock<std::mutex> guard(Mutex);
+            Cancelled = true;
+            if (Started && !ReadFinished) {
+                if (!ReadActive) {
+                    ReadFinished = true;
+                }
+                if (ReadFinished) {
+                    Stream->Finish(&Status, OnFinishedTag.Prepare());
+                }
+            }
+        }
+    }
+
+    void ReadInitialMetadata(std::unordered_multimap<TString, TString>* metadata, TReadCallback callback) override {
+        TGrpcStatus status;
+
+        {
+            std::unique_lock<std::mutex> guard(Mutex);
+            Y_VERIFY(!ReadActive, "Multiple Read/Finish calls detected");
+            if (!Finished && !HasInitialMetadata) {
+                ReadActive = true;
+                ReadCallback = std::move(callback);
+                InitialMetadata = metadata;
+                if (!ReadFinished) {
+                    Stream->ReadInitialMetadata(OnReadDoneTag.Prepare());
+                }
+                return;
+            }
+            if (!HasInitialMetadata) {
+                if (FinishedOk) {
+                    status = Status;
+                } else {
+                    status = TGrpcStatus::Internal("Unexpected error");
+                }
+            } else {
+                GetInitialMetadata(metadata);
+            }
+        }
+
+        callback(std::move(status));
+    }
+
+    void Read(TResponse* message, TReadCallback callback) override {
+        TGrpcStatus status;
+
+        {
+            std::unique_lock<std::mutex> guard(Mutex);
+            Y_VERIFY(!ReadActive, "Multiple Read/Finish calls detected");
+            if (!Finished) {
+                ReadActive = true;
+                ReadCallback = std::move(callback);
+                if (!ReadFinished) {
+                    Stream->Read(message, OnReadDoneTag.Prepare());
+                }
+                return;
+            }
+            if (FinishedOk) {
+                status = Status;
+            } else {
+                status = TGrpcStatus::Internal("Unexpected error");
+            }
+        }
+
+        if (status.Ok()) {
+            status = TGrpcStatus(grpc::StatusCode::OUT_OF_RANGE, "Read EOF");
+        }
+
+        callback(std::move(status));
+    }
+
+    void Finish(TReadCallback callback) override {
+        TGrpcStatus status;
+
+        {
+            std::unique_lock<std::mutex> guard(Mutex);
+            Y_VERIFY(!ReadActive, "Multiple Read/Finish calls detected");
+            if (!Finished) {
+                ReadActive = true;
+                FinishCallback = std::move(callback);
+                if (!ReadFinished) {
+                    ReadFinished = true;
+                }
+                Stream->Finish(&Status, OnFinishedTag.Prepare());
+                return;
+            }
+            if (FinishedOk) {
+                status = Status;
+            } else {
+                status = TGrpcStatus::Internal("Unexpected error");
+            }
+        }
+
+        callback(std::move(status));
+    }
+
+    void AddFinishedCallback(TReadCallback callback) override {
+        Y_VERIFY(callback, "Unexpected empty callback");
+
+        TGrpcStatus status;
+
+        {
+            std::unique_lock<std::mutex> guard(Mutex);
+            if (!Finished) {
+                FinishedCallbacks.emplace_back().swap(callback);
+                return;
+            }
+
+            if (FinishedOk) {
+                status = Status;
+            } else if (Cancelled) {
+                status = TGrpcStatus(grpc::StatusCode::CANCELLED, "Stream cancelled");
+            } else {
+                status = TGrpcStatus::Internal("Unexpected error");
+            }
+        }
+
+        callback(std::move(status));
+    }
+
+private:
+    void Start(TStub& stub, const TRequest& request, TAsyncRequest asyncRequest, IQueueClientContextProvider* provider) {
+        auto context = provider->CreateContext();
+        if (!context) {
+            auto callback = std::move(Callback);
+            TGrpcStatus status(grpc::StatusCode::CANCELLED, "Client is shutting down");
+            callback(std::move(status), nullptr);
+            return;
+        }
+
+        {
+            std::unique_lock<std::mutex> guard(Mutex);
+            LocalContext = context;
+            Stream = (stub.*asyncRequest)(&Context, request, context->CompletionQueue(), OnStartDoneTag.Prepare());
+        }
+
+        context->SubscribeStop([self = TPtr(this)] {
+            self->Cancel();
+        });
+    }
+
+    void OnReadDone(bool ok) {
+        TGrpcStatus status;
+        TReadCallback callback;
+        std::unordered_multimap<TString, TString>* initialMetadata = nullptr;
+
+        {
+            std::unique_lock<std::mutex> guard(Mutex);
+            Y_VERIFY(ReadActive, "Unexpected Read done callback");
+            Y_VERIFY(!ReadFinished, "Unexpected ReadFinished flag");
+
+            if (!ok || Cancelled) {
+                ReadFinished = true;
+
+                Stream->Finish(&Status, OnFinishedTag.Prepare());
+                if (!ok) {
+                    // Keep ReadActive=true, so callback is called
+                    // after the call is finished with an error
+                    return;
+                }
+            }
+
+            callback = std::move(ReadCallback);
+            ReadCallback = nullptr;
+            ReadActive = false;
+            initialMetadata = InitialMetadata;
+            InitialMetadata = nullptr;
+            HasInitialMetadata = true;
+        }
+
+        if (initialMetadata) {
+            GetInitialMetadata(initialMetadata);
+        }
+
+        callback(std::move(status));
+    }
+
+    void OnStartDone(bool ok) {
+        TReaderCallback callback;
+
+        {
+            std::unique_lock<std::mutex> guard(Mutex);
+            Started = true;
+            if (!ok || Cancelled) {
+                ReadFinished = true;
+                Stream->Finish(&Status, OnFinishedTag.Prepare());
+                return;
+            }
+            callback = std::move(Callback);
+            Callback = nullptr;
+        }
+
+        callback({ }, typename TBase::TPtr(this));
+    }
+
+    void OnFinished(bool ok) {
+        TGrpcStatus status;
+        std::vector<TReadCallback> finishedCallbacks;
+        TReaderCallback startCallback;
+        TReadCallback readCallback;
+        TReadCallback finishCallback;
+
+        {
+            std::unique_lock<std::mutex> guard(Mutex);
+
+            Finished = true;
+            FinishedOk = ok;
+            LocalContext.reset();
+
+            if (ok) {
+                status = Status;
+            } else if (Cancelled) {
+                status = TGrpcStatus(grpc::StatusCode::CANCELLED, "Stream cancelled");
+            } else {
+                status = TGrpcStatus::Internal("Unexpected error");
+            }
+
+            finishedCallbacks.swap(FinishedCallbacks);
+
+            if (Callback) {
+                Y_VERIFY(!ReadActive);
+                startCallback = std::move(Callback);
+                Callback = nullptr;
+            } else if (ReadActive) {
+                if (ReadCallback) {
+                    readCallback = std::move(ReadCallback);
+                    ReadCallback = nullptr;
+                } else {
+                    finishCallback = std::move(FinishCallback);
+                    FinishCallback = nullptr;
+                }
+                ReadActive = false;
+            }
+        }
+
+        for (auto& finishedCallback : finishedCallbacks) {
+            auto statusCopy = status;
+            finishedCallback(std::move(statusCopy));
+        }
+
+        if (startCallback) {
+            if (status.Ok()) {
+                status = TGrpcStatus(grpc::StatusCode::UNKNOWN, "Unknown stream failure");
+            }
+            startCallback(std::move(status), nullptr);
+        } else if (readCallback) {
+            if (status.Ok()) {
+                status = TGrpcStatus(grpc::StatusCode::OUT_OF_RANGE, "Read EOF");
+            }
+            readCallback(std::move(status));
+        } else if (finishCallback) {
+            finishCallback(std::move(status));
+        }
+    }
+
+    TReaderCallback Callback;
+    TAsyncReaderPtr Stream;
+    using TFixedEvent = TQueueClientFixedEvent<TSelf>;
+    std::mutex Mutex;
+    TFixedEvent OnReadDoneTag = { this, &TSelf::OnReadDone };
+    TFixedEvent OnStartDoneTag = { this, &TSelf::OnStartDone };
+    TFixedEvent OnFinishedTag = { this, &TSelf::OnFinished };
+
+    TReadCallback ReadCallback;
+    TReadCallback FinishCallback;
+    std::vector<TReadCallback> FinishedCallbacks;
+    std::unordered_multimap<TString, TString>* InitialMetadata = nullptr;
+    bool Started = false;
+    bool HasInitialMetadata = false;
+    bool ReadActive = false;
+    bool ReadFinished = false;
+    bool Finished = false;
+    bool Cancelled = false;
+    bool FinishedOk = false;
+};
+
+template<class TRequest, class TResponse>
+using TStreamConnectedCallback = std::function<void(TGrpcStatus&&, typename IStreamRequestReadWriteProcessor<TRequest, TResponse>::TPtr)>;
+
+template<class TStub, class TRequest, class TResponse>
+class TStreamRequestReadWriteProcessor
+    : public IStreamRequestReadWriteProcessor<TRequest, TResponse>
+    , public TGRpcRequestProcessorCommon {
+public:
+    using TSelf = TStreamRequestReadWriteProcessor;
+    using TBase = IStreamRequestReadWriteProcessor<TRequest, TResponse>;
+    using TPtr = TIntrusivePtr<TSelf>;
+    using TConnectedCallback = TStreamConnectedCallback<TRequest, TResponse>;
+    using TReadCallback = typename TBase::TReadCallback;
+    using TWriteCallback = typename TBase::TWriteCallback;
+    using TAsyncReaderWriterPtr = std::unique_ptr<grpc::ClientAsyncReaderWriter<TRequest, TResponse>>;
+    using TAsyncRequest = TAsyncReaderWriterPtr (TStub::*)(grpc::ClientContext*, grpc::CompletionQueue*, void*);
+
+    explicit TStreamRequestReadWriteProcessor(TConnectedCallback&& callback)
+        : ConnectedCallback(std::move(callback))
+    {
+        Y_VERIFY(ConnectedCallback, "Missing connected callback");
+    }
+
+    void Cancel() override {
+        Context.TryCancel();
+
+        {
+            std::unique_lock<std::mutex> guard(Mutex);
+            Cancelled = true;
+            if (Started && !(ReadFinished && WriteFinished)) {
+                if (!ReadActive) {
+                    ReadFinished = true;
+                }
+                if (!WriteActive) {
+                    WriteFinished = true;
+                }
+                if (ReadFinished && WriteFinished) {
+                    Stream->Finish(&Status, OnFinishedTag.Prepare());
+                }
+            }
+        }
+    }
+
+    void Write(TRequest&& request, TWriteCallback callback) override {
+        TGrpcStatus status;
+
+        {
+            std::unique_lock<std::mutex> guard(Mutex);
+            if (Cancelled || ReadFinished || WriteFinished) {
+                status = TGrpcStatus(grpc::StatusCode::CANCELLED, "Write request dropped");
+            } else if (WriteActive) {
+                auto& item = WriteQueue.emplace_back();
+                item.Callback.swap(callback);
+                item.Request.Swap(&request);
+            } else {
+                WriteActive = true;
+                WriteCallback.swap(callback);
+                Stream->Write(request, OnWriteDoneTag.Prepare());
+            }
+        }
+
+        if (!status.Ok() && callback) {
+            callback(std::move(status));
+        }
+    }
+
+    void ReadInitialMetadata(std::unordered_multimap<TString, TString>* metadata, TReadCallback callback) override {
+        TGrpcStatus status;
+
+        {
+            std::unique_lock<std::mutex> guard(Mutex);
+            Y_VERIFY(!ReadActive, "Multiple Read/Finish calls detected");
+            if (!Finished && !HasInitialMetadata) {
+                ReadActive = true;
+                ReadCallback = std::move(callback);
+                InitialMetadata = metadata;
+                if (!ReadFinished) {
+                    Stream->ReadInitialMetadata(OnReadDoneTag.Prepare());
+                }
+                return;
+            }
+            if (!HasInitialMetadata) {
+                if (FinishedOk) {
+                    status = Status;
+                } else {
+                    status = TGrpcStatus::Internal("Unexpected error");
+                }
+            } else {
+                GetInitialMetadata(metadata);
+            }
+        }
+
+        callback(std::move(status));
+    }
+
+    void Read(TResponse* message, TReadCallback callback) override {
+        TGrpcStatus status;
+
+        {
+            std::unique_lock<std::mutex> guard(Mutex);
+            Y_VERIFY(!ReadActive, "Multiple Read/Finish calls detected");
+            if (!Finished) {
+                ReadActive = true;
+                ReadCallback = std::move(callback);
+                if (!ReadFinished) {
+                    Stream->Read(message, OnReadDoneTag.Prepare());
+                }
+                return;
+            }
+            if (FinishedOk) {
+                status = Status;
+            } else {
+                status = TGrpcStatus::Internal("Unexpected error");
+            }
+        }
+
+        if (status.Ok()) {
+            status = TGrpcStatus(grpc::StatusCode::OUT_OF_RANGE, "Read EOF");
+        }
+
+        callback(std::move(status));
+    }
+
+    void Finish(TReadCallback callback) override {
+        TGrpcStatus status;
+
+        {
+            std::unique_lock<std::mutex> guard(Mutex);
+            Y_VERIFY(!ReadActive, "Multiple Read/Finish calls detected");
+            if (!Finished) {
+                ReadActive = true;
+                FinishCallback = std::move(callback);
+                if (!ReadFinished) {
+                    ReadFinished = true;
+                    if (!WriteActive) {
+                        WriteFinished = true;
+                    }
+                    if (WriteFinished) {
+                        Stream->Finish(&Status, OnFinishedTag.Prepare());
+                    }
+                }
+                return;
+            }
+            if (FinishedOk) {
+                status = Status;
+            } else {
+                status = TGrpcStatus::Internal("Unexpected error");
+            }
+        }
+
+        callback(std::move(status));
+    }
+
+    void AddFinishedCallback(TReadCallback callback) override {
+        Y_VERIFY(callback, "Unexpected empty callback");
+
+        TGrpcStatus status;
+
+        {
+            std::unique_lock<std::mutex> guard(Mutex);
+            if (!Finished) {
+                FinishedCallbacks.emplace_back().swap(callback);
+                return;
+            }
+
+            if (FinishedOk) {
+                status = Status;
+            } else if (Cancelled) {
+                status = TGrpcStatus(grpc::StatusCode::CANCELLED, "Stream cancelled");
+            } else {
+                status = TGrpcStatus::Internal("Unexpected error");
+            }
+        }
+
+        callback(std::move(status));
+    }
+
+private:
+    template<typename> friend class TServiceConnection;
+
+    void Start(TStub& stub, TAsyncRequest asyncRequest, IQueueClientContextProvider* provider) {
+        auto context = provider->CreateContext();
+        if (!context) {
+            auto callback = std::move(ConnectedCallback);
+            TGrpcStatus status(grpc::StatusCode::CANCELLED, "Client is shutting down");
+            callback(std::move(status), nullptr);
+            return;
+        }
+
+        {
+            std::unique_lock<std::mutex> guard(Mutex);
+            LocalContext = context;
+            Stream = (stub.*asyncRequest)(&Context, context->CompletionQueue(), OnConnectedTag.Prepare());
+        }
+
+        context->SubscribeStop([self = TPtr(this)] {
+            self->Cancel();
+        });
+    }
+
+private:
+    void OnConnected(bool ok) {
+        TConnectedCallback callback;
+
+        {
+            std::unique_lock<std::mutex> guard(Mutex);
+            Started = true;
+            if (!ok || Cancelled) {
+                ReadFinished = true;
+                WriteFinished = true;
+                Stream->Finish(&Status, OnFinishedTag.Prepare());
+                return;
+            }
+
+            callback = std::move(ConnectedCallback);
+            ConnectedCallback = nullptr;
+        }
+
+        callback({ }, typename TBase::TPtr(this));
+    }
+
+    void OnReadDone(bool ok) {
+        TGrpcStatus status;
+        TReadCallback callback;
+        std::unordered_multimap<TString, TString>* initialMetadata = nullptr;
+
+        {
+            std::unique_lock<std::mutex> guard(Mutex);
+            Y_VERIFY(ReadActive, "Unexpected Read done callback");
+            Y_VERIFY(!ReadFinished, "Unexpected ReadFinished flag");
+
+            if (!ok || Cancelled || WriteFinished) {
+                ReadFinished = true;
+                if (!WriteActive) {
+                    WriteFinished = true;
+                }
+                if (WriteFinished) {
+                    Stream->Finish(&Status, OnFinishedTag.Prepare());
+                }
+                if (!ok) {
+                    // Keep ReadActive=true, so callback is called
+                    // after the call is finished with an error
+                    return;
+                }
+            }
+
+            callback = std::move(ReadCallback);
+            ReadCallback = nullptr;
+            ReadActive = false;
+            initialMetadata = InitialMetadata;
+            InitialMetadata = nullptr;
+            HasInitialMetadata = true;
+        }
+
+        if (initialMetadata) {
+            GetInitialMetadata(initialMetadata);
+        }
+
+        callback(std::move(status));
+    }
+
+    void OnWriteDone(bool ok) {
+        TWriteCallback okCallback;
+
+        {
+            std::unique_lock<std::mutex> guard(Mutex);
+            Y_VERIFY(WriteActive, "Unexpected Write done callback");
+            Y_VERIFY(!WriteFinished, "Unexpected WriteFinished flag");
+
+            if (ok) {
+                okCallback.swap(WriteCallback);
+            } else if (WriteCallback) {
+                // Put callback back on the queue until OnFinished
+                auto& item = WriteQueue.emplace_front();
+                item.Callback.swap(WriteCallback);
+            }
+
+            if (!ok || Cancelled) {
+                WriteActive = false;
+                WriteFinished = true;
+                if (!ReadActive) {
+                    ReadFinished = true;
+                }
+                if (ReadFinished) {
+                    Stream->Finish(&Status, OnFinishedTag.Prepare());
+                }
+            } else if (!WriteQueue.empty()) {
+                WriteCallback.swap(WriteQueue.front().Callback);
+                Stream->Write(WriteQueue.front().Request, OnWriteDoneTag.Prepare());
+                WriteQueue.pop_front();
+            } else {
+                WriteActive = false;
+                if (ReadFinished) {
+                    WriteFinished = true;
+                    Stream->Finish(&Status, OnFinishedTag.Prepare());
+                }
+            }
+        }
+
+        if (okCallback) {
+            okCallback(TGrpcStatus());
+        }
+    }
+
+    void OnFinished(bool ok) {
+        TGrpcStatus status;
+        std::deque<TWriteItem> writesDropped;
+        std::vector<TReadCallback> finishedCallbacks;
+        TConnectedCallback connectedCallback;
+        TReadCallback readCallback;
+        TReadCallback finishCallback;
+
+        {
+            std::unique_lock<std::mutex> guard(Mutex);
+            Finished = true;
+            FinishedOk = ok;
+            LocalContext.reset();
+
+            if (ok) {
+                status = Status;
+            } else if (Cancelled) {
+                status = TGrpcStatus(grpc::StatusCode::CANCELLED, "Stream cancelled");
+            } else {
+                status = TGrpcStatus::Internal("Unexpected error");
+            }
+
+            writesDropped.swap(WriteQueue);
+            finishedCallbacks.swap(FinishedCallbacks);
+
+            if (ConnectedCallback) {
+                Y_VERIFY(!ReadActive);
+                connectedCallback = std::move(ConnectedCallback);
+                ConnectedCallback = nullptr;
+            } else if (ReadActive) {
+                if (ReadCallback) {
+                    readCallback = std::move(ReadCallback);
+                    ReadCallback = nullptr;
+                } else {
+                    finishCallback = std::move(FinishCallback);
+                    FinishCallback = nullptr;
+                }
+                ReadActive = false;
+            }
+        }
+
+        for (auto& item : writesDropped) {
+            if (item.Callback) {
+                TGrpcStatus writeStatus = status;
+                if (writeStatus.Ok()) {
+                    writeStatus = TGrpcStatus(grpc::StatusCode::CANCELLED, "Write request dropped");
+                }
+                item.Callback(std::move(writeStatus));
+            }
+        }
+
+        for (auto& finishedCallback : finishedCallbacks) {
+            TGrpcStatus statusCopy = status;
+            finishedCallback(std::move(statusCopy));
+        }
+
+        if (connectedCallback) {
+            if (status.Ok()) {
+                status = TGrpcStatus(grpc::StatusCode::UNKNOWN, "Unknown stream failure");
+            }
+            connectedCallback(std::move(status), nullptr);
+        } else if (readCallback) {
+            if (status.Ok()) {
+                status = TGrpcStatus(grpc::StatusCode::OUT_OF_RANGE, "Read EOF");
+            }
+            readCallback(std::move(status));
+        } else if (finishCallback) {
+            finishCallback(std::move(status));
+        }
+    }
+
+private:
+    struct TWriteItem {
+        TWriteCallback Callback;
+        TRequest Request;
+    };
+
+private:
+    using TFixedEvent = TQueueClientFixedEvent<TSelf>;
+
+    TFixedEvent OnConnectedTag = { this, &TSelf::OnConnected };
+    TFixedEvent OnReadDoneTag = { this, &TSelf::OnReadDone };
+    TFixedEvent OnWriteDoneTag = { this, &TSelf::OnWriteDone };
+    TFixedEvent OnFinishedTag = { this, &TSelf::OnFinished };
+
+private:
+    std::mutex Mutex;
+    TAsyncReaderWriterPtr Stream;
+    TConnectedCallback ConnectedCallback;
+    TReadCallback ReadCallback;
+    TReadCallback FinishCallback;
+    std::vector<TReadCallback> FinishedCallbacks;
+    std::deque<TWriteItem> WriteQueue;
+    TWriteCallback WriteCallback;
+    std::unordered_multimap<TString, TString>* InitialMetadata = nullptr;
+    bool Started = false;
+    bool HasInitialMetadata = false;
+    bool ReadActive = false;
+    bool ReadFinished = false;
+    bool WriteActive = false;
+    bool WriteFinished = false;
+    bool Finished = false;
+    bool Cancelled = false;
+    bool FinishedOk = false;
+};
+
+class TGRpcClientLow;
+
+template<typename TGRpcService>
+class TServiceConnection {
+    using TStub = typename TGRpcService::Stub;
+    friend class TGRpcClientLow;
+
+public:
+    /*
+     * Start simple request
+     */
+    template<typename TRequest, typename TResponse>
+    void DoRequest(const TRequest& request,
+                   TResponseCallback<TResponse> callback,
+                   typename TSimpleRequestProcessor<TStub, TRequest, TResponse>::TAsyncRequest asyncRequest,
+                   const TCallMeta& metas = { },
+                   IQueueClientContextProvider* provider = nullptr)
+    {
+        auto processor = MakeIntrusive<TSimpleRequestProcessor<TStub, TRequest, TResponse>>(std::move(callback));
+        processor->ApplyMeta(metas);
+        processor->Start(*Stub_, asyncRequest, request, provider ? provider : Provider_);
+    }
+
+    /*
+     * Start simple request
+     */
+    template<typename TRequest, typename TResponse>
+    void DoAdvancedRequest(const TRequest& request,
+                           TAdvancedResponseCallback<TResponse> callback,
+                           typename TAdvancedRequestProcessor<TStub, TRequest, TResponse>::TAsyncRequest asyncRequest,
+                           const TCallMeta& metas = { },
+                           IQueueClientContextProvider* provider = nullptr)
+    {
+        auto processor = MakeIntrusive<TAdvancedRequestProcessor<TStub, TRequest, TResponse>>(std::move(callback));
+        processor->ApplyMeta(metas);
+        processor->Start(*Stub_, asyncRequest, request, provider ? provider : Provider_);
+    }
+
+    /*
+     * Start bidirectional streamming
+     */
+    template<typename TRequest, typename TResponse>
+    void DoStreamRequest(TStreamConnectedCallback<TRequest, TResponse> callback,
+                         typename TStreamRequestReadWriteProcessor<TStub, TRequest, TResponse>::TAsyncRequest asyncRequest,
+                         const TCallMeta& metas = { },
+                         IQueueClientContextProvider* provider = nullptr)
+    {
+        auto processor = MakeIntrusive<TStreamRequestReadWriteProcessor<TStub, TRequest, TResponse>>(std::move(callback));
+        processor->ApplyMeta(metas);
+        processor->Start(*Stub_, std::move(asyncRequest), provider ? provider : Provider_);
+    }
+
+    /*
+     * Start streaming response reading (one request, many responses)
+     */
+    template<typename TRequest, typename TResponse>
+    void DoStreamRequest(const TRequest& request,
+                         TStreamReaderCallback<TResponse> callback,
+                         typename TStreamRequestReadProcessor<TStub, TRequest, TResponse>::TAsyncRequest asyncRequest,
+                         const TCallMeta& metas = { },
+                         IQueueClientContextProvider* provider = nullptr)
+    {
+        auto processor = MakeIntrusive<TStreamRequestReadProcessor<TStub, TRequest, TResponse>>(std::move(callback));
+        processor->ApplyMeta(metas);
+        processor->Start(*Stub_, request, std::move(asyncRequest), provider ? provider : Provider_);
+    }
+
+private:
+    TServiceConnection(std::shared_ptr<grpc::ChannelInterface> ci,
+                       IQueueClientContextProvider* provider)
+        : Stub_(TGRpcService::NewStub(ci))
+        , Provider_(provider)
+    {
+        Y_VERIFY(Provider_, "Connection does not have a queue provider");
+    }
+
+    TServiceConnection(TStubsHolder& holder,
+                       IQueueClientContextProvider* provider)
+        : Stub_(holder.GetOrCreateStub<TStub>())
+        , Provider_(provider)
+    {
+        Y_VERIFY(Provider_, "Connection does not have a queue provider");
+    }
+
+    std::shared_ptr<TStub> Stub_;
+    IQueueClientContextProvider* Provider_;
+};
+
+class TGRpcClientLow
+    :  public IQueueClientContextProvider
+{
+    class TContextImpl;
+    friend class TContextImpl;
+
+    enum ECqState : TAtomicBase {
+        WORKING = 0,
+        STOP_SILENT = 1,
+        STOP_EXPLICIT = 2,
+    };
+
+public:
+    explicit TGRpcClientLow(size_t numWorkerThread = DEFAULT_NUM_THREADS, bool useCompletionQueuePerThread = false);
+    ~TGRpcClientLow();
+
+    // Tries to stop all currently running requests (via their stop callbacks)
+    // Will shutdown CQ and drain events once all requests have finished
+    // No new requests may be started after this call
+    void Stop(bool wait = false);
+
+    // Waits until all currently running requests finish execution
+    void WaitIdle();
+
+    inline bool IsStopping() const {
+        switch (GetCqState()) {
+            case WORKING:
+                return false;
+            case STOP_SILENT:
+            case STOP_EXPLICIT:
+                return true;
+        }
+
+        Y_UNREACHABLE();
+    }
+
+    IQueueClientContextPtr CreateContext() override;
+
+    template<typename TGRpcService>
+    std::unique_ptr<TServiceConnection<TGRpcService>> CreateGRpcServiceConnection(const TGRpcClientConfig& config) {
+        return std::unique_ptr<TServiceConnection<TGRpcService>>(new TServiceConnection<TGRpcService>(CreateChannelInterface(config), this));
+    }
+
+    template<typename TGRpcService>
+    std::unique_ptr<TServiceConnection<TGRpcService>> CreateGRpcServiceConnection(TStubsHolder& holder) {
+        return std::unique_ptr<TServiceConnection<TGRpcService>>(new TServiceConnection<TGRpcService>(holder, this));
+    }
+
+    // Tests only, not thread-safe
+    void AddWorkerThreadForTest();
+
+private:
+    using IThreadRef = std::unique_ptr<IThreadFactory::IThread>;
+    using CompletionQueueRef = std::unique_ptr<grpc::CompletionQueue>;
+    void Init(size_t numWorkerThread);
+
+    inline ECqState GetCqState() const { return (ECqState) AtomicGet(CqState_); }
+    inline void SetCqState(ECqState state) { AtomicSet(CqState_, state); }
+
+    void StopInternal(bool silent);
+    void WaitInternal();
+
+    void ForgetContext(TContextImpl* context);
+
+private:
+    bool UseCompletionQueuePerThread_;
+    std::vector<CompletionQueueRef> CQS_;
+    std::vector<IThreadRef> WorkerThreads_;
+    TAtomic CqState_ = -1;
+
+    std::mutex Mtx_;
+    std::condition_variable ContextsEmpty_;
+    std::unordered_set<TContextImpl*> Contexts_;
+
+    std::mutex JoinMutex_;
+};
+
+} // namespace NGRpc
diff --git a/library/cpp/grpc/client/grpc_common.h b/library/cpp/grpc/client/grpc_common.h
new file mode 100644
index 00000000000..ffcdafe0458
--- /dev/null
+++ b/library/cpp/grpc/client/grpc_common.h
@@ -0,0 +1,84 @@
+#pragma once
+
+#include <grpc++/grpc++.h>
+#include <grpc++/resource_quota.h>
+
+#include <util/datetime/base.h>
+#include <unordered_map>
+#include <util/generic/string.h>
+
+constexpr ui64 DEFAULT_GRPC_MESSAGE_SIZE_LIMIT = 64000000;
+
+namespace NGrpc {
+
+struct TGRpcClientConfig {
+    TString Locator; // format host:port
+    TDuration Timeout = TDuration::Max(); // request timeout
+    ui64 MaxMessageSize = DEFAULT_GRPC_MESSAGE_SIZE_LIMIT; // Max request and response size
+    ui64 MaxInboundMessageSize = 0; // overrides MaxMessageSize for incoming requests
+    ui64 MaxOutboundMessageSize = 0; // overrides MaxMessageSize for outgoing requests
+    ui32 MaxInFlight = 0;
+    bool EnableSsl = false;
+    TString SslCaCert;  //Implicitly enables Ssl if not empty
+    grpc_compression_algorithm CompressionAlgoritm = GRPC_COMPRESS_NONE;
+    ui64 MemQuota = 0;
+    std::unordered_map<TString, TString> StringChannelParams;
+    std::unordered_map<TString, int> IntChannelParams;
+    TString LoadBalancingPolicy = { };
+    TString SslTargetNameOverride = { };
+
+    TGRpcClientConfig() = default;
+    TGRpcClientConfig(const TGRpcClientConfig&) = default;
+    TGRpcClientConfig(TGRpcClientConfig&&) = default;
+    TGRpcClientConfig& operator=(const TGRpcClientConfig&) = default;
+    TGRpcClientConfig& operator=(TGRpcClientConfig&&) = default;
+
+    TGRpcClientConfig(const TString& locator, TDuration timeout = TDuration::Max(),
+            ui64 maxMessageSize = DEFAULT_GRPC_MESSAGE_SIZE_LIMIT, ui32 maxInFlight = 0, TString caCert = "",
+            grpc_compression_algorithm compressionAlgorithm = GRPC_COMPRESS_NONE, bool enableSsl = false)
+        : Locator(locator)
+        , Timeout(timeout)
+        , MaxMessageSize(maxMessageSize)
+        , MaxInFlight(maxInFlight)
+        , EnableSsl(enableSsl)
+        , SslCaCert(caCert)
+        , CompressionAlgoritm(compressionAlgorithm)
+    {}
+};
+
+inline std::shared_ptr<grpc::ChannelInterface> CreateChannelInterface(const TGRpcClientConfig& config, grpc_socket_mutator* mutator = nullptr){
+    grpc::ChannelArguments args;
+    args.SetMaxReceiveMessageSize(config.MaxInboundMessageSize ? config.MaxInboundMessageSize : config.MaxMessageSize);
+    args.SetMaxSendMessageSize(config.MaxOutboundMessageSize ? config.MaxOutboundMessageSize : config.MaxMessageSize);
+    args.SetCompressionAlgorithm(config.CompressionAlgoritm);
+
+    for (const auto& kvp: config.StringChannelParams) {
+        args.SetString(kvp.first, kvp.second);
+    }
+
+    for (const auto& kvp: config.IntChannelParams) {
+        args.SetInt(kvp.first, kvp.second);
+    }
+
+    if (config.MemQuota) {
+        grpc::ResourceQuota quota;
+        quota.Resize(config.MemQuota);
+        args.SetResourceQuota(quota);
+    }
+    if (mutator) {
+        args.SetSocketMutator(mutator);
+    }
+    if (!config.LoadBalancingPolicy.empty()) {
+        args.SetLoadBalancingPolicyName(config.LoadBalancingPolicy);
+    }
+    if (!config.SslTargetNameOverride.empty()) {
+        args.SetSslTargetNameOverride(config.SslTargetNameOverride);
+    }
+    if (config.EnableSsl || config.SslCaCert) {
+        return grpc::CreateCustomChannel(config.Locator, grpc::SslCredentials(grpc::SslCredentialsOptions{config.SslCaCert, "", ""}), args);
+    } else {
+        return grpc::CreateCustomChannel(config.Locator, grpc::InsecureChannelCredentials(), args);
+    }
+}
+
+} // namespace NGRpc
diff --git a/library/cpp/grpc/client/ut/grpc_client_low_ut.cpp b/library/cpp/grpc/client/ut/grpc_client_low_ut.cpp
new file mode 100644
index 00000000000..b8af2a518fd
--- /dev/null
+++ b/library/cpp/grpc/client/ut/grpc_client_low_ut.cpp
@@ -0,0 +1,61 @@
+#include <library/cpp/grpc/client/grpc_client_low.h>
+
+#include <library/cpp/testing/unittest/registar.h>
+
+using namespace NGrpc;
+
+class TTestStub {
+public:
+    std::shared_ptr<grpc::ChannelInterface> ChannelInterface;
+    TTestStub(std::shared_ptr<grpc::ChannelInterface> channelInterface)
+        : ChannelInterface(channelInterface)
+    {}
+};
+
+Y_UNIT_TEST_SUITE(ChannelPoolTests) {
+    Y_UNIT_TEST(UnusedStubsHoldersDeletion) {
+        TGRpcClientConfig clientConfig("invalid_host:invalid_port");
+        TTcpKeepAliveSettings tcpKeepAliveSettings =
+        {
+            true,
+            30, // NYdb::TCP_KEEPALIVE_IDLE, unused in UT, but is necessary in constructor
+            5, // NYdb::TCP_KEEPALIVE_COUNT, unused in UT, but is necessary in constructor
+            10 // NYdb::TCP_KEEPALIVE_INTERVAL, unused in UT, but is necessary in constructor
+        };
+        auto channelPool = TChannelPool(tcpKeepAliveSettings, TDuration::MilliSeconds(250));
+        std::vector<std::weak_ptr<grpc::ChannelInterface>> ChannelInterfacesWeak;
+
+        {
+            std::vector<std::shared_ptr<TTestStub>> stubsHoldersShared;
+            auto storeStubsHolders = [&](TStubsHolder& stubsHolder) {
+                stubsHoldersShared.emplace_back(stubsHolder.GetOrCreateStub<TTestStub>());
+                ChannelInterfacesWeak.emplace_back((*stubsHoldersShared.rbegin())->ChannelInterface);
+                return;
+            };
+            for (int i = 0; i < 10; ++i) {
+                channelPool.GetStubsHolderLocked(
+                    ToString(i),
+                    clientConfig,
+                    storeStubsHolders
+                );
+            }
+        }
+
+        auto now = Now();
+        while (Now() < now + TDuration::MilliSeconds(500)){
+            Sleep(TDuration::MilliSeconds(100));
+        }
+
+        channelPool.DeleteExpiredStubsHolders();
+
+        bool allDeleted = true;
+        for (auto i = ChannelInterfacesWeak.begin(); i != ChannelInterfacesWeak.end(); ++i) {
+            allDeleted = allDeleted && i->expired();
+        }
+
+        // assertion is made for channel interfaces instead of stubs, because after stub deletion
+        // TStubsHolder has the only shared_ptr for channel interface.
+        UNIT_ASSERT_C(allDeleted, "expired stubsHolders were not deleted after timeout");
+
+    }
+} // ChannelPoolTests ut suite
\ No newline at end of file
diff --git a/library/cpp/grpc/client/ut/ya.make b/library/cpp/grpc/client/ut/ya.make
new file mode 100644
index 00000000000..eac779a99e4
--- /dev/null
+++ b/library/cpp/grpc/client/ut/ya.make
@@ -0,0 +1,11 @@
+UNITTEST_FOR(library/cpp/grpc/client)
+
+OWNER(
+	g:kikimr
+)
+
+SRCS(
+    grpc_client_low_ut.cpp
+)
+
+END()
diff --git a/library/cpp/grpc/client/ya.make b/library/cpp/grpc/client/ya.make
new file mode 100644
index 00000000000..a4e74b067cf
--- /dev/null
+++ b/library/cpp/grpc/client/ya.make
@@ -0,0 +1,20 @@
+LIBRARY()
+
+OWNER(
+    ddoarn
+    g:kikimr
+)
+
+SRCS(
+    grpc_client_low.cpp
+)
+
+PEERDIR(
+    contrib/libs/grpc
+)
+
+END()
+
+RECURSE_FOR_TESTS(
+    ut
+)
\ No newline at end of file