maybe fix livelock in zookeeper client

src/Common/ConcurrentBoundedQueue.h

@@ -2,11 +2,21 @@
 
 #include <queue>
 #include <type_traits>
+#include <atomic>
 
 #include <Poco/Mutex.h>
 #include <Poco/Semaphore.h>
 
 #include <common/MoveOrCopyIfThrow.h>
+#include <Common/Exception.h>
+
+namespace DB
+{
+namespace ErrorCodes
+{
+    extern const int LOGICAL_ERROR;
+}
+}
 
 /** A very simple thread-safe queue of limited size.
   * If you try to pop an item from an empty queue, the thread is blocked until the queue becomes nonempty.
@@ -17,9 +27,41 @@ class ConcurrentBoundedQueue
 {
 private:
     std::queue<T> queue;
-    Poco::FastMutex mutex;
+    mutable Poco::FastMutex mutex;
     Poco::Semaphore fill_count;
     Poco::Semaphore empty_count;
+    std::atomic_bool closed = false;
+
+    template <typename... Args>
+    bool tryEmplaceImpl(Args &&... args)
+    {
+        bool emplaced = true;
+
+        {
+            Poco::ScopedLock<Poco::FastMutex> lock(mutex);
+            if (closed)
+                emplaced = false;
+            else
+                queue.emplace(std::forward<Args>(args)...);
+        }
+
+        if (emplaced)
+            fill_count.set();
+        else
+            empty_count.set();
+
+        return emplaced;
+    }
+
+    void popImpl(T & x)
+    {
+        {
+            Poco::ScopedLock<Poco::FastMutex> lock(mutex);
+            detail::moveOrCopyIfThrow(std::move(queue.front()), x);
+            queue.pop();
+        }
+        empty_count.set();
+    }
 
 public:
     explicit ConcurrentBoundedQueue(size_t max_fill)
@@ -30,91 +72,75 @@ public:
     void push(const T & x)
     {
         empty_count.wait();
-        {
-            Poco::ScopedLock<Poco::FastMutex> lock(mutex);
-            queue.push(x);
-        }
-        fill_count.set();
+        if (!tryEmplaceImpl(x))
+            throw DB::Exception(DB::ErrorCodes::LOGICAL_ERROR, "tryPush/tryEmplace must be used with close()");
     }
 
     template <typename... Args>
     void emplace(Args &&... args)
     {
         empty_count.wait();
-        {
-            Poco::ScopedLock<Poco::FastMutex> lock(mutex);
-            queue.emplace(std::forward<Args>(args)...);
-        }
-        fill_count.set();
+        if (!tryEmplaceImpl(std::forward<Args>(args)...))
+            throw DB::Exception(DB::ErrorCodes::LOGICAL_ERROR, "tryPush/tryEmplace must be used with close()");
     }
 
     void pop(T & x)
     {
         fill_count.wait();
-        {
-            Poco::ScopedLock<Poco::FastMutex> lock(mutex);
-            detail::moveOrCopyIfThrow(std::move(queue.front()), x);
-            queue.pop();
-        }
-        empty_count.set();
+        popImpl(x);
     }
 
     bool tryPush(const T & x, UInt64 milliseconds = 0)
     {
-        if (empty_count.tryWait(milliseconds))
-        {
-            {
-                Poco::ScopedLock<Poco::FastMutex> lock(mutex);
-                queue.push(x);
-            }
-            fill_count.set();
-            return true;
-        }
-        return false;
+        if (!empty_count.tryWait(milliseconds))
+            return false;
+
+        return tryEmplaceImpl(x);
     }
 
     template <typename... Args>
     bool tryEmplace(UInt64 milliseconds, Args &&... args)
     {
-        if (empty_count.tryWait(milliseconds))
-        {
-            {
-                Poco::ScopedLock<Poco::FastMutex> lock(mutex);
-                queue.emplace(std::forward<Args>(args)...);
-            }
-            fill_count.set();
-            return true;
-        }
-        return false;
+        if (!empty_count.tryWait(milliseconds))
+            return false;
+
+        return tryEmplaceImpl(std::forward<Args>(args)...);
     }
 
     bool tryPop(T & x, UInt64 milliseconds = 0)
     {
-        if (fill_count.tryWait(milliseconds))
-        {
-            {
-                Poco::ScopedLock<Poco::FastMutex> lock(mutex);
-                detail::moveOrCopyIfThrow(std::move(queue.front()), x);
-                queue.pop();
-            }
-            empty_count.set();
-            return true;
-        }
-        return false;
+        if (!fill_count.tryWait(milliseconds))
+            return false;
+
+        popImpl(x);
+        return true;
     }
 
-    size_t size()
+    size_t size() const
     {
         Poco::ScopedLock<Poco::FastMutex> lock(mutex);
         return queue.size();
     }
 
-    size_t empty()
+    size_t empty() const
     {
         Poco::ScopedLock<Poco::FastMutex> lock(mutex);
         return queue.empty();
     }
 
+    /// Forbids to push new elements to queue.
+    /// Returns false if queue was not closed before call, returns true if queue was already closed.
+    bool close()
+    {
+        Poco::ScopedLock<Poco::FastMutex> lock(mutex);
+        return closed.exchange(true);
+    }
+
+    bool isClosed() const
+    {
+        return closed.load();
+    }
+
     void clear()
     {
         while (fill_count.tryWait(0))

src/Common/ZooKeeper/ZooKeeperImpl.cpp

@@ -539,7 +539,7 @@ void ZooKeeper::sendThread()
 
     try
     {
-        while (!expired)
+        while (!requests_queue.isClosed())
         {
             auto prev_bytes_sent = out->count();
 
@@ -571,7 +571,7 @@ void ZooKeeper::sendThread()
                         info.request->has_watch = true;
                     }
 
-                    if (expired)
+                    if (requests_queue.isClosed())
                     {
                         break;
                     }
@@ -616,7 +616,7 @@ void ZooKeeper::receiveThread()
     try
     {
         Int64 waited = 0;
-        while (!expired)
+        while (!requests_queue.isClosed())
         {
             auto prev_bytes_received = in->count();
 
@@ -639,7 +639,7 @@ void ZooKeeper::receiveThread()
 
             if (in->poll(max_wait))
             {
-                if (expired)
+                if (requests_queue.isClosed())
                     break;
 
                 receiveEvent();
@@ -839,12 +839,10 @@ void ZooKeeper::finalize(bool error_send, bool error_receive)
 
     auto expire_session_if_not_expired = [&]
     {
-        std::lock_guard lock(push_request_mutex);
-        if (!expired)
-        {
-            expired = true;
+        /// No new requests will appear in queue after close()
+        bool was_already_closed = requests_queue.close();
+        if (!was_already_closed)
             active_session_metric_increment.destroy();
-        }
     };
 
     try
@@ -1017,17 +1015,15 @@ void ZooKeeper::pushRequest(RequestInfo && info)
             }
         }
 
-        /// We must serialize 'pushRequest' and 'finalize' (from sendThread, receiveThread) calls
-        ///  to avoid forgotten operations in the queue when session is expired.
-        /// Invariant: when expired, no new operations will be pushed to the queue in 'pushRequest'
-        ///  and the queue will be drained in 'finalize'.
-        std::lock_guard lock(push_request_mutex);
-
-        if (expired)
+        if (requests_queue.isClosed())
             throw Exception("Session expired", Error::ZSESSIONEXPIRED);
 
         if (!requests_queue.tryPush(std::move(info), operation_timeout.totalMilliseconds()))
+        {
+            if (requests_queue.isClosed())
+                throw Exception("Session expired", Error::ZSESSIONEXPIRED);
             throw Exception("Cannot push request to queue within operation timeout", Error::ZOPERATIONTIMEOUT);
+        }
     }
     catch (...)
     {

src/Common/ZooKeeper/ZooKeeperImpl.h

@@ -121,7 +121,7 @@ public:
 
 
     /// If expired, you can only destroy the object. All other methods will throw exception.
-    bool isExpired() const override { return expired; }
+    bool isExpired() const override { return requests_queue.isClosed(); }
 
     /// Useful to check owner of ephemeral node.
     int64_t getSessionID() const override { return session_id; }
@@ -205,11 +205,9 @@ private:
     int64_t session_id = 0;
 
     std::atomic<XID> next_xid {1};
-    std::atomic<bool> expired {false};
     /// Mark session finalization start. Used to avoid simultaneous
     /// finalization from different threads. One-shot flag.
     std::atomic<bool> finalization_started {false};
-    std::mutex push_request_mutex;
 
     using clock = std::chrono::steady_clock;
 
@@ -223,7 +221,7 @@ private:
 
     using RequestsQueue = ConcurrentBoundedQueue<RequestInfo>;
 
-    RequestsQueue requests_queue{1};
+    RequestsQueue requests_queue{1024};
     void pushRequest(RequestInfo && info);
 
     using Operations = std::map<XID, RequestInfo>;