fix(Core/Database): allow reopening a DatabaseWorkerPool after a failed Open() (#27585)

src/common/Threading/PCQueue.h

@@ -102,6 +102,15 @@ public:
         _condition.notify_all();
     }
 
+    // Reopens the queue after Cancel()/Shutdown() so new consumers can be attached.
+    // Callers must make sure the previous consumers have already stopped.
+    void Reset()
+    {
+        std::lock_guard<std::mutex> lock(_queueLock);
+        _cancel = false;
+        _shutdown = false;
+    }
+
 private:
     template<typename E = T>
     typename std::enable_if<std::is_pointer<E>::value>::type DeleteQueuedObject(E& obj)

src/server/database/Database/DatabaseWorkerPool.cpp

@@ -91,6 +91,11 @@ uint32 DatabaseWorkerPool<T>::Open()
     LOG_INFO("sql.driver", "Opening DatabasePool '{}'. Asynchronous connections: {}, synchronous connections: {}.",
         GetDatabaseName(), _async_threads, _synch_threads);
 
+    _queue->Cancel();
+    _connections[IDX_ASYNC].clear();
+    _connections[IDX_SYNCH].clear();
+    _queue->Reset();
+
     uint32 error = OpenConnections(IDX_ASYNC, _async_threads);
 
     if (error)