Core/Database: Change database async thread shutdown to fix some corner cases leading to servers being stuck on shutdown (for example with exit() call)

(cherry picked from commit 11a832fa8ba2362a0efcde601e7225582326e0da)

2 files changed, 15 insertions, 7 deletions

diff --git a/src/server/database/Database/MySQLConnection.cpp b/src/server/database/Database/MySQLConnection.cpp
index 7efe93c34f7..3437fc55b1d 100644
--- a/src/server/database/Database/MySQLConnection.cpp
+++ b/src/server/database/Database/MySQLConnection.cpp
@@ -47,6 +47,12 @@ MySQLConnectionInfo::MySQLConnectionInfo(std::string const& infoString)
         ssl.assign(tokens[5]);
 }
 
+struct MySQLConnection::WorkerThread
+{
+    std::thread ThreadHandle;
+    boost::asio::executor_work_guard<Trinity::Asio::IoContext::Executor> WorkGuard;
+};
+
 MySQLConnection::MySQLConnection(MySQLConnectionInfo& connInfo, ConnectionFlags connectionFlags) :
 m_reconnecting(false),
 m_prepareError(false),
@@ -66,7 +72,8 @@ void MySQLConnection::Close()
     // Stop the worker thread before the statements are cleared
     if (m_workerThread)
     {
-        m_workerThread->join();
+        m_workerThread->WorkGuard.reset();
+        m_workerThread->ThreadHandle.join();
         m_workerThread.reset();
     }
 
@@ -444,18 +451,18 @@ uint32 MySQLConnection::GetLastError()
 
 void MySQLConnection::StartWorkerThread(Trinity::Asio::IoContext* context)
 {
-    m_workerThread = std::make_unique<std::thread>([context]
-    {
-        boost::asio::executor_work_guard executorWorkGuard = boost::asio::make_work_guard(context->get_executor());
+    boost::asio::executor_work_guard executorWorkGuard = boost::asio::make_work_guard(context->get_executor()); // construct guard before thread starts running
 
-        context->run();
+    m_workerThread = std::make_unique<WorkerThread>(WorkerThread{
+        .ThreadHandle = std::thread([context] { context->run(); }),
+        .WorkGuard = std::move(executorWorkGuard)
     });
 }
 
 std::thread::id MySQLConnection::GetWorkerThreadId() const
 {
     if (m_workerThread)
-        return m_workerThread->get_id();
+        return m_workerThread->ThreadHandle.get_id();
 
     return {};
 }
diff --git a/src/server/database/Database/MySQLConnection.h b/src/server/database/Database/MySQLConnection.h
index db8ff40a2ab..2b9a96e6a28 100644
--- a/src/server/database/Database/MySQLConnection.h
+++ b/src/server/database/Database/MySQLConnection.h
@@ -104,7 +104,8 @@ class TC_DATABASE_API MySQLConnection
     private:
         bool _HandleMySQLErrno(uint32 errNo, uint8 attempts = 5);
 
-        std::unique_ptr<std::thread> m_workerThread;        //!< Core worker thread.
+        struct WorkerThread;
+        std::unique_ptr<WorkerThread> m_workerThread;       //!< Core worker thread.
         MySQLHandle*          m_Mysql;                      //!< MySQL Handle.
         MySQLConnectionInfo&  m_connectionInfo;             //!< Connection info (used for logging)
         ConnectionFlags       m_connectionFlags;            //!< Connection flags (for preparing relevant statements)