在Win32 DLL_PROCESS_DETACH下调用std :: thread :: join函数是否安全？

Question

请查看下面的代码段//在 DLL项目中单个.cpp单元下定义的这些代码块

static std::thread sendMessageThread; // define as local static to cpp
bool  callFunction()
{
   /// Some simple code without spawning any thread or fibers
 }
void WINAPI OnEngineStart()
{
    sendMessageThread = std::thread(callFunction);
};

    BOOL WINAPI DllMain(HINSTANCE hDll, DWORD fdwReason, LPVOID lpvReserved)
    {
        switch (fdwReason)
        {
        case DLL_PROCESS_ATTACH:
            break;
        case DLL_PROCESS_DETACH:
            if (sendMessageThread.joinable())
            {
                sendMessageThread.join(); // is this safe?
            }
            break;
        case DLL_THREAD_ATTACH:
            break;
        case DLL_THREAD_DETACH:
            break;
        }

    return TRUE;
};

如果加载DLL的进程调用 OnEngineStart 函数，那么只要它卸载DLL（使用 FreeLibrary WinAPI函数），  会等到 sendMessageThread 结束吗？并继续DLL卸载程序？