SL-18721 Viewer shutdown order changes

Same thing as commit cf692c4
which was removed due to shutdown freezes.
Error thread is no longer there so doesn't cause any race sonditions,
was not able to repro any issues so will ask QA to test shutdown

indra/llcommon/threadpool.cpp

@@ -21,11 +21,12 @@
 #include "llevents.h"
 #include "stringize.h"
 
-LL::ThreadPool::ThreadPool(const std::string& name, size_t threads, size_t capacity):
+LL::ThreadPool::ThreadPool(const std::string& name, size_t threads, size_t capacity, bool auto_shutdown):
     super(name),
     mQueue(name, capacity),
     mName("ThreadPool:" + name),
-    mThreadCount(threads)
+    mThreadCount(threads),
+    mAutomaticShutdown(auto_shutdown)
 {}
 
 void LL::ThreadPool::start()
@@ -39,6 +40,13 @@ void LL::ThreadPool::start()
                 run(tname);
             });
     }
+
+    // Some threads might need to run longer than LLEventPumps
+    if (!mAutomaticShutdown)
+    {
+        return;
+    }
+
     // Listen on "LLApp", and when the app is shutting down, close the queue
     // and join the workers.
     LLEventPumps::instance().obtain("LLApp").listen(

indra/llcommon/threadpool.h

@@ -31,7 +31,7 @@ namespace LL
          * Pass ThreadPool a string name. This can be used to look up the
          * relevant WorkQueue.
          */
-        ThreadPool(const std::string& name, size_t threads=1, size_t capacity=1024);
+        ThreadPool(const std::string& name, size_t threads=1, size_t capacity=1024, bool auto_shutdown = true);
         virtual ~ThreadPool();
 
         /**
@@ -66,6 +66,7 @@ namespace LL
         std::string mName;
         size_t mThreadCount;
         std::vector<std::pair<std::string, std::thread>> mThreads;
+        bool mAutomaticShutdown;
     };
 
 } // namespace LL

indra/llwindow/llwindowwin32.cpp

@@ -828,6 +828,7 @@ void LLWindowWin32::close()
 	// Is window is already closed?
 	if (!mWindowHandle)
 	{
+        mWindowThread->close();
 		return;
 	}
 
@@ -4590,7 +4591,7 @@ std::vector<std::string> LLWindowWin32::getDynamicFallbackFontList()
 #endif // LL_WINDOWS
 
 inline LLWindowWin32::LLWindowWin32Thread::LLWindowWin32Thread()
-    : ThreadPool("Window Thread", 1, MAX_QUEUE_SIZE)
+    : ThreadPool("Window Thread", 1, MAX_QUEUE_SIZE, false)
 {
     ThreadPool::start();
 }