SL-18721 Window shutdown adjustments

On viewer shutdown
1. Instead of handling potential WM_* messages viewer is no longer
equiped to handle drop window's pointer and expect only WM_DESTROY
2. Detach thread and let it do its own thing, thread will delete itself
3. Reverts commit 1161262029f9619fb02d81575382b64d82d9cd09

Reason for the change: window was closing too early (as son as "LLApp"
status changes) without proper cleanup

2 files changed, 37 insertions, 67 deletions

diff --git a/indra/llcommon/threadpool.h b/indra/llcommon/threadpool.h
index 74056aea17..b8be7bb81a 100644
--- a/indra/llcommon/threadpool.h
+++ b/indra/llcommon/threadpool.h
@@ -55,7 +55,7 @@ namespace LL
          * ThreadPool listens for application shutdown messages on the "LLApp"
          * LLEventPump. Call close() to shut down this ThreadPool early.
          */
-        virtual void close();
+        void close();
 
         std::string getName() const { return mName; }
         size_t getWidth() const { return mThreads.size(); }
diff --git a/indra/llwindow/llwindowwin32.cpp b/indra/llwindow/llwindowwin32.cpp
index 54e5f43e87..3ffc7d3354 100644
--- a/indra/llwindow/llwindowwin32.cpp
+++ b/indra/llwindow/llwindowwin32.cpp
@@ -351,10 +351,9 @@ struct LLWindowWin32::LLWindowWin32Thread : public LL::ThreadPool
     LLWindowWin32Thread();
 
     void run() override;
-    void close() override;
 
     // closes queue, wakes thread, waits until thread closes
-    void wakeAndDestroy();
+    bool wakeAndDestroy();
 
     void glReady()
     {
@@ -425,6 +424,7 @@ struct LLWindowWin32::LLWindowWin32Thread : public LL::ThreadPool
     // *HACK: Attempt to prevent startup crashes by deferring memory accounting
     // until after some graphics setup. See SL-20177. -Cosmic,2023-09-18
     bool mGLReady = false;
+    bool mDeleteOnExit = false;
     // best guess at available video memory in MB
     std::atomic<U32> mAvailableVRAM;
 
@@ -997,7 +997,11 @@ void LLWindowWin32::close()
     mhDC = NULL;
     mWindowHandle = NULL;
     
-    mWindowThread->wakeAndDestroy();
+    if (mWindowThread->wakeAndDestroy())
+    {
+        // thread will delete itselfs once done
+        mWindowThread = NULL;
+    }
 }
 
 BOOL LLWindowWin32::isValid()
@@ -3104,10 +3108,17 @@ LRESULT CALLBACK LLWindowWin32::mainWindowProc(HWND h_wnd, UINT u_msg, WPARAM w_
         break;
         }
     }
-    else
+    else // (NULL == window_imp)
     {
-        // (NULL == window_imp)
-        LL_DEBUGS("Window") << "No window implementation to handle message with, message code: " << U32(u_msg) << LL_ENDL;
+        if (u_msg == WM_DESTROY)
+        {
+            PostQuitMessage(0);  // Posts WM_QUIT with an exit code of 0
+            return 0;
+        }
+        else
+        {
+            LL_DEBUGS("Window") << "No window implementation to handle message with, message code: " << U32(u_msg) << LL_ENDL;
+        }
     }
 
     // pass unhandled messages down to Windows
@@ -4563,25 +4574,11 @@ U32 LLWindowWin32::getAvailableVRAMMegabytes()
 #endif // LL_WINDOWS
 
 inline LLWindowWin32::LLWindowWin32Thread::LLWindowWin32Thread()
-    : LL::ThreadPool("Window Thread", 1, MAX_QUEUE_SIZE, true /*should be false, temporary workaround for SL-18721*/)
+    : LL::ThreadPool("Window Thread", 1, MAX_QUEUE_SIZE, false)
 {
     LL::ThreadPool::start();
 }
 
-void LLWindowWin32::LLWindowWin32Thread::close()
-{
-    if (!mQueue->isClosed())
-    {
-        LL_WARNS() << "Closing window thread without using destroy_window_handler" << LL_ENDL;
-        LL::ThreadPool::close();
-
-        // Workaround for SL-18721 in case window closes too early and abruptly
-        LLSplashScreen::show();
-        LLSplashScreen::update("..."); // will be updated later
-    }
-}
-
-
 /**
  * LogChange is to log changes in status while trying to avoid spamming the
  * log with repeated messages, especially in a tight loop. It refuses to log
@@ -4926,14 +4923,19 @@ void LLWindowWin32::LLWindowWin32Thread::run()
     }
 
     cleanupDX();
+
+    if (mDeleteOnExit)
+    {
+        delete this;
+    }
 }
 
-void LLWindowWin32::LLWindowWin32Thread::wakeAndDestroy()
+bool LLWindowWin32::LLWindowWin32Thread::wakeAndDestroy()
 {
     if (mQueue->isClosed())
     {
-        LL_WARNS() << "Tried to close Queue. Win32 thread Queue already closed." << LL_ENDL;
-        return;
+        LL_WARNS() << "Tried to close Queue. Win32 thread Queue already closed." <<LL_ENDL;
+        return false;
     }
 
     // Make sure we don't leave a blank toolbar button.
@@ -4972,6 +4974,15 @@ void LLWindowWin32::LLWindowWin32Thread::wakeAndDestroy()
              mGLReady = false;
          });
 
+    mDeleteOnExit = true;
+    SetWindowLongPtr(old_handle, GWLP_USERDATA, NULL);
+
+    // Let thread finish on its own and don't block main thread.
+    for (auto& pair : mThreads)
+    {
+        pair.second.detach();
+    }
+
     LL_DEBUGS("Window") << "Closing window's pool queue" << LL_ENDL;
     mQueue->close();
 
@@ -4986,49 +4997,8 @@ void LLWindowWin32::LLWindowWin32Thread::wakeAndDestroy()
         PostMessage(old_handle, WM_DUMMY_, wparam, 0x1337);
     }
 
-    // There are cases where window will refuse to close,
-    // can't wait forever on join, check state instead
-    LLTimer timeout;
-    timeout.setTimerExpirySec(2.0);
-    while (!getQueue().done() && !timeout.hasExpired() && mWindowHandleThrd)
-    {
-        ms_sleep(100);
-    }
-
-    if (getQueue().done() || mWindowHandleThrd == NULL)
-    {
-        // Window is closed, started closing or is cleaning up
-        // now wait for our single thread to die.
-        if (mWindowHandleThrd)
-        {
-            LL_INFOS("Window") << "Window is closing, waiting on pool's thread to join, time since post: " << timeout.getElapsedSeconds() << "s" << LL_ENDL;
-        }
-        else
-        {
-            LL_DEBUGS("Window") << "Waiting on pool's thread, time since post: " << timeout.getElapsedSeconds() << "s" << LL_ENDL;
-        }
-        for (auto& pair : mThreads)
-        {
-            pair.second.join();
-        }
-    }
-    else
-    {
-        // Something suspended window thread, can't afford to wait forever
-        // so kill thread instead
-        // Ex: This can happen if user starts dragging window arround (if it
-        // was visible) or a modal notification pops up
-        LL_WARNS("Window") << "Window is frozen, couldn't perform clean exit" << LL_ENDL;
-
-        for (auto& pair : mThreads)
-        {
-            // very unsafe
-            TerminateThread(pair.second.native_handle(), 0);
-            pair.second.detach();
-            cleanupDX();
-        }
-    }
     LL_DEBUGS("Window") << "thread pool shutdown complete" << LL_ENDL;
+    return true;
 }
 
 void LLWindowWin32::post(const std::function<void()>& func)