From 932e9815726182b332c52d4d4e8be1e0d2642507 Mon Sep 17 00:00:00 2001
From: rdb <git@rdb.name>
Date: Mon, 12 Aug 2019 19:34:17 +0200
Subject: [PATCH] device: fix deadlock when building with SIMPLE_THREADS=1

GetMessage blocks without yielding, so we need to use an alternative message pump using PeekMessage instead.

Fixes #704
---
 panda/src/device/winInputDeviceManager.cxx | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/panda/src/device/winInputDeviceManager.cxx b/panda/src/device/winInputDeviceManager.cxx
index 232c612186..303400a380 100644
--- a/panda/src/device/winInputDeviceManager.cxx
+++ b/panda/src/device/winInputDeviceManager.cxx
@@ -62,7 +62,9 @@ WinInputDeviceManager() :
   }
 
   // If we have threading enabled, start a thread with a message-only window
-  // loop to listen for input events.
+  // loop to listen for input events.  We can't actually just let this be
+  // handled by the main window loop, because the main window might actually
+  // have been created in a different thread.
 #ifdef HAVE_THREADS
   if (Thread::is_threading_supported()) {
     PT(Thread) thread = new InputThread(this);
@@ -518,10 +520,26 @@ thread_main() {
   }
 
   MSG msg;
+#ifdef SIMPLE_THREADS
+  // In the simple threading case, we can't block the thread waiting for a
+  // message; we yield control back if there are no more messages.
+  while (true) {
+    if (PeekMessage(&msg, nullptr, 0, 0, PM_REMOVE)) {
+      if (msg.message == WM_QUIT) {
+        break;
+      }
+      TranslateMessage(&msg);
+      DispatchMessage(&msg);
+    } else {
+      Thread::force_yield();
+    }
+  }
+#else
   while (GetMessage(&msg, nullptr, 0, 0) > 0) {
     TranslateMessage(&msg);
     DispatchMessage(&msg);
   }
+#endif
 
   if (device_cat.is_debug()) {
     device_cat.debug()