Alternative approach to thread-safe Application::quit

Signed-off-by: falkTX <falktx@falktx.com>

dgl/src/Application.cpp

@@ -50,7 +50,7 @@ void Application::quit()
 
 bool Application::isQuiting() const noexcept
 {
-    return pData->isQuitting;
+    return pData->isQuitting || pData->isQuittingInNextCycle;
 }
 
 void Application::addIdleCallback(IdleCallback* const callback)

dgl/src/ApplicationPrivateData.cpp

@@ -25,6 +25,24 @@ START_NAMESPACE_DGL
 
 typedef std::list<DGL_NAMESPACE::Window*>::reverse_iterator WindowListReverseIterator;
 
+static ThreadHandle getCurrentThreadHandle() noexcept
+{
+#ifdef DISTRHO_OS_WINDOWS
+    return GetCurrentThread();
+#else
+    return pthread_self();
+#endif
+}
+
+static bool isThisMainThread(const ThreadHandle mainThreadHandle) noexcept
+{
+#ifdef DISTRHO_OS_WINDOWS
+    return GetCurrentThread() == mainThreadHandle; // IsGUIThread ?
+#else
+    return pthread_equal(getCurrentThreadHandle(), mainThreadHandle) != 0;
+#endif
+}
+
 // --------------------------------------------------------------------------------------------------------------------
 
 Application::PrivateData::PrivateData(const bool standalone)
@@ -35,6 +53,7 @@ Application::PrivateData::PrivateData(const bool standalone)
       isQuittingInNextCycle(false),
       isStarting(true),
       visibleWindows(0),
+      mainThreadHandle(getCurrentThreadHandle()),
       windows(),
       idleCallbacks()
 {
@@ -108,10 +127,13 @@ void Application::PrivateData::quit()
 {
     DISTRHO_SAFE_ASSERT_RETURN(isStandalone,);
 
-    if (! isQuittingInNextCycle)
+    if (! isThisMainThread(mainThreadHandle))
     {
-        isQuittingInNextCycle = true;
-        return;
+        if (! isQuittingInNextCycle)
+        {
+            isQuittingInNextCycle = true;
+            return;
+        }
     }
 
     isQuitting = true;

dgl/src/ApplicationPrivateData.hpp

@@ -21,6 +21,15 @@
 
 #include <list>
 
+#ifdef DISTRHO_OS_WINDOWS
+# include <winsock2.h>
+# include <windows.h>
+typedef HANDLE ThreadHandle;
+#else
+# include <pthread.h>
+typedef pthread_t ThreadHandle;
+#endif
+
 typedef struct PuglWorldImpl PuglWorld;
 
 START_NAMESPACE_DGL
@@ -49,6 +58,9 @@ struct Application::PrivateData {
         If 0->1, application is starting. If 1->0, application is quitting/stopping. */
     uint visibleWindows;
 
+    /** Handle that identifies the main thread. Used to check if calls belong to current thread or not. */
+    ThreadHandle mainThreadHandle;
+
     /** List of windows for this application. Only used during `close`. */
     std::list<DGL_NAMESPACE::Window*> windows;