[v3 linux] initial linux implementation

v3/pkg/application/mainthread_linux.go

@@ -0,0 +1,18 @@
+//go:build linux
+
+package application
+
+func (m *linuxApp) dispatchOnMainThread(id uint) {
+	dispatchOnMainThread(id)
+}
+
+func executeOnMainThread(callbackID uint) {
+	mainThreadFunctionStoreLock.RLock()
+	fn := mainThreadFunctionStore[callbackID]
+	if fn == nil {
+		Fatal("dispatchCallback called with invalid id: %v", callbackID)
+	}
+	delete(mainThreadFunctionStore, callbackID)
+	mainThreadFunctionStoreLock.RUnlock()
+	fn()
+}