Single instance

src/singleinstance.h

@@ -0,0 +1,23 @@
+// gKeyMapper - keep exactly one GUI: a new start replaces the running instance.
+#ifndef GKEYMAPPER_SINGLEINSTANCE_H
+#define GKEYMAPPER_SINGLEINSTANCE_H
+
+#include <string>
+
+namespace gkeymapper {
+
+// Asks the instance that owns `appId` on the session bus to quit and waits until
+// it has let go of the name, so the caller can become the only instance. The
+// request goes through the app's `quit` action (exported by GApplication as
+// org.gtk.Actions); an instance that does not offer it — an older build — is
+// terminated with SIGTERM instead, after checking that the bus name really
+// belongs to a gkeymapper process.
+//
+// Returns true when the name is free afterwards, which is also the case when
+// nobody owned it. The caller still runs its usual single-instance logic, so a
+// `false` (a hung instance that cannot be closed) only means "no new window".
+bool replace_running_instance(const std::string& appId);
+
+} // namespace gkeymapper
+
+#endif // GKEYMAPPER_SINGLEINSTANCE_H