Bind to a control socket

So far using a lockfile, which kind of sucks.

We're going to connect to DBus directly, so we'll see
if it can't be used for our purposes in a simple way.

CMakeLists.txt

@@ -45,7 +45,7 @@ vala_precompile (${project_VALA_SOURCES}
 	OUTPUTS project_VALA_C
 	HEADER ${PROJECT_NAME}.h
 	SYMBOLS ${symbols_path}
-	PACKAGES gmodule-2.0 gio-2.0 gtk+-3.0 gee-0.8 sqlite3 x11)
+	PACKAGES posix gmodule-2.0 gio-2.0 gio-unix-2.0 gtk+-3.0 gee-0.8 sqlite3 x11)
 
 # Include Vala sources as header files, so they appear in the IDE
 # but CMake doesn't try to compile them directly

meson.build

@@ -16,10 +16,14 @@ dependencies = [
 	dependency('gtk+-3.0'),
 	dependency('gmodule-2.0'),
 	dependency('gio-2.0'),
+	dependency('gio-unix-2.0'),
 	dependency('gee-0.8'),
 	dependency('sqlite3'),
 	dependency('x11'),
 
+	# Only because of flock
+	meson.get_compiler('vala').find_library('posix'),
+
 	# Ours
 	dependency('xext'),
 	dependency('xextproto'),

wdmtg.vala

@@ -315,6 +315,45 @@ namespace Wdmtg {
       Config.PROJECT_NAME);
     DirUtils.create_with_parents (data_path, 0755);
 
+    // TODO: try exclusivity/invocation either via DBus directly,
+    // or via GApplication or GtkApplication:
+    //  - GtkApplication calls Gtk.init automatically during "startup" signal,
+    //    Gtk.init doesn't get command line args
+    //  - "inhibiting" makes no sense, it can't be used for mere delays
+    //     - actually, the "query-end" signal
+    //     - should check whether it tries to exit cleanly
+    //  - what is the session manager, do I have it?
+    //     - "register-session" looks useful
+    //     - GTK+ keeps the application running as long as it has windows,
+    //       though I want to keep it running forever
+    //        - g_application_hold(), perhaps
+    //  - so maybe just use GApplication, that will provide more control
+
+    // Bind to a control socket, also ensuring only one instance is running
+    var socket_path = Path.build_filename (data_path, "socket");
+
+    Posix.Flock fl = Posix.Flock () {
+      l_type = Posix.F_WRLCK,
+      l_start = 0,
+      l_whence = Posix.SEEK_SET,
+      l_len = 0
+    };
+
+    var lk = FileStream.open (socket_path + ".lock", "w");
+    if (Posix.fcntl (lk.fileno (), Posix.F_SETLK, &fl) < 0)
+      exit_fatal("failed to acquire lock: %s", Posix.errno.to_string ());
+    FileUtils.unlink (socket_path);
+
+    Socket socket;
+    try {
+      socket = new Socket (SocketFamily.UNIX, SocketType.STREAM,
+          SocketProtocol.DEFAULT);
+      socket.bind (new UnixSocketAddress (socket_path), true /* allow_reuse */);
+      socket.listen ();
+    } catch (Error e) {
+      exit_fatal ("%s: %s", socket_path, e.message);
+    }
+
     Sqlite.Database db;
     var db_path = Path.build_filename (data_path, "db.sqlite");
     int rc = Sqlite.Database.open (db_path, out db);