Month: May 2008

I have been whining about features that I want in Vala to Jürg. To make up for all the time he lost listening to me I decided to fix two Vala bugs.

The first bug I fixed was using a recursive mutex for lock statements. Code like this will work as expected now:

public class LockMe : GLib.Object { }
public class Executer : GLib.Object {
	LockMe o { get; set; }
	construct { o = new LockMe (); }
	void Internal () {
		lock (o) { }
	}
	public void Method () {
		lock (o) { Internal (); }
	}
}
public class App : GLib.Object {
	static void main (string[] args) {
		Executer e = new Executer ();
		e.Method ();
	}
}

Here’s a gdb session that most GLib programmers will recognize:

Breakpoint 1, 0x08048a87 in executer_Method ()
(gdb) break g_static_rec_mutex_lock
Breakpoint 2 at 0xb7e4d0e6
(gdb) cont
Continuing.
Breakpoint 2, 0xb7e4d0e6 in g_static_rec_mutex_lock ()
   from /usr/lib/libglib-2.0.so.0
(gdb) bt
#0  0xb7e4d0e6 in g_static_rec_mutex_lock () from /usr/lib/libglib-2.0.so.0
#1  0x08048b04 in executer_Method ()
#2  0x08049046 in app_main ()
#3  0x0804908a in main ()
(gdb) cont
Continuing.
Breakpoint 2, 0xb7e4d0e6 in g_static_rec_mutex_lock ()
   from /usr/lib/libglib-2.0.so.0
(gdb) bt
#0  0xb7e4d0e6 in g_static_rec_mutex_lock () from /usr/lib/libglib-2.0.so.0
#1  0x08048a6e in executer_Internal ()
#2  0x08048b0f in executer_Method ()
#3  0x08049046 in app_main ()
#4  0x0804908a in main ()
(gdb) cont
Continuing.
Program exited normally.
(gdb)

The second bug is supporting interfaces for D-Bus services in Vala. It goes like this:

using GLib;
[DBus (name = "org.gnome.TestServer")]
public interface TestServerAPI {
	public abstract int64 ping (string msg);
}
public class TestServer : Object, TestServerAPI {
	int64 counter;
	public int64 ping (string msg) {
		message (msg);
		return counter++;
	}
}
void main () {
	MainLoop loop = new MainLoop (null, false);
	try {
		var conn = DBus.Bus.get (DBus.BusType.SESSION);
		dynamic DBus.Object bus = conn.get_object (
			"org.freedesktop.DBus", "/org/freedesktop/DBus",
			"org.freedesktop.DBus");
		uint request_name_result = bus.RequestName ("org.gnome.TestService", 0);
		if (request_name_result == DBus.RequestNameReply.PRIMARY_OWNER) {
			// start server
			var server = new TestServer ();
			conn.register_object ("/org/gnome/test", server);
			loop.run ();
		} else {  // client
			dynamic DBus.Object test_server_object =
				conn.get_object ("org.gnome.TestService",
					"/org/gnome/test", "org.gnome.TestServer");
			int64 pong = test_server_object.ping ("Hello from Vala");
			message (pong.to_string ());
		}
        } catch (Error foo) { }
}

In Vala you can define interfaces just like in C# and Java. Interfaces imply that you can have class types that implement one or more such interfaces. Vala does not force you to implement its interfaces in Vala. You can also implement them in good-old GObject C.

Here’s a detailed example how you implement a type that implements two Vala interfaces in GObject/C:

Your application used to be single threaded and is consuming a resource that is not thread-safe. You’re splitting your application up into two or more threads. Both threads want to consume the non-thread-safe resource.

In this GNOME-Live item I explain how to use GThreadPool for this.

It’s a wiki so if you find any discrepancies in the sample and or text, just correct them. I’m subscribed so I’ll review it that way.

The GNOME-Live item is done in a similar way to the item about using asynchronous DBus bindings and the AsyncWorker item.