font.cs

class Test 
{
	public static void FontTest ()
	{           
		var r=new Random();
		for(int i=0; i<10; i++) {
			new
			System.Threading.Thread((System.Threading.ThreadStart)delegate {
				while(true) {
					Thread.Sleep(r.Next()&63);
					using(var fw=FontTable.Add (UIFont.FromName("Helvetica", 20.0f))) {
						var f = fw.Font;
						Thread.Sleep(100);
						Console.WriteLine(f.Ascender);
					}
				}
			}).Start();
		}
	}
}

// This class is thread-safe.
// Call 'Add' to add an UIFont object to the table, and dispose the value 
// returned from 'Add' when done with it.
public class FontTable 
{
	static Dictionary<IntPtr, int> dic = new Dictionary<IntPtr, int> ();

	public static FontWrapper Add (UIFont obj)
	{
		lock (dic) {
			int count;
			if (dic.TryGetValue (obj.Handle, out count)) {
				count++;
			} else {
				count = 1;
			}
			dic [obj.Handle] = count;
		}

		return new FontWrapper (obj);
	}

	internal static void Remove (UIFont obj)
	{
		lock (dic) {
			int count;
			if (!dic.TryGetValue (obj.Handle, out count))
				throw new InvalidOperationException ("Remove called without a corresponding Add");
			count--;
			if (count == 0) {
				dic.Remove (obj.Handle);
				obj.Dispose ();
			} else {
				dic [obj.Handle] = count;
			}
		}
	}

}
	
public class FontWrapper : IDisposable {
	UIFont font;
	public UIFont Font { get { return font; } }
	public FontWrapper (UIFont font)
	{
		this.font = font;
	}

	public void Dispose ()
	{
		FontTable.Remove (font);
	}
}