Multithreading System.Windows.Graphics

Multithreading System.Windows.Graphics

I know of course that I can not draw onto the same Graphics object from
different threads, but is it also true that I can not draw to different
Graphics objects in different threads?
Consider the following console program:
class Program
{
static ThreadDrawer[] drawers;
static void Main(string[] args)
{
int numThreads = 8;
drawers = new ThreadDrawer[numThreads];
for (int i = 0; i < numThreads; i++)
{
drawers[i] = new ThreadDrawer();
drawers[i].Start();
}
for (int i = 0; i < numThreads; i++)
{
drawers[i].Wait();
}
Console.WriteLine("Complete.");
Console.ReadKey();
}
class ThreadDrawer
{
private Thread thread;
private AutoResetEvent resetEvent;
public ThreadDrawer()
{
thread = new Thread(DrawRandomCircles);
resetEvent = new AutoResetEvent(false);
}
public void Start()
{
thread.Start();
}
public void Wait()
{
resetEvent.WaitOne();
}
public void DrawRandomCircles()
{
Random r = new Random(Environment.TickCount);
using (Bitmap b = new Bitmap(1000, 1000))
using (Graphics g = Graphics.FromImage(b))
{
for (int i = 0; i < 100000; i++)
{
g.DrawEllipse(Pens.Red, new Rectangle(r.Next(1000),
r.Next(1000), 200, 200));
}
}
resetEvent.Set();
}
}
}
The program creates a Bitmap in each thread and proceeds to draw random
ellipses on it using a Graphics object, also generated per thread from the
Bitmap.
Due to a requirement to use .NET 2 this is done with Threads and
AutoResetEvents instead of TPL.
The program executes without throwing an exception, but it executes
serially. Using n threads multiplies execution time by n and it is clear
to see using the task manager that only one core is being used.
Important to take note that none of this is tied to any UI element.
What is going on here? Is the Graphics object locking on a static object?