c# - Should IDisposable.Dispose() be made safe to call multiple times?

Question

Should implementations of IDisposable make Dispose() safe to call multiple times? Or the opposite? What approach to most .NET Framework classes take?

Specifically, is it safe to call System.Data.Linq.DataContext.Dispose() multiple times?

The reason I ask is because I am wondering if this extra protection is necessary:

public override void Dispose(bool disposing)
{
    // Extra protection...
    if (this.obj != null)
    {
        this.obj.Dispose();
        this.obj = null;
    }

    // Versus simply...
    this.obj.Dispose();

    base.Dispose(disposing);
}

when disposing IDisposable members of a class, or whether I should just call this.obj.Dispose() without concern for whether it has been previously called.

Answer 1

You should be safe to call it more than once, though you should probably avoid it if you can.

From the MSDN page on IDisposable.Dispose():

If an object's Dispose method is called more than once, the object must ignore all calls after the first one. The object must not throw an exception if its Dispose method is called multiple times.