Generally the finally block is guaranteed to execute.
However, a few cases forces the CLR to shutdown in case of an error. In those cases, the finally block is not run.
One such example is in the presence of a StackOverflow exception.
E.g. in the code below the finally block is not executed.
static void Main(string[] args) {
try {
Foo(1);
} catch {
Console.WriteLine("catch");
} finally {
Console.WriteLine("finally");
}
}
public static int Foo(int i) {
return Foo(i + 1);
}
The other case I am aware of is if a finalizer throws an exception. In that case the process is terminated immediately as well, and thus the guarantee doesn't apply.
The code below illustrates the problem
static void Main(string[] args) {
try {
DisposableType d = new DisposableType();
d.Dispose();
d = null;
GC.Collect();
GC.WaitForPendingFinalizers();
} catch {
Console.WriteLine("catch");
} finally {
Console.WriteLine("finally");
}
}
public class DisposableType : IDisposable {
public void Dispose() {
}
~DisposableType() {
throw new NotImplementedException();
}
}
In both cases the process terminates before both catch and finally.
I'll admit that the examples are very contrived, but they are just made to illustrate the point.
Fortunately neither happens very often.
