Question

Does Console.WriteLine block until the output has been written or does it return immediately?

If it does block is there a method of writing asynchronous output to the Console?

Answer 1

Does Console.WriteLine block until the
output has been written or does it
return immediately?

Yes.

If it does block is there a method of
writing asynchronous output to the
Console?

The solution to writing to the console without blocking is surprisingly trivial if you are using .NET 4.0. The idea is to queue up the text values and let a single dedicated thread do the Console.WriteLine calls. The producer-consumer pattern is ideal here because it preserves the temporal ordering that is implicit when using the native Console class. The reason why .NET 4.0 makes this easy is because it has the BlockingCollection class which facilitates the production of a producer-consumer pattern. If you are not using .NET 4.0 then you can get a backport by downloading the Reactive Extensions framework.

public static class NonBlockingConsole
{
  private static BlockingCollection<string> m_Queue = new BlockingCollection<string>();

  static NonBlockingConsole()
  {
    var thread = new Thread(
      () =>
      {
        while (true) Console.WriteLine(m_Queue.Take());
      });
    thread.IsBackground = true;
    thread.Start();
  }

  public static void WriteLine(string value)
  {
    m_Queue.Add(value);
  }
}