Console.WriteLine slow

Question

I run through millions of records and sometimes I have to debug using Console.WriteLine to see what is going on.

However, Console.WriteLine

Answer 1

Here is a 7 times faster implementation that bulk-writes to the Console, with a 10 msec delay. The downside is that you must remember to call Console2.Flush() at the end of the program, otherwise you may lose some output.

public static class Console2
{
    private static readonly StringBuilder _sb = new StringBuilder();
    private static volatile CancellationTokenSource _cts;
    private static int _count;

    public static void Write(string value)
    {
        lock (_sb) _sb.Append(value);
        ScheduleFlush();
    }
    public static void Write(string format, params object[] args)
    {
        lock (_sb) _sb.AppendFormat(format, args);
        ScheduleFlush();
    }
    public static void WriteLine(string value)
        => Write(value + Environment.NewLine);

    public static void WriteLine(string format, params object[] args)
        => Write(format + Environment.NewLine, args);

    public static void WriteLine()
        => WriteLine("");

    private static void ScheduleFlush()
    {
        _cts?.Cancel();
        var count = Interlocked.Increment(ref _count);
        if (count % 100 == 0) // periodically flush without cancellation
        {
            var fireAndForget = Task.Run(Flush);
        }
        else
        {
            _cts = new CancellationTokenSource();
            var token = _cts.Token;
            var fireAndForget = Task.Run(async () =>
            {
                await Task.Delay(10, token);
                Flush();
            }, token);
        }
    }

    public static void Flush()
    {
        _cts?.Cancel();
        string text;
        lock (_sb)
        {
            if (_sb.Length == 0) return;
            text = _sb.ToString();
            _sb.Clear();
        }
        Console.Write(text);
    }
}

Usage example:

for (int i = 1; i <= 1000; i++)
{
    Console2.WriteLine($"{DateTime.Now:HH:mm:ss.fff} > Line {i}");
}
Console2.Flush();

Output:

06:27:22.882 > Line 1
06:27:22.882 > Line 2
...
06:27:22.893 > Line 999
06:27:22.893 > Line 1000