Background
I have a RichTextBox control I am using essentially like a console in my WinForms application. Currently my application-wide logger posts messages using delegates and one of the listeners is this RTB. The logger synchronously sends lots of short (less than 100 char) strings denoting event calls, status messages, operation results, etc.
Posting lots of these short messages to the RTB using BeginInvoke provides UI responsiveness until heavy parallel processing starts logging lots of messages and then the UI starts posting items out of order, or the text is far behind (hundreds of milliseconds). I know this because when the processing slows down or is stopped, the console keeps writing for some time afterwords.
My temporary solution was to invoke the UI synchronously and add a blocking collection buffer. Basically taking the many small items from the Logger and combining them in a stringbuilder to be posted in aggregate to the RTB. The buffer posts items as they come if the UI can keep up, but if the queue gets too high, then it aggregates them and then posts to the UI. The RTB is thus updated piece-meal and looks jumpy when lots of things are being logged.
Question
How can I run a RichTextBox control on its own UI thread to keep other buttons on the same Form responsive during frequent but small append operations? From research, I think I need to run an STA thread and call Application.Run() on it to put the RTB on its own thread, but the examples I found lacked substantive code samples and there don't seem to be any tutorials (perhaps because what I want to do is ill advised?). Also I wasn't sure if there where any pitfalls for a single Control being on its own thread relative to the rest of the Form. (ie. Any issues closing the main form or will the STA thread for the RTB just die with the form closing? Any special disposing? etc.)
This should demonstrate the issue once you add 3 Buttons and a RichTextBox to the form. What I essentially want to accomplish is factoring away the BufferedConsumer by having the RTB on its own thread. Most of this code was hacked out verbatim from my main application, so yes, it is ugly.
using System;
using System.Collections.Concurrent;
using System.Diagnostics;
using System.Drawing;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace WindowsFormsApplication1
{
public partial class Form1 : Form
{
// Fields
private int m_taskCounter;
private static CancellationTokenSource m_tokenSource;
private bool m_buffered = true;
private static readonly object m_syncObject = new object();
// Properties
public IMessageConsole Application_Console { get; private set; }
public BufferedConsumer<StringBuilder, string> Buffer { get; private set; }
public Form1()
{
InitializeComponent();
m_tokenSource = new CancellationTokenSource();
Application_Console = new RichTextBox_To_IMessageConsole(richTextBox1);
Buffer =
new BufferedConsumer<StringBuilder, string>(
p_name: "Console Buffer",
p_appendBuffer: (sb, s) => sb.Append(s),
p_postBuffer: (sb) => Application_Console.Append(sb));
button1.Text = "Start Producer";
button2.Text = "Stop All";
button3.Text = "Toggle Buffering";
button1.Click += (o, e) => StartProducerTask();
button2.Click += (o, e) => CancelAllProducers();
button3.Click += (o, e) => ToggleBufferedConsumer();
}
public void StartProducerTask()
{
var Token = m_tokenSource.Token;
Task
.Factory.StartNew(() =>
{
var ThreadID = Interlocked.Increment(ref m_taskCounter);
StringBuilder sb = new StringBuilder();
var Count = 0;
while (!Token.IsCancellationRequested)
{
Count++;
sb.Clear();
sb
.Append("ThreadID = ")
.Append(ThreadID.ToString("000"))
.Append(", Count = ")
.AppendLine(Count.ToString());
if (m_buffered)
Buffer
.AppendCollection(sb.ToString()); // ToString mimicks real world Logger passing strings and not stringbuilders
else
Application_Console.Append(sb);
Sleep.For(1000);
}
}, Token);
}
public static void CancelAllProducers()
{
lock (m_syncObject)
{
m_tokenSource.Cancel();
m_tokenSource = new CancellationTokenSource();
}
}
public void ToggleBufferedConsumer()
{
m_buffered = !m_buffered;
}
}
public interface IMessageConsole
{
// Methods
void Append(StringBuilder p_message);
}
// http://stackoverflow.com/a/5706085/1718702
public class RichTextBox_To_IMessageConsole : IMessageConsole
{
// Constants
private const int WM_USER = 0x400;
private const int WM_SETREDRAW = 0x000B;
private const int EM_GETEVENTMASK = WM_USER + 59;
private const int EM_SETEVENTMASK = WM_USER + 69;
private const int EM_GETSCROLLPOS = WM_USER + 221;
private const int EM_SETSCROLLPOS = WM_USER + 222;
//Imports
[DllImport("user32.dll")]
private static extern IntPtr SendMessage(IntPtr hWnd, Int32 wMsg, Int32 wParam, ref Point lParam);
[DllImport("user32.dll")]
private static extern IntPtr SendMessage(IntPtr hWnd, Int32 wMsg, Int32 wParam, IntPtr lParam);
// Fields
private RichTextBox m_richTextBox;
private bool m_attachToBottom;
private Point m_scrollPoint;
private bool m_painting;
private IntPtr m_eventMask;
private int m_suspendIndex = 0;
private int m_suspendLength = 0;
public RichTextBox_To_IMessageConsole(RichTextBox p_richTextBox)
{
m_richTextBox = p_richTextBox;
var h = m_richTextBox.Handle;
m_painting = true;
m_richTextBox.DoubleClick += RichTextBox_DoubleClick;
m_richTextBox.MouseWheel += RichTextBox_MouseWheel;
}
// Methods
public void SuspendPainting()
{
if (m_painting)
{
m_suspendIndex = m_richTextBox.SelectionStart;
m_suspendLength = m_richTextBox.SelectionLength;
SendMessage(m_richTextBox.Handle, EM_GETSCROLLPOS, 0, ref m_scrollPoint);
SendMessage(m_richTextBox.Handle, WM_SETREDRAW, 0, IntPtr.Zero);
m_eventMask = SendMessage(m_richTextBox.Handle, EM_GETEVENTMASK, 0, IntPtr.Zero);
m_painting = false;
}
}
public void ResumePainting()
{
if (!m_painting)
{
m_richTextBox.Select(m_suspendIndex, m_suspendLength);
SendMessage(m_richTextBox.Handle, EM_SETSCROLLPOS, 0, ref m_scrollPoint);
SendMessage(m_richTextBox.Handle, EM_SETEVENTMASK, 0, m_eventMask);
SendMessage(m_richTextBox.Handle, WM_SETREDRAW, 1, IntPtr.Zero);
m_painting = true;
m_richTextBox.Invalidate();
}
}
public void Append(StringBuilder p_message)
{
var WatchDogTimer = Stopwatch.StartNew();
var MinimumRefreshRate = 2000;
m_richTextBox
.Invoke((Action)delegate
{
// Last resort cleanup
if (WatchDogTimer.ElapsedMilliseconds > MinimumRefreshRate)
{
// m_richTextBox.Clear(); // Real-world behaviour
// Sample App behaviour
Form1.CancelAllProducers();
}
// Stop Drawing to prevent flickering during append and
// allow Double-Click events to register properly
this.SuspendPainting();
m_richTextBox.SelectionStart = m_richTextBox.TextLength;
m_richTextBox.SelectedText = p_message.ToString();
// Cap out Max Lines and cut back down to improve responsiveness
if (m_richTextBox.Lines.Length > 4000)
{
var NewSet = new string[1000];
Array.Copy(m_richTextBox.Lines, 1000, NewSet, 0, 1000);
m_richTextBox.Lines = NewSet;
m_richTextBox.SelectionStart = m_richTextBox.TextLength;
m_richTextBox.SelectedText = "\r\n";
}
this.ResumePainting();
// AutoScroll down to display newest text
if (m_attachToBottom)
{
m_richTextBox.SelectionStart = m_richTextBox.Text.Length;
m_richTextBox.ScrollToCaret();
}
});
}
// Event Handler
void RichTextBox_DoubleClick(object sender, EventArgs e)
{
// Toggle
m_attachToBottom = !m_attachToBottom;
// Scroll to Bottom
if (m_attachToBottom)
{
m_richTextBox.SelectionStart = m_richTextBox.Text.Length;
m_richTextBox.ScrollToCaret();
}
}
void RichTextBox_MouseWheel(object sender, MouseEventArgs e)
{
m_attachToBottom = false;
}
}
public class BufferedConsumer<TBuffer, TItem> : IDisposable
where TBuffer : new()
{
// Fields
private bool m_disposed = false;
private Task m_consumer;
private string m_name;
private CancellationTokenSource m_tokenSource;
private AutoResetEvent m_flushSignal;
private BlockingCollection<TItem> m_queue;
// Constructor
public BufferedConsumer(string p_name, Action<TBuffer, TItem> p_appendBuffer, Action<TBuffer> p_postBuffer)
{
m_name = p_name;
m_queue = new BlockingCollection<TItem>();
m_tokenSource = new CancellationTokenSource();
var m_token = m_tokenSource.Token;
m_flushSignal = new AutoResetEvent(false);
m_token
.Register(() => { m_flushSignal.Set(); });
// Begin Consumer Task
m_consumer = Task.Factory.StartNew(() =>
{
//Handler
// .LogExceptions(ErrorResponse.SupressRethrow, () =>
// {
// Continuously consumes entries added to the collection, blocking-wait if empty until cancelled
while (!m_token.IsCancellationRequested)
{
// Block
m_flushSignal.WaitOne();
if (m_token.IsCancellationRequested && m_queue.Count == 0)
break;
// Consume all queued items
TBuffer PostBuffer = new TBuffer();
Console.WriteLine("Queue Count = " + m_queue.Count + ", Buffering...");
for (int i = 0; i < m_queue.Count; i++)
{
TItem Item;
m_queue.TryTake(out Item);
p_appendBuffer(PostBuffer, Item);
}
// Post Buffered Items
p_postBuffer(PostBuffer);
// Signal another Buffer loop if more items were Queued during post sequence
var QueueSize = m_queue.Count;
if (QueueSize > 0)
{
Console.WriteLine("Queue Count = " + QueueSize + ", Sleeping...");
m_flushSignal.Set();
if (QueueSize > 10 && QueueSize < 100)
Sleep.For(1000, m_token); //Allow Queue to build, reducing posting overhead if requests are very frequent
}
}
//});
}, m_token, TaskCreationOptions.LongRunning, TaskScheduler.Default);
}
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool p_disposing)
{
if (!m_disposed)
{
m_disposed = true;
if (p_disposing)
{
// Release of Managed Resources
m_tokenSource.Cancel();
m_flushSignal.Set();
m_consumer.Wait();
}
// Release of Unmanaged Resources
}
}
// Methods
public void AppendCollection(TItem p_item)
{
m_queue.Add(p_item);
m_flushSignal.Set();
}
}
public static partial class Sleep
{
public static bool For(int p_milliseconds, CancellationToken p_cancelToken = default(CancellationToken))
{
//p_milliseconds
// .MustBeEqualOrAbove(0, "p_milliseconds");
// Exit immediate if cancelled
if (p_cancelToken != default(CancellationToken))
if (p_cancelToken.IsCancellationRequested)
return true;
var SleepTimer =
new AutoResetEvent(false);
// Cancellation Callback Action
if (p_cancelToken != default(CancellationToken))
p_cancelToken
.Register(() => SleepTimer.Set());
// Block on SleepTimer
var Canceled = SleepTimer.WaitOne(p_milliseconds);
return Canceled;
}
}
}
