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Updating Winforms Label with Timer and Thread, stock app

Gist of it has probably been asked before, but I'm completely lost so I'm looking for some personal guidance. Been trying to make a stock tracker app for funsies using WinForms and the Yahoo API. Trying to get it so you can input a tracker symbol and it will make a new Label that will keep updating itself every so often. However, it keeps giving me error messages about "Cross-thread operation not valid". I've tried to do some googling, but yeah, completely lost. Here is most of the code, hope you guys can make some sense of it.
using System;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;
using YahooFinanceApi;
namespace stockpoging4
{
public partial class Form1 : Form
{
public Form1()
{
System.Globalization.CultureInfo.DefaultThreadCurrentUICulture = System.Globalization.CultureInfo.GetCultureInfo("en-US");
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
using (Prompt prompt = new Prompt("Enter the ticker symbol", "Add ticker"))
{
string result = prompt.Result;
result = result.ToUpper();
if (!string.IsNullOrEmpty(result))
{
do_Things(result);
}
}
}
public async Task<string> getStockPrices(string symbol)
{
try
{
var securities = await Yahoo.Symbols(symbol).Fields(Field.RegularMarketPrice).QueryAsync();
var aapl = securities[symbol];
var price = aapl[Field.RegularMarketPrice];
return symbol + " $" + price;
}
catch
{
return "404";
}
}
public async void do_Things(string result)
{
string price;
Label label = null;
if (label == null)
{
price = await getStockPrices(result);
label = new Label() { Name = result, Text = result + " $" + price };
flowLayoutPanel2.Controls.Add(label);
}
else
{
Thread testThread = new Thread(async delegate ()
{
uiLockingTask();
price = await getStockPrices(result);
label.Text = result + " $" + price;
label.Update();
});
}
System.Timers.Timer timer = new System.Timers.Timer(10000);
timer.Start();
timer.Elapsed += do_Things(results);
}
private void uiLockingTask() {
Thread.Sleep(5000);
}
}
}

Let me point out several things in your implementation.
You subscribe to timer.Elapsed after timer.Start that might be invalid in case of a short-timer interval
The event handler is called in background that's why you continuously get "Cross-thread operation not valid". UI components should be dispatched correctly from background threads, for example, by calling flowLayoutPanel2.BeginInvoke(new Action(() => flowLayoutPanel2.Controls.Add(label))); and label.BeginInvoke(new Action(label.Update)). This change already would fix your exception.
Despite the fact that I would implement this functionality in a different way, here I post slightly changed code that just does exactly what you need with some tweaks.
public partial class Form1 : Form
{
Task _runningTask;
CancellationTokenSource _cancellationToken;
public Form1()
{
System.Globalization.CultureInfo.DefaultThreadCurrentUICulture = System.Globalization.CultureInfo.GetCultureInfo("en-US");
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
using (Prompt prompt = new Prompt("Enter the ticker symbol", "Add ticker"))
{
string result = prompt.Result;
result = result.ToUpper();
if (!string.IsNullOrEmpty(result))
{
do_Things(result);
_cancellationToken = new CancellationTokenSource();
_runningTask = StartTimer(() => do_Things(result), _cancellationToken);
}
}
}
private void onCancelClick()
{
_cancellationToken.Cancel();
}
public async Task<string> getStockPrices(string symbol)
{
try
{
var securities = await Yahoo.Symbols(symbol).Fields(Field.RegularMarketPrice).QueryAsync();
var aapl = securities[symbol];
var price = aapl[Field.RegularMarketPrice];
return symbol + " $" + price;
}
catch
{
return "404";
}
}
private async Task StartTimer(Action action, CancellationTokenSource cancellationTokenSource)
{
try
{
while (!cancellationTokenSource.IsCancellationRequested)
{
await Task.Delay(1000, cancellationTokenSource.Token);
action();
}
}
catch (OperationCanceledException) { }
}
public async void do_Things(string result)
{
var price = await getStockPrices(result);
var label = new Label() { Name = result, Text = result + " $" + price };
flowLayoutPanel2.BeginInvoke(new Action(() => flowLayoutPanel2.Controls.Add(label)));
}
}

A much easier way is using async these days.
Here is a class which triggers an Action every interval:
public class UITimer : IDisposable
{
private readonly CancellationTokenSource _cancellationTokenSource = new CancellationTokenSource();
// use a private function which returns a task
private async Task Innerloop(TimeSpan interval, Action<UITimer> action)
{
try
{
while (!_cancellationTokenSource.IsCancellationRequested)
{
await Task.Delay(interval, _cancellationTokenSource.Token);
action(this);
}
}
catch (OperationCanceledException) { }
}
// the constructor calls the private StartTimer, (the first part will run synchroniously, until the away delay)
public UITimer(TimeSpan interval, Action<UITimer> action) =>
_ = Innerloop(interval, action);
// make sure the while loop will stop.
public void Dispose() =>
_cancellationTokenSource?.Cancel();
}
If you work with dotnet 3.0 or higher, you can use the IAsyncDisposable. With this you're able to await the DisposeAsync method, so you can await the _timerTask to be finished.
And I created a new form with this as code behind:
public partial class Form1 : Form
{
private readonly UITimer _uiTimer;
private int _counter;
public Form1()
{
InitializeComponent();
// setup the time and pass the callback action
_uiTimer = new UITimer(TimeSpan.FromSeconds(1), Update);
}
// the orgin timer is passed as parameter.
private void Update(UITimer timer)
{
// do your thing on the UI thread.
_counter++;
label1.Text= _counter.ToString();
}
private void Form1_FormClosed(object sender, FormClosedEventArgs e)
{
// make sure the time (whileloop) is stopped.
_uiTimer.Dispose();
}
}
The advantage is, that the callback runs on the UI thread but doesn't block it. The await Task.Delay(..) is using a Timer in the background, but posts the rest of the method/statemachine on the UI thread (because the UI thread has a SynchronizaionContext)
Easy but does the trick ;-)

c# Null Value Exception inside lock live data collection/aggregation

Lets suppose I have a single class that has two methods OnBarEvent & Update.
Update: subscribes to a continuous stream of data that comes in asynchronously.
OnBarEvent: will send an event out every n minutes. I am using a timer class to keep track of time and then just have SendEvent attached to the timer class event handler. Essentially, this method will be called whenever N minutes pass
The program will receive asynchronous data via OnEvent which will just summarize the data over a period of time. Once a specified time has passed, then the SendEvent will be called
namespace Common.Aggregator
{
public class BaseTimeAggregator
{
//The last time we emitted a consolidated bar
private DateTime? _lastEmit;
//The minimum timespan between creating new bars.
private readonly TimeSpan? _period;
//The working bar used for aggregating the data
private Bar _workingBar;
//The last working bar
private Bar l_workingBar;
//The Start Time
private DateTime StartTime;
private System.Timers.Timer timer;
public new event EventHandler<Bar> DataConsolidated;
private void OnBarEvent(Object source, System.Timers.ElapsedEventArgs e)
{
if (DateTime.Now > StartTime)
{
if (_workingBar != null)
{
//Console.WriteLine("New Bar: {0}", e.SignalTime);
lock (_workingBar)
{
// Fire Bar
var workingTradeBar = _workingBar as Bar;
if(l_workingBar == null)
{
decimal close_ret = workingTradeBar.Close / workingTradeBar.PreClosePrice;
workingTradeBar.Logret = (decimal)Math.Log((double)close_ret);
}
else
{
// PROBLEM: workingTradeBar can be null here for some reason
decimal value = workingTradeBar.Close / l_workingBar.Close;
workingTradeBar.Logret = (decimal) Math.Log((double)value);
}
l_workingBar = workingTradeBar;
DataConsolidated(this, workingTradeBar);
_workingBar = null;
}
}
}
}
public void Update(Tick data)
{
AggregateBar(data);
}
protected void AggregateBar(Tick data)
{
// Create New Bar
if (_workingBar == null)
{
_workingBar = new Bar(data.LastPrice, data.LastPrice, data.LastPrice, data.LastPrice);
_workingBar.PreClosePrice = data.PreClosePrice;
}
lock (_workingBar)
{
// In the case it got accessed in between
if (_workingBar == null)
{
_workingBar = new Bar(data.LastPrice, data.LastPrice, data.LastPrice, data.LastPrice);
_workingBar.PreClosePrice = data.PreClosePrice;
}
// Update Bar
_workingBar.Update(data.DataType, data.LastPrice, data.BidPrice, data.AskPrice,
data.Volume, data.BidSize, data.AskSize);
}
}
return new DateTime(
dateTime.Year,
dateTime.Month,
dateTime.Day,
hours,
minutes,
seconds,
milliseconds,
dateTime.Kind);
}
}
}
The problem I am running in to is that within the lock, when I access the workingTradeBar variable (see commented code above where "PROBLEM"), there are situations where its null and throws a system.null error. I can't figure out how it can be null given I made a check right before I entered the lock. Also, the only place I set it null is in the same method since I want to start summarizing the data after N minutes passed.
Thanks
This is different from the other question because its purely a multi-threading problem/race condition.

Some remarks:
Event handlers should get the current instance from input params, not from the local variable.
If required need store references to all Bars.
Any method that manipulates the Bars should be synchronized.
As alternative the lock-statement can be used ReaderWriterLockSlim.
namespace Common.Aggregator
{
public class BaseTimeAggregator
{
// REMOVE this field
// --> private Bar _workingBar;
private readonly object _lock = new object();
private readonly Dictionary<int, Bar> _barDictionary = new Dictionary<int, Bar>();
private void OnBarEvent(Object source, System.Timers.ElapsedEventArgs e)
{
var bar = (Bar)source;
// Manipulate with the actual instance defined in 'bar'-variable ..
}
public void Update(Tick data)
{
lock (_lock) {
AggregateBar(data);
}
}
public void Smth_method(int barId)
{
lock (_lock) {
var bar = _barDictionary[uniqueBarId];
// ..
}
}
protected void AggregateBar(Tick data)
{
var uniqueBarId = data.{some param that identify bar};
if (_barDictionary.ContainsKey(uniqueBarId)) {
_barDictionary[uniqueBarId].Update(data.DataType, data.LastPrice, data.BidPrice, data.AskPrice, data.Volume, data.BidSize, data.AskSize);
return;
}
var bar = new Bar(data.LastPrice, data.LastPrice, data.LastPrice, data.LastPrice);
bar.PreClosePrice = data.PreClosePrice;
_barDictionary[uniqueBarId] = bar;
}
}
}

How to Properly Implement BackgroundWorker in WPF with MVVM / ICommand Pattern

I have a small WPF application written primarily following MVVM pattern. The point of the program is to read the lines of a text file, parse the data from them, write that data to a list of objects, then write the data in those objects into a specifically-formatted .CSV file.
Even though I have implemented the BackgroundWorker class itself the same way I always have with other applications, this time I am invoking the RunWorkAsync() method from within the Execute() method of my ICommand. While the final output is correct and the application actually delivers the desired result, the UI STILL locks up while the BackgroundWorker is running.
I have wrapped my BackgroundWorker members and all the logic inside a class named "ReaderWriter" with a constructor that takes my ViewModel as a parameter.
By calling the "StartProcess" method of my ReaderWriter instance, the BackgroundWorker's RunWorkerAsync() is called -- this is where I was hoping it would take over on another thread and do my long-running process of reading the source file, parsing the data, and writing the new file; all while periodically doing ReportProgress() to update the ProgressBar.
Here is the code for my ReaderWriter class:
class ReaderWriter
{
private LogDataViewModel vm { get; set; }
private BackgroundWorker bw { get; set; }
public ReaderWriter(LogDataViewModel viewModel)
{
vm = viewModel;
}
public void StartProcess()
{
bw = new BackgroundWorker();
bw.WorkerReportsProgress = true;
bw.WorkerSupportsCancellation = true;
bw.DoWork += new DoWorkEventHandler(ReadFromSource);
bw.ProgressChanged += new ProgressChangedEventHandler(UpdateProgress_Read);
bw.RunWorkerCompleted += new RunWorkerCompletedEventHandler(Completed_Read);
bw.RunWorkerAsync();
}
private void ReadFromSource(object sender, DoWorkEventArgs e)
{
double records = 0;
string[] lines = File.ReadAllLines(vm.SourcePath);
int lineCount = lines.Length;
double currentLine = 0;
bw.ReportProgress(0, lineCount);
foreach (var line in lines)
{
if (line.Length > 0)
{
string syntax = line.Substring(17, 6);
switch (syntax)
{
case "$WIMDA":
string[] segments = line.Replace(": <- ", ",").Split(',');
vm.LineItems.Add(new LineItem()
{
Time = segments[0],
HgPressure = segments[2],
BarPressure = segments[4],
AirTemp = segments[6],
RelHumidity = segments[10],
TrueWindDir = segments[14],
KnotsWindSpeed = segments[18],
MpsWindSpeed = segments[20]
});
break;
case "$GPGGA":
break;
default:
break;
}
}
currentLine++;
bw.ReportProgress(1, currentLine);
}
using (StreamWriter writer = new StreamWriter(vm.OutputPath))
{
writer.WriteLine($"Time,Pressure(Bar),Pressure(Hg),AirTemp({((vm.ConvertTempSetting) ? "F" : "C")}),RelativeHumidity,TrueWindDirection,WindSpeed(Knots),WindSpeed(M/s)");
foreach (var lineItem in vm.LineItems)
{
writer.WriteLine($"{lineItem.Time},{lineItem.BarPressure},{lineItem.HgPressure},{((vm.ConvertTempSetting) ? Converters.ConvertFromCelcius(Convert.ToDouble(lineItem.AirTemp)).ToString() : lineItem.AirTemp)},{lineItem.RelHumidity},{lineItem.TrueWindDir},{lineItem.KnotsWindSpeed},{lineItem.MpsWindSpeed}");
records++;
}
}
e.Result = records;
}
private void UpdateProgress_Read(object sender, ProgressChangedEventArgs e)
{
vm.IncrementProgress();
switch (Type.GetTypeCode(e.UserState.GetType()))
{
case TypeCode.Double:
vm.IncrementProgress();
break;
case TypeCode.String:
break;
case TypeCode.Int32:
vm.AppendStatus(DateTime.Now, $"{(int)e.UserState} lines parsed from log file");
break;
default:
break;
}
if (vm.IsFirst)
{
vm.ProgressIsVisible = true;
vm.IncrementProgress();
vm.SetMaximum((int)e.UserState);
vm.IsFirst = false;
}
}
private void Completed_Read(object sender, RunWorkerCompletedEventArgs e)
{
if (e.Cancelled)
{
vm.AppendStatus(DateTime.Now, $"Conversion was cancelled by user");
}
else
{
vm.AppendStatus(DateTime.Now, $"{(double)e.Result} records written to {vm.OutputPath}");
}
vm.LineItems.Clear();
}
}
And for my ViewModel:
public class LogDataViewModel : LogDataModel
{
#region Commands
public BeginProcessCommand BeginCommand { get; set; }
public SelectOutputPathCommand OutputCommand { get; set; }
public SelectSourceCommand SourceCommand { get; set; }
public ResetCommand ResetCommand { get; set; }
#endregion
public bool IsFirst { get; set; }
public LogDataViewModel()
{
BeginCommand = new BeginProcessCommand(this);
OutputCommand = new SelectOutputPathCommand(this);
SourceCommand = new SelectSourceCommand(this);
ResetCommand = new ResetCommand(this);
PrepareViewModel();
}
private void PrepareViewModel()
{
ProgressValue = 0;
ProgressMaximum = 0;
ProgressIsVisible = false;
IsFirst = true;
OutputPath = Properties.Settings.Default.RememberedSavePath;
if (LineItems == null) LineItems = new List<LineItem>();
if (StatusActions == null) StatusActions = new ObservableCollection<StatusAction>();
AppendStatus(DateTime.Now, "Initialized Program");
}
}
And lastly, here is the Command:
public class BeginProcessCommand : ICommand
{
LogDataViewModel vm;
public BeginProcessCommand(LogDataViewModel viewModel)
{
vm = viewModel;
}
public event EventHandler CanExecuteChanged
{
add { CommandManager.RequerySuggested += value; }
remove { CommandManager.RequerySuggested -= value; }
}
public bool CanExecute(object parameter)
{
bool result = true;
if (!File.Exists(vm.SourcePath))
result = false;
try
{
if (!Directory.Exists(Path.GetDirectoryName(vm.SourcePath)))
result = false;
}
catch
{
result = false;
}
return result;
}
public void Execute(object parameter)
{
ReaderWriter rw = new ReaderWriter(vm);
rw.StartProcess();
}
}
Any help at this point is very much appreciated, as I've struggled with this for a while now and any attempt to research solutions yield no help for my particular situation. This seems like a fairly unique scenario, but I am hoping we can make it work.
Thank you!

You are using ReportProgress incorrectly and far too often (on every line in the file). It will be being hammered and every call is causing some sort of update in your UI hence locking it up.
ReportProgress is probably easiest to use by passing a percentage to it. I'm not really sure what you are doing in UpdateProgress_Read with the switch. It would be best to only update as you pass a 100th of your total lines.
set your progressBar maximum to 100
ProgressMaximum = 100;
calculate 1% of your total lines
var x = lineCount / 100;
var y = 0;
and only Report progress as you pass each 1%
currentLine++;
if((currentLine % x) == 0)
{
y++;
bw.ReportProgress(y);
}
and change UpdateProgress_Read so it just increments
private void UpdateProgress_Read(object sender, ProgressChangedEventArgs e)
{
vm.IncrementProgress();
}
you'll need to come up with better variable names then x and y! and also work out what to do if you have less than 100 lines in the file.

WebBrowser Control Slideshow Hanging after Running for Extended Time

I'm a fairly new developer and this one has me stumped.
My WinForms application is a slideshow for websites that rotates through a list of URLs, fading-in/out on each transition by using a second form as a "curtain". It's meant to run for an indefinite period of time but consistently hangs on the transition after running for a couple of days.
Form1:
HttpWebResponse response = null;
List<Slide.Doc> sList = null;
bool repeatSlideshow = true;
bool pageLoaded = false;
double curtainAnimStep = 0.05;
int errorCount = 0;
public Form1()
{
InitializeComponent();
CursorShown = false;
this.Visible = true;
this.FormBorderStyle = FormBorderStyle.None;
this.WindowState = FormWindowState.Maximized;
webBrowser1.ScrollBarsEnabled = false;
webBrowser1.ScriptErrorsSuppressed = true;
Slideshow(environment, channel);
}
public void Slideshow(string environment, string channel)
{
while (repeatSlideshow)
{
try
{
sList = Slide.convertJSONToSlide(Slide.getParams(environment, channel));
}
catch (Exception)
{
Form2 curtain = new Form2(curtainAnimStep);
curtain.Show();
waitForFade(curtain, 1);
displayError();
raiseCurtain(curtain, curtainAnimStep);
waitForFade(curtain, 0);
curtain.Dispose();
waitAround(30);
continue;
}
foreach (Slide.Doc s in sList)
{
bool slideWasDisplayed = false;
Form2 curtain = new Form2(curtainAnimStep);
curtain.Show();
waitForFade(curtain, 1);
slideWasDisplayed = displaySlide(s.URL_TEXT);
if (slideWasDisplayed == false)
{
webBrowser1.DocumentText = "<html><body style='background-color: #1C1C1C;'></body></html>";
redrawPage();
}
raiseCurtain(curtain, curtainAnimStep);
waitForFade(curtain, 0);
curtain.Dispose();
if (slideWasDisplayed == true)
{
waitAround(s.DISPLAY_SEC);
}
}
if (errorCount == sList.Count)
{
Form2 curtain = new Form2(curtainAnimStep);
curtain.Show();
waitForFade(curtain, 1);
displayError();
raiseCurtain(curtain, curtainAnimStep);
waitForFade(curtain, 0);
curtain.Dispose();
waitAround(30);
}
errorCount = 0;
Utilities.Web.WebBrowserHelper.WebBrowserHelper.ClearCache();
}
}
public bool displaySlide(string slideUrl)
{
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(slideUrl);
request.Timeout = 1000;
try
{
response = (HttpWebResponse)request.GetResponse();
webBrowser1.Navigate(slideUrl);
redrawPage();
response.Dispose();
return true;
}
catch (WebException)
{
errorCount++;
return false;
}
}
public void redrawPage()
{
while (pageLoaded == false)
{
Application.DoEvents();
}
webBrowser1.Invalidate();
Application.DoEvents();
pageLoaded = false;
}
public void raiseCurtain(Form curtain, double curtainAnimStep)
{
while (curtain.Opacity > 0)
{
curtain.Opacity -= curtainAnimStep;
Application.DoEvents();
System.Threading.Thread.Sleep(10); // How long between shifts in opacity (NOT interval between slides)
}
}
public void waitAround(int duration)
{
DateTime dt2 = DateTime.Now;
while (dt2.AddSeconds(duration) > DateTime.Now)
{
Application.DoEvents();
}
}
public void waitForFade(Form curtain, int finalOpacity)
{
while (curtain.Opacity != finalOpacity)
{
DateTime dt = DateTime.Now;
dt = dt.AddSeconds(1);
while (dt > DateTime.Now)
{
Application.DoEvents();
}
}
}
private void webBrowser1_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
{
pageLoaded = true;
}
Form2:
public Form2(double animStep)
{
InitializeComponent();
this.AnimStep = animStep;
}
public double AnimStep { get; set; }
private async void Form2_Load(object sender, EventArgs e)
{
while (Opacity < 1.0)
{
await Task.Delay(10);
Opacity += AnimStep;
}
Opacity = 1;
}
I've been working on this for a long time, but I have to admit that I genuinely don't even know what I should be looking for at this point.
Could the use of Application.DoEvents be responsible? Leaving them out breaks the application, but I can't figure out an alternative appproach.

Looking at your code (and as indicated by Noseratio) one of the things I advice is to get rid of the need for the DoEvents calls. Just remember that in Windows there is a dedicated UI thread that is used to update the controls on the form. As you are doing a lot of stuff (in loops, calling a bunch of methods) on that same UI thread the Windows controls depends on your cooperation to share some time with them, hence the calls to DoEvents.
I'm going to use a BackgroundWorker and a Timer and WaitHandle to schedule commands that will update the UI from a background thread. With that we do as little as needed on the UI thread.
Form Load
Form1 will only have a webbrowsercontrol and a backgroundworker. A queue will hold the commands that needs to be executed. From the Load event we start the Backgroundworker.
Form2 frm2 = new Form2();
Queue<ICommandExecutor> commands = new Queue<ICommandExecutor>();
private void Form1_Load(object sender, EventArgs e)
{
frm2.Show();
frm2.BringToFront();
commands.Enqueue(new LoadSlideShow(this, frm2, commands));
backgroundWorker1.RunWorkerAsync();
}
BackgroundWorker
The Backgroundworker DoWork event is the engine that runs on it's own background thread. It runs as long as there are commands found in the queue. After fetching a command it's Execute method is fired. If the command supports disposing the Dispose method is called and with that a command is processed and we start over again.
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
while(commands.Count>0)
{
ICommandExecutor cmd = commands.Dequeue();
try
{
cmd.Execute();
// dispose if we can
IDisposable sync = cmd as IDisposable;
if (sync != null)
{
sync.Dispose();
}
}
catch(Exception exp)
{
// add commands here
Trace.WriteLine("error" + exp.Message);
}
}
}
Commands
There is a standard interface available to implement a command pattern. ICommandExecutor has a single method, Execute. We can create different classes that implement this interface. Each class holds its own state and references and it can be as simple as a timer of as complex as loading a new batch of urls to show.
public class ShowSlide:ICommandExecutor
{
string url;
Form1 form;
AutoResetEvent done = new AutoResetEvent(false);
public ShowSlide(Form1 form, string url)
{
this.url = url;
this.form = form;
}
public void Execute()
{
// if we are not on the UI thread...
if (form.InvokeRequired)
{
// ... switch to it...
form.Invoke(new MethodInvoker(Execute));
}
else
{
// .. we are on the UI thread now
// reused from your code
form.displaySlide(url);
}
}
}
Here is a timer. Notice how a Timer class is used and the timerDone waithandle to make the backgroundthread continue work only if the timer has finished when Dispose is called.
public class WaitForSeconds: ICommandExecutor, IDisposable
{
int ms;
System.Threading.Timer timer;
ManualResetEvent timerDone = new ManualResetEvent(false);
public WaitForSeconds(int secs)
{
this.ms = secs * 1000;
}
public void Execute()
{
// use a timer
timer = new System.Threading.Timer(
(state) => timerDone.Set() // signal we are done
);
timerDone.Reset();
timer.Change(this.ms, Timeout.Infinite);
}
public void Dispose()
{
timerDone.WaitOne();
timerDone.Dispose();
timer.Dispose();
}
}
To setup the commands in the correct order we use the following command class implememntation that takes the Command queue, Form1 and Form2 as parameters on its constructor. The Execute command loads all url's to be fed to the webbrowser control. For each url it adds the commands that needs to be executed to the queue. At the end the this instance is added to the queue as well which means the class will be used again if all commands have been processed. The queue will there for never be empty.
public class LoadSlideShow: ICommandExecutor
{
readonly Queue<ICommandExecutor> commands;
readonly Form1 form;
readonly Form2 form2;
public LoadSlideShow(Form1 form, Form2 form2, Queue<ICommandExecutor> cmds)
{
this.form = form;
commands = cmds;
this.form2 = form2;
}
public void Execute()
{
var list = Slide.convertJSONToSlide(null);
foreach (var slide in list)
{
commands.Enqueue(new ShowSlide(form, slide.URL_TEXT));
commands.Enqueue(new WaitForSeconds(1));
//commands.Enqueue(new LowerCurtain(form2));
commands.Enqueue(new WaitForSeconds(slide.DISPLAY_SEC));
//commands.Enqueue(new RaiseCurtain(form2));
}
commands.Enqueue(this);
}
}
This is basically all there is that is needed to get a basic slideshow going.
For the so called curtain we are going to do something similar with Form2 but I'll use the BackgroundWorker_progress event as well.
Form2 the Curtain
Form2 will act as the curtain by changing it's Opacity in a loop. It has it's own backgroundworker:
ManualResetEvent stateChange = new ManualResetEvent(false);
public ManualResetEvent stateChangeDone = new ManualResetEvent(false);
private void Form2_Load(object sender, EventArgs e)
{
backgroundWorker1.RunWorkerAsync();
}
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
while(stateChange.WaitOne())
{
stateChange.Reset();
var progressDone = new AutoResetEvent(false);
int progress = 0;
using(var timer = new System.Threading.Timer(_=>
{
backgroundWorker1.ReportProgress(progress);
progress += 2;
if (progress>=100)
{
progressDone.Set();
}
}, null, 0, 25))
{
progressDone.WaitOne();
}
stateChangeDone.Set();
}
}
The background worker calls ResportProgress with an int indicating its prpgress. That causes the ProgressChanged event to be raised. Based on what state the Curtain needs to be in, we calculate the correct value for the Opacity.
private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
switch(state)
{
case Curtain.Up:
this.Opacity = e.ProgressPercentage / 100.0;
break;
case Curtain.Down:
this.Opacity = (100 - e.ProgressPercentage) / 100.0;
break;
}
}
To get this all started we create two public methods called Up and Down:
enum Curtain
{
Up,
Down
}
Curtain state;
public void Up()
{
state = Curtain.Up;
stateChange.Set();
stateChangeDone.Reset();
}
public void Down()
{
state = Curtain.Down;
stateChange.Set();
stateChangeDone.Reset();
}
With that we are only left with the implementation of the Command classes that will be added to the Command queue and handled by the background worker of Form1:
public class RaiseCurtain:ICommandExecutor, IDisposable
{
readonly Form2 form2;
public RaiseCurtain( Form2 form2)
{
this.form2 = form2;
}
public void Execute()
{
if (form2.InvokeRequired)
{
form2.Invoke(new MethodInvoker(Execute));
}
else
{
form2.BringToFront();
form2.Up();
}
}
public void Dispose()
{
form2.stateChangeDone.WaitOne();
}
}
public class LowerCurtain : ICommandExecutor,IDisposable
{
readonly Form2 form2;
public LowerCurtain(Form2 form2)
{
this.form2 = form2;
}
public void Execute()
{
if (form2.InvokeRequired)
{
form2.Invoke(new MethodInvoker(Execute));
}
else
{
form2.Down();
}
}
public void Dispose()
{
form2.stateChangeDone.WaitOne();
}
}
That is it. We have eliminated the use of DoEvents.
There is one caveat: this doesn't guarantee that the application will stop again after a couple of hours/days. The reason for this is a possible memory-leak in the webbrowser control and in my testing I did see the same effect, a slowly but steadily increasing private memory consumption while the managed memory bytes stayed virtually the same.
As none of the posts provided a definitive answer one option could be to restart your app as indicates in one of the answers here. On the plus side, you can implement this now as a Command class...

How to implement monitor and system.threading for the smokers situation

The problem that I am working on deals with out to use a functional Lock, or monitor structure, to provided exclusive access to only one member on separate threads. Below, is my class definition of the monitor (note that it is different than the actual monitor class given by c# library). What I am trying to do is make pictureboxes appear or disappear on my form.
I have attempted to add in an instance of the form so I can access the individual pictureboxes, however, my program seems to freeze.
namespace SmokersProblem
{
class monitor
{
Form1 form = new Form1();
Random num = new Random();
object obj = new object();
public monitor()
{
}
public void agent(){
form.pictureBox4.Visible = false;
int r = num.Next(1, 4);
if (r == 1)
{
// put lighter and paper on table
smoker1();
}
else if (r == 2)
{
// put lighter and tobacco on table
smoker2();
}
else
{
// put paper and tobacco on table
smoker3();
}
}
public void smoker1()
{
//lock (obj)
//{
form.pictureBox9.Visible = true;
form.pictureBox1.Visible = false;
System.Threading.Thread.Sleep(5000);
//agent();
// }
}
public void smoker2()
{
//lock (obj)
//{
form.pictureBox10.Visible = true;
form.pictureBox3.Visible = false;
System.Threading.Thread.Sleep(5000);
//agent();
//}
}
public void smoker3()
{
//lock (obj)
//{
form.pictureBox11.Visible = true;
form.pictureBox2.Visible = false;
System.Threading.Thread.Sleep(5000);
//agent();
// }
}
}
}
Below is my form code, as you can see here, i try to create three seperate threads, one for each smoker.
namespace SmokersProblem
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
Random rnd = new Random();
int num = rnd.Next(1, 4);
Object obj = new Object();
}
private void Form1_Load(object sender, EventArgs e)
{
}
private void button1_Click(object sender, EventArgs e)
{
pictureBox1.Visible = true;
pictureBox2.Visible = true;
pictureBox3.Visible = true;
pictureBox8.Visible = false;
pictureBox7.Visible = false;
pictureBox6.Visible = false;
monitor one = new monitor();
one.agent();
Thread vone = new Thread(one.smoker1);
Thread two = new Thread(one.smoker2);
Thread three = new Thread(one.smoker3);
vone.Start();
two.Start();
three.Start();
}
}
}

After implementing this, I went looking for the Smoker Thread Problem that it looks like OP is trying to implement. This code should be easily adaptable to that problem.
The reason your UI is freezing is that you're calling one.agent() without putting it in a new thread. one.agent() sleeps, which keeps your UI from processing events.
OK, I've implemented some code to do the smoker problem with labels. Obviously it could be improved, for instance by not coupling the form to the threads.
I put two different locking mechanisms in, and left one commented out.
Essentially, there are three labels that can either be "Smoking" or "Not Smoking". The main UI thread creates three threads:
Smoker1
Smoker2
Smoker3
Each of the threads continually tries to take the lock in a while loop. When they take the lock, they set their label to "Smoking", wait a few seconds, and then set their label to "Not Smoking". This uses thread safe code from this answer.
public partial class Form1 : Form
{
private bool running = false;
public Label OneLabel { get; set; }
public Label TwoLabel { get; set; }
public Label ThreeLabel { get; set; }
private MyMonitor one;
private Thread vone;
private Thread two;
private Thread three;
public Form1()
{
InitializeComponent();
OneLabel = new Label();
OneLabel.Text = "Not Smoking";
OneLabel.Location = new Point(10, 50);
OneLabel.AutoSize = true;
this.Controls.Add(OneLabel);
TwoLabel = new Label();
TwoLabel.Text = "Not Smoking";
TwoLabel.Location = new Point(150, 50);
this.Controls.Add(TwoLabel);
ThreeLabel = new Label();
ThreeLabel.Text = "Not Smoking";
ThreeLabel.Location = new Point(300, 50);
this.Controls.Add(ThreeLabel);
}
private void MainButton_Click(object sender, EventArgs e)
{
if (!running)
{
vone.Start();
two.Start();
three.Start();
MainButton.Text = "Stop";
running = true;
}
else
{
one.RequestStop();
MainButton.Text = "Run";
running = false;
}
}
private void Form1_Load(object sender, EventArgs e)
{
one = new MyMonitor(this);
vone = new Thread(one.Smoker1);
two = new Thread(one.Smoker2);
three = new Thread(one.Smoker3);
}
private void Form1_FormClosing(object sender, FormClosingEventArgs e)
{
if (running)
{
one.RequestStop();
running = false;
}
}
}
class MyMonitor
{
private int x = 1;
private Object obj = new Object();
private Form1 _form;
bool _finished = false;
public MyMonitor(Form1 form)
{
_form = form;
}
public void Smoker1()
{
while (!_finished)
{
//lock (obj)
//{
// _form.OneLabel.SetPropertyThreadSafe(() => _form.OneLabel.Text, "Smoking");
// System.Threading.Thread.Sleep(2000);
// _form.OneLabel.SetPropertyThreadSafe(() => _form.OneLabel.Text, "Not Smoking");
//}
try
{
Monitor.Enter(obj);
try
{
_form.OneLabel.SetPropertyThreadSafe(() => _form.OneLabel.Text, "Smoking");
System.Threading.Thread.Sleep(2000);
_form.OneLabel.SetPropertyThreadSafe(() => _form.OneLabel.Text, "Not Smoking");
}
finally
{
Monitor.Exit(obj);
}
}
catch (SynchronizationLockException SyncEx)
{
Console.WriteLine(SyncEx.Message);
}
}
}
public void Smoker2()
{
while (!_finished)
{
//lock (obj)
//{
// _form.TwoLabel.SetPropertyThreadSafe(() => _form.TwoLabel.Text, "Smoking");
// System.Threading.Thread.Sleep(2000);
// _form.TwoLabel.SetPropertyThreadSafe(() => _form.TwoLabel.Text, "Not Smoking");
//}
try
{
Monitor.Enter(obj);
try
{
_form.TwoLabel.SetPropertyThreadSafe(() => _form.TwoLabel.Text, "Smoking");
System.Threading.Thread.Sleep(2000);
_form.TwoLabel.SetPropertyThreadSafe(() => _form.TwoLabel.Text, "Not Smoking");
}
finally
{
Monitor.Exit(obj);
}
}
catch (SynchronizationLockException SyncEx)
{
Console.WriteLine(SyncEx.Message);
}
}
}
public void Smoker3()
{
while (!_finished)
{
//lock (obj)
//{
// _form.ThreeLabel.SetPropertyThreadSafe(() => _form.ThreeLabel.Text, "Smoking");
// System.Threading.Thread.Sleep(2000);
// _form.ThreeLabel.SetPropertyThreadSafe(() => _form.ThreeLabel.Text, "Not Smoking");
//}
try
{
Monitor.Enter(obj);
try
{
_form.ThreeLabel.SetPropertyThreadSafe(() => _form.ThreeLabel.Text, "Smoking");
System.Threading.Thread.Sleep(2000);
_form.ThreeLabel.SetPropertyThreadSafe(() => _form.ThreeLabel.Text, "Not Smoking");
}
finally
{
Monitor.Exit(obj);
}
}
catch (SynchronizationLockException SyncEx)
{
Console.WriteLine(SyncEx.Message);
}
}
}
public void RequestStop()
{
_finished = true;
}
}
//Thread Safe Extension Method
public static class Extensions
{
private delegate void SetPropertyThreadSafeDelegate<TResult>(Control #this, Expression<Func<TResult>> property, TResult value);
public static void SetPropertyThreadSafe<TResult>(this Control #this, Expression<Func<TResult>> property, TResult value)
{
var propertyInfo = (property.Body as MemberExpression).Member as PropertyInfo;
if (propertyInfo == null ||
!#this.GetType().IsSubclassOf(propertyInfo.ReflectedType) ||
#this.GetType().GetProperty(propertyInfo.Name, propertyInfo.PropertyType) == null)
{
throw new ArgumentException("The lambda expression 'property' must reference a valid property on this Control.");
}
if (#this.InvokeRequired)
{
#this.Invoke(new SetPropertyThreadSafeDelegate<TResult>(SetPropertyThreadSafe), new object[] { #this, property, value });
}
else
{
#this.GetType().InvokeMember(propertyInfo.Name, BindingFlags.SetProperty, null, #this, new object[] { value });
}
}
}

my program seems to freeze
My one.agent() is the part of the code that allows one of the smokers
to be called on, so they can smoke. Why wouldnt I want it in the main
code?
Because you shouldn't be using Sleep() from the main UI thread, which is what happens when you call one.agent() from the Button Click event. When Sleep(5000) is hit, you're telling the forms main UI thread to not do ANYTHING for five seconds, thus the freezing you're seeing.
To fix this, you'd need agent() to execute smoker1(), smoker2(), or smoker3() in a separate thread like you're doing down below.
There are several other problems with the code, however, that must also be addressed before you can "fix" your code...
The next problem lies in you creating a new instance of Form1() inside your monitor() class. This instance of Form1() is not the same one that is visible on your screen. Acting upon it is modifying an invisible form that has never even been shown. To act upon the form that is actually visible on your screen would require you to either (a) pass a reference to it into your monitor() class when you create it, or (b) have your monitor() class raise custom events that Form1() subscribes to, again when it creates monitor().
The last problem lies in you attempting to change UI controls from within a thread other than the main UI thread. This will result in a cross-thread exception (unless you've turn this off, which you shouldn't). There are various ways to overcome this problem, the most basic of which involves using delegates and the Invoke() method of the Form/Control to which you are trying to update.