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c# coding a timed operation within a for loop

I am writing a piece of code that takes a user through a guided script. The user will have a few seconds to answer before the answer will be displayed.
So far, my code looks like this:
GuidedExercise3 exercise3 = new GuidedExercise3();
string AntonioAnswer = string.Empty; // expected answer
int upperBound = exercise3.Script.Count - 1; // zero-based counting
for(int i = 0; i < upperBound; i += 2)
{
labelInstructions.Text = exercise3.Script[i].TextToSpeak;
AntonioAnswer = exercise3.Script[i+1].TextToSpeak; // answer
SetTimer(AntonioAnswer, txtAntonio); // set timer sending in the answer and the TextBox object.
sysTimer.Start();
}
The odd lines of a List contain the question and the even lines contain the expected answer. My question is how do I display the question for X seconds and then get the user's answer in this WinForms app and then display the answer when the timer elapses, keeping the user from going to the next step of the script but allowing them to answer the question (which is in a Textbox).
I examined this StackOverflow question, but it doesn't match: Implementing a loop using a timer in C#

Here's how I would handle something like this:
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
MoveNextQuestion();
timerAnswer.Interval = 5000;
timerAnswer.Start();
}
private string[] _questionsAndAnswers = new[]
{
"What colour is the sky?",
"Blue",
"What do chickens lay?",
"Eggs",
};
private int _currentIndex = -2;
private void timerAnswer_Tick(object sender, EventArgs e)
{
MoveNextQuestion();
}
private void buttonAnswer_Click(object sender, EventArgs e)
{
MoveNextQuestion();
}
private void MoveNextQuestion()
{
_currentIndex += 2;
if (_currentIndex < _questionsAndAnswers.Length)
{
labelQuestion.Text = _questionsAndAnswers[_currentIndex];
}
else
{
timerAnswer.Stop();
}
}
}

I was able to get this working fairly easily with a BackgroundWorker object. See the following article at MSDN for the exact coding. BackgroundWorker Class. In particular they have two examples in the documentation and the first example is sufficient. The BackgroundWorker class is allowing my UI to continue to accept user input while waiting on a timed answer. It displays the correct answer on the RunWorkerComplete event. So the BackgroundWorker's RunAsync gets called in my for loop.
I've run into the additional issue of the BackgroundWorker not returning control to my loop. I'm looking into that problem separately.

Visit domain model with second thread

My domain model is large tree structure that is modified by application. I would like to implement search in BackgroundWorker (separate thread to not block the UI).
Currently tree structure is implemented with ObservableCollection, that cannot be enumerated while it is modified, so my search will fail if user modifies tree while I am searching through it.
What is elegant solution for this problem? My requirements: do not block user from doing anything (operation should be async), search on separate thread (to speed things up).

Here is one way I can think of that you can achieve what you need:
When writing, use lock, create a copy of the collection, add to the copy and then re-assign the collection to the copy.
Here is some code so you can test the above method. Create a form with a ListBox and a Button. While the list is being searched on a thread, you can add items to the list using the button.
using System;
using System.Collections.Generic;
using System.Threading;
using System.Windows.Forms;
namespace WindowsForms {
public partial class Form1 : Form {
object key = new object();
private List<string> items;
public Form1() {
InitializeComponent();
items = new List<string>();
for( int i = 0; i < 100000; i++ ) {
this.items.Add( i.ToString() );
}
this.listBox1.DataSource = this.items;
}
private void Read() {
foreach( var thisItem in this.items ) {
if (thisItem.ToString() == "100000" ) {
MessageBox.Show( "Found" );
}
else {
Thread.Sleep( 100 );
}
}
}
private void buttonStation2_Click(object sender, EventArgs e) {
lock( this.key ) {
var copy = new List<string>( this.items );
copy.Add( "1000001" );
this.items = copy;
}
}
private void Form1_Shown(object sender, EventArgs e) {
Thread reader = new Thread( Read );
reader.Start();
}
}
}
You may also want to make the collection variable volatile so a cached version is not used and you always get the latest when reading. However, you really need to know what the volatile keyword does before using it so that is why I did not use it in my code and left it up to you to decide. Also, other SO users may chime in and offer their advice using volatile in the comments to this answer if they wish.
private volatile List<string> items;

C# MultiThreading: pool of calculators

I want to have a static (global) pool of calculators which are going to be accessed by a lot of different threads.
After some researching I found out that the elements of Arrays are threadsafe.
I thought that it would be good idea to store the diffrent calculators (amount unknown until runtime) in a static array (calculator[] calculators).
How do I ensure that only one calculator is being used by one calculator?
I read the whole msdn documentation so don't post "only" links please.
I have also thought about a bool array "locked" but I can't find a way to implement this threadsafe.
My code so far:
internal static class Calculators
{
private static Semaphore pool;
private static bool[] locked;
private static calcs[] neuralNetworks;
private static Thread[] threads;
internal static Calculators(){
int number = Globals.Number;
pool = new Semaphore(number, number);
locked = new bool[number];
calcs = new calcs[number];
threads = new Thread[number];
for (int index = 0; index < number; index++)
{
// all neuralNetworks are unlocked by default
locked[index] = false;
// generate one network per "countThreads"
calcs[index] = Globals.CalcObj;
// generate one thread for each neural network
threads[index] = new Thread(new ThreadStart());
}
}
private int WhichCalculators()
{
int index;
for (index = 0; index < countThreads; index++)
{
if (locked[index] == false)
{
locked[index] = true;
return index;
}
}
throw new Exception("Calculators was called, but there weren't any networks unused");
}
}
Code Update:
So should it work, if I call "WhichCalculator()" in this method?
private static void doStuff()
{
pool.WaitOne();
Monitor.Enter(thisLock);
try
{
int whichCalculator = WhichCalculator();
locked[whichCalculator] = true;
lock (calculators[whichCalculator])
{
Monitor.Exit(thisLock);
// do stuff
locked[whichCalculator] = false;
}
}
catch
{
Monitor.Exit(thisLock);
}
//Calculate();
pool.Release();
}
Question 2:
Am I right to assume, that the static constructor is going to be executed as soon as (but before) the first time this class or any member of it is going to be accessed?

Yes you have to use lock. But the array and every instance of calculator again.
If you can fill the array before you start the multithreaded section of your code you need not lock the array as well (only reading doesn't make problems due to the static content) but with resizing the array you need to lock every access to it (writing AND reading).
So your code could look like this:
Calculator calc = null;
lock(calculators)
{
calc = calculators[0];
}
lock(calc)
{
// ... do stuff
}
This way the array isn't longer locked then needed and you can lock the calculator itself.

You can lock your array. That would ensure that every array-operation is executed thread-safe.
To ensure, that each object is only used once at a time you can add a flag to it, like calculator.InUse. If you can't add a flag to the class, you can use an extension method.

C# WPF ModelVisual3D creation takes too long and cannot be done on separate thread

I have a WPF project (VS2010, .NET4.0) in which I create a rather big ModelVisual3D object (read from custom format STL file, process info, create mesh, etc.) This takes about 3-4 sec. to be created and another 2-3 sec. to do a mainViewport.Children.Add(ModelVisual3D).
I do this all in a custom class and call this method:
class My3DModel
{
...
public MyModelVisual3D createModelVisual3D(MyTypes tType, int tNumber)
{
this.myModelVisual3D = new MyModelVisual3D(tType, tNumber);
for (int i = 0, j = 0; i < this.Triangles.Length; i++)
{
this.mesh.Positions.Add(this.Triangles[i].Vertex1);
this.mesh.Positions.Add(this.Triangles[i].Vertex2);
this.mesh.Positions.Add(this.Triangles[i].Vertex3);
this.mesh.Normals.Add(this.Triangles[i].Normal);
this.mesh.Normals.Add(this.Triangles[i].Normal);
this.mesh.Normals.Add(this.Triangles[i].Normal);
this.mesh.TriangleIndices.Add(j++);
this.mesh.TriangleIndices.Add(j++);
this.mesh.TriangleIndices.Add(j++);
}
this.model3DGroup.Children.Add(new GeometryModel3D(this.mesh, material));
this.myModelVisual3D.Content = this.model3DGroup;
return this.myModelVisual3D;
}
}
The return value is also a custom class I created:
class ToothModelVisual3D : ModelVisual3D
{
//VARIABLES
private MyTypes myType;
private int number;
//OPERATORS
public MyTypes MyType
{get { return myType; } set { myType = value; }}
public int Number
{get { return number; } set { number = value;}}
public ToothModelVisual3D() { }
public ToothModelVisual3D(MyTypes tType, int tNumber) { MyType = tType; Number = tNumber; }
}
All I want to do is the following once in the beginning of the program:
{
My3DModel myModel;
myModel = new My3DModel();
myModel.readFileBytes("C:\\registered\\" + 1 + ".stl");
myModel.loadTriangles();
mainViewport.Children.Add(myModel.createModelVisual3D(MyTypes.Sometype, 1);
}
If I do it on the main thread the UI hangs. If I do it on a worker thread and invoke mainViewport.Children.Add(...) it says it cannot access the resourses created on that worker thread. Help?!
From what I understand I've reached a point where I have two threads and resources belonging to each of them (mainViewport => UIThread & myModel => WorkerThread). Neither thread can access directly the other's resource but creating and using myModel on the UIThread makes it hang... All I want to do is have enough responsiveness from the UI, so the user may minimize the program while waiting for it to load the models, nothing more. How can I do that? Is there a way to do all the CPU heavy work on the UIThread, so no resource conflicts arise and have a worker thread that only handles UI for that time?
PS: I've tried with Thread, BackgroundWorker & Task<TResult> classes. Results were similar if not to say the same.
PPS: The full version will load massive models which will load more than 30-40 sec...

I recently came across the same issue when porting an XNA application to WPF.
In my case I partially resolved this by using a background thread to load the positions, normals, and indices from file. Then in that same thread, construct a memory stream containing XAML for the Model3DGroup with the GeometryModel3D and MeshGeometry3D.
Then, in the UI thread, once the memory stream is available, load the model...
Model3DGroup model = System.Windows.Markup.XamlReader.Load(memoryStream) as Model3DGroup;
There is still a delay, but as file access is done in a background thread, it is not as severe.

Sorry for the late answer, but I actually managed to workaround the problem long time ago the following way:
delegate void myDelegate();
private void fileOpenButton_Click(object sender, RoutedEventArgs e)
{
try
{
Thread ViewportLoaderThread = new Thread(loadViewportItemsAsync);
ViewportLoaderThread.IsBackground = true;
ViewportLoaderThread.Start();
}
catch (Exception err) { UtilsProgram.writeErrorLog(err.ToString()); }
}
private void loadViewportItemsAsync()
{
try
{
//TRY to browse for a file
if (!browseForFile()) return;
Dispatcher.Invoke(new Action(() => { myStatusBar.Visibility = System.Windows.Visibility.Visible; menuItemHelpDemo.IsEnabled = false; }), null);
//Load file, unpack, decrypt, load STLs and create ModelGroup3D objects
UtilsDen.DenModel = new DenLoader(UtilsDen.Filename, UtilsDen.Certificate, UtilsDen.PrivateKey, this);
//Load the models to viewport async
myDelegate asyncDel = new myDelegate(sendModelsToViewportAsync);
this.Dispatcher.BeginInvoke(asyncDel, null);
}
catch (Exception err) { MessageBox.Show(UtilsProgram.langDict["msg18"]); UtilsProgram.writeErrorLog(err.ToString()); }
}
private void sendModelsToViewportAsync()
{
for (int i = 0; i < UtilsDen.DenModel.StlFilesCount; i++)
{
//Add the models to MAIN VIEWPORT
ModelVisual3D modelVisual = new ModelVisual3D();
GeometryModel3D geometryModel = new GeometryModel3D();
Model3DGroup modelGroup = new Model3DGroup();
geometryModel = new GeometryModel3D(UtilsDen.DenModel.StlModels[i].MeshGeometry, UtilsDen.Material);
modelGroup.Children.Add(geometryModel);
modelVisual.Content = modelGroup;
mainViewport.Children.Add(toothModelVisual);
}
}
The key was to use the this.Dispatcher.BeginInvoke(asyncDel, null); as it works on the main thread, but does not lag it, because it is executed asynchronously.

Using a delegate still appears to introduce a lag on the UI, a better solution is create the model in a worker thread and then freeze it. The model can then be cloned by the UI thread without the annoying exception. This works for me with models which take 25 seconds or more to load. The only issue I've found with this is that it doesn't work if the model contains a texture.

How to abort specific thread in task parallel library with C#

I have this tricky task I've been trying to achieve for quiet sometime but till now I couldn't think of anything to make it work. anyway here is the scenario...
I have a winform application contains a listview and a button.
the listview contains 1 column which holds the data I need to pass to my functions later on. the column contains lets say 50 rows containing a list of links.
Now I have this function which I'm using to fetch and grab the contents of these links (5 links at a time) with parallel multithreaded mode using (Task Parallel Library):
//List<int> currentWorkingItem //contains the indices of the items in listview
//List<string> URLsList //contains the URLs of the items in listview
Parallel.ForEach(URLsList, new ParallelOptions() { MaxDegreeOfParallelism = 5 }, (url, i, j) =>
{
//show to user this link is currently being downloaded by highlighting the item to green...
this.BeginInvoke((Action)(delegate()
{
//current working item
mylistview.Items[currentWorkingItem[(int)j]].BackColor = green;
}));
//here I download the contents of every link in the list...
string HtmlResponse = GetPageResponse(url);
//do further processing....
});
Now the above code works perfectly... but sometimes I want the user to abort certain thread which is currently running and continue with the rest of the threads in the list... is that achievable in this? if so please help me out.. I'd really appreciate any solution or suggestions..

Try using Task library with cancellation tokens. I find it more elegant and safer approach to do your thing. Here is a quote good example of doing that:
using System;
using System.Threading.Tasks;
using System.Threading;
namespace CancelTask
{
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Press 1 to cancel task");
var cTokenSource = new CancellationTokenSource();
// Create a cancellation token from CancellationTokenSource
var cToken = cTokenSource.Token;
// Create a task and pass the cancellation token
var t1 = Task<int>.Factory.StartNew(()
=> GenerateNumbers(cToken), cToken);
// to register a delegate for a callback when a
// cancellation request is made
cToken.Register(() => cancelNotification());
// If user presses 1, request cancellation.
if (Console.ReadKey().KeyChar == '1')
{
// cancelling task
cTokenSource.Cancel();
}
Console.ReadLine();
}
static int GenerateNumbers(CancellationToken ct)
{
int i;
for (i = 0; i < 10; i++)
{
Console.WriteLine("Method1 - Number: {0}", i);
Thread.Sleep(1000);
// poll the IsCancellationRequested property
// to check if cancellation was requested
if (ct.IsCancellationRequested)
{
break;
}
}
return i;
}
// Notify when task is cancelled
static void cancelNotification()
{
Console.WriteLine("Cancellation request made!!");
}
}
}
Original article could be found here: http://www.dotnetcurry.com/ShowArticle.aspx?ID=493

ok after struggling with this I finally found an efficient and an easy solution for this..
it required me only a hashtable which contains the indicies of the selected items in the listview and a simple bool value. the index is the key and the bool (true, false) is the value. the bool value is like an (on/off) switch indicates that the current loop is aborted or not.. so in order to abort specific thread simple I need to pass the key(the index) of the selected item on my listview to the foreach loop and check if the bool switch is on or off and that's basically it...
so my final code will be like this:
//I declared the hashtable outside the function so I can manage it from different source.
private Hashtable abortingItem;
Now when I click grab button it should fill the hashtable with the selected indicies...
abortingItem = new Hashtable();
for (int i = 0; i < myURLslist.SelectedItems.Count(); i++)
{
//false means don't abort this.. let it run
abortingItem.Add(myURLslist.SelectedItems[i].index, false);
}
//here should be the code of my thread to run the process of grabbing the URLs (the foreach loop)
//..........................
now if I need to abort specific item all I need is to select the item in the listview and click abort button
private void abort_Click(object sender, EventArgs e)
{
if (abortingItem != null)
{
for (int u = 0; u < myURLslist.SelectedIndices.Count; u++)
{
//true means abort this item
abortingItem[myURLslist.SelectedIndices[u]] = true;
}
}
}
In my foreach loop all I need is a simple if else statement to check if the bool is on or off:
//List<int> currentWorkingItem //contains the indices of the items in listview
//List<string> URLsList //contains the URLs of the items in listview
Parallel.ForEach(URLsList, new ParallelOptions() { MaxDegreeOfParallelism = 5 }, (url, i, j) =>
{
//aborting
if (!(bool)abortingItem[currentWorkingItem[(int)j]])
{
//show to user this link is currently being downloaded by highlighting the item to green...
this.BeginInvoke((Action)(delegate()
{
//current working item
mylistview.Items[currentWorkingItem[(int)j]].BackColor = green;
}));
//here I download the contents of every link in the list...
string HtmlResponse = GetPageResponse(url);
//do further processing....
}
else
{
//aborted
}
});
that's simply it..