Develop Reference

Refreshing SUDOKU solver

I made a SUDOKU solver. When is solve a number it should be written to the screen but it's happen only when the solver is done. Why only then the screen is refreshing when it is done?
ii is the number, jj is the row, ll is the column
private void MainForm_Load(object sender, EventArgs e)
{
...
Thread tr2 = new Thread(adatbszal);
tr2.Start();
}
private void adatbszal()
{
while (fut)
{
Thread.Sleep(10);
if (adat[jj, ll] != 0)
{
SetText(jj, ll, adat[jj, ll].ToString());
}
else
{
SetText(jj, ll, "");
}
}
}
private void SetText(int i, int j, string adat2)
{
if (adatB[i,j].InvokeRequired)
{
valami d = new valami(SetText);
Invoke(d, new object[] { i, j, adat2 });
}
else
{
adatB[i, j].Text = adat2;
}
}
...
Thread th = new Thread(solver);
th.Start();
full project: https://drive.google.com/file/d/1sZTA4Ledfwl3romBY2UTvUoU9MZfY35g/view?usp=sharing

I would suggest putting a breakpoint on Invoke(d, new object[] { i, j, adat2 }); to verify that it is being reached, and when it is, add a breakpoint to if (adatB[i,j].InvokeRequired) before stepping, then make sure that the same parameters are being received to verify that the Invoke is triggering SetText as expected. (Step Into would be simpler, but I'm not sure that would work on an Invoke Line.)
If all that is working, then check if the display updates then adatB[i, j].Text = adat2; executes in the debugger.

I think your code is updating the display like you want it to, but it's not working properly in other regards. In one of my tests, it is just setting the first cell to "2" over and over again, so you won't see any change. You need to verify that the code is doing the right work before you verify that the display is updating properly. I think you may see many problems from having 3 threads running simultaneously which can all update or read the same global values when other threads are assuming these values (like jj) are not changing between lines. I would suggest not sharing data between threads if you are not very experienced with multi-threaded programming. Perhaps you can re-implement this as a single-threaded program that calls an update function periodically instead.

How can I start and stop a looping thread in ASP MVC 4?

I'm working on a simple application that hooks into Wirecast, a streaming software, and forces it to change it source every X seconds. I thought that this would be a good way for me to learn ASP MVC 4, but I'm not very familiar with it and have run into some problems. I'd like the user to be able to enable and disable the loop by selecting a radio button and hitting "Apply", or something similar. Starting the loop works fine, but I'm unable to end it. The way I'm trying to do this is to create a thread that runs the loop and start the thread when the user selects the "Enable Loop" radio button, and abort the thread when they select "Disable Loop". I can see that the Abort method is getting called, but the thread is still running. The relevant code is below:
public Thread loop = new Thread(new ThreadStart(ThreadLoop));
[HttpPost]
public ActionResult Loop(Models.Loop model)
{
if (model.doLoop == true)
{
loop.Start();
}
else
{
loop.Abort();
}
return View();
}
public static void ThreadLoop()
{
object oWirecast = GetWirecast();
object oDocument = Late.Invoke(oWirecast, "DocumentByIndex", 1);
object oNormalLayer = Late.Invoke(oDocument, "LayerByName", "normal");
shotCount = (int)Late.Invoke(oNormalLayer, "ShotCount");
int shot = 0;
while (true)
{
shot = shot + 1;
if (shot > shotCount)
{
shot = shot % shotCount;
}
int shot_id = (int)Late.Invoke(oNormalLayer, "ShotIDByIndex", shot);
Late.Set(oNormalLayer, "ActiveShotID", shot_id);
Late.Invoke(oNormalLayer, "Go");
Thread.Sleep(3000);
}
}
So, if you see any problems with this, or can point me in the right direction, I'd love your help. If I can help you help me in any way, just let me know. Thank you!

the DefaultControllerFactory of ASP.NET MVC is not thread safe, every request creates a new controller instance
see http://msdn.microsoft.com/en-us/library/system.web.mvc.defaultcontrollerfactory.aspx

How to run a method in a loop only once?

I'm using a switch as a state manager for my XNA game. The switch is a part of main update method, so it's run every frame. Sometimes I need to set a timer value and it should only be set once per method call. There are multiple methods that set the timer per case, so it can't use the current and previous state numbers to check if it's ok to overwrite previous time.
case "state 34": {
SetTime(theTime); // should run only once
// other things
if (TheTimeisRight(time)) // runs every call
{
SetTime(theTime); // should run only once
if (TheTimeisRight(time))
{ /* some methods */ }
}
break; }
How can I make this work, or is there a better way to do this without going outside the switch? (changing SetTime method is ok, but I wouldn't like to clutter up the switch with additional code)

Another method: Introduce a wrapper around the method you want to call:
public sealed class RunOnceAction
{
private readonly Action F;
private bool hasRun;
public RunOnceAction(Action f)
{
F = f;
}
public void run()
{
if (hasRun) return;
F();
hasRun = true;
}
}
Then create var setTimeOnce = new RunOnceAction(() => SetTime(theTime)); before the switch statement, and call there as setTimeOnce.run(). Adjust for parameters/return values as necessary.

If you don't want to mess with boolean variables ala hasSetTimeAlready, you can always introduce another state that calls the method, then proceeds to the original state.

Put the call outside the loop.
You might need a separate conditional statement to determine whether it should run at all, but that's got to be infinitely better than trying to use flags and/or various other smelly-code approaches to control repetitions of the call.
Edit:
here is what I mean by putting it in one place outside of the switch:
if (someCondition && someOtherCondition && yetAnotherCondition)
setTime(theTime); // just one call, in one place, gets executed once
switch(someValue)
{
case "state 34": {
//SetTime(theTime); // no longer necessary
// other things
if (TheTimeisRight(time)) // runs every call
{
//SetTime(theTime); // no longer necessary
if (TheTimeisRight(time))
{ /* some methods */ }
}
break;
...etc...
}
A word of advice: use an enumeration for your switch value rather than a string.
To be brutally honest, this is about as much as anyone can realistically help you with this without seeing a more complete code sample (I think the sample you gave us is somewhat contrived and not quite accurate to what you have?). Chances are that the best way to get round this problem is to deconstruct the switch statement and start again because either maintaining a state machine is not the best way to handle this situation or you need to introduce some other states.

I have resorted to using HashSet<int> to check if the current SetTime(time, num) method has not been called before with if (!hashSet.Contains(num)).
void SetTime(int time, int num)
{
if (!hashSet.Contains(num))
{
theTime = time;
hashSet.Add(num);
}
}
Sure doesn't look too cool, but works and it doesn't damage method call too much (visually), so the switch's readability is saved.

Implementation of BeginUpdate and EndUpdate

1) I'm working on a project and I saw this piece of code, I don't understand what is the point of the Monitor.Lock statement. Can someone explain what its trying to do?
2) the postscript underscroll in the parameter name is really annoying, anyone else seen this naming convention?
public class FieldsChangeableHelper<T> : IFieldsChangeable<T>
{
object _lock;
int _lockCount;
FieldChanges<T> _changes;
public FieldsChangeableHelper()
{
_lock = new object();
_lockCount = 0;
}
public void AddChange(T field_, object oldValue_)
{
if (_changes == null)
_changes = new FieldChanges<T>(field_, oldValue_);
else
_changes.AddChange(field_, oldValue_);
if (RaiseEvent(_changes))
_changes = null;
}
#region IFieldsChangeable Members
public void BeginUpdate()
{
if (System.Threading.Interlocked.Increment(ref _lockCount) == 1)
Monitor.Enter(_lock);
}
public void EndUpdate()
{
if (System.Threading.Interlocked.Decrement(ref _lockCount) == 0)
{
FieldChanges<T> changes = _changes;
_changes = null;
Monitor.Exit(_lock);
RaiseEvent(changes);
}
}
protected bool RaiseEvent(FieldChanges<T> changes_)
{
if (_lockCount == 0 && Changed != null && changes_ != null)
{
Changed(this, changes_);
return true;
}
return false;
}
public event FieldsChanged<T> Changed;
#endregion
}

Monitor.Lock locks the portion of code when multiple thread tries to execute the same piece in parallel. It is made to ensure that only 1 guy is altering/executing the context. Look at the MSDN.
Although its best practice that the locking object is always static, but in your case it is not. Which might pose some problem if your instantiating multiple objects on an open type.
Note one thing, in generics static on open T is different for different type, i.e static member in an Open Type class in your case is different for T i.e DateTime, string, etc.
In csharp, private members of a type are usually named with prefixed _

The way i read it: BeginUpdate() ensures that the current thread calling has exclusive access to the instance and that change events practically will be batched and raised once EndUpdate is called. The author wanted to deal with recursion by itself (e.g. calling BeginUpdate() on the same thread multiple times) and a mechanism to batch UpdateEvents untill after the lock has been released. Because, there is a potential deadlock when raising Events when you still have a lock on yourself. event subscribers might want to access your members and therefore have to lock the sender instance which is already locked.
The whole conditional locking is not required (if my analyses is correct ofcourse) since locks based on the Monitor class are recursive and counted.
There is another problem with the locking mechanism, that is: currently when one thread holds a lock. The second thread wont even wait for the lock but will simply continue without a lock since the lock is conditional! this seems like a big bug!
Regarding the naming convention. I use it myself for a way of differentiating privates from parameters and locals. Its a preference which many C# coding conventions recommend. This helps in a case like this:
void Method(int number)
{
// no need to refer to this since:
//this.number = number;
// can be replaced with
_number = number;
}

c# class - make function or method call and pass control

I'm not sure if my title is really correct. I've looked around and searched but not found anything so please forgive me if my problem has been answered already.
What I would like to do is call a function but not have to come back to the calling line of code. e.g
public static void temp(obj) {
switch (obj.id) {
case "1" :
if(blah) {
obj.id = "2";
temp(obj);
}
break;
case "2" :
obj.response = "done";
break;
}
}
so basically I dont want to eventually come back to my temp(obj) in the first case and fully pass control. Does this make sense, is it even possible and my architecture is all wrong?
Thank you for your time.

Let me see if I understand the question:
You've got a function Foo(), which calls function Bar(). (I wanted to remove the recursion you had in your example for simplicity, please correct me if that was important.) When function Bar() returns, you want control to pass not back to Foo(), but to Foo's caller?
This is probably possible in lower-level languages, like C, by hacking the stack and not placing Foo()'s return address there, so that when Bar() tried to return, it would jump to Foo's caller instead.
However, in C#, no. The call stack is a stack, and control will pass back in order. The only thing you can do would be to put a return statement after each call to Bar().
Edit:
"recursive calls without them being recursive"
How about this:
bool doItAgain = true;
while(doItAgain)
{
doItAgain = false;
// process, with your switch statement or whatever.
if(...)
{
doItAgain = true;
continue; // if necessary, skip any code after this statement. May not be necessary if you have things set up right.
}
}

If this were C++, you could eliminate the break and let the case "1" fall through, but this is not allowed in C# switch statements.
public static void temp(obj) {
if (obj.id == "1") {
obj.id = "2";
temp(obj);
}
if (obj.id == "2")
obj.response = "done";
}
Do you need the recursive call? This code retains your recursive call and sets obj.response to "done" after changing obj.id to "2". However, obj.response is set twice because of the recursive call. What are you trying to do?

I'm not sure what you exactly intend, but it sounds like a callback to me. Here is one possible example:
void DoSome()
{
ThreadPool.QueueUserWorkItem(new WaitCallback(delegate { RunMe(); ReturnTo(); }));
}
void RunMe() { }
void ReturnTo() { }
You start in DoSome() and continue, when RunMe is finished ReturnMe is called.