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The point is that your semaphore allows three threads to run the protected code block at the same time. All three threads are trying to modify the same shared state at the same time.
The ++ operator is not atomic - it reads the value, increments it, and writes it back, which takes three operations. With multiple threads, those operations can be interleaved, resulting in incorrect behaviour.
The Interlocked.Increment operator is atomic. No other thread can sneak code into the middle of the operation.
(Interlocked operations using a 64-bit type on a 32-bit OS will only be atomic with respect to each other. Accessing the value without using the Interlocked class will still have problems.)
For anything more complicated that a single numeric variable, you need to use some kind of coordination primitive to protect the shared state. What you use will depend on how the state will be accessed. For example, if most accesses are reading the state, and only a few are modifying the state, a ReaderWriterLockSlim[^] would probably be a good choice.
Ultimately, the best option is to avoid shared state wherever possible.
Threading in C# - Part 2 - Basic Synchronization[^]
"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer
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i am trying to make the simplest c# application - connect to the LG TV and send a command like KEY_UP.
the tv is using WEBOS 3.0 and it is possible to connect and control it using android remote when they are connected to the same network via wifi.
this is an example i found on the net:
LG tv app to display the list of messages - Stack Overflow[^]
i tried posting the json using postman to the TV's address and it replies with "hello world".
i have no idea how to pair with it in order to be able to make the command or any other command work.
Have anyone done this and can point me to an example? i couldn't find one that can help with this and LG doesn't seem to have client SDK for .net.
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Is it worth having a look at the SDK itself?
Every day, thousands of innocent plants are killed by vegetarians.
Help end the violence EAT BACON
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What UI are you writing for?
Never underestimate the power of human stupidity
RAH
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MyCroft is right - we need to know which UI you are working with, because there are different ListView controls for WinForms, WPF, websites, etc. and any solution will depend on exactly which one you are trying to use.
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I'm looking for an example of highlighting cell the listView of winform or an example of an employee timestamp based on the listView cell color, you can see the attached image file above.
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I have a problem with making a simple SelectedIndex to work with the SelectionChanged.
The same piece of code worked perfectly well with the button click as the event handler but it doesn't work with the selection changed...
All I want is to have a ComboBox with a default value selected,
TextBox displaying this value below, and changing every time I change the selection.
<ComboBox x:Name="BetonCombo" Margin="5" Grid.Column="0" Padding="2" HorizontalAlignment="Center" Width="150" SelectedValuePath="Content" SelectionChanged="BetonCombo_SelectionChanged">
<ComboBoxItem>C16/20 (B20)</ComboBoxItem>
<ComboBoxItem>C20/25 (B25)</ComboBoxItem>
<ComboBoxItem>C25/30 (B30)</ComboBoxItem>
<ComboBoxItem IsSelected="True">C30/37 (B37)</ComboBoxItem>
<ComboBoxItem>C35/45 (B45)</ComboBoxItem>
</ComboBox>
private void BetonCombo_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
int mBetonIndex = BetonCombo.SelectedIndex;
double[] Fck = new double[5];
Fck[0] = 20;
Fck[1] = 25;
Fck[2] = 30;
Fck[3] = 37;
Fck[4] = 45;
double mFck = Fck[mBetonIndex];
fck.Text = mFck.ToString() + " MPa";
}
I am getting this exception
System.NullReferenceException: 'Object reference not set to an instance of an object.' with the last line of code highlighted as the problem (fck.Text = mFck.ToString() + " MPa";).
I don't understand how I could get a null reference if the exact same code worked perfectly fine in the button click event handler? Do I need to set a default value of the ComboBox differently than with a IsSelected=true?
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You get a null reference, probably because C# is case sensitive.
So fck is not the same as Fck and the chances are that when you SelectionChanged event happens, the rest of your code hasn't done anything useful with fck yet. But we can't see the code, so we can't help.
So, it's going to be up to you.
Fortunately, you have a tool available to you which will help you find out what is going on: the debugger.
Put a breakpoint on the first line in the function, and run your code through the debugger. Then look at your code, and at your data and work out what should happen manually. Then single step each line checking that what you expected to happen is exactly what did. When it isn't, that's when you have a problem, and you can back-track (or run it again and look more closely) to find out why.
Sorry, but we can't do that for you - time for you to learn a new (and very, very useful) skill: debugging!
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Haha, thanks  Debugging is actually the next thing I was about to get into.
But actually I found out what was the problem with my code, but it's very strange.
When I removed the IsSelected="true" from the ComboBox item parameters, everything works just fine.
It looks like the SelectionChanged event handler is fired by itself at the start of the program when the IsSelected parameter is resolved...
but now I have no default value in my combo box at the start of the program tho
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Well yes, of course it is!
And it comes in with an SelectedIndex value of -1 to tell you "there is nothing selected"
So reset the property, and try checking for a negative index!
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Looks like code from TMS?
Bastard Programmer from Hell 
If you can't read my code, try converting it here[^]
"If you just follow the bacon Eddy, wherever it leads you, then you won't have to think about politics." -- Some Bell.
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Eddy Vluggen wrote: Looks like code from TMS
Teenage Mutant Sparrows?
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A company that I used to work which automated concrete-factories; didn't have much coding-guidelines in those days, but terms like "f***" were forbidden because it looks sh*tty during a presentation.
So, one of the coworkers started using variable names like "fck" and "yf" (standing for yuck fou).
Good memories 
Bastard Programmer from Hell
If you can't read my code, try converting it here[^]
"If you just follow the bacon Eddy, wherever it leads you, then you won't have to think about politics." -- Some Bell.
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It's not for any company, just my own little project to make life easier 
In general the purpose of this program is going to be calculating the stirrup spacing and longitudinal reinforcement in a concrete beam subjected to shear and torsion.
Btw, I have another problem to solve... is there any easy way to create method inside a class that would automatically add a property of this instance to a list?
For example I have a class:
class Beton
{
public string Label { get; set; }
public double Fck { get; set; }
public double Fcm { get; set; }
public double Fctm { get; set; }
public double Ecm { get; set; }
{
}
}
Now I want to make 3 instances of this class:
Beton B20 = new Beton();
B20.Label = "C16/20 (B20)";
B20.Fck = 20;
Beton B25 = new Beton();
B25.Label = "C20/25 (B25)";
B25.Fck = 25;
Beton B30 = new Beton();
B30.Label = "C25/30 (B30)";
B30.Fck = 25;
and I want that the list below would be automatically created when I instantiate a class:
List<string> comboBoxList = new List<string>();
comboBoxList.Add(B20.Label);
comboBoxList.Add(B25.Label);
comboBoxList.Add(B30.Label);
comboBoxList.Add(B37.Label);
Is this possible?
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Yes:
public class Beton
{
private static List<Beton> all = new List<Beton>();
public Beton()
{
...
all.Add(this);
}
}Because the collection is static there is only one instance of teh collection which is shared by all instances of the Beton Class.
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Thank you for the answer.
It looks like I am still missing something, I got the error that my list doesn't exist in the current context in the main window.
Is something more supposed to be in the "..." place in your snippet?
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
Beton B20 = new Beton();
B20.Nazwa = "C16/20 (B20)";
B20.Fck = 20;
Beton B25 = new Beton();
B25.Nazwa = "C20/25 (B25)";
B25.Fck = 25;
Beton B30 = new Beton();
B30.Nazwa = "C25/30 (B30)";
B30.Fck = 25;
Beton B37 = new Beton();
B37.Nazwa = "C30/37 (B37)";
B37.Fck = 37;
BetonCombo.ItemsSource = comboBoxList;
public class Beton
{
public string Label { get; set; }
public double Fck { get; set; }
public double Fcm { get; set; }
public double Fctm { get; set; }
public double Ecm { get; set; }
private static List<Beton> comboBoxList = new List<Beton>();
public Beton()
{
comboBoxList.Add(this);
}
}
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That's because it's a part of the Beton class, not the MainWindow class.
If you want to access the collection, then I'd provide a get-only property (or a GetAll method) which returns a copy of the list as part of the Beton Class:
public class Beton
{
public static List<Beton> All
{ get { return new List<Beton>(all);} }
...
}That way, the outside world can't mess with your collection!
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modified 4-Aug-18 10:09am.
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I tried to get this to work, but I had to give up after like 3 hours.
For now I left a manually declared list after instantiating the class.
In general I got the "cannot implicitly convert Beton to String", or "Beton to Int", or "List<string> to string", etc, whie trying different ways of writing this.
I don't really know what should be the output of using class name as the List Type (as in List < Beton>) and adding .Add(This) to it. Is it supposed to add every property of the instantiated class as an object regardless of its type to the List?
I am looking for some good toutorial about types accepted by the List object, etc. Is there something you could recommend? For now I didn't find anything thorough enough.
Anyway, thanks for posting, I will do some more search on it in free time.
modified 4-Aug-18 18:17pm.
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C# is a "strongly typed language": it doesn't try to do (most) conversions for you, and if a List contains Beton objects, then accessing the collection returns an instance of a Beton, not the individual properties of that class.
Think of it this way: A Car Park contains instances of Cars, each located in a specific bay. If you model that, then the CarPark object is a Collection of ParkingSpaces each of which can contain a single Car:
public class Car
{
public string Registration { get; set; }
public Color Color { get; set; }
}
public class ParkingSpace
{
public Car Car { get; set; }
public int Level { get; set; }
public int Row { get; set; }
public int Column { get; set; }
}
...
List<ParkingSpace> carPark = new List<ParkingSpace>();
...
foreach (ParkingSpace ps in carPark)
{
Car c = ps.Car;
Console.WriteLine("{0} is a {1} car, on floor {2}, Row {3}, Bay {4}.",
c.Registration,
c.Color,
ps.Level,
ps.Row,
ps.Column);
}You can drive a car away and park a new one in the same space without changing the collection, or the actual spaces - you just set the new value of the ParkingSpace.Car property.
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Thank you, it works perfectly well now, it just cut like 20% of my code
The only thing left for me is to properly assing the scope for variables and collections.
I can't access my collections in the event handlers in main.
I tried to just set them to public or to make a new list with a {get} setting that returns them, but none of that works for me.
What is generally the best way to make variables and collections availible to all scopes in main window? Should I try to do it with the {get} settings on all variables and collections?
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Look at the example I gave you for the All property, and it's static - which means you access it with just the class name from anywhere in your code that can access the Beton class:
List<Beton> allInstances = Beton.All; And it returns you a copy of the current collection.
Don't make the "raw" collection public - that lets the outside world remove instances which is a bad idea!
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OriginalGriff wrote: Don't make the "raw" collection public - that lets the outside world remove instances which is a bad idea!
List(T).AsReadOnly Method (System.Collections.Generic)[^]
Bastard Programmer from Hell
If you can't read my code, try converting it here[^]
"If you just follow the bacon Eddy, wherever it leads you, then you won't have to think about politics." -- Some Bell.
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Good idea.  Possibly a little advanced for the OP though! 
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I already abstained from suggesting an interface to an abstract beton-class called concrete.
..and then implementing a concrete concrete
Bastard Programmer from Hell
If you can't read my code, try converting it here[^]
"If you just follow the bacon Eddy, wherever it leads you, then you won't have to think about politics." -- Some Bell.
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