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Index out of range, how!?
I am trying to return the last value of a list:
public int GetControllerState()
{
// return the last controllerState in the list
if (controllerStateList != null)
{
if (controllerStateList.Count > 0)
{
return (int)controllerStateList[controllerStateList.Count - 1];
}
else
{
return 0;
}
}
else
{
return 0;
}
}
The above methodsometimes throws
"An unhandled exception of type 'System.ArgumentOutOfRangeException' occurred in mscorlib.dll
Additional information: Index was out of range. Must be non-negative and less than the size of the collection."
and breaks on the return statement of the above code, the thing is, when I check the values in the debugger, i can see:
|controllerStateList.Count = 2|
|controllerStateList.Count - 1 = 1|
and |controllerStateList[1] = PERFORMING_RUN|
So, this just shouldnt be happening! Not sure if I am being stupid or not, thanks.
It might be worth saying I am accessing this from a different thread? I have declaired the controllerStateList as volatile, Ill try to build a simple example and see if It does it in that
Well, I'm even more stumped now - I have made a program with two threads, one accessing the list, the other writing to the list (its compilable, you can test it!) And I never get the index error, everything says this error just shouldnt happen! Even the debugger! And that it works sometimes, when performing the same thing...
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
namespace TestingIndexError2
{
public class Integer //stupid I know
{
public int value;
public Integer(int value)
{
this.value = value;
}
}
public class Worker
{
private Program program;
public Worker(Program program)
{
this.program = program;
}
// This method will be called when the thread is started.
public void DoWork()
{
while (!_shouldStop)
{
Console.WriteLine("top: " + program.GetTopOfList());
Console.WriteLine();
program.PrintList();
Console.WriteLine();
}
Console.WriteLine("worker thread: terminating.");
}
public void RequestStop()
{
_shouldStop = true;
}
// Volatile is used as hint to the compiler that this data
// member will be accessed by multiple threads.
private volatile bool _shouldStop;
}
public class Program
{
public List<Integer> list;
static void Main(string[] args)
{
Program p = new Program();
p.Run();
}
public void Run()
{
// Create the thread object. This does not start the thread.
Worker workerObject = new Worker(this);
Thread workerThread = new Thread(workerObject.DoWork);
// Start the worker thread.
workerThread.Start();
Console.WriteLine("main thread: Starting worker thread...");
// Loop until worker thread activates.
while (!workerThread.IsAlive) ;
// Put the main thread to sleep for 1 millisecond to
// allow the worker thread to do some work:
Thread.Sleep(1);
list = new List<Integer>();
Random random = new Random();
int i = 0;
while (i < 10000)
{
if (random.Next(0, 2) > 0)
{
// randomly adds an item to top of list
list.Add( new Integer(random.Next(0, 10)) );
}
if (random.Next(0, 3) > 1)
{
//randomly removes items from top of list
RemoveTopOfList();
}
Thread.Sleep(10);
i++;
}
// Request that the worker thread stop itself:
workerObject.RequestStop();
// Use the Join method to block the current thread
// until the object's thread terminates.
workerThread.Join();
Console.WriteLine("main thread: Worker thread has terminated.");
}
public void PrintList(){
if (list!=null)
for (int i = 0 ; i < list.Count ; i++ )
Console.Write(list[i].value+ " " );
}
public int GetTopOfList()
{
// return the last controllerState in the list
if (list != null)
{
if (list.Count > 0)
{
return (list[list.Count - 1]).value;
}
else
{
return 0;
}
}
else
{
return 0;
}
}
private void RemoveTopOfList()
{
//remove the top controllerState
if (list != null)
{
if (list.Count > 0)
{
list.RemoveAt(list.Count - 1);
}
if (list.Count == 0)
{
list.Add( new Integer(0) );
}
}
}
}
}
if you want to try it
Success in failing! The following produces the error, i believe that it is the printing that makes this different to the aboce (when commented out it seemed to run ok) the only way I can think that that would effect anything is introduce a delay in the other thread, so i assume i am not making things threadsafe properly...
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
namespace TestingIndexError2
{
public class Integer //stupid I know
{
public int value;
public Integer(int value)
{
this.value = value;
}
}
public class Worker
{
private Program program;
public Worker(Program program)
{
this.program = program;
}
// This method will be called when the thread is started.
public void DoWork()
{
int i1 = 0;
int i2 = 0;
while (!_shouldStop)
{
i1 = program.GetTopOfList();
if (i1 != i2)
Console.WriteLine("top: " + program.GetTopOfList());
i2 = i1;
//Console.WriteLine();
//program.PrintList();
//Console.WriteLine();
}
Console.WriteLine("worker thread: terminating.");
}
public void RequestStop()
{
_shouldStop = true;
}
// Volatile is used as hint to the compiler that this data
// member will be accessed by multiple threads.
private volatile bool _shouldStop;
}
public class Program
{
public List<Integer> list;
static void Main(string[] args)
{
Program p = new Program();
p.Run();
}
public void Run()
{
// Create the thread object. This does not start the thread.
Worker workerObject = new Worker(this);
Thread workerThread = new Thread(workerObject.DoWork);
// Start the worker thread.
workerThread.Start();
Console.WriteLine("main thread: Starting worker thread...");
// Loop until worker thread activates.
while (!workerThread.IsAlive) ;
// Put the main thread to sleep for 1 millisecond to
// allow the worker thread to do some work:
Thread.Sleep(1);
list = new List<Integer>();
Random random = new Random();
int i = 0;
while (i < 10000)
{
if (random.Next(0, 2) > 0)
{
list.Add( new Integer(random.Next(0, 10)) );
}
if (random.Next(0, 3) > 1)
{
RemoveTopOfList();
}
Thread.Sleep(10);
i++;
}
// Request that the worker thread stop itself:
workerObject.RequestStop();
// Use the Join method to block the current thread
// until the object's thread terminates.
workerThread.Join();
Console.WriteLine("main thread: Worker thread has terminated.");
}
public void PrintList(){
if (list!=null)
for (int i = 0 ; i < list.Count ; i++ )
Console.Write(list[i].value+ " " );
}
public int GetTopOfList()
{
// return the last controllerState in the list
if (list != null)
{
if (list.Count > 0)
{
if ((list[list.Count - 1]) != null)
{
return (list[list.Count - 1]).value;
}
else
{
return 0;
}
}
else
{
return 0;
}
}
else
{
return 0;
}
}
private void RemoveTopOfList()
{
//remove the top controllerState
if (list != null)
{
if (list.Count > 0)
{
list.RemoveAt(list.Count - 1);
}
if (list.Count == 0)
{
list.Add( new Integer(0) );
}
}
}
}
} Momerath
Nearly a Senior Poster
3,386 posts since Aug 2010
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public int GetTopOfList()
{
if (list != null)
{
lock (list)
{
if (list.Count > 0)
{
Integer iI = list[list.Count - 1];
if (iI != null)
{
return iI.value;
}
}
}
}
return 0;
}
private void RemoveTopOfList()
{
if (list != null)
{
lock (list)
{
if (list.Count > 0)
{
list.RemoveAt(list.Count - 1);
}
if (list.Count == 0)
{
list.Add(new Integer(0));
}
}
}
}
Works Thanks!
I have one question though:
Integer iI = list[list.Count - 1];
if (iI != null)
{
return iI.value;
}
works, but
if (list[list.Count - 1] != null)
{
return list[list.Count - 1].value;
}
causes a:
A first chance exception of type 'System.NullReferenceException' occurred in TestingIndexError2.exe
An unhandled exception of type 'System.NullReferenceException' occurred in TestingIndexError2.exe
Additional information: Object reference not set to an instance of an object.
But I can't see why..?
This article has been dead for over three months
You
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