I have a class with the following method:
public List<Bike> bikesCopy { get { List<Bike> bs; lock (_bikes) bs = new List<Bike>(_bikes); return bs; } } Which makes a copy of another list, private List<Bike> _bikes;
The strange thing now is, that I get the following error:
Destination array was not long enough. Check destIndex and length, and the array's lower bounds.
What is the problem here?
I would say the error lies in the object _bikes not being thread safe. As commented, somewhere there is a modify of the _bikes object that is not being lock'ed.
It is a split second error where the variable bs is set up to a size X when the size of _bikes is measured. In the next split second as it is about to fill the list, the _bikes object has increased in size giving the error.
So go over your code. Find all references of your _bikes object and make sure they are thread safe handled (with lock).
Well you could try:
using System.Linq; //ToList() is an extension function defined here ... lock(_bikes) return _bikes.ToList(); The details of the exception are discussed here: Why doesn't a foreach loop work in certain cases?
Not really an answer, more a research comment.
I ran into the same problem and did a quick test. I tried with the code below and could not get this code to throw the ArgumentException: Destination array was not long enough. But when I remove the .ToList() from the line
return allLines.ToList().ToArray(); it immediately crashes.
This is the demo code and even the IDE tells me, I should remove the ToList() call as it seems redundant.
using System; using System.Collections.Generic; using System.Linq; using System.Threading; namespace ConsoleApp1 { class Program { static void Main() { List<string> thelist = new List<string>(); Thread producer = new Thread(() => { while (true) { thelist.Add("a" + DateTime.Now); } }); Thread transformer = new Thread(() => { while (true) { string[] thearray = thelist.ToList().ToArray(); Console.WriteLine(thearray.Length); } }); producer.Start(); transformer.Start(); Console.ReadKey(true); } } } I really wonder, why it would not crash, as the List is also backed by an array.