index changes in try-catch & threads

Question

I am trying to download a file in multiple parts simultaneously for that I am using threads

            for (int i = 0; i < 5; i++)
            {
                try
                {
                    Thread chunkThread = new Thread(() =>
                    {
                        Console.WriteLine("try_index" + i);
                    });
                    chunkThread.Start();
                }
                catch (Exception e)
                {
                    Console.WriteLine("catch_index" + i);
                }
                if (i == 0)
                {
                    Console.WriteLine("here");
                }
            }

since downloading works fine I cleared that code when I watch the Console.Writelines it always writes wrong I thought its gonna write

try_index0
here
try_index1
try_index2
try_index3
try_index4

but the result is

here
try_index1
try_index2
try_index4
try_index5
try_index5

or something like that but always not I wanted and always a 5 involves for parts of the download I keep a list with a start and end bytes of the parts and since it gets 5 my code crashes it is something about new thread but I am too noob to understand how can I fix ?

It's a very common gotcha! Create a copy of the loop variable inside the loop, see the linked answer — canton7, Feb 04 '20 at 14:16
@Jawad I dont care about order.I care about the right indexes — eomer, Feb 04 '20 at 14:21
@canton7 if I dont use new Thread I dont get any wrong index its not about closures — eomer, Feb 04 '20 at 14:24
@eomer It very much is about closures: people hit this problem all the time. Just try it ;) — canton7, Feb 04 '20 at 14:25
`for (int i = 0; i < 5; i++) { int j = i; ... new Thread(() => Console.WriteLine("try_index " + j)); ... }` — canton7, Feb 04 '20 at 14:26

index changes in try-catch & threads

0 Answers0