working with threads - add to collection

List<int> data=new List<int>();
foreach(int id in ids){
    var myThread=new Thread(new ThreadStart(Work));
    myThread.Start(id);
}


Work(){
}

Method Work does some processing on the received id开发者_C百科 and then adds the result to the data list? How can I add data to the collection from each thread? How would my code look like? thanks

If you're using .NET 4, I strongly suggest you use Parallel Extensions instead. For example:

var list = ids.AsParallel()
              .Select(Work)
              .ToList();

where Work is:

public int Work(int id)
{
    ...
}

so that it can receive the id appropriately. If you're not keen on the method conversion, you could add a lambda expression:

var list = ids.AsParallel()
              .Select(id => Work(id))
              .ToList();

Either way, this will avoid creating more threads than you really need, and deal with the thread safety side of things without you having to manage the locks yourself.

First of all, you need to protect your multithreaded access with a lock. Second, you need to pass the parameter to your thread (or use lambda which can capture the local variable; beware that if you capture loop variable, it will change the value during the loop, so you ought to have a local copy).

object collectionLock = new object();
List<int> data = new List<int>();

foreach (int id in ids)
{
    Thread t = new Thread(Worker);
    t.Start(id);
}

void Worker(object o)
{
    int id = (int)o;
    lock(collectionLock)
    {
        data.Add(id);
    }
}

you can pass and retrieve data (using callbacks) from threads. See MSDN article.

Example:

    public class SomeClass
    {
        public static List<int> data = new List<int>();
        public static readonly object obj = new object();

        public void SomeMethod(int[] ids)
        {
            foreach (int id in ids)
            {
                Work w = new Work();
                w.Data = id;
                w.callback = ResultCallback; 
                var myThread = new Thread(new ThreadStart(w.DoWork));
                myThread.Start();
            }
        }

        public static void ResultCallback(int d)
        {        
            lock (obj)
            {        
                data.Add(d);
            }
        }

    }

    public delegate void ExampleCallback(int data); 
    class Work
    {
        public int Data { get; set; }
        public ExampleCallback callback;

        public void DoWork()
        {                
            Console.WriteLine("Instance thread procedure. Data={0}", Data);
            if (callback != null)
                callback(Data);
        }

    }