.NET parallel processing of ArrayList

Question

I am trying to implement multithreading for the first time and run into some unexpected problems, hope you can help.

Here's a snippet of code that is causing me problems:

ArrayList recordsCollection = new ArrayList();
ArrayList batchCollection = null;
int idx = 0;

while(true)
{
  // Some code to generate and assign new batchCollection here
  recordsCollection.Add(batchCollection);

  ThreadPool.QueueUserWorkItem(delegate
  {
    ProcessCollection(recordsCollection.GetRange(idx, 1));
  });
  Interlocked.Increment(ref idx);
}

private void ProcessCollection(ArrayList collection)
{
   // Do some work on collection here
}

As soon as the Process Collection method is called and I try to iterate through the collection, I get "Invalid range in base list."

Thanks in advance!

Update: Guys, thank you all and everyone. Thanks to your suggestions, I was able to greatly simplify and make it work.

Answer 1

You have a couple of problems.

• , , .
• .

, batchCollection, recordsCollection , .

.

ArrayList recordsCollection = new ArrayList();  
ArrayList batchCollection = null;  
int idx = 0;  

while(true)  
{  
  lock (recordsCollection) 
  {
    recordsCollection.Add(batchCollection);  
  }

  int capturedIndex = idx; // Used for proper capturing.

  ThreadPool.QueueUserWorkItem(delegate  
  {
    ArrayList range;
    lock (recordsCollection)
    {
      range = recordsCollection.GetRange(capturedIndex, 1);
    }
    ProcessCollection(range);  
  });  

  idx++;
}  

, , , ...

List<List<Record>> recordsCollection = new ArrayList();  
List<Record> batchCollection = null;  

while(true)  
{  
  recordsCollection.Add(batchCollection);

  List<List<Record>> range = new List<List<Record>>();
  range.Add(batchCollection);

  ThreadPool.QueueUserWorkItem(delegate  
  {
    ProcessCollection(range);  
  });      
}  

Answer 2

Interlocked.Increment . , idx , .

" ", , , . , . , .

:

int j = idx;
ThreadPool.QueueUserWorkItem(delegate
{
    ProcessCollection(recordsCollection.GetRange(j, 1));
});

:

• #

:

Answer 3

. : http://en.wikipedia.org/wiki/Closure_(computer_science)

, getRange, ?

.

    private void wee()
    {
        List<List<string>> recordsCollection = new List<List<string>>();

        //int idx = 0;

        while(true)
        {
            //scope the batchcollection here if you want to start a thread with an anonymous delegate
            List<string> batchCollection = null;
            // Some code to generate and assign new batchCollection here
            recordsCollection.Add(batchCollection);

              ThreadPool.QueueUserWorkItem(delegate
              {
                  ProcessCollection(batchCollection);
              });
              //Interlocked.Increment(ref idx);
        }
    }
    private void ProcessCollection(List<string> collection)
    {
        // Do some work on collection here
    }

, , , idx.

Also, remember that exceptions cause a call stack: http://www.codeproject.com/KB/architecture/exceptionbestpractices.aspx

Greetings!