Question

Basically what I want to do is this psuedo code

List<DatabaseRecord> records;

List<ChangedItem> changedItems;

Parallel.ForEach<DatabaseRecord>(records, (item, loopState) =>
{
    if (item.HasChanged)
    {
        lock (changedItems)
        {
            changedItems.Add(new ChangedItem(item));
        }
    }
});

But what I’m worried about is locking on the changedItems. While it works, I have heard that it has to serialize the locked object over and over. Is there a better way of doing this?

Answer 1

Could you use a ConcurrentCollection for your changedItems. Something like ConcurrentQueue? Then you wouldn’t need to lock at all.

Update:

With regard to the ConcurrentQueue, the Enqueue won’t block the thread in keeping the operation thread safe. It stays in user mode with a SpinWait…

public void Enqueue(T item)
{
    SpinWait wait = new SpinWait();
    while (!this.m_tail.TryAppend(item, ref this.m_tail))
    {
        wait.SpinOnce();
    }
}