Parallel tree traversal in C#

Question

I need to traverse a tree quickly, and I would like to do it in parallel. I\'d rather use the parallel extensions than manually spin up a bunch of threads.

My current co

Answer 1

Perhaps using a List or Array instead of queue would help. Also use another List/Array to populate the next nodes to visit. You won't be processing list that until you finish the entire width first anyway. Something like this:

List todoList = new List();
todoList.Add(node);
while (todoList.Count > 0)
{
    // we'll be adding next nodes to process to this list so it needs to be thread-safe
    // or just sync access to a non-threadsafe list
    // if you know approx how many nodes you expect, you can pre-size the list
    ThreadSafeList nextList = new ThreadSafeList();  

    //todoList is readonly/static so can cache Count in simple variable
    int maxIndex  =  todoList.Count-1;
    // process todoList in parallel
    Parallel.For(0, maxIndex, i =>
    {
        // if list reads are thread-safe then no need to sync, otherwise sync
        Node x = todoList[i];

        //process x;
        // e.g. do somehting, get childrenNodesToWorkOnNext, etc.

        // add any child nodes that need to be processed next
        // e.g. nextList.add(childrenNodesToWorkOnNext);
    });

   // done with parallel processing by here so use the next todo list
   todoList = nextList;
)