ReaderWriteLockSlim or Lock

Question

I m using ConcurrentBag to store object in run time. At some point I need to empty the bag and store the bag content to a list. This is what i do:

        IList<T> list = new List<T>();

        lock (bag)
        {
            T pixel;

            while (bag.TryTake(out pixel))
            {
                list.Add(pixel);
            }
        }

My Question is with synchronization, As far as I read in the book lock is faster than others synchronization methods. Source -- http://www.albahari.com/threading/part2.aspx.

Performance is my second concern, I d like to know if I can use ReaderWriterLockSlim at this point. What would be the benefit of using ReaderWriterLockSlim? The reason is that, I dont want this operation to block incoming requests.

If yes, Should I use Upgradable Lock?

Any ideas ? Comments?

Are you running into specific performance problems with this code, or just experimenting with stuff? — Roman, Sep 30 '11 at 17:56
Lose the lock. ConcurrentBag is highly optimized for a case where the thread that fills the bag is the same as the one that empties it. If that is not the case in your specific usage then experiment with, say, a Queue and an explicit lock. — Hans Passant, Sep 30 '11 at 18:21

Jim Mischel · Accepted Answer · 2011-09-30T18:06:01.280

I'm not sure why you're using the lock. The whole idea behind ConcurrentBag is that it's concurrent.

Unless you're just trying to prevent some other thread from taking things or adding things to the bag while you're emptying it.

Re-reading your question, I'm pretty sure you don't want to synchronize access here at all. ConcurrentBag allows multiple threads to Take and Add, without you having to do any explicit synchronization.

If you lock the bag, then no other thread can add or remove things while your code is running. Assuming, of course, that you protect every other access to the bag with a lock. And once you do that, you've completely defeated the purpose of having a lock-free concurrent data structure. Your data structure has become a poorly-performing list that's controlled by a lock.

Same thing if you use a reader-writer lock. You'd have to synchronize every access.

You don't need to add any explicit synchronization in this case. Ditch the lock.

ok, this operation takes 0.0002 seconds. I m not worried about performance as it s already fast enough. I wanted to see if it s more logical to use RWSLIM. I need to empty the bag, that s why I m locking it. — DarthVader, Sep 30 '11 at 18:00

score 1 · Answer 2 · answered Sep 30 '11 at 21:05

Lock is great when threads will do a lot of operations in a row(bursty - low contention)

RWSlim is great when you have a lot more read locks than write locks(read heavy - high read contention)

Lockless is great when you need a multiple readers and/or writers all working at the same time(mix of read/write - lots of contention)

ReaderWriteLockSlim or Lock

2 Answers2