Adding to concurrent collections

Question

When working with a concurrent collection (for example ConcurrentDictionary) should I use TryAdd method, or just a plain old index assignment? I mean, do TryAdd method blocks when adding, so if another thread would try to remove the value it would have to wait until add is complete?

http://msdn.microsoft.com/en-us/library/dd267291.aspx That's enough? Nothing in sense of thread safety. — Hamlet Hakobyan, Jan 13 '13 at 14:21

score 2 · Answer 1 · answered Jan 13 '13 at 14:20

Both the indexer's setter and Add call TryAdd internally.

public TValue this[TKey key]
{
  get { /*Irrelevant*/ }
  set
  {
    if ((object) key == null)
      throw new ArgumentNullException("key");
    TValue resultingValue;
    this.TryAddInternal(key, value, true, true, out resultingValue);
  }
}

Add method:

void IDictionary<TKey, TValue>.Add(TKey key, TValue value)
{
  if (!this.TryAdd(key, value))
    throw new ArgumentException(this.GetResource("ConcurrentDictionary_KeyAlreadyExisted"));
}

score 2 · Accepted Answer · answered Jan 13 '13 at 14:35

2

The prefix try has nothing to do with thread safety. It is just exception-free version of Add.

answered Jan 13 '13 at 14:35

Hamlet Hakobyan

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So if I want my code to be thread safe what should I do? Are concurrent collections thread safe "by default", and so I may as well just use index assignment? – Marek M. Jan 13 '13 at 14:41

Adding to concurrent collections

2 Answers2