Question

Am I right in thinking this is the correct use of a Concurrent Dictionary

private ConcurrentDictionary<int,long> myDic = new ConcurrentDictionary<int,long>();

//Main thread at program startup

for(int i = 0; i < 4; i++)
{
  myDic.Add(i, 0);
}

//Separate threads use this to update a value

myDic[InputID] = newLongValue;

I have no locks etc and am just updating the value in the dictionary even though multiple threads might be trying to do the same.

Answer 1

It depends on what you mean by thread-safe.

From MSDN – How to: Add and Remove Items from a ConcurrentDictionary:

ConcurrentDictionary<TKey, TValue> is designed for multithreaded scenarios. You do not have to use locks in your code to add or remove items from the collection. However, it is always possible for one thread to retrieve a value, and another thread to immediately update the collection by giving the same key a new value.

So, it is possible to get an inconsistent view of the value of an item in the dictionary.