Is the list order of a ConcurrentDictionary guaranteed?

Question

I am using a ConcurrentDictionary to store log-lines, and when I need to display them to the user I call ToList() to generate a list. But the weird thing is that some users receive the most recent lines first in the list, while they should logically be last.

Is this because ConcurrentDictionary doesnt guarantee a persistent order on the IEnumerate interface, or what can be the reason?

Bagwell

Sort by the a DateTime value when displaying the data. – Ruiz

@Ruiz I was planning on doing that, but its sort of a workaround. Id like to understand why it happens first. – Bagwell

Related: Is ConcurrentDictionary always add item by order in C#? – Geomancer

Answer 1

No ConcurrentDictionary (and Dictionary<T> for that matter) does not guarantee the ordering of the keys in the list. You'll have to use a different data type or perform the sorting yourself. For non-concurrent code you would use SortedDictionary<T>, but I don't believe there is an analogue in the concurrent collections.

Trygve

Answer 2

No. The list order of ConcurrentDictionary is NOT guaranteed, lines can come out in any order.

Palila