Why isn't Parallel.ForEach running multiple threads?

Question

Today i tried do some optimization to foreach statement, that works on XDocument.

Before optimization:

foreach (XElement el         


        

Answer 1

From the problem description, there is nothing that explains why the TPL is not spawning more threads.

There is no evidence in the question that is even the problem. That can be fixed quite easily: you could log the thread id, before you enter the loop, and as the first thing you do inside your loop.

If it is always the same number, it is the TPL failing to spawn threads. You should then try different versions of your code and what change triggers the TPL to serialize everything. One reason could be if there are a small number of elements in your list. The TPL partitions your collection, and if you have only a few items, you might end up with only one batch. This behavior is configurable by the way.

It could be you are inadvertedly taking a lock in in the loop, then you will be seeing lots of different numbers, but no speedup. Then, simplify the code until the problem vanishes.