c# - Multiple Parallel.ForEach loops in .Net

Question

In a .Net process, there is only one managed thread pool. We can set the minimum and maximum thread count as needed via public properties.

In .Net, we also have Parallel.ForEach that gets its threads from this managed thread pool under the hood.

In Parallel.ForEach we can also set the MaxDegreeOfParallelism to limit the maximum number of threads.

I have two Parallel.ForEach running in parrallel. One has MaxDegreeOfParallelism set to 3 and the other has set to 7.

My question is: Does both my Parallel.ForEach loops use the same thread pool under the hood. If yes, how does Parallel.ForEach limits the threads with MaxDegreeOfParallelism. How multiple Parallel.ForEach loops and one managed thread pool work together? It'll really help if you can provide a high level explanation or some pointers before I peak into the .net core source code.

Answer 1

• Does both my Parallel.ForEach loops use the same thread pool under the hood.

  Yes

• How does Parallel.ForEach limits the threads with MaxDegreeOfParallelism.

  ParallelOptions.MaxDegreeOfParallelism Gets or sets the maximum number of concurrent tasks enabled by this ParallelOptions instance.

  By default, methods on the Parallel class attempt to use all available processors, are non-cancelable, and target the default TaskScheduler (TaskScheduler.Default). ParallelOptions enables overriding these defaults.

• How multiple Parallel.ForEach loops and one managed thread pool work together?

  They share the same thread pool. As it is described here:

  Generally, you do not need to modify this setting. However, you may choose to set it explicitly in advanced usage scenarios such as these:

  When you're running multiple algorithms concurrently and want to manually define how much of the system each algorithm can utilize. You can set a MaxDegreeOfParallelism value for each.