Parallel.foreach how many threads

Parallel Extensions uses an appropriate number of cores, based on how many you physically have and how many are already busy. It allocates work for each core and then uses a technique called work stealing to let each thread process its own queue efficiently and only need to do any expensive cross-thread access when it really needs to. Have a look at the PFX Team Blog for loads of information about how it allocates work and all kinds of other topics.

On a single core machine ForEach partitions chunks of the collection it's working on between a number of threads, but that number is calculated based on an algorithm that takes into account and appears to continually monitor the work done by the threads it's allocating to the ForEach.

Here, in this article, I am going to keep the focus on the Parallel Foreach method in C. In a standard Foreach loop, each iteration processes a single item from the collection and will process all the items one by one only.

However, the Parallel Foreach method executes multiple iterations at the same time on different processors or processor cores. This may open the possibility of synchronization problems. So, the loop is ideally suited to processes where each iteration is independent of the others.

Note: We need to use parallel loops such as Parallel. ForEach method to speed up operations where an expensive, independent operation needs to be performed for each input of a sequence. A sequential Foreach loop in C :. A parallel Foreach loop in C :. The parallel version of the loop uses the static ForEach method of the Parallel class.

There are many overloaded versions available for this method. This is the simplest overloaded version that accepts two arguments. The first one is the collection of objects that will be enumerated.

Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Does Parallel. ForEach limit the number of active threads? Ask Question. Asked 12 years, 4 months ago. Active 3 years, 11 months ago. Viewed 58k times.

Jader Dias Jader Dias Add a comment. Active Oldest Votes. Note that in some cases you can specify the degree of parallelism you want, too. Jon Skeet Jon Skeet 1. I was using Parallel. Very simple code. Over the period of a few hours I watched the Parallel library spin off over 8, threads. I have tested it multiple times now with the same result. It could start threads for some degenerate 'DoSomething'. ForEach with a non-generic collection, you can use the Enumerable.

Cast extension method to convert the collection to a generic collection, as shown in the following example:. PLINQ enables you to use declarative query syntax to express the loop behavior. You can compile the code as a console application for. NET Framework or as a console application for. NET Core. From the command line, you can use either the. NET CLI commands for example, dotnet new console or dotnet new console -lang vb , or you can create the file and use the command-line compiler for a.

NET Framework application. To run a.