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I am using the tpl to process thousands of files in a multithreaded fashion.All good.

However there is some part of the application that I must process those files single thread.

Setting maxdegreeParallelism=1 means 1 thread x core is this correct?

When you dont you parallelism and you have 4 cores does it still use 1 thread x core?

The problem is that tpl does lot of hard work for you and also not been very familiar with threading does not help.

Bottom line I need to make sure that maxdegreeParallelism=1 is single threaded

Sorry for silly question but could not find a straight answer by googling.

svick
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user9969
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  • You can improve your question by clarifying what types you're working with, and what you're setting your `maxdegreeParallelism=1` on. – Kirill Shlenskiy Jul 29 '14 at 05:54

2 Answers2

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Documentation doesnt say anything about CPU-Cores but concurrent operations. So this means, setting to 1 equals 1 Thread in total. Though it is a different thread than the callingthread.

Fiddle to poorly prove assumption.

CSharpie
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  • Hi,thanks for your reply what you saying is "1" will run one thread regardless of how many CPU you have,but not on the main thread but on a background thread.Is that what you are saying? – user9969 Aug 03 '14 at 06:31
  • Yep "Though it is a different thread than the callingthread." – CSharpie Aug 03 '14 at 11:31
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See here.

No. It is not the case that necessarily one thread is run per core when you set the `MaxDegreePrallelism". It has a different meaning. It limits the number of parallel tasks done in the entire parallel operation. If you set that to one, it basically renders your parallel approach useless.

The TPL schedules a task on the threadpool. Once the task is scheduled, the threadpool decides how all the tasks to be done are to be distributed among threads, cores and processors. This is based on certain heuristics like the virtual address space, number of threads currently in blocked state, etc.

Now, if you mean that there is a part of your application in which the tasks should be done in a sequential form, there are ways to achieve that. Take a look at ContinueWith.

Community
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Farhad Alizadeh Noori
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  • Hi,I had totally given up on the reply.Thanks for your time.Let me get this right.Setting MaxDegreeParallelism=1 it will actually run singleThreaded and as you say it will render the TPL useless. In a way this achieves what I want to do in the short term,till I read a bit more about ContinueWith.Are you saying using continueWith I could execute some parts in parallel and some sequential?Any examples?Many thanks – user9969 Aug 03 '14 at 06:28
  • Well your definition of the problem may be too general for a proper response, but yes. Using 'ContinueWith' you can queue a bunch of tasks and then have the program ContinueWith another task when all the previous parallel tasks are done. Take a look at [here](http://msdn.microsoft.com/en-ca/library/dd270696(v=vs.110).aspx) for an example. – Farhad Alizadeh Noori Aug 05 '14 at 14:33