Revisions to Parallel.ForEach vs Task.Run and Task.WhenAll

Rollback to Revision 2

edited Jan 19, 2023 at 5:09

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I have seen Parallel.ForEach blocks the calling thread until the specified actions complete. However, it does not automatically await async method callsused inappropriately, similar to how normally callingand I figured an async method without awaiting itexample in this question would continue without waiting for the async method to completehelp.

An example ofWhen you run the code below in a Console app, you will see how the tasks executed in Parallel.ForEach not automatically awaiting an async method call:doesn't block the calling thread. This could be okay if you don't care about the result (positive or negative) but if you do need the result, you should make sure to use Task.WhenAll.

Using the Parallel.ForEach doeswith a Task will not automatically await async actionsblock the calling thread. If you need to wait for async actions to completecare about the result, make sure to await themthe tasks.

Corrected that Parallel.ForEach does wait for its actions to complete, but acts like most other code that does not await async action.

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edit approved Jan 18, 2023 at 22:34

Andrew D. Bond

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I have seen Parallel.ForEach used inappropriatelyblocks the calling thread until the specified actions complete. However, and I figuredit does not automatically await async method calls, similar to how normally calling an example in this questionasync method without awaiting it would helpcontinue without waiting for the async method to complete.

When you run the code below in a Console app, you will see how the tasks executed inAn example of Parallel.ForEach doesn't block the calling thread. This could be okay if you don't care about the result (positive or negative) but if you do need the result, you should make sure to use Task.WhenAll.not automatically awaiting an async method call:

Using the Parallel.ForEach with a Task willdoes not block the calling threadautomatically await async actions. If you care about the resultneed to wait for async actions to complete, make sure to await the tasksthem.