任务并行库 - LongRunning任务与多个Continuations

Question

I'm researching the usage of the Task Parallel Library for a work project I'm doing and want to understand the advantages/disadvantages of long running tasks. I haven't got a real-life example yet, just want to understand the theory behind this.

From what the MSDN pages say about task schedulers and this SO question , it would seem as though it is best to avoid long-running tasks as much as possible so that you are not creating threads outside of the ThreadPool. But say you did have a task which was going to take a long time to complete, instead of this:

Task.Factory.StartNew(() => DoTimeConsumingWork(), TaskCreationOptions.LongRunning)

Could you try and split up your work into smaller, quicker units of work and use task continuations, like this:

Task.Factory
    .StartNew(() => DoWorkPart1())
    .ContinueWith(t => DoWorkPart2())
    .ContinueWith(t => DoWorkPart3())
    //...etc

Would this approach be any more beneficial or is it overkill for what it is trying to achieve?

Answer 1

it would seem as though it is best to avoid long-running tasks as much as possible

Not entirely correct. If you need it then you will have to make/allocate a thread somehow and then the Task with LongRunning option is probably the best choice. The flag simply informs the scheduler the Task might take a while so that the scheduler can anticipate. It might even ignore the option.

Could you try and split up your work into smaller, quicker units of work a

If you can, then do it. But not al taks are so easily separated.

Answer 2

When you specify TaskCreationOptions.LongRunning mostly it assigns a dedicated thread from outside of thread pool.

I would suggest simply go for BackgroundWorker class which makes sure your long running task will be ran on a separate dedicated thread instead of a thread from thread pool