Parallelism in .NET – Part 16, Creating Tasks via a TaskFactory

The Task class in the Task Parallel Library supplies a large set of features.  However, when creating the task, and assigning it to a TaskScheduler, and starting the Task, there are quite a few steps involved.  This gets even more cumbersome when multiple tasks are involved.  Each task must be constructed, duplicating any options required, then started individually, potentially on a specific scheduler.  At first glance, this makes the new Task class seem like more work than ThreadPool.QueueUserWorkItem in .NET 3.5.

In order to simplify this process, and make Tasks simple to use in simple cases, without sacrificing their power and flexibility, the Task Parallel Library added a new class: TaskFactory.

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MEF CompositionInitializer for WPF

The Managed Extensibility Framework is an amazingly useful addition to the .NET Framework.  I was very excited to see System.ComponentModel.Composition added to the core framework.  Personally, I feel that MEF is one tool I’ve always been missing in my .NET development.

Unfortunately, one perfect scenario for MEF tends to fall short of it’s full potential is in Windows Presentation Foundation development.  In particular, there are many times when the XAML parser constructs objects in WPF development, which makes composition of those parts difficult.  The current release of MEF (Preview Release 9) addresses this for Silverlight developers via System.ComponentModel.Composition.CompositionInitializer.  However, there is no equivalent class for WPF developers.

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Parallelism in .NET – Part 15, Making Tasks Run: The TaskScheduler

In my introduction to the Task class, I specifically made mention that the Task class does not directly provide it’s own execution.  In addition, I made a strong point that the Task class itself is not directly related to threads or multithreading.  Rather, the Task class is used to implement our decomposition of tasks

Once we’ve implemented our tasks, we need to execute them.  In the Task Parallel Library, the execution of Tasks is handled via an instance of the TaskScheduler class.

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Parallelism in .NET – Part 14, The Different Forms of Task

Before discussing Task creation and actual usage in concurrent environments, I will briefly expand upon my introduction of the Task class and provide a short explanation of the distinct forms of Task.  The Task Parallel Library includes four distinct, though related, variations on the Task class.

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Parallelism in .NET – Part 13, Introducing the Task class

Once we’ve used a task-based decomposition to decompose a problem, we need a clean abstraction usable to implement the resulting decomposition.  Given that task decomposition is founded upon defining discrete tasks, .NET 4 has introduced a new API for dealing with task related issues, the aptly named Task class.

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Parallelism in .NET – Part 12, More on Task Decomposition

Many tasks can be decomposed using a Data Decomposition approach, but often, this is not appropriate.  Frequently, decomposing the problem into distinctive tasks that must be performed is a more natural abstraction.

However, as I mentioned in Part 1, Task Decomposition tends to be a bit more difficult than data decomposition, and can require a bit more effort.  Before we being parallelizing our algorithm based on the tasks being performed, we need to decompose our problem, and take special care of certain considerations such as ordering and grouping of tasks.

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Parallelism in .NET – Part 11, Divide and Conquer via Parallel.Invoke

Many algorithms are easily written to work via recursion.  For example, most data-oriented tasks where a tree of data must be processed are much more easily handled by starting at the root, and recursively “walking” the tree.  Some algorithms work this way on flat data structures, such as arrays, as well.  This is a form of divide and conquer: an algorithm design which is based around breaking up a set of work recursively, “dividing” the total work in each recursive step, and “conquering” the work when the remaining work is small enough to be solved easily.

Recursive algorithms, especially ones based on a form of divide and conquer, are often a very good candidate for parallelization.

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Parallelism in .NET – Part 10, Cancellation in PLINQ and the Parallel class

Many routines are parallelized because they are long running processes.  When writing an algorithm that will run for a long period of time, its typically a good practice to allow that routine to be cancelled.  I previously discussed terminating a parallel loop from within, but have not demonstrated how a routine can be cancelled from the caller’s perspective.  Cancellation in PLINQ and the Task Parallel Library is handled through a new, unified cooperative cancellation model introduced with .NET 4.0.

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Parallelism in .NET – Part 9, Configuration in PLINQ and TPL

Parallel LINQ and the Task Parallel Library contain many options for configuration.  Although the default configuration options are often ideal, there are times when customizing the behavior is desirable.  Both frameworks provide full configuration support.

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Parallelism in .NET – Part 8, PLINQ’s ForAll Method

Parallel LINQ extends LINQ to Objects, and is typically very similar.  However, as I previously discussed, there are some differences.  Although the standard way to handle simple Data Parellelism is via Parallel.ForEach, it’s possible to do the same thing via PLINQ.

PLINQ adds a new method unavailable in standard LINQ which provides new functionality…

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