Parallel.ForEach or Task.Factory.StartNew: Which is Better for Parallel Performance?

Performance comparison of Parallel.ForEach vs. Task.Factory.StartNew: Which parallel method is better?

In parallel programming, choosing the appropriate execution method is crucial to efficiency. This article dives into the differences between two commonly used techniques: Parallel.ForEach and Task.Factory.StartNew.

Understanding Parallel.ForEach

Parallel.ForEach is a member of the Parallel class in the Task Parallel Library (TPL). It provides a way to perform operations in parallel on each element in a collection. Unlike Task.Factory.StartNew, it does not create a separate task object for each item in the collection. Instead, it utilizes Partitioner<T> to distribute work efficiently. This results in lower overhead and faster execution times, especially when working with large collections.

Understanding Task.Factory.StartNew

Task.Factory.StartNew is another method commonly used for parallel execution. It creates a new task for each item in the collection. While this approach provides greater flexibility and control over the execution process, it may also introduce more overhead. The overhead associated with creating new tasks for each project may outweigh any potential benefits of parallelization.

Performance Considerations

When performance is the main concern, Parallel.ForEach is usually the better choice. It improves performance by batching work items and reducing overhead. This is especially noticeable in large collections, where creating a single task can be very expensive.

Asynchronous execution

While Parallel.ForEach operates synchronously by default, you can also make it asynchronous using a Task.Factory.StartNew wrapper:

<code class="language-csharp">Task.Factory.StartNew(() => Parallel.ForEach<T>(items, item => DoSomething(item)));</code>

This approach combines the best of both approaches, allowing for parallel execution while maintaining Task.Factory.StartNew’s asynchronous behavior.

Conclusion

The choice between

Parallel.ForEach and Task.Factory.StartNew depends on the specific needs of the application. For efficient parallel execution, especially when working with large collections, Parallel.ForEach is the recommended choice due to its lower overhead and better performance. If you need asynchronous behavior, you can use the async Parallel.ForEach wrapper.

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