FAQ Archives | .NET Parallel Programming

FAQ :: StartNew() with TaskScheduler.FromCurrentSynchronizationContext() doesn’t work?

Danny ShihOctober 15, 2010Oct 15, 201010/15/10

We’ve seen a number of folks write the following code to execute on the UI thread and get unexpected behavior. TaskScheduler uiScheduler = TaskScheduler.FromCurrentSynchronizationContext();Task uiTask = Task.Factory.StartNew(delegate{ // … Update UI component; BUG!}, uiScheduler);The issue is that the StartN

FAQ :: TaskScheduler.UnobservedTaskException event doesn’t work?

Danny ShihAugust 5, 2010Aug 5, 201008/5/10

Recall that if exceptions thrown from Task bodies are left unobserved, they will be escalated. In .NET 4, this means that TPL will throw them on the finalizer after the Task objects are available for garbage collection. The UnobservedTaskException event on the TaskScheduler class was added as a last-resort method to observe such ex

FAQ :: Parallel.ForEach and non-generic collections?

Danny ShihMarch 2, 2010Mar 2, 201003/2/10

.NET 2.0 introduced Generics to allow enhanced code reusability and type safety. Since then, generic collections (IEnumerable<T>, List<T>, Dictionary<T>, etc.) have become standard and are recommended over their non-generic counterparts (IEnumerable, ArrayList, HashTable, etc.). As a result, Parallel.ForEach only

FAQ :: Which .NET language is best for parallelism?

Danny ShihFebruary 11, 2010Feb 11, 201002/11/10

The new parallelization support in the .NET Framework 4 is implemented purely in libraries and the runtime and does not require special compiler support. Therefore, it is available to all compliant .NET languages. This includes all of the managed languages that ship as part of Visual Studio 2010 (Visual C#, Visual Basic, Visual F#,

FAQ :: Are all of the new concurrent collections lock-free?

Danny ShihJanuary 26, 2010Jan 26, 201001/26/10

(This answer is based on the .NET Framework 4. As the details below are undocumented implementation details, they may change in future releases.)No. All of the collections in the new System.Collections.Concurrent namespace employ lock-free techniques to some extent in order to achieve general performance benefits, but traditional l

FAQ :: You talk about performance, speedup, and efficiency…what do you mean exactly?

Danny ShihJanuary 19, 2010Jan 19, 201001/19/10

All of these terms are overloaded, even in the context of parallel computing. However, we’ve used them extensively to describe how well our parallel algorithms and demo applications work. And sometimes, we throw them around carelessly on the blog, forums, etc., so here are our general definitions.Performance is an attribute t

FAQ :: The Debugger does not correctly handle Task exceptions?

Danny ShihJanuary 11, 2010Jan 11, 201001/11/10

The following code correctly observes and handles a Task exception and should print “gotcha!” to the console. By default though, the Debugger will report a crash.Task t = Task.Factory.StartNew(() => { throw new Exception("poo"); }); try { t.Wait(); } catch (AggregateException) { Console.WriteLine("gotcha!"); } The issue ha

FAQ :: Why is the speedup not X on my X-way machine?

Danny ShihJanuary 5, 2010Jan 5, 201001/5/10

We’ll be regularly posting answers to frequently asked questions that we’ve gotten on the forum, internal email lists, etc. Here’s the first – enjoy! Why is the speedup not X on my X-way machine? Or, why does my parallel code run slower? Less than ideal speedup can typically be attributed to two things: 1.

.NET Parallel Programming