.NET Parallel Programming

All about Async/Await, System.Threading.Tasks, System.Collections.Concurrent, System.Linq, and more…

New TaskCreationOptions and TaskContinuationOptions in .NET 4.5

Astute users of the Task Parallel Library might have noticed three new options available across TaskCreationOptions and TaskContinuationOptions in .NET 4.5: DenyChildAttach, HideScheduler, and (on TaskContinuationOptions) LazyCancellation.  I wanted to take a few minutes to share more about what these are and why we added them.

Forking in async methods

Given that .NET 4.5 has only recently been released in its final form, it’s not surprising that many folks are still very new to the async/await keywords and have misconceptions about what they are and what they do (I’ve tried to clarify some of these in this Async/Await FAQ). 

Implementing Then with Await

In a post a while ago, I talked about sequential composition of asynchronous operations.  Now that we have the async/await keywords in C# and Visual Basic, such composition is trivial, and async/await are indeed the recommended way to achieve such composition with these languages.

Processing tasks as they complete

Recently I’ve had several folks ask me about how to process the results of tasks as those tasks complete.
A developer will have multiple tasks representing asynchronous operations they’ve initiated, and they want to process the results of these tasks, e.g.

ExecutionContext vs SynchronizationContext

I’ve been asked a few times recently various questions about ExecutionContext and SynchronizationContext, for example what the differences are between them, what it means to “flow” them, and how they relate to the new async/await keywords in C# and Visual Basic. 

Using async/await in WinRT async operations

Several weeks ago, I wrote a post for the Windows 8 app developer blog that was all about using await and AsTask to consume WinRT async operations.  I’ve now published a follow-up post that’s all about exposing .NET tasks as WinRT async operation. 

Performance consideration for Async/Await and MarshalByRefObject

In the previous “What’s New for Parallelism in Visual Studio 2012 RC” blog post, I mentioned briefly that for the .NET 4.5 Release Candidate, StreamReader.ReadLineAsync experienced a significant performance improvement over Beta.  There’s an intriguing story behind that, one I thought I’d share here.

ConcurrentQueue holding on to a few dequeued elements

Since .NET 4’s release, I’ve received several questions about a peculiar behavior of ConcurrentQueue<T> having to do with memory management.
With Queue<T>, List<T>, and other such data structures in the .NET Framework, when you remove an element from the collection, the collection internally wipes out its reference to the stored element,

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New Task APIs in .NET 4.6

There are several nice API-level enhancements to the Task Parallel Library in .NET 4.6, which you can grab a preview of as part of the Visual Studio 2015 CTP.
Task.From*
.NET 4.5 had a Task.FromResult method.  This method makes it quick and easy to manufacture a new Task for a known result value,

.NET memory allocation profiling and Tasks

The .NET Framework blog published this morning a guest post from yours truly on .NET Memory Allocation Profiling with Visual Studio 2012.  As you’re trying to improve the performance, throughput, and memory usage of code that uses Tasks, the described profiler in Visual Studio can be a valuable tool in your tool belt (of course,

Tasks, Monads, and LINQ

A few years back, Wes Dyer wrote a great post on monads, and more recently, Eric Lippert wrote a terrific blog series exploring monads and C#. In that series, Eric alluded to Task<TResult> several times, so I thought I’d share a few related thoughts on Task<TResult>

“Invoke the method with await”… ugh!

I can be a bit sensitive when it comes to language and how concepts are conveyed.  I think it’s important to be accurate, even if not precise, when describing what something is or how to use it, as otherwise the folks to whom you’re communicating can easily form the wrong mental model for that thing. 

MVP Summit presentation on async

Lucian Wischik and I presented an “async clinic” at the MVP Summit in Bellevue this week.  The async/await keywords in C# and Visual Basic drastically simplify asynchronous programming, but that of course doesn’t mean that using them is without any gotchas: the goal of the discussion was to highlight some of the key areas in which we see developers struggling with asynchronous development and to help provide guidance on avoiding and overcoming those roadblocks. 

Psychic Debugging of Async Methods

These days it’s not uncommon for me to receive an email or read a forum post from someone concerned about a problem they’re experiencing with an async method they’ve written, and they’re seeking help debugging the issue.  Sometimes plenty of information about the bug is conveyed,

Cooperatively pausing async methods

Recently I was writing an app that processed a bunch of files asynchronously.  As with the Windows copy file dialog, I wanted to be able to provide the user with a button that would pause the processing operation.
To achieve that,

C# memory model articles

Igor Ostrovsky is one of the minds behind the parallel programming support in the .NET Framework.  Igor’s recently written a great set of articles for MSDN Magazine to cover “The C# Memory Model in Theory and Practice“.  Part 1 is available now in the December 2012 issue,

PLINQ and Int32.MaxValue

In both .NET 4 and .NET 4.5, PLINQ supports enumerables with up to Int32.MaxValue elements.  Beyond that limit, PLINQ will throw an overflow exception.  LINQ to Objects itself has this limitation with certain query operators (such as the indexed Select operator which counts the elements processed),

How do I cancel non-cancelable async operations?

This is a question I hear relatively frequently:

“I have an async operation that’s not cancelable.  How do I cancel it?”

The construction of the question often makes me chuckle, but I understand and appreciate what’s really being asked.  The developer typically isn’t asking how to cancel the operation itself (if they are asking that,