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• Multilevel asynchronous method call pattern in c#

  - by michajas

  Hi, I have design problem regarding async calls to method. I'd like to know best/good pattern to call async method, which calls another async method, which calls another async method :) In other words, I have WCF service reference created with async methods and I want to call them from another async method which is called by other async method. All this for non blocking GUI. Thanks!

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• Adding Async=true to the page- no side effects noticed.

  - by Michael Freidgeim

  Recently I needed to implement PageAsyncTask  in .Net 4 web forms application.According to http://msdn.microsoft.com/en-us/library/system.web.ui.pageasynctask.aspx"A PageAsyncTask object must be registered to the page through the RegisterAsyncTask method. The page itself does not have to be processed asynchronously to execute asynchronous tasks. You can set the Async attribute to either true (as shown in the following code example) or false on the page directive and the asynchronous tasks will still be processed asynchronously:<%@ Page Async="true" %>When the Async attribute is set to false, the thread that executes the page will be blocked until all asynchronous tasks are complete."I was worry about any site effects if I will set  Async=true on the existing page.The only documented restrictions, that I found are that@Async is not compatible with @AspCompat and Transaction attributes (from @ Page directive  MSDN article). In other words, Asynchronous pages do not work when the AspCompat attribute is set to true or the Transactionattribute is set to a value other than Disabled in the @ Page directiveFrom our tests we conclude, that adding Async=true to the page is quite safe, even if you don't always call Async tasks from the page

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• Async & Await in C# with Xamarin

  - by Wallym

   One of the great things about the .NET Framework is that Microsoft has worked long and hard to improve many features. Since the initial release of .NET 1.0, there has been support for threading via .NET threads as well as an application-level threadpool. This provided a great starting point when compared to Visual Basic 6 and classic ASP programming. The release of.NET 4 brought significant improvements in the area of threading, asynchronous operations and parallel operations. While the improvements made working with asynchronous operations easier, new problems were introduced, since many of these operations work based on callbacks. For example: How should a developer handle error checking? The program flow tends to be non-linear. Fixing bugs can be problematic. It is hard for a developer to get an understanding of what is happening within an application. The release of .NET 4.5 (and C# 5.0), in the fall of 2012, was a blockbuster update with regards to asynchronous operations and threads. Microsoft has added C# language keywords to take this non-linear callback-based program flow and turn it into a much more linear flow. Recently, Xamarin has updated Xamarin.Android and Xamarin.iOS to support async. This article will look at how Xamarin has implemented the .NET 4.5/C# 5 support into their Xamarin.iOS and Xamarin.Android productions. There are three general areas that I'll focus on: A general look at the asynchronous support in Xamarin's mobile products. This includes async, await, and the implications that this has for cross-platform code. The new HttpClient class that is provided in .NET 4.5/Mono 3.2. Xamarin's extensions for asynchronous operations for Android and iOS. FYI: Be aware that sometimes the OpenWeatherMap API breaks, for no reason.  I found this out after I shipped the article in.

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• why the exception is not caught?

  - by Álvaro García

  I have the following code: List<MyEntity> lstAllMyRecords = miDbContext.MyEntity.ToList<MyEntity>(); foreach MyEntity iterator in lstMainRecord) { tasks.Add( TaskEx.Run(() => { try { checkData(lstAllMyRecords.Where(n => n.IDReference == iterator.IDReference).ToList<MyEntity>()); } catch CustomRepository ex) { //handle my custom repository } catch (Exception) { throw; } }) ); }//foreach Task.WaitAll(tasks.ToArray()); I get all the records from my data base and in the foreach loop, I group all the records that have the same IDReference. Thenk I check if the data is correct with the method chekData. The checkData method throw a custom exception if something is wrong. I would like to catch this exception to handle it. But the problem is that with this code the exceptions are not caught and all seem to work without errors, but I know that this is not true. I try to check only one group of records that I know that has problems. If I check only one group of registrers, the loop is execute once and then only task is created. In this case the exception is caught, but if I have many groups, then any exception s thrwon. Why when I only have one task the exception is caught and with many groups are not? Thanks.

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• How to perform a Depth First Search iteratively using async/parallel processing?

  - by Prabhu

  Here is a method that does a DFS search and returns a list of all items given a top level item id. How could I modify this to take advantage of parallel processing? Currently, the call to get the sub items is made one by one for each item in the stack. It would be nice if I could get the sub items for multiple items in the stack at the same time, and populate my return list faster. How could I do this (either using async/await or TPL, or anything else) in a thread safe manner? private async Task<IList<Item>> GetItemsAsync(string topItemId) { var items = new List<Item>(); var topItem = await GetItemAsync(topItemId); Stack<Item> stack = new Stack<Item>(); stack.Push(topItem); while (stack.Count > 0) { var item = stack.Pop(); items.Add(item); var subItems = await GetSubItemsAsync(item.SubId); foreach (var subItem in subItems) { stack.Push(subItem); } } return items; } EDIT: I was thinking of something along these lines, but it's not coming together: var tasks = stack.Select(async item => { items.Add(item); var subItems = await GetSubItemsAsync(item.SubId); foreach (var subItem in subItems) { stack.Push(subItem); } }).ToList(); if (tasks.Any()) await Task.WhenAll(tasks); UPDATE: If I wanted to chunk the tasks, would something like this work? foreach (var batch in items.BatchesOf(100)) { var tasks = batch.Select(async item => { await DoSomething(item); }).ToList(); if (tasks.Any()) { await Task.WhenAll(tasks); } } The language I'm using is C#.

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• C# 5: At last, async without the pain

  - by Alex.Davies

  For me, the best feature in Visual Studio 11 is the async and await keywords that come with C# 5. I am a big fan of asynchronous programming: it frees up resources, in particular the thread that a piece of code needs to run in. That lets that thread run something else, while waiting for your long-running operation to complete. That's really important if that thread is the UI thread, or if it's holding a lock because it accesses some data structure. Before C# 5, I think I was about the only person in the world who really cared about asynchronous programming. The trouble was that you had to go to extreme lengths to make code asynchronous. I would forever be writing methods that, instead of returning a value, accepted an extra argument that is a "continuation". Then, when calling the method, I'd have to pass a lambda in to it, which contained all the stuff that needed to happen after the method finished. Here is a real snippet of code that is in .NET Demon: m_BuildControl.FilterEnabledForBuilding(     projects,     enabledProjects = m_OutOfDateProjectFinder.FilterNeedsBuilding(         enabledProjects,         newDirtyProjects =         {             // Mark any currently broken projects as dirty             newDirtyProjects.UnionWith(m_BrokenProjects);             // Copy what we found into the set of dirty things             m_DirtyProjects = newDirtyProjects;             RunSomeBuilds();         })); It's just obtuse. Who puts a lambda inside a lambda like that? Well, me obviously. But surely enabledProjects should just be the return value of FilterEnabledForBuilding? And newDirtyProjects should just be the return value of FilterNeedsBuilding? C# 5 async/await lets you write asynchronous code without it looking so stupid. Here's what I plan to change that code to, once we upgrade to VS 11: var enabledProjects = await m_BuildControl.FilterEnabledForBuilding(projects); var newDirtyProjects = await m_OutOfDateProjectFinder.FilterNeedsBuilding(enabledProjects); // Mark any currently broken projects as dirty newDirtyProjects.UnionWith(m_BrokenProjects); // Copy what we found into the set of dirty things m_DirtyProjects = newDirtyProjects; RunSomeBuilds(); Much easier to read! But how is this the same code? If we were on the UI thread, doesn't the UI thread have to block while FilterEnabledForBuilding runs? No, it doesn't, and that's the magic of the await keyword! It cuts your method up into its constituent pieces, much like I did manually with lambdas before. When you run it, only the piece up to the first await actually runs. The rest is passed to FilterEnabledForBuilding as a continuation, which will get called back whenever that method is finished. In the meantime, our thread returns, and can go back to making the UI responsive, or whatever else threads do in their spare time. This is actually a massive simplification, and if you're interested in all the gory details, and speed hacks that the await keyword actually does for you, I recommend Jon Skeet's blog posts about it.

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• Dispatch request to an Async Servlet from managed bean generate exception

  - by Thang Pham

  when a button click, I need to have stuff running in my background, so I have a async Servlet. From my managed bean, if I do redirect, it works great (meaning that it execute my run() method inside my class that extends Runnable correctly). Like this String url = externalContext.getRequestContextPath() + "/ReportExecutionServlet"; externalContext.redirect(url); But if I switch to dispatch, like this externalContext.redirect("/ReportExecutionServlet"); it fail when I try to obtain the AsyncContext AsyncContext aCtx = request.startAsync(request, response); The error is below Caused By: java.lang.IllegalStateException: The async-support is disabled on this request: weblogic.servlet.internal.ServletRequestImpl Any idea how to fix this please? NOTE: This is how to execute my async servlet, just in case: AsyncContext aCtx = request.startAsync(request, response); //delegate long running process to an "async" thread aCtx.addListener(new AsyncListener() { @Override public void onComplete(AsyncEvent event) throws IOException { logger.log(Level.INFO, "ReportExecutionServlet handle async request - onComplete"); } @Override public void onTimeout(AsyncEvent event) throws IOException { logger.log(Level.WARNING, "ReportExecutionServlet handle async request - onTimeout"); } @Override public void onError(AsyncEvent event) throws IOException { logger.log(Level.SEVERE, "ReportExecutionServlet handle async request - onError"); } @Override public void onStartAsync(AsyncEvent event) throws IOException { logger.log(Level.INFO, "ReportExecutionServlet handle async request - onStartAsync"); } }); // Start another service ScheduledThreadPoolExecutor executor = new ScheduledThreadPoolExecutor(10); executor.execute(new AsyncRequestReportProcessor(aCtx));

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• jQuery .ajax() call to page method works in FF only when async is false

  - by Steve

  I'm calling a page method using .ajax() and it works in IE8 whatever the value of async is. However, in FF3.6, it only works with async set to false. When async is set to true, in Firebug, I just see status aborted. The page validates. I can work with async set to false, but any clues as to why FF can't work with async set to true? $("[id$='_www']").click(function() { var hhh = false; $.ajax({ async: false, cache: false, type: "POST", url: "/abc/def.aspx/jkl", contentType: "application/json; charset=utf-8", dataType: "json", data: "{ 'eee': '" + window.location.href.match(/\d{1,3}$/) + "', 'ttt': '" + $("[id$='_zzz']").val() + "' }", success: function(msg) { $("#ggg").html(msg.d); }, error: function(xhr, err) { hhh = true; } }); return hhh; });

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• DDDSouthWest 4.0 26th May 2012 - Async 20/20 presentation

  - by Liam Westley

  As I wasn’t voted in with my nominated sessions I presented a 20/20 talk on the new async functionality coming with the .Net Framework.  This was based on the PechaKucha presentation format, where you have only 20 slides with only 20 seconds per slide, and it progresses automatically. It was the first I’d attempted, so thanks to the organisers for allowing me to have a go. Although creating the slide deck was definitely easier than a one hour presentation, it was much more stressful giving the talk by the end of the 6m 40s. I’m not going to upload the slide deck (it won’t make much sense) but I did record the audio and used the excellent Camtasia to create a video of the slide deck with that audio which you can watch over here, https://vimeo.com/42957952

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• DDDNorth2 Bradford, 13th October 2012 - Async Patterns presentation and source code

  - by Liam Westley

  Many thanks to Andy Westgarth and his team for organising a fantastic conference at the rather elegant Bradford University School of Management. Also, a big congratulations to all the delegates who gave up there free time to come and hear us speak and who were, in general, enthusiastic and asked some cracking questions to keep us speakers on our toes. For those who attended my Async my source code and presentation are now available on GitHub, https://github.com/westleyl/DDDNorth2-AsyncPatterns If you are new to Git then the easiest client to install is GitHub for Windows, a graphical UI for accessing GitHub. Personally, I also have TortoiseGit installed – the file explorer add-in that works in a familiar manner to TortoiseSVN. As I mentioned during the presentation I have not included the sample data, the music files, in the source code placed on GitHub but I have included instructions on how to download them from http://silents.bandcamp.com and place them in the correct folders. What I forgot to mention is that Windows Media Player by default does not play Ogg Vorbis and Flac music files, however you can download the codec installer for these, for free, from http://xiph.org/dshow. I am planning to break down this little project into a series of blog posts, with each pattern being a single blog post over several weeks. In these I will flesh out the background behind the pattern, the basic goal being achieved and how to monitor the progress of the sample data being processed. Basically, what I said during the presentation and is missing from the slides.

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• F#: Tell me what I'm missing about using Async.Parallel

  - by JBristow

  ok, so I'm doing ProjectEuler Problem #14, and I'm fiddling around with optimizations in order to feel f# out. in the following code: let evenrule n = n / 2L let oddrule n = 3L * n + 1L let applyRule n = if n % 2L = 0L then evenrule n else oddrule n let runRules n = let rec loop a final = if a = 1L then final else loop (applyRule a) (final + 1L) n, loop (int64 n) 1L let testlist = seq {for i in 3 .. 2 .. 1000000 do yield i } let getAns sq = sq |> Seq.head let seqfil (a,acc) (b,curr) = if acc = curr then (a,acc) else if acc < curr then (b,curr) else (a,acc) let pmap f l = seq { for a in l do yield async {return f a} } |> Seq.map Async.RunSynchronously let pmap2 f l = seq { for a in l do yield async {return f a} } |> Async.Parallel |> Async.RunSynchronously let procseq f l = l |> f runRules |> Seq.reduce seqfil |> fst let timer = System.Diagnostics.Stopwatch() timer.Start() let ans1 = testlist |> procseq Seq.map // 837799 00:00:08.6251990 printfn "%A\t%A" ans1 timer.Elapsed timer.Reset() timer.Start() let ans2 = testlist |> procseq pmap printfn "%A\t%A" ans2 timer.Elapsed // 837799 00:00:12.3010250 timer.Reset() timer.Start() let ans3 = testlist |> procseq pmap2 printfn "%A\t%A" ans3 timer.Elapsed // 837799 00:00:58.2413990 timer.Reset() Why does the Async.Parallel code run REALLY slow in comparison to the straight up map? I know I shouldn't see that much of an effect, since I'm only on a dual core mac. Please note that I do NOT want help solving problem #14, I just want to know what's up with my parallel code.

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• What happens differently when you add a task Asynchronously on GAE?

  - by Ben Grunfeld

  Google's doc on async tasks assumes knowledge of the difference between regular and asynchronously added tasks. add_async(task, transactional=False, rpc=None) Asynchronously add a Task or a list of Tasks to this Queue. How is adding tasks asynchronously different to adding them regularly. I.e. what is the difference between using add(task, transactional=False) and add_async(task, transactional=False, rpc=None) I've heard that adding tasks regularly blocks certain things. Any explanation of what it blocks and how, and how async tasks don't block would be greatly appreciated.

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• Execute a SSIS package in Sync or Async mode from SQL Server 2012

  - by Davide Mauri

  Today I had to schedule a package stored in the shiny new SSIS Catalog store that can be enabled with SQL Server 2012. (http://msdn.microsoft.com/en-us/library/hh479588(v=SQL.110).aspx) Once your packages are stored here, they will be executed using the new stored procedures created for this purpose. This is the script that will get executed if you try to execute your packages right from management studio or through a SQL Server Agent job, will be similar to the following: Declare @execution_id bigint EXEC [SSISDB].[catalog].[create_execution] @package_name='my_package.dtsx', @execution_id=@execution_id OUTPUT, @folder_name=N'BI', @project_name=N'DWH', @use32bitruntime=False, @reference_id=Null Select @execution_id DECLARE @var0 smallint = 1 EXEC [SSISDB].[catalog].[set_execution_parameter_value] @execution_id,  @object_type=50, @parameter_name=N'LOGGING_LEVEL', @parameter_value=@var0 DECLARE @var1 bit = 0 EXEC [SSISDB].[catalog].[set_execution_parameter_value] @execution_id,  @object_type=50, @parameter_name=N'DUMP_ON_ERROR', @parameter_value=@var1 EXEC [SSISDB].[catalog].[start_execution] @execution_id GO The problem here is that the procedure will simply start the execution of the package and will return as soon as the package as been started…thus giving you the opportunity to execute packages asynchrously from your T-SQL code. This is just *great*, but what happens if I what to execute a package and WAIT for it to finish (and thus having a synchronous execution of it)? You have to be sure that you add the “SYNCHRONIZED” parameter to the package execution. Before the start_execution procedure: exec [SSISDB].[catalog].[set_execution_parameter_value] @execution_id,  @object_type=50, @parameter_name=N'SYNCHRONIZED', @parameter_value=1 And that’s it . PS From the RC0, the SYNCHRONIZED parameter is automatically added each time you schedule a package execution through the SQL Server Agent. If you’re using an external scheduler, just keep this post in mind .

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• Asynch a synchronous method with await async

  - by Sahil Malik

  SharePoint, WCF and Azure Trainings: more information Stock this in “bag of tricks”, but very frequently we run into APIs that do not offer Asynch methods.But between C# ‘s amazing set of features, and asynch await keywords, there is a lot you can do. For instance, consider this code - Read full article ....

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• Asynchrony in C# 5 (Part II)

  - by javarg

  This article is a continuation of the series of asynchronous features included in the new Async CTP preview for next versions of C# and VB. Check out Part I for more information. So, let’s continue with TPL Dataflow: Asynchronous functions TPL Dataflow Task based asynchronous Pattern Part II: TPL Dataflow Definition (by quote of Async CTP doc): “TPL Dataflow (TDF) is a new .NET library for building concurrent applications. It promotes actor/agent-oriented designs through primitives for in-process message passing, dataflow, and pipelining. TDF builds upon the APIs and scheduling infrastructure provided by the Task Parallel Library (TPL) in .NET 4, and integrates with the language support for asynchrony provided by C#, Visual Basic, and F#.” This means: data manipulation processed asynchronously. “TPL Dataflow is focused on providing building blocks for message passing and parallelizing CPU- and I/O-intensive applications”. Data manipulation is another hot area when designing asynchronous and parallel applications: how do you sync data access in a parallel environment? how do you avoid concurrency issues? how do you notify when data is available? how do you control how much data is waiting to be consumed? etc.  Dataflow Blocks TDF provides data and action processing blocks. Imagine having preconfigured data processing pipelines to choose from, depending on the type of behavior you want. The most basic block is the BufferBlock<T>, which provides an storage for some kind of data (instances of <T>). So, let’s review data processing blocks available. Blocks a categorized into three groups: Buffering Blocks Executor Blocks Joining Blocks Think of them as electronic circuitry components :).. 1. BufferBlock<T>: it is a FIFO (First in First Out) queue. You can Post data to it and then Receive it synchronously or asynchronously. It synchronizes data consumption for only one receiver at a time (you can have many receivers but only one will actually process it). 2. BroadcastBlock<T>: same FIFO queue for messages (instances of <T>) but link the receiving event to all consumers (it makes the data available for consumption to N number of consumers). The developer can provide a function to make a copy of the data if necessary. 3. WriteOnceBlock<T>: it stores only one value and once it’s been set, it can never be replaced or overwritten again (immutable after being set). As with BroadcastBlock<T>, all consumers can obtain a copy of the value. 4. ActionBlock<TInput>: this executor block allows us to define an operation to be executed when posting data to the queue. Thus, we must pass in a delegate/lambda when creating the block. Posting data will result in an execution of the delegate for each data in the queue. You could also specify how many parallel executions to allow (degree of parallelism). 5. TransformBlock<TInput, TOutput>: this is an executor block designed to transform each input, that is way it defines an output parameter. It ensures messages are processed and delivered in order. 6. TransformManyBlock<TInput, TOutput>: similar to TransformBlock but produces one or more outputs from each input. 7. BatchBlock<T>: combines N single items into one batch item (it buffers and batches inputs). 8. JoinBlock<T1, T2, …>: it generates tuples from all inputs (it aggregates inputs). Inputs could be of any type you want (T1, T2, etc.). 9. BatchJoinBlock<T1, T2, …>: aggregates tuples of collections. It generates collections for each type of input and then creates a tuple to contain each collection (Tuple<IList<T1>, IList<T2>>). Next time I will show some examples of usage for each TDF block. * Images taken from Microsoft’s Async CTP documentation.

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• How can I use nested Async (WCF) calls within foreach loops in Silverlight ?

  - by Peter St Angelo

  The following code contains a few nested async calls within some foreach loops. I know the silverlight/wcf calls are called asyncrously -but how can I ensure that my wcfPhotographers, wcfCategories and wcfCategories objects are ready before the foreach loop start? I'm sure I am going about this all the wrong way -and would appreciate an help you could give. private void PopulateControl() { List<CustomPhotographer> PhotographerList = new List<CustomPhotographer>(); proxy.GetPhotographerNamesCompleted += proxy_GetPhotographerNamesCompleted; proxy.GetPhotographerNamesAsync(); //for each photographer foreach (var eachPhotographer in wcfPhotographers) { CustomPhotographer thisPhotographer = new CustomPhotographer(); thisPhotographer.PhotographerName = eachPhotographer.ContactName; thisPhotographer.PhotographerId = eachPhotographer.PhotographerID; thisPhotographer.Categories = new List<CustomCategory>(); proxy.GetCategoryNamesFilteredByPhotographerCompleted += proxy_GetCategoryNamesFilteredByPhotographerCompleted; proxy.GetCategoryNamesFilteredByPhotographerAsync(thisPhotographer.PhotographerId); // for each category foreach (var eachCatergory in wcfCategories) { CustomCategory thisCategory = new CustomCategory(); thisCategory.CategoryName = eachCatergory.CategoryName; thisCategory.CategoryId = eachCatergory.CategoryID; thisCategory.SubCategories = new List<CustomSubCategory>(); proxy.GetSubCategoryNamesFilteredByCategoryCompleted += proxy_GetSubCategoryNamesFilteredByCategoryCompleted; proxy.GetSubCategoryNamesFilteredByCategoryAsync(thisPhotographer.PhotographerId,thisCategory.CategoryId); // for each subcategory foreach(var eachSubCatergory in wcfSubCategories) { CustomSubCategory thisSubCatergory = new CustomSubCategory(); thisSubCatergory.SubCategoryName = eachSubCatergory.SubCategoryName; thisSubCatergory.SubCategoryId = eachSubCatergory.SubCategoryID; } thisPhotographer.Categories.Add(thisCategory); } PhotographerList.Add(thisPhotographer); } PhotographerNames.ItemsSource = PhotographerList; } void proxy_GetPhotographerNamesCompleted(object sender, GetPhotographerNamesCompletedEventArgs e) { wcfPhotographers = e.Result.ToList(); } void proxy_GetCategoryNamesFilteredByPhotographerCompleted(object sender, GetCategoryNamesFilteredByPhotographerCompletedEventArgs e) { wcfCategories = e.Result.ToList(); } void proxy_GetSubCategoryNamesFilteredByCategoryCompleted(object sender, GetSubCategoryNamesFilteredByCategoryCompletedEventArgs e) { wcfSubCategories = e.Result.ToList(); }

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• C# webservice async callback not getting called on HTTP 407 error.

  - by Ben

  Hi, I am trying to test the use-case of a customer having a proxy with login credentials, trying to use our webservice from our client. If the request is synchronous, my job is easy. Catch the WebException, check for the 407 code, and prompt the user for the login credentials. However, for async requests, I seem to be running into a problem: the callback is never getting called! I ran a wireshark trace and did indeed see that the HTTP 407 error was being passed back, so I am bewildered as to what to do. Here is the code that sets up the callback and starts the request: TravelService.TravelServiceImplService svc = new TravelService.TravelServiceImplService(); svc.Url = svcUrl; svc.CreateEventCompleted += CbkCreateEventCompleted; svc.CreateEventAsync(crReq, req); And the code that was generated when I consumed the WSDL: public void CreateEventAsync(TravelServiceCreateEventRequest CreateEventRequest, object userState) { if ((this.CreateEventOperationCompleted == null)) { this.CreateEventOperationCompleted = new System.Threading.SendOrPostCallback(this.OnCreateEventOperationCompleted); } this.InvokeAsync("CreateEvent", new object[] { CreateEventRequest}, this.CreateEventOperationCompleted, userState); } private void OnCreateEventOperationCompleted(object arg) { if ((this.CreateEventCompleted != null)) { System.Web.Services.Protocols.InvokeCompletedEventArgs invokeArgs = ((System.Web.Services.Protocols.InvokeCompletedEventArgs)(arg)); this.CreateEventCompleted(this, new CreateEventCompletedEventArgs(invokeArgs.Results, invokeArgs.Error, invokeArgs.Cancelled, invokeArgs.UserState)); } } Debugging the WS code, I found that even the SoapHttpClientProtocol.InvokeAsync method was not calling its callback as well. Am I missing some sort of configuration?

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• Async.Parallel or Array.Parallel.Map ?

  - by gurteen2

  Hello- I'm trying to implement a pattern I read from Don Syme's blog (http://blogs.msdn.com/dsyme/archive/2010/01/09/async-and-parallel-design-patterns-in-f-parallelizing-cpu-and-i-o-computations.aspx) which suggests that there are opportunities for massive performance improvements from leveraging asynchronous I/O. I am currently trying to take a piece of code that "works" one way, using Array.Parallel.Map, and see if I can somehow achieve the same result using Async.Parallel, but I really don't understand Async.Parallel, and cannot get anything to work. I have a piece of code (simplified below to illustrate the point) that successfully retrieves an array of data for one cusip. (A price series, for example) let getStockData cusip = let D = DataProvider() let arr = D.GetPriceSeries(cusip) return arr let data = Array.Parallel.map (fun x -> getStockData x) stockCusips So this approach contructs an array of arrays, by making a connection over the internet to my data vendor for each stock (which could be as many as 3000) and returns me an array of arrays (1 per stock, with a price series for each one). I admittedly don't understand what goes on underneath Array.Parallel.map, but am wondering if this is a scenario where there are resources wasted under the hood, and it actually could be faster using asynchronous I/O? So to test this out, I have attempted to make this function using asyncs, and I think that the function below follows the pattern in Don Syme's article using the URLs, but it won't compile with "let!". let getStockDataAsync cusip = async { let D = DataProvider() let! arr = D.GetData(cusip) return arr } The error I get is: This expression was expected to have type Async<'a but here has type obj It compiles fine with "let" instead of "let!", but I had thought the whole point was that you need the exclamation point in order for the command to run without blocking a thread. So the first question really is, what's wrong with my syntax above, in getStockDataAsync, and then at a higher level, can anyone offer some additional insight about asychronous I/O and whether the scenario I have presented would benefit from it, making it potentially much, much faster than Array.Parallel.map? Thanks so much.

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• FlexUnit nested async tests

  - by sharvey

  I'm trying to test some async functionality in flex 4. My test has two stages : var loader:MySuperLoader = new MySuperLoader() loader.load('foo.swf'); loader.addEventListener(Event.COMPLETE, Async.asyncHandler(this, function(e:Event):void { loader.removeEventListener(Event.COMPLETE, arguments.callee); var foo:* = loader.content; loader.load('bar.swf'); loader.addEventListener(Event.COMPLETE, Async.asyncHandler(this, function(e:Event):void { /* This call to asyncHandler generates the error */ }, 5000)); }, 5000)); The second call to asyncHandler generates an error saying : Error: Cannot add asynchronous functionality to methods defined by Test,Before or After that are not marked async Is there a way to test such funcitonality?

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• Rebol Multitasking with Async: why do I get Invalid port spec

  - by Rebol Tutorial

  I tried http://www.mail-archive.com/[email protected]/msg19437.html (I just changed to www.reboltutorial.com) : do http://www.rebol.it/giesse/async-protocol.r handler: func [port [port!] state [word! error!] /local tmp cmd] [ if error? :state [print mold disarm state return true] switch state [ connect [ ; do HTTP request insert port {GET /files/2009/10/word.png HTTP/1.0^M^JHost: www.reboltutorial.com^M^J^M^J} false ] read [false] write [false] close [ ; get data data: copy port close port ;print copy/part data find data "^M^J^M^J" data: to binary! find/tail data "^M^J^M^J" other/image: attempt [load data] other/text: "" show other false ] ] ] port: open async://www.reboltutorial.com:80 port/awake: :handler view layout [ across me: box 100x100 random 255.255.255 0:00:00.5 feel [ engage: func [f a e] [ if a = 'time [ me/color: random 255.255.255 show me ] ] ] other: box 100x100 255.255.255 "Downloading image..." Return Area 208x100 "You can type here while downloading." ] ] But I'm getting this error: >> port: open async://reboltutorial.com:80 ** Access Error: Invalid port spec: async://reboltutorial.com:80 ** Near: port: open async://reboltutorial.com:80 >> port/awake: :handler ** Script Error: port has no value ** Near: port/awake: :handler

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• Testing Async downloads with ASIHTTPRequest

  - by Baishampayan Ghose

  I am writing a simple library using ASIHTTPRequest where I am fetching URLs in an async manner. My problem is that the main function that I have written to test my lib exits before the async calls are finished. I am very new to Obj C and iPhone development, can anyone suggest a good way to wait before all the requests are finished in the main function? Currently, my main function looks like this - int main(int argc, char *argv[]) { NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; IBGApp *ibgapp = [[IBGApp alloc] init]; IBGLib *ibgl = [[IBGLib alloc] initWithUsername:@"joe" andPassword:@"xxx"]; // The two method calls below download URLs async. [ibgl downloadURL:@"http://yahoo.com/" withRequestDelegate:ibgapp andRequestSelector:@selector(logData:)]; [ibgl downloadURL:@"http://google.com/" withRequestDelegate:ibgapp andRequestSelector:@selector(logData:)]; [pool release]; return 0; // I reach here before the async calls are done. } So what is the best way to wait till the async calls are done? I tried putting sleep, but obviously doesn't work.

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• How can I await the first completed async task of a list in .Net?

  - by Eyal

  My input is a long list of files located on an Amazon S3 server. I'd like to download the metadata of the files, compute the hashes of the local files, and compare the metadata hash with the local files' hash. Currently, I use a loop to start all the metadata downloads asynchronously, then as each completes, compute MD5 on the local file if needed and compare. Here's the code (just the relevant lines): Dim s3client As New AmazonS3Client(KeyId.Text, keySecret.Text) Dim responseTasks As New List(Of System.Tuple(Of ListViewItem, Task(Of GetObjectMetadataResponse))) For Each lvi As ListViewItem In lvStatus.Items Dim gomr As New Amazon.S3.Model.GetObjectMetadataRequest gomr.BucketName = S3FileDialog.GetBucketName(lvi.SubItems(2).Text) gomr.Key = S3FileDialog.GetPrefix(lvi.SubItems(2).Text) responseTasks.Add(New System.Tuple(Of ListViewItem, Task(Of GetObjectMetadataResponse))(lvi, s3client.GetObjectMetadataAsync(gomr))) Next For Each t As System.Tuple(Of ListViewItem, Task(Of GetObjectMetadataResponse)) In responseTasks Dim response As GetObjectMetadataResponse = Await t.Item2 If response.ETag.Trim(""""c) = MD5CalcFile(lvi.SubItems(1).Text) Then lvi.SubItems(3).Text = "Match" UpdateLvi(lvi) End If Next I've got two problems: I'm awaiting the reponses in the order that I made them. I'd rather process them in the order that they complete so that I get them faster. The MD5 calculation is long and synchronous. I tried making it async but the process locked up. I think that the MD5 task was added to the end of .Net's task list and it didn't get to run until all the downloads completed. Ideally, I process the response as they arrive, not in order, and the MD5 is asynchronous but gets a chance to run. Edit: Incorporating WhenAll, it looks like this now: Dim s3client As New Amazon.S3.AmazonS3Client(KeyId.Text, keySecret.Text) Dim responseTasks As New Dictionary(Of Task(Of GetObjectMetadataResponse), ListViewItem) For Each lvi As ListViewItem In lvStatus.Items Dim gomr As New Amazon.S3.Model.GetObjectMetadataRequest gomr.BucketName = S3FileDialog.GetBucketName(lvi.SubItems(2).Text) gomr.Key = S3FileDialog.GetPrefix(lvi.SubItems(2).Text) responseTasks.Add(s3client.GetObjectMetadataAsync(gomr), lvi) Next Dim startTime As DateTimeOffset = DateTimeOffset.Now Do While responseTasks.Count > 0 Dim currentTask As Task(Of GetObjectMetadataResponse) = Await Task.WhenAny(responseTasks.Keys) Dim response As GetObjectMetadataResponse = Await currentTask If response.ETag.Trim(""""c) = MD5CalcFile(lvi.SubItems(1).Text) Then lvi.SubItems(3).Text = "Match" UpdateLvi(lvi) End If Loop MsgBox((DateTimeOffset.Now - startTime).ToString) The UI locks up momentarily whenever MDSCalcFile is done. The whole loop takes about 45s and the first file's MD5 result happens within 1s of starting. If I change the line to: If response.ETag.Trim(""""c) = Await Task.Run(Function () MD5CalcFile(lvi.SubItems(1).Text)) Then The UI doesn't lock up when MD5CalcFile is done. The whole loop takes about 75s, up from 45s, and the first file's MD5 result happens after 40s of waiting.

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• You can step over await

  - by Alex Davies

  I’ve just found the coolest feature of VS 2012 by far. I thought that being able to silence an exception from the “exception was thrown” popup was awesome, and the “reload all” button when a project file changes is amazing, but this is way beyond all of that. You can step over awaits when you debug your code!! With F10!!! Ok, so that may not sound such a big deal. You can step over ifs and whiles and no-one is celebrating. But await is different. await actually stops your method, signs up to be notified when a Task is finished,  returns, and resumes your method at some indeterminate point in the future. You could even end up continuing on a completely different thread. All that happens, and all I have to do is press F10. I used to have to painstakingly set a breakpoint on the first line of my callback before stepping over any asynchronous method. Even when we started using async, my mouse would instinctively click the margin every time I wanted to go past an await. And the times I was driven insane by my breakpoint getting hit by some other path of execution I don’t care about. I think this might have been introduced in the VS11 Beta, I’m pretty sure I tried it in the Async CTP in VS2010 and it didn’t work. Now it does! Woop!

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• WCF: Server Not Found - from trace Empty Message when run async but works fine from console app?

  - by MrTortoise

  Todays cause of hair loss has been the following scenario: I have a service that takes 2 strings and returns another. This service uses basicHttpBinding <basicHttpBinding> <binding name="basicHttpNoSec"> <security mode="None" /> </binding> </basicHttpBinding> Anyway, it works fine from a console test app. I have a silverlight app sat on top which implements another basicHttpBinding service that simply reuses the contract in the other service and the silverlight App uses this service. I have a console app that confirms that this service is working and set up with basichttpbinding. I have all the clientAccessPolicy stuff in place. when I run the silverlight app the difference is that it runs everything async ... as such the only message i directly get back rom wcf is server not found. When i enable tracing I dig down to this message - as I know the methods work and the parameteres i pass in will return a valid string i am really puzzled at to what the cause is. any help much appreciated. <E2ETraceEvent xmlns="http://schemas.microsoft.com/2004/06/E2ETraceEvent"> <System xmlns="http://schemas.microsoft.com/2004/06/windows/eventlog/system"> <EventID>131075</EventID> <Type>3</Type> <SubType Name="Error">0</SubType> <Level>2</Level> <TimeCreated SystemTime="2010-06-07T14:17:40.6639249Z" /> <Source Name="System.ServiceModel" /> <Correlation ActivityID="{8ea9530e-12f4-4a82-9c26-dd2e23264c3c}" /> <Execution ProcessName="aspnet_wp" ProcessID="4616" ThreadID="6" /> <Channel /> <Computer>5JC2Y2J</Computer> </System> <ApplicationData> <TraceData> <DataItem> <TraceRecord xmlns="http://schemas.microsoft.com/2004/10/E2ETraceEvent/TraceRecord" Severity="Error"> <TraceIdentifier>http://msdn.microsoft.com/en-GB/library/System.ServiceModel.Diagnostics.ThrowingException.aspx</TraceIdentifier> <Description>Throwing an exception.</Description> <AppDomain>/LM/w3svc/1/ROOT/CopSilverlight.Web-1-129203938565564172</AppDomain> <Exception> <ExceptionType>System.ServiceModel.ProtocolException, System.ServiceModel, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</ExceptionType> <Message>There is a problem with the XML that was received from the network. See inner exception for more details.</Message> <StackTrace> at System.ServiceModel.Channels.HttpRequestContext.CreateMessage() at System.ServiceModel.Channels.HttpChannelListener.HttpContextReceived(HttpRequestContext context, Action callback) at System.ServiceModel.Activation.HostedHttpTransportManager.HttpContextReceived(HostedHttpRequestAsyncResult result) at System.ServiceModel.Activation.HostedHttpRequestAsyncResult.HandleRequest() at System.ServiceModel.Activation.HostedHttpRequestAsyncResult.BeginRequest() at System.ServiceModel.Activation.HostedHttpRequestAsyncResult.OnBeginRequest(Object state) at System.Runtime.IOThreadScheduler.ScheduledOverlapped.IOCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* nativeOverlapped) at System.Runtime.Fx.IOCompletionThunk.UnhandledExceptionFrame(UInt32 error, UInt32 bytesRead, NativeOverlapped* nativeOverlapped) at System.Threading._IOCompletionCallback.PerformIOCompletionCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* pOVERLAP) </StackTrace> <ExceptionString>System.ServiceModel.ProtocolException: There is a problem with the XML that was received from the network. See inner exception for more details. ---&gt; System.Xml.XmlException: The body of the message cannot be read because it is empty. --- End of inner exception stack trace ---</ExceptionString> <InnerException> <ExceptionType>System.Xml.XmlException, System.Xml, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</ExceptionType> <Message>The body of the message cannot be read because it is empty.</Message> <StackTrace> at System.ServiceModel.Channels.HttpRequestContext.CreateMessage() at System.ServiceModel.Channels.HttpChannelListener.HttpContextReceived(HttpRequestContext context, Action callback) at System.ServiceModel.Activation.HostedHttpTransportManager.HttpContextReceived(HostedHttpRequestAsyncResult result) at System.ServiceModel.Activation.HostedHttpRequestAsyncResult.HandleRequest() at System.ServiceModel.Activation.HostedHttpRequestAsyncResult.BeginRequest() at System.ServiceModel.Activation.HostedHttpRequestAsyncResult.OnBeginRequest(Object state) at System.Runtime.IOThreadScheduler.ScheduledOverlapped.IOCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* nativeOverlapped) at System.Runtime.Fx.IOCompletionThunk.UnhandledExceptionFrame(UInt32 error, UInt32 bytesRead, NativeOverlapped* nativeOverlapped) at System.Threading._IOCompletionCallback.PerformIOCompletionCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* pOVERLAP) </StackTrace> <ExceptionString>System.Xml.XmlException: The body of the message cannot be read because it is empty.</ExceptionString> </InnerException> </Exception> </TraceRecord> </DataItem> </TraceData> </ApplicationData> </E2ETraceEvent>

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• Asynchronous Streaming in ASP.NET WebApi

  - by andresv

   Hi everyone, if you use the cool MVC4 WebApi you might encounter yourself in a common situation where you need to return a rather large amount of data (most probably from a database) and you want to accomplish two things: Use streaming so the client fetch the data as needed, and that directly correlates to more fetching in the server side (from our database, for example) without consuming large amounts of memory. Leverage the new MVC4 WebApi and .NET 4.5 async/await asynchronous execution model to free ASP.NET Threadpool threads (if possible).  So, #1 and #2 are not directly related to each other and we could implement our code fulfilling one or the other, or both. The main point about #1 is that we want our method to immediately return to the caller a stream, and that client side stream be represented by a server side stream that gets written (and its related database fetch) only when needed. In this case we would need some form of "state machine" that keeps running in the server and "knows" what is the next thing to fetch into the output stream when the client ask for more content. This technique is generally called a "continuation" and is nothing new in .NET, in fact using an IEnumerable<> interface and the "yield return" keyword does exactly that, so our first impulse might be to write our WebApi method more or less like this:           public IEnumerable<Metadata> Get([FromUri] int accountId)         {             // Execute the command and get a reader             using (var reader = GetMetadataListReader(accountId))             {                 // Read rows asynchronously, put data into buffer and write asynchronously                 while (reader.Read())                 {                     yield return MapRecord(reader);                 }             }         }   While the above method works, unfortunately it doesn't accomplish our objective of returning immediately to the caller, and that's because the MVC WebApi infrastructure doesn't yet recognize our intentions and when it finds an IEnumerable return value, enumerates it before returning to the client its values. To prove my point, I can code a test method that calls this method, for example:        [TestMethod]         public void StreamedDownload()         {             var baseUrl = @"http://localhost:57771/api/metadata/1";             var client = new HttpClient();             var sw = Stopwatch.StartNew();             var stream = client.GetStreamAsync(baseUrl).Result;             sw.Stop();             Debug.WriteLine("Elapsed time Call: {0}ms", sw.ElapsedMilliseconds); } So, I would expect the line "var stream = client.GetStreamAsync(baseUrl).Result" returns immediately without server-side fetching of all data in the database reader, and this didn't happened. To make the behavior more evident, you could insert a wait time (like Thread.Sleep(1000);) inside the "while" loop, and you will see that the client call (GetStreamAsync) is not going to return control after n seconds (being n == number of reader records being fetched).Ok, we know this doesn't work, and the question would be: is there a way to do it?Fortunately, YES!  and is not very difficult although a little more convoluted than our simple IEnumerable return value. Maybe in the future this scenario will be automatically detected and supported in MVC/WebApi.The solution to our needs is to use a very handy class named PushStreamContent and then our method signature needs to change to accommodate this, returning an HttpResponseMessage instead of our previously used IEnumerable<>. The final code will be something like this: public HttpResponseMessage Get([FromUri] int accountId)         {             HttpResponseMessage response = Request.CreateResponse();             // Create push content with a delegate that will get called when it is time to write out              // the response.             response.Content = new PushStreamContent(                 async (outputStream, httpContent, transportContext) =>                 {                     try                     {                         // Execute the command and get a reader                         using (var reader = GetMetadataListReader(accountId))                         {                             // Read rows asynchronously, put data into buffer and write asynchronously                             while (await reader.ReadAsync())                             {                                 var rec = MapRecord(reader);                                 var str = await JsonConvert.SerializeObjectAsync(rec);                                 var buffer = UTF8Encoding.UTF8.GetBytes(str);                                 // Write out data to output stream                                 await outputStream.WriteAsync(buffer, 0, buffer.Length);                             }                         }                     }                     catch(HttpException ex)                     {                         if (ex.ErrorCode == -2147023667) // The remote host closed the connection.                          {                             return;                         }                     }                     finally                     {                         // Close output stream as we are done                         outputStream.Close();                     }                 });             return response;         } As an extra bonus, all involved classes used already support async/await asynchronous execution model, so taking advantage of that was very easy. Please note that the PushStreamContent class receives in its constructor a lambda (specifically an Action) and we decorated our anonymous method with the async keyword (not a very well known technique but quite handy) so we can await over the I/O intensive calls we execute like reading from the database reader, serializing our entity and finally writing to the output stream.  Well, if we execute the test again we will immediately notice that the a line returns immediately and then the rest of the server code is executed only when the client reads through the obtained stream, therefore we get low memory usage and far greater scalability for our beloved application serving big chunks of data.Enjoy!Andrés.        

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