Thistopic contains information about new and enhanced features in Windows Presentation Foundation WPF version 4. This topic contains the following sections. Services are applications which run in the background to perform a particular function. Example Tracking geolocation. In order to create a service we have to create. In this section, we cover the multithreading APIs new to Framework 4. Parallel LINQ or PLINQ The Parallel class. WPF Viewmodel Collection Binding not updating. Hi,I have an Observable. Collection in my View. Model that Im binding to the Items. Source of a Combo. Box. The problem Im having is in the Get. Wpf Updating Ui From Background Thread' title='Wpf Updating Ui From Background Thread' />By using BeginInvoke you are actually executing the code on the UI thread. You only need to use this when you are updating your UI from the background worker thread. Hi, I have an ObservableCollection in my ViewModel that Im binding to the ItemsSource of a ComboBox. The problem Im having is in the GetDatabases method. Databases method where it adds a string to the Database collection. If I add a Break. Point to the Setter, it is only fired when the collection is initialized, and NOT when an item is added to the collection. Therefore, the Combo. Box is always empty. All is currently running on the same thread, but Id also like to look at putting the Get. All. Server method into a Task. Factory. Start. New so it runs on a different thread and doesnt interrupt the UI animation, but when I do this the Servers collection is populated, but the Combo. Box on the UI isnt updated. So, The main problem is the Databases collection not updating the UI when an item is added. Property. Changed. Event. Handler Property. Changed region Public Bindable Properties private Observable. Collectionlt String servers public Observable. Collectionlt String Servers get return servers set servers value On. Property. Changednew Property. Changed. Event. ArgsServers private Observable. Collectionlt String databases public Observable. Collectionlt String Databases get return databases set databases value On. Property. Changednew Property. Changed. Event. ArgsDatabases private String selectedserver public String Selected. Server get return selectedserver set if selectedservervalue selectedserver value Clear the database list if the selected server changes Server. Changed On. Property. Changednew Property. Changed. Event. ArgsSelected. Server private String selecteddatabase public String Selected. Database get return selecteddatabase set selecteddatabase value On. Property. Changednew Property. Changed. Event. ArgsSelected. Database private String backupfilename public String Backup. Filename get return backupfilename set backupfilename value On. Property. Changednew Property. Changed. Event. ArgsBackup. Filename private String username public String Username get return username set username value On. Property. Changednew Property. Changed. Event. ArgsUsername private String password public String Password get return password set password value On. Property. Changednew Property. Changed. Event. ArgsPassword private readonly ICommand beginconnect public ICommand Connect. Database. Command get return beginconnect private readonly ICommand begin. Backup public ICommand Begin. Backup. Command get return begin. Backup private readonly ICommand begin. Choose. File public ICommand Choose. File. Command get return begin. Choose. File endregion region Relay Commands public class Relay. Command ICommand private Action handler public Relay. CommandAction handler handler handler private bool is. Enabled public bool Is. Enabled get return is. Enabled set if value is. Enabled is. Enabled value if Can. Execute. Changed null Can. Execute. Changedthis, Event. Args. Empty public bool Can. Executeobject parameter return Is. Enabled public event Event. Handler Can. Execute. Changed public void Executeobject parameter handler endregion public Datasources. View. Model beginconnect new Relay. CommandConnect. To. Database Is. Enabled true begin. Backup new Relay. CommandInitiate. Backup Is. Enabled true begin. Choose. File new Relay. CommandChoose. File. Path Is. Enabled true Get. All. Server if String. Is. Null. Or. EmptyBackup. Filename Backup. Filename C SQLBackups protected virtual void On. Property. ChangedProperty. Changed. Event. Args e if this. Property. Changed null this. Property. Changedthis, e To Get All Server private void Get. All. Server Data. Table dt Smo. Application. Enum. Available. Sql. Serversfalse if Servers null Servers new Observable. Collectionlt string if dt. Rows. Count 0 foreach Data. Row dr in dt. Rows Servers. AdddrName. To. String To Get All Data. Base of a Selected Server private void Get. All. Data. Base if Databases null Databases new Observable. Collectionlt String var Sql. Con new System. Data. Sql. Client. Sql. Connectionserver Selected. Server uid Username pwd Password Sql. Con. Open var Sql. Com new System. Data. Sql. Client. Sql. Command Sql. Com. Connection Sql. Con Sql. Com. Command. Type Command. Type. Stored. Procedure Sql. Com. Command. Text spdatabases System. Data. Sql. Client. Sql. Data. Reader Sql. DR Sql. DR Sql. Com. Execute. Reader while Sql. DR. Read Databases. AddSql. DR. Get. String0 Select all. Open in new window. Threading in C Part 5. Threading in CJoseph Albahari. Last updated 2. 01. Translations. Japanese. Download PDFAcknowledgements. Huge thanks to Stephen Toub, Jon Skeet and Mitch Wheat for their feedback. Stephen Toub whose input shaped the entire threading article and the. C 4. 0 in a Nutshell. In this section, we cover the multithreading APIs new to. Framework 4. 0 for leveraging multicore processors These APIs are collectively known loosely as PFX. Parallel Framework. The Parallel. class together with the task parallelism. Task Parallel Library. TPL. Framework 4. We covered. these previously Youll need to be comfortable with the fundamentals in Parts. All the code listings in the parallel programming sections are available as interactive samples in LINQPad. LINQPad is a C code scratchpad and is ideal for testing code snippets without having to create a surrounding class, project or solution. To access the samples, click Download More Samples in LINQPads Samples tab in the bottom left, and select C 4. Nutshell More Chapters. In recent times, CPU clock speeds have stagnated and. This is. problematic for us as programmers because our standard single threaded code. Leveraging multiple cores is easy for most server. Partition it into small chunks. Execute those chunks in parallel via multithreading. Collate the results as they become available, in a thread safe. Although you can do all of this with the classic. A further problem is that the usual strategy of locking for thread safety. The PFX libraries have been designed specifically to help. Programming to leverage multicores or multiple processors is. This is a. subset of the broader concept of multithreading. There are two strategies for partitioning work among threads. When a set of tasks must be performed on many data values. This is called data parallelism. In contrast. with task parallelism we partition the tasks. In general, data parallelism is easier and scales better. Also, data parallelism. Data parallelism is also conducive to structured parallelism, which means that parallel. In contrast, task. Structured parallelism. PFX comprises two layers of functionality. The higher. layer consists of two structured data parallelism APIs PLINQ and the Parallel class. The lower layer contains. PLINQ offers the richest functionality it automates all. Its called declarative because you simply declare. LINQ query. and let the Framework take care of the implementation details. In contrast, the. In the case of the Parallel. The concurrent collections and spinning primitives help. These are important. PFX has been designed to work not only with todays hardware, but also. If you want to move. Its the same with dividing an algorithm among 3. The concurrent collections are tuned specifically for highly concurrent access. PLINQ and the Parallel class themselves rely on the concurrent. The primary use case for PFX is parallel programming. A challenge in leveraging multicores is Amdahls law. For. instance, if only two thirds of an algorithms execution time is. So, before proceeding, its worth verifying that the. Its also worth considering whether your. Theres a trade off, though, in that some. The easiest gains come with whats called embarrassingly parallel problems where a job can. Examples include many image. An example of a nonembarrassingly parallel problem is. PLINQ automatically parallelizes local LINQ queries. PLINQ. has the advantage of being easy to use in that it offloads the burden of both. Framework. To use PLINQ, simply call As. Parallel. on the input sequence and then continue the LINQ query as usual. The following. query calculates the prime numbers between 3 and 1. Calculate prime numbers using a simple unoptimized algorithm. NB All code listings in this chapter are available as interactive code snippets in LINQPad. To activate these samples, click Download More Samples in LINQPads Samples tab in the. C 4. 0 in a Nutshell More Chapters. IEnumerablelt int numbers Enumerable. Range 3, 1. 00. 00. Query. from n in numbers. As. Parallel. where Enumerable. Range 2, int Math. Sqrt n. All i n i 0. Query. To. Array. As. Parallel is an extension. System. Linq. Parallel. Enumerable. It wraps. Parallel. Querylt TSource. LINQ query operators that you subsequently call to bind to an. Parallel. Enumerable. These provide parallel implementations of each of the standard query operators. Essentially, they work by partitioning the input sequence into chunks that. Calling As. Sequential unwraps. Parallel. Query sequence so that subsequent query. This. is necessary before calling methods that have side effects or are not. For query operators that accept two input sequences Join, Group. Join, Concat, Union, Intersect, Except, and Zip, you must apply As. Parallel. to both input sequences otherwise, an exception is thrown. You dont. however, need to keep applying As. Parallel to a query. PLINQs query operators output another Parallel. Query sequence. In fact, calling As. Parallel again introduces inefficiency in that it forces. Sequence. As. Parallel           Wraps sequence in Parallel. Querylt int. Where n n 1. Outputs another Parallel. Querylt int. As. Parallel           Unnecessary and inefficient Select n n n. Not all query operators can be effectively parallelized. For those that cannot, PLINQ implements the. PLINQ may also operate sequentially if it. PLINQ is only for local collections it doesnt work with. LINQ to SQL or Entity Framework because in those cases the LINQ translates into. SQL which then executes on a database server. However, you can use. PLINQ to perform additional local querying on the result sets obtained from. If a PLINQ query throws an exception, its rethrown as. Aggregate. Exception whose Inner. Exceptions. property contains the real exception or exceptions. See Working with Aggregate. Exception. for details. Like ordinary LINQ queries, PLINQ queries are lazily. This means that execution is triggered only when you begin consuming. To. Array. or an operator that returns a single element or value. As you enumerate the results, though, execution proceeds. A sequential. query is powered entirely by the consumer in a pull fashion each element. A. parallel query ordinarily uses independent threads to fetch elements from the. CD. players. It then processes the elements in parallel through the query chain. If the consumer pauses or breaks out of the enumeration early, the. CPU time or memory. You can tweak PLINQs buffering behavior by calling With. Merge. Options after As. Parallel. The default value of Auto. Buffered generally gives. Not. Buffered disables the. Fully. Buffered caches the entire result set before. Order. By and Reverse operators naturally work this way, as do the. A side effect of parallelizing the query operators is that. In other words, LINQs. If you need order preservation, you can force it by. As. Ordered after As. Parallel. my. Collection. As. Parallel. As. Ordered. Calling As. Ordered incurs a. PLINQ must keep track of. You can negate the effect of As. Ordered. later in a query by calling As. Unordered this. introduces a random shuffle point which allows the query to execute more. So if you wanted to preserve input sequence. Sequence. As. Parallel. As. Ordered. Query. Operator. 1. Query. Acs Reagent Chemicals 9Th Edition more. Operator. 2. As. Unordered       From here on, ordering doesnt matter. Query. Operator. 3. As. Ordered is not the default. In other. words, if As. Ordered was the default, youd have to. As. Unordered to the majority of your parallel. There are currently some practical limitations on what. PLINQ can parallelize. These limitations may loosen with subsequent service. Framework versions. The following query operators prevent a query from being. Take, Take. While. Skip, and Skip. While. The indexed versions of Select, Select. Many, and Element. At. Most query operators change the indexing position of.