vb.net qr code reader free PARALLELIZATION AND THREADING ENHANCEMENTS in Visual Basic .NET

Maker QR Code ISO/IEC18004 in Visual Basic .NET PARALLELIZATION AND THREADING ENHANCEMENTS

The concurrent collection classes are thread-safe versions of many of the existing collection classes that should be used for multithreaded or parallelized applications. They can all be found lurking in the System.Collections.Concurrent namespace. When you use any of these classes, it is not necessary to write any locking code because these classes will take care of locking for you. MSDN documentation states that these classes will also offer superior performance to ArrayList and generic list classes when accessed from multiple threads.

Thread-safe version of stack (LIFO collection).

Thread-safe version of queue (FIFO collection).

ConcurrentBag is a thread-safe, unordered, high-performance collection of items contained in System.dll. ConcurrentBags are used when it is not important to maintain the order of items in the collection. ConcurrentBags also allow the insertion of duplicates. ConcurrentBags can be very useful in multithreaded environments because each thread that accesses the bag has its own dequeue. When the dequeue is empty for an individual thread, it will then access the bottom of another thread s dequeue reducing the chance of contention occurring. Note that this same technique is used within the thread pool for providing load balancing.

BlockingCollection is a collection that enforces upper and lower boundaries in a thread-safe manner. If you attempt to add an item when the upper or lower bounds have been reached, the operation will be blocked, and execution will pause. If on the other hand, you attempt to remove an item when the BlockingCollection is empty, this operation will also be blocked. This is useful for a number of scenarios, such as the following: Increasing performance by allowing threads to both retrieve and add data from it. For example, it could read from disk or network while another processes items. Preventing additions to a collection until the existing items are processed.

The following example creates two threads: one that will read from the blocking collection and another to add items to it. Note that we can enumerate through the collection and add to it at the same time, which is not possible with previous collection types.

CAUTION It is important to note that the enumeration will continue indefinitely until the CompleteAdding() method is called.

System; System.Collections.Generic; System.Linq; System.Text; System.Dynamic; System.Threading.Tasks; System.Diagnostics; System.Threading; System.Collections.Concurrent;

namespace ConsoleApplication7 { class Program { public static BlockingCollection<string> blockingCol = new BlockingCollection<string>(5); public static string[] Alphabet = new string[5] { "a", "b", "c", "d", "e" }; static void Main(string[] args) { ThreadPool.QueueUserWorkItem(new WaitCallback(ReadItems)); Console.WriteLine("Created thread to read items"); //Creating thread to read items note how we are already enumurating collection! ThreadPool.QueueUserWorkItem(new WaitCallback(AddItems)); Console.WriteLine("Created thread that will add items"); //Stop app closing Console.ReadKey(); } public static void AddItems(object StateInfo) { int i = 0; while (i < 200) { blockingCol.Add(i++.ToString()); Thread.Sleep(10); } }

public static void ReadItems(object StateInfo) { //Warning this will run forever unless blockingCol.CompleteAdding() is called foreach (object o in blockingCol.GetConsumingEnumerable()) { Console.WriteLine("Read item: " + o.ToString()); } } } }

.NET 4.0 introduces a number of synchronization classes (discussed in the following sections).

The Barrier class allows you to synchronize threads at a specific point. The MSDN documentation has a good analogy: the barrier class works a bit like a few friends driving from different cities and agreeing to meet up at a gas station (the barrier) before continuing their journey. The following example creates two threads: one thread will take twice as long as the other to complete its work. When both threads have completed their work, execution will continue after the call to SignalAndWait()() has been made by both threads. using System.Threading; class Program { static Barrier MyBarrier; static void Main(string[] args) { //There will be two participants in this barrier MyBarrier = new Barrier(2); Thread shortTask = new Thread(new ThreadStart(DoSomethingShort)); shortTask.Start(); Thread longTask = new Thread(new ThreadStart(DoSomethingLong)); longTask.Start(); Console.ReadKey(); } static void DoSomethingShort() { Console.WriteLine("Doing a short task for 5 seconds"); Thread.Sleep(5000); Console.WriteLine("Completed short task");