Thursday, 30 June 2016

Creating TPL Dataflow meshes to construct pipelines of computations

The TPL DataFlow Library allows the creation of simple and more complex data meshes that propagate data computations and exceptions using the Nuget package Microsoft.Tpl.DataFlow Let's look at how we can create a compound mesh to do three calculations that is considered as a single mesh. These simple examples appear to give simple computations as these a huge overhead in complexity. Of course, you would use Microsoft.Tpl.DataFlow for more complex scenarios, the simple example is just used for clarity. Consider the following code: First off, make sure you add a reference to Microsoft.Tpl.Dataflow, since TPL Dataflow is not part of the base class Library BCL in .NET. In the Nuget Package Explorer commandline in VS:
Install-Package Microsoft.Tpl.DataFlow

using System;
using System.Collections.Generic;
using System.Threading.Tasks;
using System.Threading.Tasks.Dataflow;

namespace DataFlowDemo
{

    class Program
    {

        static void Main(string[] args)
        {
            //TplDataDemo();
            SecondTplDataDemo();
            Console.WriteLine("Press any key to continue ..");
            Console.ReadKey();
        }

        private static async void SecondTplDataDemo()
        {
            int[] nums = { 1, 13, 26, 14, 29, 15 };
            Console.WriteLine("Input numbers: ");
            foreach (var n in nums)
                Console.WriteLine(n);
            IPropagatorBlock<int, int> compountBlock = GetPropagatorBlock();
            Console.WriteLine("Pipeline: " + "x = (x * 2) => (x + 2) => (x / 2)");
            foreach (var num in nums)
            {
                compountBlock.Post(num);
            }
            try
            {

                while (true)
                {
                    try
                    {
                        Task<int> f = compountBlock.ReceiveAsync(TimeSpan.FromSeconds(1));
                        await f;
                        await Task.Delay(1000);
                        Console.WriteLine(f.Result);
                    }
                    catch (TimeoutException err)
                    {
                        //Console.WriteLine(err.Message);
                        break;
                    }
                    catch (Exception err)
                    {
                        //Console.WriteLine(err.Message);
                        throw err;
                    }
                }

            }
            catch (Exception err)
            {
                Console.WriteLine(err.Message);
            }
        }

        private static IPropagatorBlock<int, int> GetPropagatorBlock()
        {
            var multiplyBlock = new TransformBlock<int, int>(item => item * 2);
            var addBlock = new TransformBlock<int, int>(item => item + 2);
            var divideBlock = new TransformBlock<int, int>(item => item / 2);

            var flowCompletion = new DataflowLinkOptions { PropagateCompletion = true };
            multiplyBlock.LinkTo(addBlock, flowCompletion);
            addBlock.LinkTo(divideBlock, flowCompletion);

            return DataflowBlock.Encapsulate(multiplyBlock, divideBlock);
        }
  }

We build up the steps of the computation pipeline as a TransformBlock. The multiplyblock is linked to the addBlock and the divideBlock is then linked to the addBlock. We got a pipeline like this: multiplyBlock-addBlock-divideBlock. Each computation will then be: y = (x * 2) => z = y + 2 => w = z / 2. We also use the Encapsulate method to glue together the start step and the end step. We then get the following output:
Input numbers:
1
13
26
14
29
15
Pipeline: x = (x * 2) => (x + 2) => (x / 2)
2
14
27
15
30
16
Press any key to continue ..
Test out TPL Dataflow sample above (VS 2015 solution here: VS Solution With sample code above (.zip)

Wednesday, 29 June 2016

Wrapping Asynchronous Programming Model (APM) to Task-based Asynchronous Pattern (TAP)

Let's look at how we can wrap classic Begin and End methods used in APM to the newer Task-based Asynchronous Pattern (TAP). Many methods of older framework Versions of .NET support such APM methods and we want to wrap or adapt them to support TAP and async await. Example code:

using System;
using System.IO;
using System.Net;
using System.Text;
using System.Threading.Tasks;

namespace ApmToTap
{
    class Program
    {

        static void Main(string[] args)
        {
            DownloadDemo();

            Console.WriteLine();
            Console.ReadKey();
        }

        private static async void DownloadDemo()
        {
            WebRequest wr = WebRequest.Create("https://t.co/UrkiLgN1BC");
            try
            {
                var response = await wr.GetResponseFromAsync();
                using (Stream stream = response.GetResponseStream())
                {
                    StreamReader reader = new StreamReader(stream, Encoding.UTF8);
                    Console.WriteLine(reader.ReadToEnd());
                }
            }
            catch (Exception err)
            {
                Console.WriteLine(err.Message);
            }
        }
    }

    public static class WebRequestExtensions
    {

        public static Task<WebResponse> GetResponseFromAsync(this WebRequest request)
        {
            return Task<WebResponse>.Factory.FromAsync(request.BeginGetResponse,
                request.EndGetResponse, null);
        }

    }

}

We use the Task<T>Factory.FromAsync method and provide the delegates for the Begin and End methods used in APM. We then provide just null as the AsyncState parameter, as this is not needed. We then can await the Task we create here and get the functionality Task provides such as information of how the asynchronous operation went, exceptions and so on. And of course we can also get the result we usually retrieve in the End method using APM. So there you have it. To use TAP With APM methods, you can use the Task<T>FromAsync method.

High performance Producer-Consumer scenario using Nito.AsyncEx

The Nuget Library "Nito.AsyncEx" contains powerful collections that makes it possible to create asynchronous collections that support Producer-Consumer scenarios. First off, let us install the Nuget package:

Install-Package Nito.AsyncEx


using Nito.AsyncEx;
using System;
using System.Collections.Concurrent;
using System.Threading.Tasks;

namespace AsyncCollectionDemo
{
    class Program
    {

        private static readonly AsyncCollection<int> _asyncStack = new AsyncCollection<int>(new ConcurrentStack<int>(), maxCount: 1);


        static void Main(string[] args)
        {
            ProducerConsumerDemo();
        }

        private static async void ConsumerThread()
        {
            await Task.Run(async () =>
             {
                 //Consumer code 
                 while (await _asyncStack.OutputAvailableAsync())
                 {
                     Console.WriteLine(await _asyncStack.TakeAsync());
                     //Thread.Sleep(1000);
                 }
             });
        }

        private static async void ProducerConsumerDemo()
        {
            ConsumerThread();
            //Producer code 
            await _asyncStack.AddAsync(7);
            await _asyncStack.AddAsync(13);
            await _asyncStack.AddAsync(19);
            _asyncStack.CompleteAdding();


            Console.WriteLine("Press any key to continue ..");
            Console.ReadKey(); 
        }

    }
}

We can use the AsyncCollection to create one or multiple producer threads and then return the results to the consumer threads. The benefit of this Collection compared to the BlockingCollection in BCL is that since it supports async, the consumer can be an UI thread for example. So you can have code that produces results and delivers them back to the user Interface. You can ofcourse skip using the ConcurrentStack if you want a FIFO ordering instead of the stack's LIFO ordering. The creator of Nito.AsyncEx is created by Stephen Cleary, which also is the author of the good book "Concurrency in C# Cookboox" which is an O'Reilly book.

Producer-Consumer scenario in .NET using BlockingCollection

The BCL contains helpful classes to build your producer-consumer scenarios. We want to have a thread or several that produces data and one or several threads that consume that data. In this article I will show a simple single producer, single consumer scenario. BlockingCollection contains the necessary logic to support this. Consider the following code:


using System;
using System.Collections.Concurrent;
using System.Threading;
using System.Threading.Tasks;

namespace BlockingCollection
{
    class Program
    {

        private static readonly BlockingCollection<int> _blockingQueue = new BlockingCollection<int>(boundedCapacity: 1); 


        static void Main(string[] args)
        {
            Task.Run(() =>
            {
                foreach (var item in _blockingQueue.GetConsumingEnumerable())
                {
                    Console.WriteLine("Hey I got this item: " + item + "!");
                    Thread.Sleep(1000);
                }

            });

            int[] nums = { 1, 3, 8, 11, 94, 28 };
            foreach (var n in nums)
                _blockingQueue.Add(n);
            _blockingQueue.CompleteAdding();

            Console.WriteLine("Hit the any key!");
            Console.ReadKey(); 
        }

    }
}


We create a blocking collection with a bound capacity of one item. This will only accept a single item at a time. This means that our second call to the .Add() method will actually block. We also use the .CompleteAdding() method to signal that we are finished filling up values. It is also important to start up our consumer before the blocking call. I use Task.Run()here to start up a new thread. We will inside that thread Call the .GetConsumingEnumerable() to set up our consumer. Note that I also use Thread.Sleep to make the consumer wait a bit, this is only for testing and normally you would of course not wait here. Note also that you could spawn multiple consumers with Task.Run or similar to support 1 producer, multiple consumers scenarios. For multiple producers you could use a single shared blocking collection or possibly multiple blocking collections. BlockingCollection is very flexible. It is important that you call .CompleteAdding() on your producer side to allow the consumers to finish also their execution.
What if you want to not have a FIFO ordering in your Producer-Consumer scenario, but say a LIFO scenario? As you probably can see, if you instantiate the BlockingCollection, the constructor takes overloads to somethhing called an IProducerConsumerCollection Collection. So we just adjust our instantiation like the following (note that I had to remove the boundedCapacity here set to 1 to make it work!):

   private static readonly BlockingCollection<int> _blockingQueue = new BlockingCollection<int>(
            new ConcurrentStack<int>()); 

So now we get our new output:

Hit the any key!
Hey I got this item: 28!
Hey I got this item: 94!
Hey I got this item: 11!
Hey I got this item: 8!
Hey I got this item: 3!
Hey I got this item: 1!

The BCL contains several interesting classes in the System.Collections.Concurrent namespace. Happy .NET coding!

Monday, 20 June 2016

How to open up a SQL connection with SQL Management studio 2012 through Powershell

Sometimes it is nice to just log into a SQL server database with just running a command. To maintain security, we let our user input the password manually and use Powershell to start up SQL Server Management Studio 2012. If you got another version of SQL Server Management Server (SSMS), just adjust the path to ManagementStudio.

$domain="SOMEDOMAIN"
$user="SomeUser"
$workingdir="c:\Program Files (x86)\Microsoft SQL Server\110\Tools\Binn\ManagementStudio"
$databaseserver="somedbserver.somedomain.net"
$cmd="ssms.exe"
$arguments=" -S $databaseserver" 

$domainuser = $domain + "\" + $user

$response = Read-host "Enter password" -AsSecureString 
#$secpasswd = [Runtime.InteropServices.Marshal]::PtrToStringAuto([Runtime.InteropServices.Marshal]::SecureStringToBSTR($response))

$credential = New-Object System.Management.Automation.PSCredential ($domainuser, $response)

Start-Process -WorkingDirectory $workingdir -FilePath $cmd -Argument $arguments -Credential $credential 

You can add an icon on your desktop and assign it a shortcut to powershell and then paste the script above to a .ps1 file and then as the argument of the shortcut point to a .ps1 with the script above.

Wednesday, 1 June 2016

How to display the SQL involved for in Entity Framework programatically with DbContext and ObjectContext

As a developer, we often use an Object-Relational Mapper (ORM) to abstract from the way we work with a database. Gone are the days of building a SqLCommand object, setting the CommandText and executing row by row the result set, as used with ADO.NET. Today, most .NET developers use EntityFramework to work with the database. But this abstraction is all and well, and makes us work more efficient. Sadly, many developers are agnostic to the fact that despite they get the results out from the database, they do often do so in a slow manner. The reason of this is often not that there is a lot of data in the database, but we use Entity Framework queries that generate the wrong sql, i.e we get the results, but the SQL involved got a poor performance. You can use LinqPad for example to display the SQL involved in Entity Framework queries. But we can also achieve this using programatically methods, with C#. Here is an extension class I wrote to achieve this. The extension methods works with both data contexts that inherit from DbContext and data contexts that inherit from ObjectContext.

using System;
using System.Data.Entity.Core.Objects;
using System.Linq;
using System.Reflection;

namespace Hemit.OpPlan.Data.EntityFramework
{
    
    public static class IQueryableExtensions
    {

        /// <summary>
        /// Shows the sql the IQueryable query will be generated into and executed on the database
        /// </summary>
        /// <param name="query">The IQueryable to analyze</param>
        /// <param name="decodeParameters">Set to true if this method should try decoding the parameters</param>
        /// <remarks>This is the generated SQL query in use for Entity Framework. This works using ObjectContext</remarks>
        public static string ShowSqlUsingObjectContext(this IQueryable query, bool decodeParameters = false)
        {
            var objectQuery = (ObjectQuery)query; 
           
            string result = ((ObjectQuery)query).ToTraceString();

            if (!decodeParameters)
                return result; 

            foreach (var p in objectQuery.Parameters)
            {
                string valueString = p.Value != null ? p.Value.ToString() : string.Empty;
                if (p.ParameterType == typeof(string) || p.ParameterType == typeof(DateTime))
                    valueString = "'" + valueString + "'";
                result = result.Replace("@" +p.Name, p.Value != null ? valueString : string.Empty); 
            }
            return result; 
        }

        public static string ShowSqlUsingDbContext(this IQueryable query, bool decodeParameters = false)
        {
            var memberInfo = query.GetType().BaseType;
            if (memberInfo != null)
            {
                var internalQueryField = 
                memberInfo.GetFields(BindingFlags.NonPublic
              | BindingFlags.Instance).FirstOrDefault(f => f.Name.Equals("_internalQuery"));
                if (internalQueryField != null)
                {
                    var internalQuery = internalQueryField.GetValue(query);
                    var objectQueryField =
                        internalQuery.GetType().GetProperty("ObjectQuery"); 

                    // Here's your ObjectQuery!
                    if (objectQueryField != null)
                    {
                        var objectQuery = objectQueryField.GetValue(internalQuery) as ObjectQuery;
                        string sql = ShowSqlUsingObjectContext(objectQuery, decodeParameters);
                        return sql;
                    }
                }
            }

            return null;
        }

    }
}

Note that when we use an IQueryable inside a DbContext, the BaseType is actually a DbQuery, and this wraps the ObjectQuery inside a field called "_internalQuery". In addition, we get a property inside this field that is called "ObjectQuery". So we can get hold of the ObjectQuery inside a DbQuery. When we got hold of the ObjectQuery, it is easy to decode the contents using ToTraceString() method and if we want to further decode the parameters EntityFramework generates, we can do so using the Parameters property of ObjectQuery. We can then interpolate the SQL parametrization and get the SQL string most readable, if we like this form. Of course, some developers rather like the parametrized version. There may be some queries that don't have any parameters at all, but this is fine. Of course, all this parametrization business is to hinder SQL injection. Please do not resort to creating methods that accepts such "clean sql", you may easily generate an attack vector into your system if you try do adjusts queries so and not being careful. With this extension method we can easily test it out:

using SomeAcme.EntityFramework;
using Nunit.Framework; 

[Test]
public void TestGettingSomeSql(){

 using (var context = new SomeAcmeContext()){
  IQueryable query = context.SomeDataEntity.Where(x => x.SomeProperty == 123).AsQueryable();
  
  string sql = string.Empty; 

  //If this is a dbContext: 

   sql = query.ShowSqlUsingDbContext(decodeParameters: true);

   //Or if this is an ObjectContext: 

   sql = query.ShowSqlUsingObjectContext(decodeParameters: true); 

   Console.WriteLine(sql);

 }
}

We create a query, using the .AsQueryable() extension method in Linq and we then pass the IQueryable object to the extension methods of the class shown earlier. Of course, the extension method to use depends on the type of data context you work with. Either a DbContext or an ObjectContext.