Skip to main content

Task Parallel Library - Refresher - Stop an Iteration

I have been talking about the Task Parallel Library (TPL) 2 years back , when it was in CTP, I was taking a class on High Performance Computing yesterday, and I just remembered that I have forgotten all about this library :).

This library has now been officially released with .Net 4.0 and Microsoft recommend you to actually use this library if possible when writing concurrent programs, so that your program can take maximum advantage on the numbers of processes that you have.

I thought of posting a sample code as a refresher,.
Here is the example, I have a list of Customer objects and I need to get the object that matches a specific criteria, lets say the Name property should be "F".

Here is how my Customer object looks like.

public class Customer
{
public int ID { get; set; }
public string Name { get; set; }
public int Age { get; set; }
}

Lets assume that the Name property is unique.

If I was to write the algorithm for this in .Net 1.1 or .Net 2.0 my logic would look like this.

foreach (Customer c in dataSource)
{

if (c.Name == "F")
{
result = c;
break;
}
}

This code will run in the same thread, unless you want to write a partition algorithm and then give crunches of the data source to different threads.

This is where TPL comes in to play, if I was using TPL I would write this code like this.

Customer result = null;
IList dataSource = GetMockDataSource(); //Get the data

Parallel.For(0, dataSource.Count, (i, state) =>
{
if (!state.IsStopped)
{
Customer c = dataSource[i];
if (c.Name == "F")
{
result = c;
state.Stop();

}
Console.WriteLine(c.Name);
}

});

This is what happens under the cover, the TPL runtime would partition the array (in our case we are using mere numbers and accessing the Customer object through the index) and create threads and give crunches of the indexes to each and every thread. The runtime can actually now spawn thread on different cores according to resource availability. By comparison this will increase performance as we are dividing the Customer list into crunches and each crunch is processed by different threads managed by the runtime.

Lets examine the code,
Line number 1 and 2 says it all, line number 3 is the place where we are using the TPL library.
The Parallel class is within the System.Threading.Tasks namespace, the static method For has many overloads, in the one that we used, the first parameter specifies the index the loop should start from and the second parameter specifies where the loop should end.

The 3 parameter, takes in an Action Delegate of type , for simplicity I have implemented it as a lambda function.
Within the lambda function, I check if the current Customer object satisfies our criteria, if so I use the ParallelLoopState object to signal to the runtime that we should now stop all iterations as we have found what we have been looking for by signaling ParallelLoopState.Stop().

When you call the Stop method on the ParallelLoopState object, the runtime will not create any more iteration , however, it cannot stop the iteration that have already started, so we explicitly check if the some other thread has signaled to stop by checking the IsStopped property of the ParallelLoopState object.

Although this example could have been done more efficiently using PLINQ, I chose the task library to show the underlining basics.

Comments

Popular posts from this blog

Hosting WCF services on IIS or Windows Services?

There came one of those questions from the client whether to use II7 hosting or windows service hosting for WCF services. I tried recollecting a few points and thought of writing it down. WCF applications can be hosted in 2 main ways - In a Windows service - On IIS 7 and above When WCF was first released, IIS 6 did not support hosting WCF applications that support Non-HTTP communication like Net.TCP or Net.MSMQ and developers had to rely on hosting these services on Windows Services. With the release of IIS 7, it was possible to deploy these Non-Http based applications also on IIS 7. Following are the benefits of using IIS 7 to host WCF applications Less development effort Hosting on Windows service, mandates the creating of a Windows service installer project on windows service and writing code to instantiate the service, whereas the service could just be hosted on IIS by creating an application on IIS, no further development is needed, just the service implementa

The maximum nametable character count quota (16384) has been exceeded

Some of our services were growing and the other day it hit the quote, I could not update the service references, nor was I able to run the WCFTest client. An error is diplayed saying " The maximum nametable character count quota (16384) has been exceeded " The problem was with the mex endpoint, where the XML that was sent was too much for the client to handle, this can be fixed by do the following. Just paste the lines below within the configuration section of the devenve.exe.config and the svcutil.exe.config files found at the locations C:\Program Files\Microsoft Visual Studio 9.0\Common7\IDE , C:\Program Files\Microsoft SDKs\Windows\v6.0A\bin Restart IIS and you are done. The detailed error that you get is the following : Error: Cannot obtain Metadata from net.tcp://localhost:8731/ Services/SecurityManager/mex If this is a Windows (R) Communication Foundation service to which you have access, please check that you have enabled metadata publishing at the specified address. F

ASP.NEt 2.0 Viewstate and good practices

View state is one of the most important features of ASP.NET because it enables stateful programming over a stateless protocol such as HTTP. Used without strict criteria, though, the view state can easily become a burden for pages. Since view state is packed with the page, it increases size of HTTP response and request. Fortunately the overall size of the __VIEWSTATE hidden field (in ASP.NET 2.0) in most cases is as small as half the size of the corresponding field in ASP.NET 1.x. The content of the _VIEWSTATE field (in client side) represent the state of the page when it was last processed on the server. Although sent to the client, the view state doesn't contain any information that should be consumed by the client. In ASP.NET 1.x, if you disable view state of controls, some of them are unable to raise events hence control become unusable. When we bind data to a grid, server encodes and put whole grid in to view state, which will increase size of view state (proportional to the