Parallel Extensions to the .NET Framework Forum

Example to speed up Sample Generation

Wed, 25 Nov 2009 09:25:43 Z

Hi, wondering if anyone out there can give me an example of how they would parallelize this function.... It should be doable.... i just cant crack it..

    Public Function RandomArray(ByVal iSamples As Integer, ByVal dMu As Double, ByVal dSigma As Double) As Double()
        Dim oRnd As New Random
        Dim dRandomVariate As Double
        Dim dSample As Double
        Dim lstSamples As New Generic.List(Of Double)

        For i As Integer = 0 To iSamples - 1
            dRandomVariate = Math.Sqrt(-2 * Math.Log(oRnd.NextDouble)) * Math.Sin(2 * Math.PI * oRnd.NextDouble)
            dSample = Math.Exp(dMu + dSigma * dRandomVariate)

            lstSamples.Add(dSample)
        Next

        Return lstSamples.ToArray
    End Function

Application, cores and threads

Tue, 24 Nov 2009 07:19:28 Z

Apologies for asking a real stupid question but it's been boiling for some time.

Question: So far I've been writing single prototype to see it perform better using multi-core/TPL, I was wondering if all major application/services (say 50 or more) on my box start using core-thread-affinity/concurrency what would be the impact in terms of overall performance versus if so many applications do not use or say a very limited number of applications use concurrency i.e. the way it is today?. Has anyone studied the performance difference between the two? In terms of battery life I am sure concurrency would make cores suck lot more power?

Also though it would defeat the purpose of having concurrency in first place, but can we have a system wide policy where we can specify to use only X number of cores for concurrency. Also can we some how be biased on applications which start recently or are in the main view to get more number of cores as compared to the service which has been running for say last week?

Producer/Consumer pattern question

Tue, 24 Nov 2009 09:29:30 Z

Hello,

Here is my code :

BlockingCollection<long> bc = new BlockingCollection<long>(2);

var producer = Task.Factory.StartNew(() =>
{
  for (long i = 0; i < 10; i++)
  {
    bc.Add(i);
  }

  bc.CompleteAdding();
});

var consumer = Task.Factory.StartNew(() =>
{
  Parallel.ForEach<long>(bc.GetConsumingEnumerable(), id =>
  {
    Console.WriteLine(id);
    Thread.Sleep(2000);
  });
});

consumer.Wait();

The consumer is not working as I would like because it empties the collection too fast and the producer continues to add elements.
Like this I lose the benefit of boundedcapacity = 2.
I'd like the consumer to create 2 background tasks and wait for completion before letting the producer adding new elements.

Thanks.

philippe

Nested Parallel.ForEach ?

Mon, 23 Nov 2009 17:22:54 Z

I have been reading http://msdn.microsoft.com/en-us/library/dd460720(VS.100).aspx and found it very interesting, but I have a question.

What if my code looks something like this:

Parallel.ForEach(arrayA, currentA =>
{
    foreach (int currentB in arrayB)
    {
        foreach (int currentC in arrayC)
        {
            // do something here
        }
    }
}
);

Do I only need the Parallel.ForEach on the first loop (like the code above) or on all foreach-statements?

Would you please post the ProfilerExamples.csproj that you demonstrated at PDC '09?

Sun, 22 Nov 2009 14:36:14 Z

Would you please post the ProfilerExamples.csproj that you demonstrated at PDC '09? (is not part of ParallelProgrammingSamples_Beta2.zip)

Thank you.

p.s. - Stephen T. - fantastic presentation; i wish that i had seen it first in '08 or been paying attention on channel 9 - will follow from now on.

Updating a progress bar from inside a Parallel.For

Fri, 06 Feb 2009 19:40:51 Z

Hi,

I'm using the CTP for .NET 3.5 in VS2008

I have 2 problems.

1/
I have a custom Control with a ProgressBar and a processing Engine object.

At the heart of the Engine object is a Parellel.For 'loop'.

I wish to step the ProgressBar from within the loop and am failing to do so usefully.

I first tried firing an event from inside the loop which was received by the control which then updated the progressbar ( see code below). This failed to return and the whole loop hung.

private delegate void ThreadSafedelegate();

                ThreadSafedelegate update = delegate()
                    {
                        progressBar.Value++;
                        Application.DoEvents();
                    };

                if (InvokeRequired)
                    Invoke(update);
                else
                    update();
                System.Diagnostics.Trace.WriteLine("After update"); // this line never reached

Using Parallel.Invoke(Step) fared no better.

I then used Task.Create(() => Step(), TaskCreationOptions.Detached) to fire the event. This rather wonderfully ran all the processing loops and only afterwards fired all the step events!

I've considered passing the control to the engine and then calling the control step function directly, but I can't see this helping as the problem appears to be in dealing with the control UI than with firing the event.

Any suggestions about how I could go about this?

2/ in a similar situation to the above I have an abort button on the control and I use that to set a flag which is examined in the processing engine Parallel.For 'loop' to call state.Stop(). All well and good, but when the loop is running no button clicks are processed by the form. When I insert an Application.DoEvents() in the loop, the behaviour doesn't change except that the engine eventually crashes with the following message:-

System.InvalidOperationException was unhandled
Message="The Undo operation encountered a context that is different from what was applied in the corresponding Set operation. The possible cause is that a context was Set on the thread and not reverted(undone)."
Source="mscorlib"
StackTrace:
       at System.Threading.SynchronizationContextSwitcher.Undo()
       at System.Threading.ExecutionContextSwitcher.Undo()
       at System.Threading.ExecutionContext.runFinallyCode(Object userData, Boolean exceptionThrown)
       at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteBackoutCodeHelper(Object backoutCode, Object userData, Boolean exceptionThrown)
       at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData)
       at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.Tasks.Task.Execute(Boolean stolen)
       at System.Threading.Tasks.TaskBase.InvokeStolen()
       at System.Threading.ConcurrencyScheduler.InternalContext.Dispatch()
       at System.Threading.ConcurrencyScheduler.ThreadInternalContext.ThreadStartBridge(IntPtr dummy)
InnerException:

Any suggestions?

Cheers
Graham

Released! Parallel Extensions to the .NET Framework 3.5 June 2008 CTP

Mon, 02 Jun 2008 17:01:45 Z

Parallel Extensions to the .NET Framework simplifies development by providing library-based support for introducing concurrency into applications written with any .NET language, including C# and Visual Basic. It includes the Task Parallel Library (TPL), which provides imperative data and task parallelism; Parallel LINQ (PLINQ), which provides declarative data parallelism; and all new Coordination Data Structures (CDS), which provide support for work coordination and managing shared state.

In addition to CDS, this upgrade provides several improvements, including a new scheduler that is more robust, efficient, and scalable. TPL also exposes new functionality, including methods for continuations. PLINQ now runs on top of TPL, clarifies order-preservation, and provides several new operators.

Thanks,

documentation on Parallel Programming with .NET 4 Beta 2 Samples

Thu, 19 Nov 2009 00:23:42 Z

Where is it?

Thank you.

Why can't I pass ParallelOptions/TokenSource as a function member to my Task function?

Thu, 19 Nov 2009 08:00:14 Z

Do we always need to make CancellationTokenSource a static or a member variable to access from the parallel function (Test) in the below code for example? It would have been better if we could pass CancellationTokenSource as a function parameter like parallelloopstate that way we can create static libraries that would consist of only core parallel logic? Please correct me if i have overlooked at something?

using System;

using System.Threading;

using System.Threading.Tasks;

namespace ConsoleApplication1

{

class Program

{

static ParallelOptions po = new ParallelOptions();

static CancellationTokenSource cts = new CancellationTokenSource();

static void Main(string[] args)

{

try

{

ParallelLoopResult result = Parallel.For(1, 100000, po, Test);

}

catch(AggregateException exception)

{

//handle code here

}

Console.ReadKey();

}

public static void Test(int number, ParallelLoopState loopState)

{

if (cts.IsCancellationRequested) // cts is accessed here because it's static member variable, why can't we pass this as a function variable member?

{

Console.WriteLine("returning");

cts.Token.ThrowIfCancellationRequested();

}

Parallel computing in .net 3.5 Sp1 to read large chunk of textfile into objects

Tue, 17 Nov 2009 13:21:27 Z

I have a more then 100 meg of file.I am reading the file and loading it into my objects line by line. I am now investigating how can i improve it.Can I use parallel programming in .net 3.5 Sp1 to improve my time My current code is
Also I completely new in this.
Let me know if I need to install any thing on development machine and on the deployment server or not

My current code for loading the file is

private void LoadObjects()
{
    Stopwatch stopWatch = new Stopwatch();
    stopWatch.Start();

    StreamReader reader = File.OpenText(@"c:\TestFile.txt");
    StringBuilder line = new StringBuilder(reader.ReadLine());
    BookObject objBook = null;
    List<BookObject> objBookList = new List<BookObject>();
    while (line != null && line.ToString().Length > 0)
    {
        objBook = new BookObject();
        objBook.Property1 = line.ToString().Substring(0, 27);
        objBook.Property2 = line.ToString().Substring(28, 5);
        objBook.Property3 = line.ToString().Substring(53, 8);
        objBook.Property4 = line.ToString().Substring(62, 8);
        objBookList.Add(objBook);
        line = new StringBuilder(reader.ReadLine());
    }
    reader.Close();

    stopWatch.Stop();
    TimeSpan ts = stopWatch.Elapsed;
    MessageBox.Show("Loaded in [" + ts.Milliseconds.ToString() + " milliseconds or " + ts.Seconds.ToString() + " Seconds");

}

Kamran Shahid Senior Software Engineer/Analyst (MCP,MCAD,MCSD.NET,MCTS,MCPD.net[web])

What is a best way to do a cancellable sleep for subsecond period of time?

Wed, 18 Nov 2009 00:00:22 Z

Hi,

Here is my scenario - I need tasks that perform work lazily - after a small delay (~100ms) and only if it is not cancelled by that time.
Basically we have situations where we know that there is a work to be done (user input, other assync changes...), but want to do it only if nothing happens in the next 100ms.

I see two possible solutions - start task with

1)
Sleep(DELAY)
cancellationToken.ThrowIfCancellationRequested()

(we will hog the thread for the time of DELAY)

or

2)
Threading.SpinWait.SpinUntil(Function() cancellationToken.IsCancellationRequested, DELAY)
cancellationToken.ThrowIfCancellationRequested()

(spinning may waste some CPU resources)

It is not very important to have precise timings. I am just wondering what would be the best way to sleep for subsecond period when running in a Task? Or what other factors I should consider?

Thanks,
Vladimir

Task Comunication

Wed, 18 Nov 2009 19:22:14 Z

I am a web developer and very often we will start a task "thread" and have the ui watch it till it finishes we also have other tasks talk to each other. I guess my question is there code show how Tasks can communicate together?

How to Set TaskManager to PLINQ

Thu, 26 Feb 2009 08:35:14 Z

Hello,

in early version of PFX we have such overloaded verstion of PLINQ's AsParallel extenstion method:
http://my.safaribooksonline.com/9780321434821/app02lev1sec2

public static IParallelEnumerable<TSource> AsParallel<TSource>(
this IEnumerable<TSource> source,
TaskManager taskManager
);

But in June08 CTP as far as I can understand we lose that ability.
How to set users' TaskManager to PLINQ ?

Thank you

Task Dispose best practice?

Mon, 16 Nov 2009 07:05:36 Z

When working with Tasks, especially continuations and nested tasks (attached or unattached), what would be the recommended approach for disposing the tasks?

e.g. in a situation something along these lines...

Task.Factory.StartNew(() =>
{
	// do things
}).ContinueWith(t =>
{
	// do things
	Task.Factory.StartNew(() =>
	{
		// do things
	});
})
.ContinueWith(t =>
{
	// do things
});

Thanks,
Matt

F# & parallel performance

Wed, 04 Nov 2009 19:00:32 Z

I was playing with "Samples for Parallel Programming with the .NET Framework 4 (http://code.msdn.microsoft.com/ParExtSamples)" and just tested the release version of Raytracer_CSharp and Raytracer_FSharp. The speed of both were the same in single threaded mode and interestingly the memory usage of F#version was less than the C# version. But when I switched to parallel mode, the C# version was faster than the F# version. I had a look at the CPU consumption and found out that the C# version was consuming 92% to 96% of CPU time while the F# version about 82% to 87%. Any explanation for this behavior?

Thanks,
Bijan

Parallel.For problem

Thu, 29 Oct 2009 19:52:01 Z

Hello All

I am trying to create an application in which there are around 10 dll's each working sequentially. Now I want to make the app multi threaded . the application checks if it can find name of machine through interface and if it does it starts doing different tests on machine(computer). So , suppose listbox have 3 computer names , it will make entry in 1st table say id=1, name=server 1and move to check drivers on machine ....
to make it multithreaded this is what I am trying ......

Parallel.For(0, listBox1.Items.Count - 1, delegate(int i) gbl.strComputer = listBox1.Items[i].ToString(); 

{

Logs.Logging(gbl.logFilePath, " ", true);

Logs.Logging(gbl.logFilePath, "Establishing Connection to......." + gbl.strComputer, true); Conn.fnConnect(gbl.strComputer, gbl.logFilePath); 

 

if (returnConnect == 0) // if able to connect start pulling the information

{

 id = Machine_Information.InsertServerInformation(gbl.strComputer, gbl.logFilePath);

 if (id == 0) 
{

Logs.Logging(gbl.logFilePath, "Processing FAILED on " + gbl.strComputer, true); 
Logs.Logging(gbl.logFilePath, " ", true);

}

 else
{


 

Driver Information 

 

Logs.Logging(gbl.logFilePath, "Task 4 STARTED : Getting Driver Information", true); 

 

Driver_Information.InsertDriverInformation(gbl.logFilePath, gbl.strComputer, id); 

 

if (driverInfoCollector) 

 

Logs.Logging(gbl.logFilePath, "Task 4 Finished : Driver Information inserted in Driver Table", true); 

 

else

{

 

Logs.Logging(gbl.logFilePath, "Task 4 Failed. Some or All drivers are not written to database. ", true); 

 

#endregion

 


}

Problem is After adding Parallel.for in the code , it inserts bad information. Sometimes , its just entering same information sometimes its not entering anything . When i try to step through the code , it waits at some lines indefinitely and next time it steps through ssamr line in very fast.

PLease let me know , what is the procedure of using this library to do something like :

if(listbox.item.count >0)
{
put information in 1st table

if(information inserted in 1st table )
{
use primary key of 1st table that is "id" as input in second dll and put information in 2nd table
use primary key of 1st table that is "id" as input in third dll and put information in 3rd table
use primary key of 1st table that is "id" as input in fourth dll and put information in 4th table
and so on ....................
}

go back to second item of list and try to put information in 1st table and use its id for other tables....

}

Please let me know what exactly needs to be done here ?
Thanks
Varun

Is this the correct forum for this HPC question?

Mon, 02 Nov 2009 17:41:54 Z

I am trying to run some of the Microsoft HPC examples and my jobs sit in the Configuring state. I have completed the To-Do list and have a 3 node configuration using the Network Topology Selection # 5 - All nodes only on an Enterprise network. I have successfully run the following Microsoft examples using my credentials which are a member of the Administrators group on all nodes:

Connecting to a Cluster (http://msdn.microsoft.com/en-us/library/cc853425(VS.85).aspx)
Using Active Directory to Find the Head Nodes (http://msdn.microsoft.com/en-us/library/cc907077(VS.85).aspx)
Getting a List of Nodes in the Cluster (http://msdn.microsoft.com/en-us/library/cc853436(VS.85).aspx)
Getting a List of Jobs (http://msdn.microsoft.com/en-us/library/cc853435(VS.85).aspx)

When attempting the next example: Creating and Submitting a Job (http://msdn.microsoft.com/en-us/library/cc853426(VS.85).aspx), the jobs list in the Job Management queue with the Configuring state and do not proceed. I have to cancel them. I substituted the:

task.CommandLine = "<COMMANDGOESHERE>";

with the name of an exe that resides on all nodes in the cluster that just sets the value of an integer and exits. When stepping through debug, after the following call:

scheduler.SubmitJob(job, @"<domain\username>", null);

(modified to use my domain/id), the WaitOne blocking call never returns. Any help is greatly appreciated.
Thanks,
jkastrinos

When BlockingCollection.TakeFromAny() return -1?

Tue, 20 Oct 2009 16:03:20 Z

Hi2all!

I have one question: when BlockingCollection<(Of <T>)>.TakeFromAny() static method return -1?

I read MSDN Docs that TakeFromAny() returns:
The index of the collection in the collections array from which the item was removed, or -1 if an item could not be removed.

Ok, but when item couldn't be removed? When collections parameter array contains empty not completed BlockingCollection<T> instances, the thread, called TakeFromAny() is blocked.

Let me to show you an example. I have console application:

using System;
using System.Collections.Generic;
//using System.Linq;
using System.Text;
using System.Collections.Concurrent;
using System.Threading;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            BlockingCollection<int> col1 = new BlockingCollection<int>();
            BlockingCollection<int> col2 = new BlockingCollection<int>();


            //Timer t1 = new Timer(delegate
            //    {
            //       // col1.Add(111);
            //        col1.CompleteAdding();

            //    }, null, 1000, Timeout.Infinite);
            //Timer t2 = new Timer(delegate
            //    {
            //        //col2.Add(222);
            //        //Thread.SpinWait(30000000);
            //        col2.CompleteAdding();
                    

            //    }, null, 2000, Timeout.Infinite);

            Console.WriteLine(DateTime.Now.ToLongTimeString());
            
            int value;
            int indexOfCollection = BlockingCollection<int>.TakeFromAny(new[] { col1, col2 }, out value);
            Console.WriteLine(DateTime.Now.ToLongTimeString() + " " + value + " index = "+indexOfCollection);

            Console.WriteLine("Done");
            Console.ReadLine();
        }
    }
}

In this case main app thread is blocked forever. If I uncomment lines with 2 timers creation, I have ArgumentException : At least one of the specified collections is marked as complete with regards to additions.
Parameter name: collections
If I uncomment additional lines, where call Add method to both collections - it's ok, I take 111 value from col1.

So I can't imagine situation, where TryTakeFrom() returns -1. Can you explain me, when it's possible?

Thanks in advance!

P.S. My Env: windows 2008 R2 RC, VS 2010 beta 2.

Did Future get dropped from .Net Framework 4.0?

Thu, 29 Oct 2009 16:44:09 Z

I'm curious, did Future<T> get dropped from .Net Framework 4.0? If so, why? And what do we use in its place?

Error - The name ‘Parallel’ does not exist in the current context - Parallel.For, VS2010, beta 2

Tue, 27 Oct 2009 12:35:18 Z

I installed VS2010 beta 2 ultimate.

I tried to use Paralel.For with c# but I got the message:
"The name ‘Parallel’ does not exist in the current context"

I set the properties of my project and to compile for the .Net 4.0 Framework.
What else I can do resolve the problem?

Thanks in advance

Ami

Scability Question

Wed, 28 Oct 2009 19:33:02 Z

I am using a two Quad-core (8 cores in total) system and my program gives:

        1         2          4         6       8
        31.25   16.77   8.44    8.38    4.24

I wonder why there is no improvement from CPU=4 to CPU=6. Thank you.

The program is:

namespace Benchmark
{
    using System;
    using System.Threading;
    using System.Threading.Tasks;

    public class Benchmark
    {
        private static double[] xgk = new double[17];
        private static double[] wgk = new double[17];
        private static double[] wg = new double[8];

        public static double Eval(double x)
        {
            double sum = 0.0;
            int i, j;

            for (i = 3; i < 100000; i++)
            {
                for (j = 3; j < 100; j++)
                {
                    sum += Math.Pow(i + 0.01 * j, x);
                }
            }
            return sum;
        }

        public static double Run(int CPU)
        {
            int order = 15;
            double half, a;
            double res1, res2, res3, res4;
            double[] fv1 = new double[17];
            double[] fv2 = new double[17];

            half = a = 0.5;
            res1 = res2 = res3 = res4 = 0.0;

            ParallelOptions options = new ParallelOptions();
            options.MaxDegreeOfParallelism = CPU;
            Object mutex = new Object();

            long time = (DateTime.Now.Ticks - 621355968000000000) / 10000;
            Parallel.For(0, order / 2, options,
                () =>
                {
                    return (new double[3]);
                }, (j, state, local) =>
                {
                    double b = half * xgk[2 * j + 1];
                    double fval1 = Eval(a - b);
                    double fval2 = Eval(a + b);
                    fv1[2 * j + 1] = fval1;
                    fv2[2 * j + 1] = fval2;
                    double fsum = fval1 + fval2;
                    // local[0] = res1, local[1] = res2, local[2] = res3
                    local[0] += wg[j] * fsum;
                    local[1] += wgk[2 * j + 1] * fsum;
                    local[2] += wgk[2 * j + 1] * (System.Math.Abs(fval1) + System.Math.Abs(fval2));
                    return local;
                },
            local =>
            {
                lock (mutex)
                {
                    res1 += local[0];
                    res2 += local[1];
                    res3 += local[2];
                }
            });

            Parallel.For(0, (order + 1) / 2, options,
                () =>
                {
                    return (new double[2]);
                }, (j, state, local) =>
                {
                    double b = half * xgk[2 * j];
                    double fval1 = Eval(a - b);
                    double fval2 = Eval(a + b);
                    fv1[2 * j] = fval1;
                    fv2[2 * j] = fval2;
                    double fsum = fval1 + fval2;
                    // local[0] = res2, local[1] = res4
                    local[0] += wgk[2 * j] * fsum;
                    local[1] += wgk[2 * j] * (System.Math.Abs(fval1) + System.Math.Abs(fval2));
                    return local;
                },
            local =>
            {
                lock (mutex)
                {
                    res2 += local[0];
                    res4 += local[1];
                }
            });
            time = (DateTime.Now.Ticks - 621355968000000000) / 10000 - time;

            return ((double) time / 1000.0);
        }

        public static void Main(string[] args)
        {
            int[] cpu = { 1, 2, 4, 6, 8 };
            double[] time = new double[cpu.Length];
            int CPU;
            Random rand = new Random();

            // setup input.
            for (int i = 0; i < wgk.Length; i++)
            {
                wgk[i] = rand.NextDouble();
                wgk[i] = rand.NextDouble();
            }

            for (int i = 0; i < wg.Length; i++) wg[i] = rand.NextDouble();

            // Run
            for (int index = 0; index < cpu.Length; index++)
            {
                CPU = cpu[index];
                time[index] = Run(CPU);
            }

            Console.WriteLine("\t1\t2\t4\t6\t8");
            for (int j = 0; j < cpu.Length; j++) Console.Write("\t{0, 0:F2}", time[j]);
            Console.WriteLine();
        }
    }
}

Cancellation Framework in Beta 2 (CancellationTokenSource and Token)

Fri, 23 Oct 2009 08:42:52 Z

Hello,

I've a simple question about the new Cancellation Framework in .NET 4.0 Beta 2. I saw the example in the PFX Team Blog about using the new approach and I've some doubts about the using of the Token. Here is my example:

public static void Example1()
{
    CancellationTokenSource cts = new CancellationTokenSource();
    Task myTask = Task.Factory.StartNew(() =>
    {
        for (; ; )
        {
            Console.WriteLine("Check for cancellation ...");
            cts.Token.ThrowIfCancellationRequested();
            Console.WriteLine("wait");
            Thread.CurrentThread.Join(500);
        }

    }, cts.Token);
    Thread.CurrentThread.Join(2000);
    cts.Cancel();
}

I need to understand the second parameter: Task.Factory.StartNew(..., CancellationToken). It is possible to use this value inside the created Task in the user code? I noticed that the value is assigned inside the Task class to an internal structure. Since the property Task.Current is removed, I've no reference to the Task instance itself. In the examle above I'm able to access the Token, because the CancellationTokenSource instance is declared as global variable. When I change the example to the version below, I've the same result (but I think it is not correct ...):

public static void Example1()
{
    CancellationTokenSource cts = new CancellationTokenSource();
    Task myTask = Task.Factory.StartNew(() =>
    {
        Task.Factory.StartNew(() =>
        {
            for (; ; )
            {
                Console.WriteLine("Check for cancellation ...");
                cts.Token.ThrowIfCancellationRequested();
                Console.WriteLine("wait INNER");
                Thread.CurrentThread.Join(500);
            }
        }, cts.Token);

        for (; ; )
        {
            Console.WriteLine("Check for cancellation ...");
            token.ThrowIfCancellationRequested();
            Console.WriteLine("wait");
            Thread.CurrentThread.Join(500);
        }

    });
    Thread.CurrentThread.Join(2000);
    cts.Cancel();
}

In the example above I've removed the second parameter during the call to StartNew. I'm able to use the cts.Token inside the Task, because the the variable is available in this scope.
What happens inside the Task with the Token? It is necessary to pass everytime the token to the Task object?
Do you have a best practice or a pattern to use the Cancellation Framework correct?

Parallel Managed Code - VS.NET 2010 Beta 2

Thu, 22 Oct 2009 10:34:21 Z

Hi All,

Just wondering what the status of the Parallel work in the Beta 2 release of VS.NET and .NET?

Is it all baked in now? What about changes/features?

Thanks,

Phil.

Low CPU Utilization

Tue, 06 Oct 2009 07:56:23 Z

Hi,

I’m running Daniel Moth’s example of b-tree traversal from PDC 2008 (http://www.microsoft.com/emea/teched2008/developer/tv/default.aspx?vid=59#) using Tasks, on beta1 bits.

When I run it on an 8-core system (Win2008 Server) I see that I’m only hitting max of 60-70% CPU utilization (all cores come into play). In dual-core I see around 80% utilization.

Is this expected? Shouldn’t it be around 100% utilization?

This is the actual code:

static void TreeTraversal_TaskPerNode(Tree tree)

{

if (tree == null)

return;

Task left = new Task((o) => TreeTraversal_TaskPerNode(tree.Left), TaskCreationOptions.None);

left.Start();

Task right = new Task((o) => TreeTraversal_TaskPerNode(tree.Right), TaskCreationOptions.None);

right.Start();

left.Wait();

right.Wait();

ProcessItem(tree.Data);

}

Thanks,

Aviv.

Basic Concurrent data structures question

Mon, 19 Oct 2009 18:40:05 Z

Hi2all!

I have one conceptual question to Parallel Fx team. For example, I have 1 concurrent queue with 3 elements. And 2 threads try to dequeue 1 element simultaneously. MSDN documentation noticed:
"Return Value Type: System . Boolean
true if an element was removed and returned from the beggining of the ConcurrentQueue< (Of < ( T> ) > ) succesfully; otherwise, false . "
Ok, and what about described situation? Both threads returns two first values from queue? Or 2nd thread returns false?

Can you explain me, when exactly TryDequeue() method return false?

Thank you!

Different output of 2 seemingly same code snippet

Wed, 14 Oct 2009 12:28:17 Z

Consider following console application:

    class Program
    {
        static void Main (string[] args) {
            string targetPath = @"D:\Test";

            var files = Directory.GetFiles (targetPath);

            //Parallel method
            Parallel.ForEach (files, f => Console.WriteLine (f));

            //Classic method
            foreach (string f in files)
                Task.Factory.StartNew (() => Console.WriteLine (f));

            Console.ReadLine ();
        }
    }

Assume that I have four files in "D:\Test" folder: "1.txt", "2.txt", "3.txt", "4.txt".

When I run about program, first method i.e. Parallel method prints (correctly):

D:\Test\1.txt

D:\Test\2.txt

D:\Test\3.txt

D:\Test\4.txt

But the classic method prints:

D:\Test\4.txt

Why do classic way doesn't work whereas Parallel one does?

P.S.: Please let me know if you need me to explain why do I need to use classic foreach.

Creating many classes instances in parallel

Tue, 06 Oct 2009 07:21:36 Z

Hello,

My scenario is the following :
I have a server app that creates entitty collections and transforms those into DTO (data transport objects - WCF).
List<CustomerDTO> custDto = new List<CustomerDTO>
foreach (CustomerEntity cust in custEntities)
custDto.Add(cust.ToDto());
This consists of only creating an object (DTO) and filling its properties with the entity properties.
Can I expect some performace improvements on a multicore machine by using parallel extension ?
One important thing is that the order should remain the same since it is the result of an ORDER BY.

Thanks

philippe

Self Replicating Task

Fri, 14 Aug 2009 05:48:28 Z

In the CTP there was an option to Create a Task with the option SelfReplicating, I can't seem to find that option in .NET 4. Has this functionality been lost from the Task based API.

Parallel.For Slows Down with more cores

Fri, 02 Oct 2009 12:19:34 Z

Hi,

I'm running my test app on Intel Xeon 514 / 2.33 GHz, 2 Sockets, 2 Cores each, 4 GB RAM

the test app is a Monte Carlo Scenario that creates 500.000 objects of Type Mandelbrot; each object creates random values and forecasts 20 days; the result is 500.000 x 20 random values

the code looks like:

for (int CurrentDayOfForecast = 0; CurrentDayOfForecast < ForecastRange; CurrentDayOfForecast++)
{
    #region Calculate Current Day
    Parallel.ForEach(Mandelbrot, delegate(_30DaysUpDown_II_Mandelbrot CurrentMandelbrot)
    {
        CurrentMandelbrot.Forecast(CurrentDayOfForecast);
    });
    #endregion
}

when I run this code on 1 Socket (2 cores) the server is utilized at 45-48% and the code finishes after 40 seconds
when I run this code on 2 Sockes (4 cores) the server is utilized at 96-98% and the code finishes after 55 seconds

so more cores = slow down

Any hints?

Determining current Task ID from within an addin or debugger visualizer

Wed, 30 Sep 2009 10:56:53 Z

Suppose I halt at a breakpoint when debugging an application. From within an addin or debugger visualizer I can access the debugger object, and from that determine the thread that was executing when the breakpoint was hit. But I can't see any way of determining the task (or even the ID of the task) that was executing at that point. I can get this information via the Parallel Tasks panel, by finding the row with the yellow arrow, so the information is clearly available at some level. But I'd like to access this information programmatically, so is there a method that can be called to return the ID of the task currently running on a given thread that can be called when an application is "suspended" at a breakpoint?

Barrier question

Mon, 28 Sep 2009 20:01:37 Z

I got the following output for a run of the example below. The way I used the Barrier must be wrong because I expect the cpu (# of threads created) to be the same, e.g. cpu = 5 for every line. What is the correct way to use it? Thank you.

cpu = 4, i = 1
cpu = 4, i = 2
cpu = 4, i = 3
cpu = 4, i = 0
cpu = 5, i = 0
cpu = 5, i = 4
cpu = 5, i = 2
cpu = 5, i = 1
cpu = 5, i = 3
cpu = 5, i = 3
cpu = 5, i = 0
cpu = 5, i = 4
cpu = 5, i = 1
cpu = 5, i = 2
cpu = 5, i = 0
cpu = 5, i = 0

============================ code example ====================

public static void Main(string[] args)
        {
            int cpu = 0;
            double[,] mutex = new double[1, 1];
            Barrier barrier = new Barrier(0);
            System.Threading.Tasks.Parallel.For(0, 16, () =>
            {
                barrier.AddParticipant();
                lock (mutex)
                {
                    int id = cpu;
                    cpu++;
                    return id;
                }

            }, (i, state, local) =>
            {
                barrier.SignalAndWait();
                Console.WriteLine("cpu = " + cpu + ", i = " + local);
                for (int j = 0; j < 20000000; j++) { }
                return local;
            },
            local =>
            {
                barrier.RemoveParticipant();
            });
        }

Iterating over a DataColumnCollection

Thu, 24 Sep 2009 20:26:27 Z

In a recent project, I discovered the hard way that iterating over a columns collection, even read-only is not thread-safe. I.e. something like:

Parallel.Foreach(..
   foreach(DataColumn foo in mytable.Columns)
   ...

My question is whether using indexes in a standard For loop is thread-safe. I.e. instead of the above, something like:

Parallel.Foreach(..
   for(var i = 0; i < mytable.Columns.Count; i++)
   ...

It should be noted that I'm using the June CTP of the Parallel Extentions for .NET 3.5.

loop increment

Mon, 28 Sep 2009 20:19:29 Z

How to convert a for with a increment to Parallel.For?

for (int i = 0; i < n; i += block)
{
...
}

Break out of Parallel.Foreach in June CTP

Thu, 24 Sep 2009 20:27:40 Z

How do you break out of a Parallel.Foreach loop in the June CTP? I see that in the .NET 4.0 extensions they have added the ability to do so, but how do you do it in the previous set of extensions?

How does the Parallel Tasks debugging window get access to the list of current tasks?

Thu, 24 Sep 2009 15:31:22 Z

I'm writing a Visual Studio debugging visualizer and I'd like to be able to access the state of all the current tasks in the process being debugged when it is halted at a breakpoint. The Parallel Tasks debugging window illustrates that there must be some way of doing this, but I've not found anything in the various threading APIs that gives me access to this infomation. The closest thing I found was the GetScheduledTasks

method in the TaskScheduler class. But using reflection to call this (as it's protected) on the default scheduler only produced a subset of the tasks shown in the tasks debugging window. And I couldn't see anything else that would enumerate all the current task schedulers, so I'm presumably going down a dead end. So does anyone know how the Parallel Tasks debugging window gets hold of the list of current tasks?

Cancel Tasks within Parallel.Invoke

Sat, 19 Sep 2009 18:08:50 Z

I've checked out the code from the Parallel.Invoke method, especially the method with the ParallelOptions parameter. I noticed that the method throws an exception when the CancellationToken is set to CANCELED (IsCancellationRequested=true -> OperationCanceledException). That is good! But how can I cancel the created task objects? It is possible? At the moment I've no access to the created task objects and the CancellationToken is not transfered to the task objects.

VB Parallel.For sample to calc Primes with run times for Intel Core i7 Processor

Mon, 21 Sep 2009 21:06:28 Z

VB Parallel.For Test Application calculating Primes with ParallelExtensions to .NET 3.5

These are run times from the code that follows:

         Non-Parallel Time: H:M:S   0:  0:  0.2 #Primes:     78,498 [7.85%] for Range: 1 - 1,000,000
             Parallel Time: H:M:S   0:  0:  0.2 #Primes:     78,498 [7.85%] for Range: 1 - 1,000,000
  SieveOfErathothenes Time: H:M:S   0:  0:    0 #Primes:     78,498 [7.85%] for Range: 1 - 1,000,000
SieveOfErathoParallel Time: H:M:S   0:  0:  0.3 #Primes:     78,498 [7.85%] for Range: 1 - 1,000,000
         Non-Parallel Time: H:M:S   0:  2: 10.8 #Primes:  5,761,455 [5.76%] for Range: 1 - 100,000,000
             Parallel Time: H:M:S   0:  0: 22.8 #Primes:  5,761,455 [5.76%] for Range: 1 - 100,000,000
  SieveOfErathothenes Time: H:M:S   0:  0:  1.7 #Primes:  5,761,455 [5.76%] for Range: 1 - 100,000,000
SieveOfErathoParallel Time: H:M:S   0:  0: 19.6 #Primes:  5,761,455 [5.76%] for Range: 1 - 100,000,000
         Non-Parallel Time: H:M:S   1:  7: 54.1 #Primes: 50,847,534 [5.08%] for Range: 1 - 1,000,000,000
             Parallel Time: H:M:S   0: 11:  6.7 #Primes: 50,847,534 [5.08%] for Range: 1 - 1,000,000,000
  SieveOfErathothenes Time: H:M:S   0:  0:   20 #Primes: 50,847,534 [5.08%] for Range: 1 - 1,000,000,000
SieveOfErathoParallel Time: H:M:S   0:  5: 30.7 #Primes: 50,847,534 [5.08%] for Range: 1 - 1,000,000,000


Note: Add Reference to Project, Browse Tab: C:\Program Files (x86)\Microsoft Parallel Extensions Jun08 CTP\System.Threading

Imports System.Threading.Tasks
Imports System.Threading

Public Class Form1
  Dim primeCounter As Integer

  'Form objects to add:
  ' Button: btnCalcPrimes, btnSieveOfEratosthenes
  ' Textboxes: txtStartInteger, txtEndInteger, txtPrimes [multi-line, font:Courier New, 8.25pt, size 840x440], txtCounter
  ' Checkbox: chkCalcParallel, chkListPrimes, chkShowMiscount, chkClearText

  Private Sub btnCalcPrimes_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCalcPrimes.Click
    Dim i, j, miscount As Integer
    Dim pcMiscount, pcPrimes As Single
    Dim firstInteger As Integer = CInt(txtStartInteger.Text)
    Dim lastInteger As Integer = CInt(txtEndInteger.Text)
    Dim results(lastInteger) As Boolean
    Dim s As String = ""
    Dim duration As String = "start"
    getDuration(duration)

    primeCounter = 0
    If chkClearText.Checked Then txtPrimes.Text = ""
    txtPrimes.Refresh()

    If firstInteger Mod 2 = 0 Then firstInteger += 1 'do odds only

    If chkCalcParallel.Checked Then
      Parallel.For(firstInteger, lastInteger, 2, Function(index As Integer) Prime(index, results))

      duration = ""
      getDuration(duration)

      j = 0
      For i = 1 To lastInteger
        If results(i) Then j += 1
      Next
      Debug.Print(primeCounter.ToString)
      miscount = j - primeCounter
      pcMiscount = Math.Round(100 * (miscount / j), 2)
      primeCounter = j
    Else
      For i = firstInteger To lastInteger Step 2
        Prime(i, results)
        If primeCounter Mod 100000 = 0 Then
          txtCounter.Text = primeCounter.ToString
          txtCounter.Refresh()
        End If
      Next

      duration = ""
      getDuration(duration)
    End If

    txtCounter.Text = primeCounter
    txtCounter.Refresh()
    pcPrimes = Math.Round(100 * (primeCounter / (CInt(txtEndInteger.Text) - CInt(txtStartInteger.Text) + 1)), 2)

    s = IIf(chkCalcParallel.Checked, "             ", "         Non-") + "Parallel Time: " + duration + " #Primes: " + prnr(primeCounter.ToString, 8) _
      + " [" + pcPrimes.ToString + "%] for Range: " + txtStartInteger.Text + " - " + txtEndInteger.Text _
      + IIf(chkCalcParallel.Checked And chkShowMiscount.Checked, " miscount: " + miscount.ToString _
      + " [" + pcMiscount.ToString + "%]", "") + vbCrLf

    If chkListPrimes.Checked Then s += getPrimeList(results)

    txtPrimes.Text = s

  End Sub

  Function Prime(ByVal index As Integer, ByVal results As Boolean())
    Dim i, j As Integer
    j = Math.Sqrt(index)
    results(index) = False

    If index = 1 Then '2 is the first prime
      Prime = Nothing
      results(index + 1) = True
      primeCounter += 1
      Exit Function
    End If

    If j < 3 Then
      Prime = Nothing
      results(index) = True
      primeCounter += 1
      Exit Function
    End If

    For i = 3 To j Step 2 'checking odds only in Prime
      If index Mod i = 0 Then
        Prime = Nothing
        results(index) = False
        Exit Function
      End If
    Next
    Prime = Nothing
    results(index) = True
    primeCounter += 1
  End Function

  Public Function prnl(ByVal s As String, ByVal i As Integer) As String
    If s = "" Then
      s = " "
      If i = 0 Then i = 1
    End If
    If s.Length > i Then s = Mid(s, 1, i - 1) + "?"
    prnl = Trim(s) + Space(i - Len(Trim(s)))
  End Function

  Public Function prnr(ByVal s As String, ByVal i As Integer) As String
    If s = "" Then
      s = " "
      If i = 0 Then i = 1
    End If
    If s.Length > i Then s = Mid(s, 1, i - 1) + "?"
    prnr = Space(i - Len(Trim(s))) + Trim(s)
  End Function

  Private Sub getDuration(ByRef s As String)
    Dim hrs, mins As Integer
    Dim secs As Single
    Static dtstart As DateTime
    Dim dtnow As DateTime
    Dim ts As TimeSpan

    If s.ToLower = "start" Then
      dtstart = DateTime.Now
      s = dtstart
    Else
      dtnow = DateTime.Now
      ts = dtnow.Subtract(dtstart).Duration
      hrs = Int(ts.TotalHours)
      mins = Int(ts.TotalMinutes) - hrs * 60
      secs = Math.Round((ts.TotalSeconds) - mins * 60 - hrs * 3600, 1)
      s = "H:M:S " + prnr(hrs.ToString, 3) + ":" + prnr(mins.ToString, 3) + ":" + prnr(secs.ToString, 5)
    End If
  End Sub

  Private Sub txtStartInteger_Leave(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles txtStartInteger.Leave
    txtStartInteger.Text = Format(CInt(txtStartInteger.Text), "###,###,###,###,###")
  End Sub

  Private Sub txtEndInteger_Leave(ByVal sender As Object, ByVal e As System.EventArgs) Handles txtEndInteger.Leave
    txtEndInteger.Text = Format(CInt(txtEndInteger.Text), "###,###,###,###,###")
  End Sub

  Private Sub txtCounter_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles txtCounter.TextChanged
    If txtCounter.Text <> " " Then
      txtCounter.Text = Format(CInt(txtCounter.Text), "###,###,###,###,###")
    End If
  End Sub

  Private Sub btnSieveOfErathsthenes_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSieveOfErathsthenes.Click
    Dim i, j, sqrlastInteger As Integer
    Dim firstInteger As Integer = CInt(txtStartInteger.Text)
    Dim lastInteger As Integer = CInt(txtEndInteger.Text)
    Dim pcPrimes As Single
    Dim s As String
    Dim duration As String = "start"
    getDuration(duration)

    If chkClearText.Checked Then txtPrimes.Text = ""

    sqrlastInteger = CInt(Math.Sqrt(lastInteger))

    Dim A(lastInteger) As Boolean

    For i = Math.Max(firstInteger, 2) To lastInteger
      A(i) = True
    Next

    'set every multiple of 2 through sqrlastInteger to false, the rest are Primes

    ' eliminate odd composite numbers
    If chkCalcParallel.Checked Then
      For i = 3 To sqrlastInteger Step 2
        Parallel.For(2 * i, lastInteger, i, Function(index As Integer) Prime(index, A))
      Next
    Else
      For i = 3 To sqrlastInteger Step 2
        If A(i) Then
          For j = 2 * i To lastInteger Step i
            A(j) = False
          Next
        End If
      Next
    End If

    ' eliminate all evens
    For i = 4 To lastInteger Step 2
      A(i) = False
    Next

    duration = ""
    getDuration(duration)

    j = 0
    For i = firstInteger To lastInteger
      If A(i) Then j += 1
    Next

    primeCounter = j
    txtCounter.Text = primeCounter
    txtCounter.Refresh()
    pcPrimes = Math.Round(100 * (primeCounter / (CInt(txtEndInteger.Text) - CInt(txtStartInteger.Text) + 1)), 2)

    s = IIf(chkCalcParallel.Checked, "SieveOfErathoParallel", "  SieveOfErathothenes") + " Time: " + duration + " #Primes: " _
      + prnr(primeCounter.ToString, 8) + " [" + pcPrimes.ToString + "%] for Range: " + txtStartInteger.Text + " - " + txtEndInteger.Text + vbCrLf

    If chkListPrimes.Checked Then s += getPrimeList(A)

    txtPrimes.Text += s

  End Sub

  Function EliminateNonPrimes(ByVal index As Integer, ByVal results As Boolean())
    results(index) = False
    Return False
  End Function

  Function getPrimeList(ByVal A As Boolean()) As String
    Dim i, j As Integer
    Dim s As String = ""

    j = 0
    For i = 1 To A.GetUpperBound(0)
      If A(i) Then
        j += 1
        If j Mod 10 = 0 Then 'end of row prime # counter
          s += prnr(i.ToString, 10)
          s += prnr(j.ToString, 10) + vbCrLf
        Else
          s += prnr(i.ToString, 10)
        End If
      End If
    Next

    If j Mod 10 <> 0 Then
      Dim k As Integer = (11 - (j Mod 10)) * 10
      s += prnr(j.ToString, k) + vbCrLf
    End If
    getPrimeList = s
  End Function
End Class

DanielHOfer

Parallel work on 3D Data Structure?

Thu, 10 Sep 2009 15:04:11 Z

VB 2008 & .net 3.5 Parallel Extensions, Vista Ultimate, 12GB memory, Intel Core(TM) i7 CPU. (4 cores). Affinity as set to all 8 "cpu's".:

I'm reading 15 criscrossing vertical 2D planes of geologic data from a 1-D data structure, Vels(i).V and averaging values within a given horizontal radius to a uniform spaced 3d bin volume array, Vsmooth(j, k, layer). I process 1 layer in each call to Coresow, so no data element in the input structure or output array is used in more than 1 layer. The current layer is determined inside Coresow. There is also a data structure I use to lookup the relationship between i's and the j, k bin location.

My non-parallel time through 101 layers took ~46 minutes.

For i = 1 To Layers
CoreSow()
Next

My Parallel.For trial took ~26 hours, parallel automatically set up 20 threads at a time, only 1 core was used though, at ~13% cpu.

Parallel.For(1, Layers, AddressOf CoreSow)

My Tasks trial took ~17 hours, I wanted to use only 4 cores at a time, and they were, but the total CPU Usage was still ~15%.

For i = 1 To Layers Step 4
k = -1
For j = i To i + 3 '4 layers at a time
k += 1 'in cores 0 to 3
t(k) = Tasks.Task.Create(AddressOf CoreSow)
Next j
Task.WaitAll(t(0), t(1), t(2), t(3))
Next i

The results were corrrect from all 3 runs.

Is there a problem in referencing the same input and output data structures/arrays even though no common elements are used in more than 1 call to Coresow?

Is there a good source of VB example code?

Thanks for your help.

DanielHOfer

ContinueWith issue

Tue, 15 Sep 2009 21:10:42 Z

Hi
Can anybody explains me why the following code don't write anything in the Console. Thanks
Matthieu

static void Main(string[] args)
{
    Task t = null;
    t = new Task(() =>
    {
        for (int i = 0; i < 10; i++)
            t.ContinueWith(t2 => Console.WriteLine(i));
    });
    t.Start();
    t.Wait();
}

Questions about PLINQ

Thu, 10 Sep 2009 18:35:29 Z

Hi,

I have a couple of questions about PLINQ - one general and one specific -

(1) -> I have been using LINQ (and now PLINQ) extensively and in particular like the functional abstraction it gives you in terms of just saying what tasks you want parallelized (not how) and it is done for you - and then I see all these posts about Imperative function calls like Tasks.Create, Tasks.Wait(), Parallel.ForAll() etc - so my question is - am I missing out on really cool API functions under the hood in TPL, when I have been just going gaga over PLINQ - in other words what are the class of problems for which I must leave PLINQ because its ineffective and then code imperatively using such calls - i understand these are broad questions - but necessary to wrap my mind around these new technologies...

(2) -> Specifically, I have some PLINQ code where I am reading sequentially from a System.Data.DataReader and creating a lazy list using yield return - whose consumption I will then attempt to parallelize after calling .AsParallel() on the list - my question is have I really parallelized the consumption of the list or its production? - would multiple tasks be working to get me as many records from the database - or is it one task getting all the records and many tasks then consuming it?

Thanks in advance...

jaydd