You can specify a `MaxDegreeOfParallelism` in a `ParallelOptions` parameter:

    Parallel.ForEach(
        listOfWebpages,
        new ParallelOptions { MaxDegreeOfParallelism = 4 },
        webpage =&gt; { Download(webpage); }
    );

MSDN: [Parallel.ForEach](http://msdn.microsoft.com/en-us/library/dd783747.aspx)

MSDN: [ParallelOptions.MaxDegreeOfParallelism](http://msdn.microsoft.com/en-us/library/system.threading.tasks.paralleloptions.maxdegreeofparallelism.aspx)

You can use ParallelOptions and set MaxDegreeOfParallelism to limit the number of concurrent threads:

    Parallel.ForEach(
        listOfwebpages, 
        new ParallelOptions{MaxDegreeOfParallelism=2}, 
        webpage =&gt; {Download(webpage);});     

Use another overload of `Parallel.Foreach` that takes a [`ParallelOptions`][1] instance, and set `MaxDegreeOfParallelism` to limit how many instances execute in parallel.


  [1]: http://msdn.microsoft.com/en-us/library/system.threading.tasks.paralleloptions.aspx

And for the VB.net users (syntax is weird and difficult to find)...

    Parallel.ForEach(listOfWebpages, New ParallelOptions() With {.MaxDegreeOfParallelism = 8}, Sub(webpage)
    ......end sub)  

                                                                                   

I get this error when I try to source a large SQL file (a big `INSERT` query).

    mysql&gt;  source file.sql
    ERROR 2006 (HY000): MySQL server has gone away
    No connection. Trying to reconnect...
    Connection id:    2
    Current database: *** NONE ***
    
    ERROR 2006 (HY000): MySQL server has gone away
    No connection. Trying to reconnect...
    Connection id:    3
    Current database: *** NONE ***

Nothing in the table is updated.  I&#39;ve tried deleting and undeleting the table/database, as well as restarting MySQL.  None of these things resolve the problem.

Here is my max-packet size:

    +--------------------+---------+
    | Variable_name      | Value   |
    +--------------------+---------+
    | max_allowed_packet | 1048576 |
    +--------------------+---------+

Here is the file size:

    $ ls -s file.sql 
    79512 file.sql

When I try the other method...

    $ ./mysql -u root -p my_db &lt; file.sql
    Enter password: 
    ERROR 2006 (HY000) at line 1: MySQL server has gone away

ERROR 2006 (HY000): MySQL server has gone away

I saw this list of major version numbers for Java in another post:

&gt; * Java 1.2 uses major version 46
&gt; * Java 1.3 uses major version 47
&gt; * Java 1.4 uses major version 48
&gt; * Java 5 uses major version 49
&gt; * Java 6 uses major version 50
&gt; * Java 7 uses major version 51
&gt; * Java 8 uses major version 52
&gt; * Java 9 uses major version 53
&gt; * Java 10 uses major version 54
&gt; * Java 11 uses major version 55
&gt; * Java 12 uses major version 56
&gt; * Java 13 uses major version 57
&gt; * Java 14 uses major version 58
&gt; * Java 15 uses major version 59
&gt; * Java 16 uses major version 60
&gt; * Java 17 uses major version 61
&gt; * Java 18 uses major version 62
&gt; * Java 19 uses major version 63

Where does this list come from? Is there a specific reference for this? Preferably something that shows minor versions too?

List of Java class file format major version numbers?

I have a Parallel.ForEach() async loop with which I download some webpages. My bandwidth is limited so I can download only x pages per time but Parallel.ForEach executes whole list of desired webpages.

Is there a way to limit thread number or any other limiter while running Parallel.ForEach?

Demo code:

    Parallel.ForEach(listOfWebpages, webpage =&gt; {
      Download(webpage);
    });

The real task has nothing to do with webpages, so creative web crawling solutions won&#39;t help.



How can I limit Parallel.ForEach?

I have a Parallel.ForEach() async loop with which I download some webpages. My bandwidth is limited so I can download only x pages per time but Parallel.ForEach executes whole list of desired webpages.
Is there a way to limit thread number or any other limiter while running Parallel.ForEach?
Demo code:
<pre><code class="hljs language-ini">Parallel.ForEach(listOfWebpages, webpage => {
 Download(webpage);
});
</code></pre>
The real task has nothing to do with webpages, so creative web crawling solutions won't help.

Are there situations where it is appropriate to use a `try-finally` block without a `catch` block?

Use a &#39;try-finally&#39; block without a &#39;catch&#39; block

How can I check if `IOException` is a &quot;Not enough disk space&quot; exception type?

At the moment I check to see if the message matches something like &quot;Not enough disk space&quot;, but I know that this won&#39;t work if the OS language is not English.

How to check if IOException is Not-Enough-Disk-Space-Exception type?

    string tags = &quot;9,3,12,43,2&quot;
    
    List&lt;int&gt; TagIds = tags.Split(&#39;,&#39;);

This doesn&#39;t work cause the split method returns a string[]

How can I convert comma separated string into a List&lt;int&gt;

The .NET Framework ships with [System.Runtime.Serialization.Json.DataContractJsonSerializer][1] and [System.Web.Script.Serialization.JavaScriptSerializer][2], both of which de/serialize JSON. How do I know when to choose one of these types over the other? MSDN doesn&#39;t make it clear what their relative advantages are.

We have several projects that consume or emit JSON, and the class selected for each thus far has depended on the opinion of the primary dev on each project. Some are simple, two have complex logic regarding producing managed types from JSON (the types do not map closely to the streams) but don&#39;t have any emphasis on speed, one requires speed. None interact with WCF, at least as of now. 

While I&#39;m interested in alternative libraries, I am hoping that somebody might have an answer to my question too. 


  [1]: http://msdn.microsoft.com/en-us/library/system.runtime.serialization.json.datacontractjsonserializer.aspx
  [2]: http://msdn.microsoft.com/en-us/library/system.web.script.serialization.javascriptserializer.aspx

What&#39;s the difference between DataContractJsonSerializer and JavaScriptSerializer?

There is a lot of code in one of our projects that looks like this:

    internal static class Extensions
    {
        public static string AddFoo(this string s)
        {
            if (s == null)
            {
                return &quot;Foo&quot;;
            }

            return $({s}Foo);
        }
    }

Is there any explicit reason to do this other than &quot;it is easier to make the type public later?&quot;

I suspect it only matters in very strange edge cases (reflection in Silverlight) or not at all.

Why use a public method in an internal class?

Here&#39;s the About.cshtml from the default MVC 3 template:


    @{
        ViewBag.Title = &quot;About Us&quot;;
    }
    
    &lt;h2&gt;About&lt;/h2&gt;
    &lt;p&gt;
         Put content here.
    &lt;/p&gt;

I would expect that a reference to the _ViewStart file would be found in the `About.cshtml`, but clearly it&#39;s not.

I&#39;ve looked in `global.asax` and `web.config`, but I can&#39;t find out how the `About.cshtml` file is &quot;linked&quot; with the layout from the _ViewStart file. 

Everything works as expected, I&#39;d just like to know what&#39;s going on under the hood...


Where and how is the _ViewStart.cshtml layout file linked?

I want to understand the scenarios where [`IEqualityComparer&lt;T&gt;`](http://msdn.microsoft.com/en-us/library/ms132151.aspx) and [`IEquatable&lt;T&gt;`](http://msdn.microsoft.com/en-us/library/ms131187.aspx) should be used.
The MSDN documentation for both looks very similar. 

What is the difference between IEqualityComparer&lt;T&gt; and IEquatable&lt;T&gt;?

I have been playing round with the `Async CTP` this morning and have a simple program with a `button` and a `label`. Click the `button` and it starts updating the `label`, stop the `button` it stops writing to the `label`. However, I&#39;m not sure how to reset the `CancellationTokenSource` so that I can restart the process. 

My code:

    public partial class MainWindow : Window
    {
        CancellationTokenSource cts = new CancellationTokenSource();
        public MainWindow()
        {
            InitializeComponent();
            button.Content = &quot;Start&quot;;
        }

        async Task DoWork(CancellationToken cancelToken)
        {
            int i = 0;
            while (!cancelToken.IsCancellationRequested)
            {
                label.Content = i++.ToString();
                await TaskEx.Delay(50, cancelToken);
            }
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            if (button.Content == &quot;Start&quot;)
            {
                button.Content = &quot;Stop&quot;;
                DoWork(cts.Token);
            }
            else
            {
                button.Content = &quot;Start&quot;;
                cts.Cancel();
            }
        }
    }

How to reset a CancellationToken properly?

During the Techdays here in the Netherlands Steve Sanderson gave a presentation about [*C#5, ASP.NET MVC 4, and asynchronous Web*.][1] 

He explained that when requests take a long time to finish, all the threads from the threadpool become busy and new requests have to wait. The server can&#39;t handle the load and everything slows down.

He then showed how the use of async webrequests improves performance because the work is then delegated to another thread and the threadpool can respond quickly to new incoming requests. He even demoed this and showed that 50 concurrent requests first took 50 * 1s but with the async behavior in place only 1,2 s in total.

But after seeing this I still have some questions.

1. **Why can&#39;t we just use a bigger threadpool? Isn&#39;t using async/await to bring up another thread slower then just increasing the threadpool from the start? It&#39;s not like the server we run on suddenly get more threads or something?** 

2. **The request from the user is still waiting for the async thread to finish. If the thread from the pool is doing something else, how is the &#39;UI&#39; thread kept busy? Steve mentioned something about &#39;a smart kernel that knows when something is finished&#39;. How does this work?**


  [1]: http://channel9.msdn.com/Events/TechDays/Techdays-2012-the-Netherlands/2287

Why use async requests instead of using a larger threadpool?

One simple question: is it possible to return a value in `AsyncTask`?

    //AsyncTask is a member class
    private class MyTask extends AsyncTask&lt;Void, Void, Void&gt;{

	    protected Void doInBackground(Void... params) {
             //do stuff
             return null;
	    }

	    @Override
	    protected void onPostExecute(Void result) {
	        //do stuff
            //how to return a value to the calling method?
	    }
	}

And then within my `Activity`/`Fragment`:

    // The task is started from activity
    myTask.execute()
    // something like this?
    myvalue = myTask.getvalue() 

**EDIT:
This was asked a long time ago where I wasn&#39;t familiar with Java, now that I&#39;m better with it, I &#39;ll do a quick summary:**

The point of async task is that the task is `asynchronous`, meaning that after you call `execute()` on the task, the task starts running on a thread of its own. returning a value from asynctask would be pointless because the original calling thread has already carried on doing other stuff (thus the task is asynchronous). 

Think of time:
At one point of time, you started a task that will run in parallel with the main thread. When the parallel-running task completed, time has also elapsed on the main thread. The parallel task cannot go back in time to return a value to the main thread.

I was coming from C so I didn&#39;t know much about this. But it seems that lots of people are having the same question so I thought I would clear it up a bit.




Return a value from AsyncTask in Android

Check out this [code][1] :

    &lt;a href=&quot;#&quot; id=&quot;link&quot;&gt;Link&lt;/a&gt;
    &lt;span&gt;Moving&lt;/span&gt;

    $(&#39;#link&#39;).click(function () {
        console.log(&quot;Enter&quot;);
        $(&#39;#link&#39;).animate({ width: 200 }, 2000, function() {
             console.log(&quot;finished&quot;);            
        });    
        console.log(&quot;Exit&quot;);    
    });

As you can see in the console, the &quot;animate&quot; function is asynchronous, and it &quot;fork&quot;s the flow of the event handler block code. In fact :

    $(&#39;#link&#39;).click(function () {
        console.log(&quot;Enter&quot;);
        asyncFunct();
        console.log(&quot;Exit&quot;);    
    });
    
    function asyncFunct() {
        console.log(&quot;finished&quot;);
    }

follow the flow of the block code!

If I wish to create my `function asyncFunct() { }` with this behaviour, how can I do it with javascript/jquery? I think there is a strategy without the use of  `setTimeout()`
    ​

  [1]: http://jsfiddle.net/5H9XT/5/

How can I create an Asynchronous function in Javascript?

There is a new app setting in asp.net 4.5

    &lt;add key=&quot;aspnet:UseTaskFriendlySynchronizationContext&quot; value=&quot;true&quot; /&gt;



code like this can run in asp.net 4.0

    protected void Button1_Click(object sender, EventArgs e)
    {
        CallAysnc();
    }

    public void CallAysnc()
    {
        AsyncOperation asyncOp = AsyncOperationManager.CreateOperation(Guid.NewGuid().ToString());

        WebClient client = new WebClient();
        client.DownloadStringCompleted += (object sender, DownloadStringCompletedEventArgs e) =&gt;
        {
            asyncOp.PostOperationCompleted(CallCompleted, e.Result);
        };
        client.DownloadStringAsync(new Uri(&quot;http://www.google.com&quot;));
    }

    private void CallCompleted(object args)
    {
        Response.Write(args.ToString());
    }

But it doesn&#39;t work in asp.net 4.5,and when I remove the new appsetting,it works again!

So what&#39;s the meaning of &quot;UseTaskFriendlySynchronizationContext&quot; ?

What&#39;s the meaning of &quot;UseTaskFriendlySynchronizationContext&quot;?

I am using Parallel.ForEach and I am doing some database updates, now without setting MaxDegreeOfParallelism , a dual core processor machine results in sql client timeouts, where else quad core processor machine somehow does not timeout.

Now I have no control over what kind of processor cores are available where my code runs, but is there some settings I can change with MaxDegreeOfParallelism that will probably run less operations simultaneously and not result in timeouts?

I can increase timeouts but it isnt a good solution, if on lower CPU I can process less operations simultaneously, that will put less load on cpu.

Ok I have read all other posts and MSDN too, but will setting MaxDegreeOfParallelism to lower value make my quad core machines suffer?

For example, is there anyway to do something like, if CPU has two cores, then use 20, if CPU has four cores then 40?

What does MaxDegreeOfParallelism do?

In a metro app, I need to execute a number of WCF calls. There are a significant number of calls to be made, so I need to do them in a parallel loop.  The problem is that the parallel loop exits before the WCF calls are all complete.

How would you refactor this to work as expected?

    var ids = new List&lt;string&gt;() { &quot;1&quot;, &quot;2&quot;, &quot;3&quot;, &quot;4&quot;, &quot;5&quot;, &quot;6&quot;, &quot;7&quot;, &quot;8&quot;, &quot;9&quot;, &quot;10&quot; };
    var customers = new  System.Collections.Concurrent.BlockingCollection&lt;Customer&gt;();

    Parallel.ForEach(ids, async i =&gt;
    {
        ICustomerRepo repo = new CustomerRepo();
        var cust = await repo.GetCustomer(i);
        customers.Add(cust);
    });

    foreach ( var customer in customers )
    {
        Console.WriteLine(customer.ID);
    }

    Console.ReadKey();

Nesting await in Parallel.ForEach

I am a bit of confused about `Parallel.ForEach`.  
What is `Parallel.ForEach` and what does it exactly do?  
Please don&#39;t reference any MSDN link.  

Here&#39;s a simple example : 

    string[] lines = File.ReadAllLines(txtProxyListPath.Text);
    List&lt;string&gt; list_lines = new List&lt;string&gt;(lines);

    foreach (string line in list_lines)
    {
        //My Stuff
    }

How can I rewrite this example with `Parallel.ForEach`?


How can I convert this foreach code to Parallel.ForEach?

**How do I break out of an [parallel.for][1] loop?**

I have a pretty complex statement which looks like the following: 

    Parallel.ForEach&lt;ColorIndexHolder&gt;(ColorIndex.AsEnumerable(),
        new Action&lt;ColorIndexHolder&gt;((ColorIndexHolder Element) =&gt;
        {
            if (Element.StartIndex &lt;= I &amp;&amp; Element.StartIndex + Element.Length &gt;= I)
            {
                Found = true;
                break;
            }
        }));


Using parallel class, I can optimize this process by far. However; I cannot figure out how to break the parallel loop? The `break;` statement throws following syntax error: 

&gt; No enclosing loops out of which to break or continue

  [1]: http://msdn.microsoft.com/en-us/library/system.threading.tasks.parallel.for.aspx

Break parallel.foreach?

I&#39;m calling a slow webservice in parallel. Things were great until I realized I need to get some information back from the service. But I don&#39;t see where to get the values back. I can&#39;t write to the database, HttpContext.Current appears to be null inside of a method called using Parallel.ForEach

Below is a sample program (in your mind, please imagine a slow web service instead of a string concatenation)


    using System;
    using System.Threading.Tasks;
    
    class Program
    {
        static void Main(string[] args)
        {
            WordMaker m = new WordMaker();
            m.MakeIt();
        }
        public class WordMaker
        {
            public void MakeIt()
            {
                string[] words = { &quot;ack&quot;, &quot;ook&quot; };
                ParallelLoopResult result = Parallel.ForEach(words, word =&gt; AddB(word));
                Console.WriteLine(&quot;Where did my results go?&quot;);
                Console.ReadKey();
            }
            public string AddB(string word)
            {
                return &quot;b&quot; + word;
            }
        }
    
    }



Content Type	Original Author	Original Content on Stackoverflow
Question	eugeneK	View Question on Stackoverflow
Solution 1 - C#	Nick Butler	View Answer on Stackoverflow
Solution 2 - C#	rikitikitik	View Answer on Stackoverflow
Solution 3 - C#	Richard	View Answer on Stackoverflow
Solution 4 - C#	user3496060	View Answer on Stackoverflow

How can I limit Parallel.ForEach?

C# Problem Overview

C# Solutions

Solution 1 - C#

Solution 2 - C#

Solution 3 - C#

Solution 4 - C#

List of Java class file format major version numbers?

ERROR 2006 (HY000): MySQL server has gone away

Attributions