You can invoke it normally and then `await` the returned task:

    Task&lt;Car&gt; result = (Task&lt;Car&gt;)method.Invoke(obj, null);
    await result;

***Let me caveat by saying that this may be better suited as an html/css question but (a) I&#39;m not too familiar with those techniques and (b) I wanted to keep it all in the family (R family) if possible.***

I would like to use `knitr` to write academic style reports (**APA 6 type guidelines**) using Rmarkdown.  I&#39;ve got most aspects worked out but not page breaking.  I can manually set page breaks with something like:

    # report
    
    ```{r setup, include=FALSE}
    # set global chunk options
    opts_chunk$set(cache=TRUE)
    ```
    ------
    ## Page 1
    
    ```{r plot1}
    plot(1:10, 1:10)
    ```
    ------
    ## Page 2

In the following .Rmd I&#39;d like to programatically set those breaks after n lines/n distance.  So let&#39;s say after 8 inches or 140 lines. 

    # report
    
    ```{r setup, include=FALSE}
    # set global chunk options
    opts_chunk$set(cache=TRUE)
    ```
    Initial Text. Yay!

    ```{r plot1}
    plot(1:10, 1:10)
    ```
   
    More Text.  Outstanding.  What Hadley&#39;s not calling it plyr2?

    ```{r plot2, fig.width=4, fig.height=4}
    plot(1:10, 1:10)
    ```

    `r paste(rep(&quot;So much text so little time!&quot;, 10000))`

How can I programatically set page breaks after n distance.  This is similar to how `LaTeX` would break a file into pages so if a figure takes too much space it would be forced to the next page.

**EDIT** Found this from a friend: http://www.w3.org/TR/css3-page/  may be helpful.


knitr/Rmd: page break after n lines/n distance

i have several buttons and i need a popover for each.  
i want it like this:  
when my user click on one of them, i want others to be hidden. so only one popover is shown  
check and help me correcting this example plz:  

&lt;!-- language: lang-js --&gt;

    var mycontent=&#39;&lt;div class=&quot;btn-group&quot;&gt; &lt;button class=&quot;btn&quot;&gt;Left&lt;/button&gt; &lt;button class=&quot;btn&quot;&gt;Middle&lt;/button&gt; &lt;button class=&quot;btn&quot;&gt;Right&lt;/button&gt; &lt;/div&gt;&#39;
     
&lt;!-- language: lang-js --&gt;

    $(&#39;.btn&#39;).popover({
        html: true,
        content:mycontent,
        trigger: &#39;manual&#39;
    }).click(function(e) {
        $(this).popover(&#39;toggle&#39;);
        e.stopPropagation();
    });
    
    $(&#39;html&#39;).click(function(e) {
         $(&#39;.btn&#39;).popover(&#39;hide&#39;);
    });

my html:

&lt;!-- language: lang-html --&gt;

    &lt;ul&gt;
        &lt;li&gt;
            &lt;a href=&quot;#&quot; class=&quot;btn&quot; data-toggle=&quot;popover&quot; data-placement=&quot;bottom&quot; title=&quot;&quot; &gt;Popover&lt;/a&gt;
        &lt;/li&gt;
        &lt;li&gt;
           &lt;a href=&quot;#&quot; class=&quot;btn&quot; data-toggle=&quot;popover&quot; data-placement=&quot;bottom&quot; title=&quot;&quot; &gt;Popover&lt;/a&gt; 
        &lt;/li&gt;
    &lt;/ul&gt;

[jsfiddle example][1]


  [1]: http://jsfiddle.net/moalla/fsRaN/2/

adding something like the code bellow solved my problem somehow:

&lt;!-- language: lang-js --&gt;

    $(&#39;.btn&#39;).click(function(e) {
         $(&#39;.btn&#39;).popover(&#39;hide&#39;);
    });
but by clicking twice on each button it goes wrong

Show one popover and hide other popovers

I have an ansyc method


    public Task&lt;Car&gt; GetCar()
    {

    }

I can call this method async and await:

     Car car = await GetCar()

How can I invoke the method using MethodInfo.Invoke and await for the result asynchronously.

     MethodInfo method = obj.GetMethod(&quot;GetCar&quot;);
     method.Invoke( obj, null)

.Net Invoke async method and await

I have an ansyc method
<pre><code class="hljs language-arduino">public Task&#x3C;Car> GetCar()
{

}
</code></pre>
I can call this method async and await:
<pre><code class="hljs language-ini"> Car car = await GetCar()
</code></pre>
How can I invoke the method using MethodInfo.Invoke and await for the result asynchronously.
<pre><code class="hljs language-ini"> MethodInfo method = obj.GetMethod("GetCar");
 method.Invoke( obj, null)
</code></pre>

I have below code in c# 4.0.

    //Dictionary object with Key as string and Value as List of Component type object
    Dictionary&lt;String, List&lt;Component&gt;&gt; dic = new Dictionary&lt;String, List&lt;Component&gt;&gt;();
    
    //Here I am trying to do the loping for List&lt;Component&gt;
    foreach (List&lt;Component&gt; lstComp in dic.Values.ToList())
    {
    	// Below I am trying to get first component from the lstComp object.
        // Can we achieve same thing using LINQ?
        // Which one will give more performance as well as good object handling?
    	Component depCountry = lstComp[0].ComponentValue(&quot;Dep&quot;);
    }



How to get first object out from List&lt;Object&gt; using Linq

Im creating a Login using a `window control` to allow a user to login into a `WPF` application that I am creating. 

So far, I have created a method that checks whether the user has entered in the correct credentials for the `username` and `password` in a `textbox` on the login screen, `binding` two `properties`. 

I have achieved this by creating a `bool` method, like so;

    public bool CheckLogin()
    {
        var user = context.Users.Where(i =&gt; i.Username == this.Username).SingleOrDefault();

        if (user == null)
        {
            MessageBox.Show(&quot;Unable to Login, incorrect credentials.&quot;);
            return false;
        }
        else if (this.Username == user.Username || this.Password.ToString() == user.Password)
        {
            MessageBox.Show(&quot;Welcome &quot; + user.Username + &quot;, you have successfully logged in.&quot;);

            return true;
        }
        else
        {
            MessageBox.Show(&quot;Unable to Login, incorrect credentials.&quot;);
            return false;
        }
    }

    public ICommand ShowLoginCommand
    {
        get
        {
            if (this.showLoginCommand == null)
            {
                this.showLoginCommand = new RelayCommand(this.LoginExecute, null);
            }
            return this.showLoginCommand;
        }
    }

    private void LoginExecute()
    {
        this.CheckLogin();
    } 

I also have a `command` that I `bind` to my button within the `xaml` like so;

    &lt;Button Name=&quot;btnLogin&quot; IsDefault=&quot;True&quot; Content=&quot;Login&quot; Command=&quot;{Binding ShowLoginCommand}&quot; /&gt;

When I enter in the username and password it executes the appropriated code, whether it being right, or wrong. But how can I close this window from the ViewModel when both username and password are correct?

I have previously tried using a `dialog modal` but it didn&#39;t quite work out. Furthermore, within my app.xaml, I have done something like the following, which loads the login page first, then once true, loads the actual application.

    private void ApplicationStart(object sender, StartupEventArgs e)
    {
        Current.ShutdownMode = ShutdownMode.OnExplicitShutdown;

        var dialog = new UserView();

        if (dialog.ShowDialog() == true)
        {
            var mainWindow = new MainWindow();
            Current.ShutdownMode = ShutdownMode.OnMainWindowClose;
            Current.MainWindow = mainWindow;
            mainWindow.Show();
        }
        else
        {
            MessageBox.Show(&quot;Unable to load application.&quot;, &quot;Error&quot;, MessageBoxButton.OK);
            Current.Shutdown(-1);
        }
    }

**Question: How can I close the Login `Window control` from the ViewModel?**

Thanks in advance.

Close Window from ViewModel

I&#39;m banging my head on my desk with this binding error..  I have checked several of the postings for the `BindingExpression` path error and cannot see anything that works with my situation.


Anyway, I have a custom control called `IncrementingTextBox`.  I am trying to disable it whenever the user &#39;checks&#39; the `CheckBox` above it.

I have a binding on the `CheckBox` `IsChecked` property that is working fine and is firing when it is supposed to.  It is correctly setting the `UseSensorLength` property on the ConfigurationModel.

However, the binding on the `IncrementingTextBox` `IsEnabled` property is causing a `BindingExpression` path error and so doesn&#39;t update at all.

As a test, I tried in the code behind to enable and disable the control and it works just fine, but I can&#39;t seem to get the Binding to work on it.

Here is a snippet from my xaml:



    ...
    
    DataContext=&quot;{Binding RelativeSource={RelativeSource Self}}&quot;
    
    ...
    ...
    
    &lt;CheckBox Content=&quot;Use Sensor Length&quot; Margin=&quot;30,6,0,0&quot; 
              IsChecked=&quot;{Binding ConfigurationModel.UseSensorLength, Mode=TwoWay}&quot;/&gt;
    
    &lt;local:IncrementingTextBox x:Name=&quot;video_length_textbox&quot; Margin=&quot;0,0,0,5&quot; 
                               IsTextEnabled=&quot;False&quot; 
                               IsEnabled=&quot;{Binding ConfigurationModel.DontUseSensorLength}&quot; 
                               ValueChanged=&quot;VideoEventValueChanged&quot;/&gt;

And Here is a snippet from my ConfigurationModel:


    public bool DontUseSensorLength
    {
        get { return !UseSensorLength; }
    }
    
    public bool UseSensorLength
    {
       get { return _useSensorLength; }
       set 
       { 
          _useSensorLength = value; 
          OnPropertyChanged(&quot;UseSensorLength&quot;); 
          OnPropertyChanged(&quot;DontUseSensorLength&quot;);
       }
    }


Here is the error message I am getting in my output window when running the app:

&gt; System.Windows.Data Error: 40 : BindingExpression path error:
&gt; &#39;ConfigurationModel&#39; property not found on &#39;object&#39;
&gt; &#39;&#39;IncrementingTextBox&#39; (Name=&#39;video_length_textbox&#39;)&#39;.
&gt; BindingExpression:Path=ConfigurationModel.DontUseSensorLength;
&gt; DataItem=&#39;IncrementingTextBox&#39; (Name=&#39;video_length_textbox&#39;); target
&gt; element is &#39;IncrementingTextBox&#39; (Name=&#39;video_length_textbox&#39;); target
&gt; property is &#39;IsEnabled&#39; (type &#39;Boolean&#39;)



Remember, the &#39;UseSensorLength&#39; property binding is working fine, but the &#39;DontUseSensorLength&#39; binding is causing the above &#39;BindingExpression path error&#39;.


WPF Error 40 BindingExpression path error: property not found on &#39;object&#39;

I&#39;m trying to get started with ASP.NET MVC Ajax calls.

**Controller:**

    public class AjaxTestController : Controller
    {
        //
        // GET: /AjaxTest/
        public ActionResult Index()
        {
            return View();
        }
    
        public ActionResult FirstAjax()
        {
            return Json(&quot;chamara&quot;, JsonRequestBehavior.AllowGet);
        }   
    }

**View:**

   

    &lt;head runat=&quot;server&quot;&gt;
        &lt;title&gt;FirstAjax&lt;/title&gt;
        &lt;script src=&quot;http://code.jquery.com/jquery-1.9.1.js&quot;&gt;&lt;/script&gt;
        &lt;script src=&quot;http://ajax.googleapis.com/ajax/libs/jquery/2.0.0/jquery.min.js&quot;&gt;&lt;/script&gt;
        &lt;script type=&quot;text/javascript&quot;&gt;
            $(document).ready(function () {
                var serviceURL = &#39;/AjaxTest/FirstAjax&#39;;
        
                $.ajax({
                    type: &quot;POST&quot;,
                    url: serviceURL,
                    data: param = &quot;&quot;,
                    contentType: &quot;application/json; charset=utf-8&quot;,
                    dataType: &quot;json&quot;,
                    success: successFunc,
                    error: errorFunc
                });
        
                function successFunc(data, status) {     
                    alert(data);
                }
        
                function errorFunc() {
                    alert(&#39;error&#39;);
                }
            });
        &lt;/script&gt;
    &lt;/head&gt;

I just need to print an alert with the controller method returning data. Above code just print &quot;chamara&quot; on my view. An alert is not firing.

**UPDATE**

I modified my controller as below and it start working. I don&#39;t have an clear idea why it&#39;s working now. Some one please explain. The parameter &quot;a&quot; does not related i added it because i can not add two methods with same method name and parameters.I think this might not be the solution but its working

 
    public class AjaxTestController : Controller
        {
            //
            // GET: /AjaxTest/
            [HttpGet]
            public ActionResult FirstAjax()
            {
                return View();
            }
    
            [HttpPost]
            public ActionResult FirstAjax(string a)
            {
                return Json(&quot;chamara&quot;, JsonRequestBehavior.AllowGet);
            }
        }

Making a Simple Ajax call to controller in asp.net mvc

I am trying to see if a file exists before using it in an MVC controller:

    string path = &quot;content/image.jpg&quot;;

    if (File.Exists(path))
    { 
        //Other code
    }

The `File` keyword is underlined in red, and the compiler shows an error:

&gt; `System.Web.MVC.Controller.File(string, string, string)` is a
&gt; &#39;method&#39;, witch is not valid in the given context.

How can I use `File.Exists()` in a controller?


Why can&#39;t I use System.IO.File methods in an MVC controller?

I often find myself creating a [`Dictionary`][dict] with a non-trivial value class (e.g. [`List`][list]), and then always writing the same code pattern when filling in data.

For example:

&lt;!-- language: lang-csharp --&gt;

    var dict = new Dictionary&lt;string, List&lt;string&gt;&gt;();
    string key = &quot;foo&quot;;
    string aValueForKey = &quot;bar&quot;;

That is, I want to insert `&quot;bar&quot;` into the list that corresponds to key `&quot;foo&quot;`, where key `&quot;foo&quot;` might not be mapped to anything.

This is where I use the ever-repeating pattern:

&lt;!-- language: lang-csharp --&gt;

    List&lt;string&gt; keyValues;
    if (!dict.TryGetValue(key, out keyValues))
      dict.Add(key, keyValues = new List&lt;string&gt;());
    keyValues.Add(aValueForKey);

Is there a more elegant way of doing this?

Related questions that don&#39;t have answers to this question:

* [Is there an IDictionary implementation that returns null on missing key instead of throwing?][1]
* [Find-or-insert with only one lookup in c# dictionary][2]
* [Dictionary returning a default value if the key does not exist][3]

 [dict]: http://msdn.microsoft.com/en-us/library/xfhwa508.aspx
 [list]: http://msdn.microsoft.com/en-us/library/6sh2ey19.aspx
 [1]: https://stackoverflow.com/q/538729/974531
 [2]: https://stackoverflow.com/q/6408916/974531
 [3]: https://stackoverflow.com/q/2601477/974531

.NET Dictionary: get or create new

Java 1.8 is receiving the `Optional&lt;T&gt;` class, that allows us to explicitly say when a method may return a null value and &quot;force&quot; its consumer to verify if it is not null (`isPresent()`) before using it.

I see C# has `Nullable&lt;T&gt;`, that does something similar, but with basic types. It seems to be used for DB queries, to distinguish when a value exists and is 0 from when it doesn&#39;t exist and is null.

But it seems that C#&#39;s `Nullable&lt;T&gt;`doesn&#39;t work for objects, only for basic types, while Java&#39;s `Optional&lt;T&gt;` only works for objects and not for basic types.

Is there a Nullable/Optional class in C#, that forces us to test if object exists before extracting and using it?

Optional return in C#.Net

I am trying to create a lambda expression for a nested property at run-time from the name of the propert. Basically I am trying to create the lambda expression specified by:

    var expression = CreateExpression&lt;Foo, object&gt;(foo =&gt; foo.myBar.name);

    private static Expression CreateExpression&lt;TEntity, TReturn&gt;(Expression&lt;Func&lt;TEntity, TReturn&gt;&gt; expression)
    {
        return (expression as Expression);
    }

With the classes:

    class Foo
    {
        public Bar myBar { get; set; }
    }
    class Bar
    {
        public string name { get; set; }
    }

However all I am given is the type of `Foo` and the string `&quot;myBar.name&quot;`

If it were a normal property such as just needing the value `&quot;myBar&quot;` then I could use the following:


    private static LambdaExpression GetPropertyAccessLambda(Type type, string propertyName)
    {
        ParameterExpression odataItParameter = Expression.Parameter(type, &quot;$it&quot;);
        MemberExpression propertyAccess = Expression.Property(odataItParameter, propertyName);
        return Expression.Lambda(propertyAccess, odataItParameter);
    }

However this code does not work for nested properties and I&#39;m not sure how to create the LambdaExpression to do the work of `foo.myBar.name`.

I think it&#39;s going to be something like this:

    GetExpression(Expression.Call(GetExpression(Foo, &quot;myBar&quot;), &quot;name&quot;))

But I can&#39;t seem to work out how to get it all working, or if there&#39;s a better way to do this at run-time.

Construct LambdaExpression for nested property from string

This code is from Charles Pettzold&#39;s &quot;Programming Windows Sixth Edition&quot; book:

    public object Convert(object value, Type targetType, object parameter, string language) 
    { 
        return ((double)value).ToString(&quot;N0&quot;); 
    }

`ToString(&quot;N0&quot;)` is supposed to print the value with comma separators and no decimal points. I cannot find the reference to appropriate `ToString` overload and `&quot;N0&quot;` format in the documentation. Please point me to the right place in .NET documentation.

What is ToString(&quot;N0&quot;) format?

I recently created a simple application for testing the HTTP call throughput that can be generated in an asynchronous manner vs a classical multithreaded approach.

The application is a able to perform a predefined number of HTTP calls and at the end it displays the total time needed to perform them. During my tests, all HTTP calls were made to my local IIS sever and they retrieved a small text file (12 bytes in size).

The most important part of the code for the asynchronous implementation is listed below:

    public async void TestAsync()
    {
    	this.TestInit();
    	HttpClient httpClient = new HttpClient();
    
    	for (int i = 0; i &lt; NUMBER_OF_REQUESTS; i++)
    	{
    		ProcessUrlAsync(httpClient);
    	}
    }
    
    private async void ProcessUrlAsync(HttpClient httpClient)
    {
    	HttpResponseMessage httpResponse = null;
    
    	try
    	{
    		Task&lt;HttpResponseMessage&gt; getTask = httpClient.GetAsync(URL);
    		httpResponse = await getTask;
    
    		Interlocked.Increment(ref _successfulCalls);
    	}
    	catch (Exception ex)
    	{
    		Interlocked.Increment(ref _failedCalls);
    	}
    	finally
    	{ 
    		if(httpResponse != null) httpResponse.Dispose();
    	}
    
    	lock (_syncLock)
    	{
    		_itemsLeft--;
    		if (_itemsLeft == 0)
    		{
    			_utcEndTime = DateTime.UtcNow;
    			this.DisplayTestResults();
    		}
    	}
    }

The most important part of the multithreading implementation is listed below:

    public void TestParallel2()
    {
    	this.TestInit();
    	ServicePointManager.DefaultConnectionLimit = 100;
    
    	for (int i = 0; i &lt; NUMBER_OF_REQUESTS; i++)
    	{
    		Task.Run(() =&gt;
    		{
    			try
    			{
    				this.PerformWebRequestGet();
    				Interlocked.Increment(ref _successfulCalls);
    			}
    			catch (Exception ex)
    			{
    				Interlocked.Increment(ref _failedCalls);
    			}
    
    			lock (_syncLock)
    			{
    				_itemsLeft--;
    				if (_itemsLeft == 0)
    				{
    					_utcEndTime = DateTime.UtcNow;
    					this.DisplayTestResults();
    				}
    			}
    		});
    	}
    }
    
    private void PerformWebRequestGet()
    { 
    	HttpWebRequest request = null;
    	HttpWebResponse response = null;
    
    	try
    	{
    		request = (HttpWebRequest)WebRequest.Create(URL);
    		request.Method = &quot;GET&quot;;
    		request.KeepAlive = true;
    		response = (HttpWebResponse)request.GetResponse();
    	}
    	finally
    	{
    		if (response != null) response.Close();
    	}
    }

Running the tests revealed that the multithreaded version was faster. It took it around 0.6 seconds to complete for 10k requests, while the async one took around 2 seconds to complete for the same amount of load. This was a bit of a surprise, because I was expecting the async one to be faster. Maybe it was because of the fact that my HTTP calls were very fast. In a real world scenario, where the server should perform a more meaningful operation and where there should also be some network latency, the results might be reversed.

However, what really concerns me is the way HttpClient behaves when the load is increased. Since it takes it around 2 seconds to deliver 10k messages, I thought it would take it around 20 seconds to deliver 10 times the number of messages, but running the test showed that it needs around 50 seconds to deliver the 100k messages. Furthermore, it usually takes it more than 2 minutes to deliver 200k messages and often, a few thousands of them (3-4k) fail with the following exception:

&gt;    An operation on a socket could not be performed because the system lacked sufficient buffer space or because a queue was full.

I checked the IIS logs and operations that failed never got to the server. They failed within the client. I ran the tests on a Windows 7 machine with the default range of ephemeral ports of 49152 to 65535. Running netstat showed that around 5-6k ports were being used during tests, so in theory there should have been many more available. If the lack of ports was indeed the cause of the exceptions it means that either netstat didn&#39;t properly report the situation or HttClient only uses a maximum number of ports after which it starts throwing exceptions.

By contrast, the multithread approach of generating HTTP calls behaved very predictable. I took it around 0.6 seconds for 10k messages, around 5.5 seconds for 100k messages and as expected around 55 seconds for 1 million messages. None of the messages failed. Further more, while it ran, it never used more than 55 MB of RAM (according to Windows Task Manager). The memory used when sending messages asynchronously grew proportionally with the load. It used around 500 MB of RAM during the 200k messages tests.

I think there are two main reasons for the above results. The first one is that HttpClient seems to be very greedy in creating new connections with the server. The high number of used ports reported by netstat means that it probably doesn&#39;t benefit much from HTTP keep-alive.

The second is that HttpClient doesn&#39;t seem to have a throttling mechanism. In fact this seems to be a general problem related to async operations. If you need to perform a very large number of operations they will all be started at once and then their continuations will be executed as they are available. In theory this should be ok, because in async operations the load is on external systems but as proved above this is not entirely the case. Having a big number of requests started at once will increase the memory usage and slow down the entire execution.

I managed to obtain better results, memory and execution time wise, by limiting the maximum number of asynchronous requests with a simple but primitive delay mechanism:

    public async void TestAsyncWithDelay()
    {
    	this.TestInit();
    	HttpClient httpClient = new HttpClient();
    
    	for (int i = 0; i &lt; NUMBER_OF_REQUESTS; i++)
    	{
    		if (_activeRequestsCount &gt;= MAX_CONCURENT_REQUESTS)
    			await Task.Delay(DELAY_TIME);
    
    		ProcessUrlAsyncWithReqCount(httpClient);
    	}
    }

It would be really useful if HttpClient included a mechanism for limiting the number of concurrent requests. When using the Task class (which is based on the .Net thread pool) throttling is automatically achieved by limiting the number of concurrent threads.

For a complete overview, I have also created a version of the async test based on HttpWebRequest rather than HttpClient and managed to obtain much better results. For a start, it allows setting a limit on the number of concurrent connections (with ServicePointManager.DefaultConnectionLimit or via config), which means that it never ran out of ports and never failed on any request (HttpClient, by default, is based on HttpWebRequest, but it seems to ignore the connection limit setting).

The async HttpWebRequest approach was still about 50 - 60% slower than the multithreading one, but it was predictable and reliable. The only downside to it was that it used a huge amount of memory under big load. For example it needed around 1.6 GB for sending 1 million requests. By limiting the number of concurrent requests (like I did above for HttpClient) I managed to reduce the used memory to just 20 MB and obtain an execution time just 10% slower than the multithreading approach.

After this lengthy presentation, my questions are: Is the HttpClient class from .Net 4.5 a bad choice for intensive load applications? Is there any way to throttle it, which should fix the problems I mention about? How about the async flavor of HttpWebRequest?

**Update (thanks @Stephen Cleary)**

As it turns out, HttpClient, just like HttpWebRequest (on which it is based by default), can have its number of concurrent connections on the same host limited with ServicePointManager.DefaultConnectionLimit. The strange thing is that according to [MSDN](http://msdn.microsoft.com/en-us/library/system.net.servicepointmanager.defaultconnectionlimit.aspx), the default value for the connection limit is 2. I also checked that on my side using the debugger which pointed that indeed 2 is the default value. However, it seems that unless explicitly setting a value to ServicePointManager.DefaultConnectionLimit, the default value will be ignored. Since I didn&#39;t explicitly set a value for it during my HttpClient tests I thought it was ignored.

After setting ServicePointManager.DefaultConnectionLimit to 100 HttpClient became reliable and predictable (netstat confirms that only 100 ports are used). It is still slower than async HttpWebRequest (by about 40%), but strangely, it uses less memory. For the test which involves 1 million requests, it used a maximum of 550 MB, compared to 1.6 GB in the async HttpWebRequest.

So, while HttpClient in combination ServicePointManager.DefaultConnectionLimit seem to ensure reliability (at least for the scenario where all the calls are being made towards the same host), it still looks like its performance is negatively impacted by the lack of a proper throttling mechanism. Something that would limit the concurrent number of requests to a configurable value and put the rest in a queue would make it much more suitable for high scalability scenarios.

Is async HttpClient from .Net 4.5 a bad choice for intensive load applications?

I&#39;m building a Windows Store app, and I have some code that needs to be posted to the UI thread.

For that, i&#39;d like to retrieve the CoreDispatcher and use it to post the code.

It seems that there are a few ways to do so:

    // First way
    Windows.ApplicationModel.Core.CoreApplication.GetCurrentView().CoreWindow.Dispatcher;
    
    // Second way
    Window.Current.Dispatcher;


I wonder which one is correct? or if both are equivalent?

Correct way to get the CoreDispatcher in a Windows Store app

I need to call an `async` method in a `catch` block before throwing again the exception (with its stack trace) like this :

    try
    {
    	// Do something
    }
    catch
    {
    	// &lt;- Clean things here with async methods
    	throw;
    }

But unfortunately you can&#39;t use `await` in a `catch` or `finally` block. I learned it&#39;s because the compiler doesn&#39;t have any way to go back in a `catch` block to execute what is after your `await` instruction or something like that...

I tried to use `Task.Wait()` to replace `await` and I got a deadlock. I searched on the Web how I could avoid this and found [this site][1].

Since I can&#39;t change the `async` methods nor do I know if they use `ConfigureAwait(false)`, I created these methods which take a `Func&lt;Task&gt;` that starts an async method once we are on a different thread (to avoid a deadlock) and waits for its completion:

    public static void AwaitTaskSync(Func&lt;Task&gt; action)
    {
    	Task.Run(async () =&gt; await action().ConfigureAwait(false)).Wait();
    }

    public static TResult AwaitTaskSync&lt;TResult&gt;(Func&lt;Task&lt;TResult&gt;&gt; action)
    {
    	return Task.Run(async () =&gt; await action().ConfigureAwait(false)).Result;
    }

    public static void AwaitSync(Func&lt;IAsyncAction&gt; action)
    {
    	AwaitTaskSync(() =&gt; action().AsTask());
    }

    public static TResult AwaitSync&lt;TResult&gt;(Func&lt;IAsyncOperation&lt;TResult&gt;&gt; action)
    {
    	return AwaitTaskSync(() =&gt; action().AsTask());
    }

So my questions is: Do you think this code is okay?

Of course, if you have some enhancements or know a better approach, I&#39;m listening! :)

  [1]: http://www.tugberkugurlu.com/archive/the-perfect-recipe-to-shoot-yourself-in-the-foot-ending-up-with-a-deadlock-using-the-c-sharp-5-0-asynchronous-language-features

A good solution for await in try/catch/finally?

I copied below code from [this][1]  link.But when I am compiling this code I am getting  an **entry point cannot be marked with the &#39;async&#39; modifier**. How can I make this code compilable?

    class Program
    {
        static async void Main(string[] args)
        {
            Task&lt;string&gt; getWebPageTask = GetWebPageAsync(&quot;http://msdn.microsoft.com&quot;);

            Debug.WriteLine(&quot;In startButton_Click before await&quot;);
            string webText = await getWebPageTask;
            Debug.WriteLine(&quot;Characters received: &quot; + webText.Length.ToString()); 
        }
        
        private static async Task&lt;string&gt; GetWebPageAsync(string url)
        {
            // Start an async task. 
            Task&lt;string&gt; getStringTask = (new HttpClient()).GetStringAsync(url);

            // Await the task. This is what happens: 
            // 1. Execution immediately returns to the calling method, returning a 
            //    different task from the task created in the previous statement. 
            //    Execution in this method is suspended. 
            // 2. When the task created in the previous statement completes, the 
            //    result from the GetStringAsync method is produced by the Await 
            //    statement, and execution continues within this method. 
            Debug.WriteLine(&quot;In GetWebPageAsync before await&quot;);
            string webText = await getStringTask;
            Debug.WriteLine(&quot;In GetWebPageAsync after await&quot;);

            return webText;
        }

        // Output: 
        //   In GetWebPageAsync before await 
        //   In startButton_Click before await 
        //   In GetWebPageAsync after await 
        //   Characters received: 44306
    }

  [1]: http://blogs.msdn.com/b/csharpfaq/archive/2012/06/26/understanding-a-simple-async-program.aspx

An entry point cannot be marked with the &#39;async&#39; modifier

I&#39;m trying to understand async await in the simplest form.  I want to create a very simple method that adds two numbers for the sake of this example, granted, it&#39;s no processing time at all, it&#39;s just a matter of formulating an example here.

### Example 1

    private async Task DoWork1Async()
    {
        int result = 1 + 2;
    }

### Example 2

    private async Task DoWork2Async()
    {
        Task.Run( () =&gt;
        {
            int result = 1 + 2;
        });
    }

If I await `DoWork1Async()` will the code run synchronously or asynchronously?

Do I need to wrap the sync code with `Task.Run` to make the method awaitable AND asynchronous so as not to block the UI thread?

I&#39;m trying to figure out if my method is a `Task` or returns `Task&lt;T&gt;` do I need to wrap the code with `Task.Run` to make it asynchronous.

I see examples on the net where people are awaiting code that has nothing async within and not wrapped in a `Task.Run` or `StartNew`.

Content Type	Original Author	Original Content on Stackoverflow
Question	ajp	View Question on Stackoverflow
Solution 1 - C#	Stephen Cleary	View Answer on Stackoverflow

.Net Invoke async method and await

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