You should prefix it with a namespace:

    if (System.IO.File.Exists(picPath))
    { 
        //Other code
    }

The reason for that is because you are writing this code inside a controller action which already defines a [`File`][1] method on the Controller class.


  [1]: http://msdn.microsoft.com/en-us/library/dd492897%28v=vs.108%29.aspx

How can the `wait()` and `notify()` methods be called on Objects that are not Threads? That doesn&#39;t really make sense, does it?

Surely, it must make sense, however, because the two methods are available for all Java objects. Can someone provide an explanation? I am having trouble understanding how to communicate between threads using `wait()` and `notify()`.


How can the wait() and notify() methods be called on Objects that are not threads?

I try computing **`Ackermann(4,1)`** and there&#39;s a big difference in performance between different languages/compilers. Below are results on my **Core i7 3820QM, 16G, Ubuntu 12.10 64bit**, 

**C: 1.6s**, `gcc -O3` *(with gcc 4.7.2)*

    int ack(int m, int n) {
      if (m == 0) return n+1;
      if (n == 0) return ack(m-1, 1);
      return ack(m-1, ack(m, n-1));
    }
    
    int main() {
      printf(&quot;%d\n&quot;, ack(4,1));
      return 0;
    }


**OCaml: 3.6s**, `ocamlopt` *(with ocaml 3.12.1)*

    let rec ack = function
      | 0,n -&gt; n+1
      | m,0 -&gt; ack (m-1, 1)
      | m,n -&gt; ack (m-1, ack (m, n-1))
    in print_int (ack (4, 1))


**Standard ML: 5.1s** `mlton -codegen c -cc-opt -O3` *(with mlton 20100608)*

    fun ack 0 n = n+1
      | ack m 0 = ack (m-1) 1
      | ack m n = ack (m-1) (ack m (n-1));
    print (Int.toString (ack 4 1));


**Racket: 11.5s** `racket` *(with racket v5.3.3)*

    (require racket/unsafe/ops)
    
    (define + unsafe-fx+)
    (define - unsafe-fx-)
    (define (ack m n)
      (cond
        [(zero? m) (+ n 1)]
        [(zero? n) (ack (- m 1) 1)]
        [else (ack (- m 1) (ack m (- n 1)))]))
    
    (time (ack 4 1))

&lt;strike&gt;**Haskell: unfinished**, killed by system after 22s `ghc -O2` *(with ghc 7.4.2)*&lt;/strike&gt;

**Haskell: 1.8s** `ajhc` *(with ajhc 0.8.0.4)*

    main = print $ ack 4 1
      where ack :: Int -&gt; Int -&gt; Int
            ack 0 n = n+1
            ack m 0 = ack (m-1) 1
            ack m n = ack (m-1) (ack m (n-1))


The Haskell version is the only one that fails to terminate properly because it takes too much memory. It freezes my machine and fills the swap space before getting killed.
What can I do to improve it without heavily fuglifying the code?

**EDIT**: I appreciate some of the asymptotically smarter solutions, but they are not exactly what I am asking for. This is more about seeing whether the compiler handles certain patterns in a reasonably efficient way (stack, tail calls, unboxing, etc.) than computing the ackermann function.

**EDIT 2**: As pointed out by several responses, this seems to be [a bug in recent versions of GHC][1]. I try the same code with [AJHC][2] and get much better performance.

Thank you very much :)


  [1]: http://hackage.haskell.org/trac/ghc/ticket/7850
  [2]: http://ajhc.metasepi.org/

Ackermann very inefficient with Haskell/GHC

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 am trying to see if a file exists before using it in an MVC controller:
<pre><code class="hljs language-ini">string path = "content/image.jpg";

if (File.Exists(path))
{ 
 //Other code
}
</code></pre>
The <code>File</code> keyword is underlined in red, and the compiler shows an error:
> <code>System.Web.MVC.Controller.File(string, string, string)</code> is a
> 'method', witch is not valid in the given context.
How can I use <code>File.Exists()</code> in a 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

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 asking the question already asked (and even answered) here:
https://stackoverflow.com/questions/5885739/why-are-some-textboxes-not-accepting-control-a-shortcut-to-select-all-by-defau

But that answer doesn&#39;t work for me. I have this code:

    public class LoginForm : Form
    {
        private TextBox tbUsername;
        
        public LoginForm()
        {
            tbUsername = new TextBox();
            tbUsername.ShortcutsEnabled = true;
            tbUsername.Multiline = false;
            Controls.Add(tbUsername);
        }
    }

The textbox shows up, I can write on it, I can cut, copy and paste text on it without any problems.
But when I try to press &lt;kbd&gt;Ctrl&lt;/kbd&gt;+&lt;kbd&gt;A&lt;/kbd&gt; I only hear a &quot;bling&quot; similar to the bling that you hear if you try to erase text from an empty textbox (try it with your browser&#39;s address bar).

How can I allow ctrl+a with TextBox in winform?

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

What&#39;s the difference between `@Html.Label()`, `@Html.LabelFor()` and `@Html.LabelForModel()` methods?



What&#39;s the difference between Html.Label, Html.LabelFor and Html.LabelForModel

I have the following model which is wrapped in my view model

    public class FloorPlanSettingsModel
    {
        public int Id { get; set; }
        public int? MainFloorPlanId { get; set; }
        public string ImageDirectory { get; set; }
        public string ThumbnailDirectory { get; set; }
        public string IconsDirectory { get; set; }
    }

How do I access one of the above properties from Javascript?

I tried this, but I got &quot;undefined&quot;

    var floorplanSettings = &quot;@Model.FloorPlanSettings&quot;;
    alert(floorplanSettings.IconsDirectory);

Accessing MVC&#39;s model property from Javascript

I am starting to learn the webapi and find myself doing stuff that makes sense in an MVC project but may not make sense in.

Normally in an MVC project I make ViewModels and use that as the parameter or pass them back with the view.

Since there are no views in webapi I guess it does not make sense to have a ViewModel as parameter.

I am wondering maybe if I should just have as a Parameter my EF domains(code first) and put data annotations on top of these. I normally would put the annotations over the view model properties as I liked this over the domain.

However what is stopping me from doing this is I am not 100% clear how my MVC site would work. 

Does the MVC site just spit back simples views and then you use Jquery to call your webapi or do you just call MVC action methods that directly just call the same methods the Webapi would call?

If is the second way then I rather put the data annotations on my view model again but then I am putting the same ones on both the EF domain and VM&#39;s and that seem redundant. 



Does it Make Sense to have ViewModels in the Webapi?

I have a large(ish) form in MVC.

I need to be able to generate an excel file containing data from a subset of that form. 

The tricky bit is that this shouldn&#39;t affect the rest of the form and so I want to do it via AJAX. I&#39;ve come across a few questions on SO that seem to be related, but I can&#39;t quite work out what the answers mean.

This one seems the closest to what I&#39;m after: [asp-net-mvc-downloading-excel][1] - but I&#39;m not sure I understand the response, and it is a couple years old now. I also came across another article (can&#39;t find it anymore) about using an iframe to handle the file download, but I&#39;m not sure how to get this working with MVC.

My excel file returns fine if I&#39;m doing a full post back but I can&#39;t get it working with AJAX in mvc.


  [1]: https://stackoverflow.com/questions/6747532/asp-net-mvc-downloading-excel

Download Excel file via AJAX MVC

If I have the Authorize attribute on both the controller and the action, which one will take the effect? Or will both take effect?

Asp.net MVC4: Authorize on both controller and action

From the [doc][1], 
&gt;Modes &#39;r+&#39;, &#39;w+&#39; and &#39;a+&#39; open the file for updating (note that &#39;w+&#39; truncates the file). Append &#39;b&#39; to the mode to open the file in binary mode, on systems that differentiate between binary and text files; on systems that don’t have this distinction, adding the &#39;b&#39; has no effect.

and [here][2]
&gt;w+ :  Opens a file for both writing and reading. Overwrites the existing file if the file exists. If the file does not exist, creates a new file for reading and writing.

But, how to read a file open with `w+`? 

[1]:http://docs.python.org/2/library/functions.html#open
[2]: http://www.tutorialspoint.com/python/python_files_io.htm

Confused by python file mode &quot;w+&quot;

I want to check if file exists in my package folder, but I don&#39;t want to create a new one.

    File file = new File(filePath);
    if(file.exists()) 
         return true;

Does this code check without creating a new file?

Android; Check if file exists without creating a new one

I have a batch file that I intend to distribute to our customers to run a software task. 

We distribute them as a folder or `.zip` with the files inside. Inside, there is the batch files and another folder with the files needed to run the batch.

Normally, when you make a batch, you type the path where the files are. But I won&#39;t know where the files are. The files will still be kept inside the master folder, but I need to have the batch find that folder to run the files.

So for example: If they have the master folder on the desktop and they run it, it would need to be something like `&quot;C:\Users\Username\Desktop&quot;` to run. You would have the batch CD to that location. 

But what if they run it from documents? I don&#39;t know the username, so I have to somehow have the batch find this. Any code and/or instructions would be great.

How do I find the current directory of a batch file, and then use it for the path?

Is it possible to dump a raw RTSP stream to file and then later decode the file to something playable?

Currently I&#39;m using FFmpeg to receive and decode the stream, saving it to an mp4 file.  This works perfectly, but is CPU intensive, and will severely limit the number of RTSP streams I can receive simultaneously on my server.

I would like to save the stream to file without decoding it, and delay the decoding part to when the file needs to be opened.

Is this possible?

I have tried VLC, which is even more CPU intensive than FFmpeg.  I&#39;ve also looked at [this question][1] where the answer says dumping RTSP to file is not useful, and [this question][2], where the comment below the question says &quot;Raw RTSP content is not well suited for save and replay...&quot;, which seems to indicate that there is way.

Thanks in advance!

---
**EDIT**
Here is the command I&#39;m using for FFmpeg:

`ffmpeg -i rtsp://@192.168.241.1:62159 -r 15 C:/DB_Videos/2013-04-30 17_18_34.703.mp4 `

[1]:https://stackoverflow.com/questions/15543014/dump-rtsp-to-file-like-rtmpdump
[2]:https://stackoverflow.com/questions/7932389/rtsp-stream-capturing

How to dump raw RTSP stream to file?

I want to import two kinds of CSV files, some use &quot;;&quot; for delimiter and others use &quot;,&quot;. So far I have been switching between the next two lines:

    reader=csv.reader(f,delimiter=&#39;;&#39;)

or

    reader=csv.reader(f,delimiter=&#39;,&#39;)

Is it possible not to specify the delimiter and to let the program check for the right delimiter?

The solutions below (Blender and sharth) seem to work well for comma-separated files (generated with Libroffice) but not for semicolon-separated files (generated with MS Office). Here are the first lines of one semicolon-separated file:

    ReleveAnnee;ReleveMois;NoOrdre;TitreRMC;AdopCSRegleVote;AdopCSAbs;AdoptCSContre;NoCELEX;ProposAnnee;ProposChrono;ProposOrigine;NoUniqueAnnee;NoUniqueType;NoUniqueChrono;PropoSplittee;Suite2LecturePE;Council PATH;Notes
    1999;1;1;1999/83/EC: Council Decision of 18 January 1999 authorising the Kingdom of Denmark to apply or to continue to apply reductions in, or exemptions from, excise duties on certain mineral oils used for specific purposes, in accordance with the procedure provided for in Article 8(4) of Directive 92/81/EEC;U;;;31999D0083;1998;577;COM;NULL;CS;NULL;;;;Propos* are missing on Celex document
    1999;1;2;1999/81/EC: Council Decision of 18 January 1999 authorising the Kingdom of Spain to apply a measure derogating from Articles 2 and 28a(1) of the Sixth Directive (77/388/EEC) on the harmonisation of the laws of the Member States relating to turnover taxes;U;;;31999D0081;1998;184;COM;NULL;CS;NULL;;;;Propos* are missing on Celex document

Content Type	Original Author	Original Content on Stackoverflow
Question	Pomster	View Question on Stackoverflow
Solution 1 - C#	Darin Dimitrov	View Answer on Stackoverflow

Why can't I use System.IO.File methods in an MVC controller?

C# Problem Overview

C# Solutions

Solution 1 - C#

Ackermann very inefficient with Haskell/GHC

How can the wait() and notify() methods be called on Objects that are not threads?

Attributions