HttpClient in using statement

Question

hi i read this article You're using HttpClient wrong and it is destabilizing your software the article is suggesting these 2

Make your HttpClient static
Do not dispose of or wrap your HttpClient in a using unless you explicitly are looking for a particular behaviour (such as causing your services to fail)

now a newbie on c# like me would just follow it like the code posted on the article here is the original code the he said would make the application fail

using System;
using System.Net.Http;
namespace ConsoleApplication
{
    public class Program
    {
        public static void Main(string[] args)
        {
            Console.WriteLine("Starting connections");
            for(int i = 0; i<10; i++)
            {
                using(var client = new HttpClient())
                {
                    var result = client.GetAsync("http://aspnetmonsters.com").Result;
                    Console.WriteLine(result.StatusCode);
                }
            }
            Console.WriteLine("Connections done");
        }
    }
}

and to fix it he gave this code:

using System;
using System.Net.Http;
namespace ConsoleApplication
{
    public class Program
    {
        private static HttpClient Client = new HttpClient();
        public static void Main(string[] args)
        {
            Console.WriteLine("Starting connections");
            for(int i = 0; i<10; i++)
            {
                var result = Client.GetAsync("http://aspnetmonsters.com").Result;
                Console.WriteLine(result.StatusCode);
            }
            Console.WriteLine("Connections done");
            Console.ReadLine();
        }
    }
}

now being curious like any newbie i thought of the for loop inside the using statement will the effect be the same as the latter?

thank you

Putting the for loop within the using statement will allow for the reuse of the client though not static for the life time of the main method. — Nkosi
– Nkosi, Commented Oct 22, 2016 at 1:00

Community · Accepted Answer · 2020-06-20 09:12:55Z

37

The difference is that in the top loop, you're creating 10 total HttpClient objects, using each once, and then disposing of each, while in the bottom, you're creating just one HttpClient and reusing it.

The point of the article is that it's quite inefficient - and wholly unnecessary - to make a new HttpClient object every time you want to make a web service call. Since HttpClient is not only reusable but thread-safe, the preferred method is to make a single HttpClient and reuse it until your program is done making http connections.

Edit

It sounds like you were asking about why not this:

using System;
using System.Net.Http;
namespace ConsoleApplication
{
    public class Program
    {

        public static void Main(string[] args)
        {
            Console.WriteLine("Starting connections");
            using (var client = new HttpClient())
            {
                for(int i = 0; i<10; i++)
                {
                    var result = Client.GetAsync("http://aspnetmonsters.com").Result;
                    Console.WriteLine(result.StatusCode);
                }
            }
            Console.WriteLine("Connections done");
            Console.ReadLine();
        }
    }
}

In this specific case there's no difference. The important thing is that the HttpClient is reused until every request is done. In most realistic scenarios, having a static property for an HttpClient makes the most sense to accomplish this goal.

The reason they say "don't use using" is that using implies your HttpClient is a local variable within a method, and in most cases that isn't what you want. In this specific case, every http request from the program happens within one method which is called only once, so a variable that is local to that method is fine - you end up with one HttpClient that is reused until all requests have occurred and then is disposed.

edited Jun 20, 2020 at 9:12

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answered Oct 22, 2016 at 0:53

PMV

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6 Comments

saarrrr Over a year ago

It also consumes finite socket resources every time you make one. See codereview.stackexchange.com/questions/69950/…

angelogogo Over a year ago

well yes that's what the article is saying but i am asking what's the difference between putting the for loop inside the using statement versus that of the given code

PMV Over a year ago

In that specific case? None at all, since the lifetime of the static object is no different from the lifetime of the Main() method of that application. In the case where you're doing an event-driven program like WinForms, WPF, etc., a public static field/property is a decent way to share this across the entire life of your program.

angelogogo Over a year ago

i am about to post that code thank you for saving me the time yes that is what i am talking about

angelogogo Over a year ago

my bad i didn't notice the declaration of the static variable above

|

Jasen · Accepted Answer · 2017-08-15 19:20:10Z

23

Adding an answer to reference Microsoft's docs:

https://learn.microsoft.com/en-us/aspnet/web-api/overview/advanced/calling-a-web-api-from-a-net-client

HttpClient is intended to be instantiated once and re-used throughout the life of an application. Especially in server applications, creating a new HttpClient instance for every request will exhaust the number of sockets available under heavy loads. This will result in SocketException errors.

answered Aug 15, 2017 at 19:20

Jasen

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1 Comment

marbel82 Over a year ago

You are absolutely right => aspnetmonsters.com/2016/08/2016-08-27-httpclientwrong

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