HttpContext is null in a method called inside Parallel.For

Question

Posting this question after trying a lot. Doing normal for is not an option because we need to do a large amount of processing in very less time.

I have GetDataFor() inside which HttpContext.Current is used.

The code looks like this:

public void SomeMethod()
{
    var context = HttpContext.Current;

    Parallel.For(0, 100, i =>
    {
        var data = GetDataFor(i, context);
    });
}

public data GetDataFor(int i, HttpContext context)
{
    Uri requestUri = null;
    if (HttpContext.Current != null)
    {
        requestUri = HttpContext.Current.Request.Url;
        sCookie = string.Format("{0}", HttpContext.Current.Request.Headers["cookie"]);
    }
    else
    {
        requestUri = context.Request.Url;
    }

    //do something
    return data;
}

Everything works fine inside normal for loop. However, when I call it inside Parallel.For and pass HttpContext.Current, HttpContext.Current.Request, HttpContext.Current.Request.Url as method parameters:

HttpContext.Current cannot be serialized because it does not have a parameterless constructor

Passing HttpContextBase httpContext = null as parameter throws:

To be XML serializable, types which inherit from ICollection must have an implementation of Add(System.Object) at all levels of their inheritance hierarchy. System.Web.HttpApplicationStateBase does not implement Add(System.Object).

Tried making a property:

public string[] httpContextData
{
    get
    {
        string requestUrl = HttpContext.Current.Request.Url.ToString();
        string sCookie = string.Format("{0}", HttpContext.Current.Request.Headers["cookie"]);
        return new string[] { requestUrl, sCookie };
    }
}

and using in method:

var contextData = httpContextData;

which throws:

System.Uri cannot be serialized because it does not have a parameterless constructor

I did all this to send it's reference and state but unable to understand why the problem is not solving.

How do I use HttpContext.Current inside Parallel.For? What am I doing wrong here?

Btw, the needed stuff are:

HttpContext.Current.Request.Url and HttpContext.Current.Request.Headers["cookie"]

Is there anyway you can show your actual code? You've done a good job of explaining what you are doing, but I feel like there must be some key detail your accidentally leaving out. The error you are receiving just doesn't make sense to me given your explanation. — Mark Rucker, Feb 18 '16 at 15:58
@MarkRucker Sure I also feel that adding code will help future readers (**myself** included). I hope my recent [update](http://stackoverflow.com/posts/35483658/revisions) is [mcve](stackoverflow.com/help/mcve) — Zameer Ansari, Feb 18 '16 at 16:40

Igor · Accepted Answer · 2016-02-18T14:25:49.260

3

HttpContext.Current is only available (not null) inside request-handling threads. Parallel.For creates multiple threads, none of which is has access to HttpContext.Current.

You have to pass all data that code in Parallel.For threads needs either through

local variables assigned before the loop or
TLocal instance used in Parallel.For<TLocal>.

In any event, code such as HttpContext.Current.... is out.

edited Feb 18 '16 at 14:25

answered Feb 18 '16 at 14:17

Igor

15,833
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So, I shall pass `HttpContext.Current.Request.Url` and `HttpContext.Current.Request.Headers["cookie"]` as params? I have tried them :( I'll try [`TLocal`](https://www.google.com/search?q=TLocal) and get back – Zameer Ansari Feb 18 '16 at 14:33
I declared `string requestUrl = HttpContext.Current.Request.Url.ToString();` and `string sCookie = string.Format("{0}", HttpContext.Current.Request.Headers["cookie"]);` and passing them as normal string *and not complex serial objects* did the trick. Thanks! – Zameer Ansari Feb 18 '16 at 15:12

score 0 · Answer 2 · edited Jun 20 '20 at 09:12

The code is proprietary hence I'm only posting the relevant parts:

Since passing the following objects:

HttpContext.Current
HttpContext.Current.Request
HttpContext.Current.Request.Url

as params to GetDataFor was throwing so many errors.

Also, my needs were only

request url which can be re-generated by passing url as string to it's constructor
and a request header's value which is essentially a string

I only passed string to GetDataFor() method:

public void SomeMethod()
{
    string requestUrl = HttpContext.Current.Request.Url.ToString();
    string sCookie = string.Format("{0}", HttpContext.Current.Request.Headers["cookie"]);

    Parallel.For(0, 100, i =>
    {
        var data = GetDataFor(i,
    requestUrl: requestUrl,
    sCookie: sCookie);
    });
}

public data GetDataFor(int i, string requestUrl = null, string sCookie = null)
{
    Uri requestUri = null;
    if (HttpContext.Current != null)
    {
        requestUri = HttpContext.Current.Request.Url;
        sCookie = string.Format("{0}", HttpContext.Current.Request.Headers["cookie"]);
    }
    else
    {
        requestUri = new Uri(requestUrl);
    }

    //do something
    return data;
}

@MarkRucker The project did compiled well, but when I tried to run, the error was shown as a yellow red ASP.NET stack trace. — Zameer Ansari, Feb 18 '16 at 17:42
well I'm just not sure. I guess it is just one of those weird bugs. It sounds like you have a working solution, so if it were me I'd just run with that. — Mark Rucker, Feb 18 '16 at 20:00

HttpContext is null in a method called inside Parallel.For

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