Application.Run () Cause to Hang Program

Question

I have some links in my program which I must open the links in Web Browser one by one and enter some data in Web page.

The links list is provided in GUI Thread. But I need to do some works with links outside of Main Thread to avoid of Lagging and Hanging the GUI. And I need to open links one after the other. I mean if a thread starts to working, the next thread will start only when the thread finish works.

Another important thing about Links list is that when threads are created and working, Links List is updating.

So I created a worker thread which manages starting of another Threads.

I have two AutoResetEvents, one for checking the list that is empty or not (postInQueue). If the list is empty, it's wait until a link will added to list and calls postInQueue.set().

The second one is threadInProgress that when a thread is started working, it's waiting until the thread calls threadInProgress.set();

AutoResetEvent threadInProgress = new AutoResetEvent(False);
AutoResetEvent postInQueue = new AutoResetEvent (False);
List<String> links = new List<String>;
public MainForm(){
InitializeComponent();
    Thread threadManager = new Thread( () => 
    {
        while(true){
            if (postsQueue.Count == 0)
                postInQueue.WaitOne();
            Thread t2 = new Thread(() => {
                linkProcess(links[0]);
            };
            t2.SetApartmentState(ApartmentState.STA);
            t2.Start();
            threadInProgress.WaitOne(60000);
            links.RemoveAt(0);
        }
    });
    threadManager.start();
}
public void linkProcess(String link){
    WebBrowser webBrowser = new WebBrowser();
    webBrowser.DocumentCompleted += (s , e) => {
        //Enter some data in webBrowser
        Application.ExitThread();
        threadInProgress.set();
    };
    webBrowser.Navigate(link);
    Application.Run();
}

I Must call Application.Run() in each thread to DocumentCompleted Event will be called.

This code works well for two or three first links but next threads will be stuck in Application.Run() until threadInProgress.WaitOne(60000); send timeout.

Two first links works correct but then I realized that CPU usage is 0%. When I click on break all, I see that the thread is stucking in Application.Run().

What is the problem?

In a forum, someone advise me to use process except thread... How can this be possible? And would be helpful?

Answer 1

All of this thread stuff is insane - especially threads that invoke threads and then calling Application.Run to stop threads exiting. It's just overkill.

Here's what I would use:

string uri = "https://www.mywebsite.com/customer/account/loginPost/";
string html;

using (var wc = new WebClient())
{
    wc.Headers[HttpRequestHeader.ContentType] = "application/x-www-form-urlencoded";

    var nvc = new System.Collections.Specialized.NameValueCollection()
    {
        { "form_key", "BaqsPklZGXt3Kq5o" },
        { "login[username]", "user@domain.com" },
        { "login[password]", "myfunkypassword" },
        { "send", "" },
    };

    byte[] result = wc.UploadValues(uri, nvc);

    html = System.Text.Encoding.UTF8.GetString(result);
}

This can all be wrapped up as as async call, or just pushed to a normal background worker thread. I would like to know precisely what you're trying to do before I would try turning this into a method - that would mean seeing the code that you're currently using.

You would need to figure out what name-value pairs you need. I use a Chrome extension called "Request Maker". It puts a little envelope icon on the address bar that you can click after performing some action on a page. It lets you see the requests that were made and to get all of the parameters out.

Answer 2

This is architected in a very bad way. Normally, you have one UI thread and one call to Application.Run(). If you want to show new UI forms call into that thread using (for example) Invoke and start the new form there.

This simplifies everything considerably. If you do that a lot of the threading and eventing goes away and your problem disappears in the process.

Application.Run is supposed to block. After all it runs the app until the app is supposed to exit. Normally, you'd pass a form to it. Not sure what your intention is given the code posted. linkProcess probably should place the browser control into a form. Without a form the control cannot appear anywhere.

Answer 3

Ok... I coudn't find out the reason of hanging when calling Application.Run(). I searched internet and all I found was some questions about Application.Run() with different scenarios but without answer!

But at least I found a way to use WebBrowser.DocumentComplete event in another thread without using Application.Run()!

I start a Thread insist of Application.Run() which run until WebBrowser.DocumentComplete event will be call and finish it works!

Thread t1 = new Thread ( () => {

    AutoResetEvent keepMeAlive = new AutoResetEvent( False );

    webBrowser1.DocumentComplete += (s , e) => {
        //Do Some Stuff

        keepMeAlive.set();
    };

    webBrowser1.Navigate("www.google.com");

    Thread keepAlive = new Thread ( () =>{
        keepMeAlive.WaitOne();
    });
    keepAlive.Start();
});