Develop Reference

Creating a push or background service that checks remote server

General idea of what I need:
I am porting an Android app to iOS (Using Xamarin, but I can translate to C# from objective C easily enough) that relies heavily on the AlarmManager to do background checks on an HTML page on a website that I don't own. AlarmManager is essentially a task scheduler for Android. The user would set the frequency to whatever they desired.
What I've tried:
Background fetching:
app.SetMinimumBackgroundFetchInterval(240);
UNUserNotificationCenter.Current.RequestAuthorization(UNAuthorizationOptions.Alert, (approved, err) =>
{
// Handle approval
});
UNUserNotificationCenter.Current.Delegate = new WEBSITEFUNCTIONS.UserNotificationCenterDelegate();
return base.FinishedLaunching(app, options);
public override void PerformFetch(UIApplication application, Action<UIBackgroundFetchResult> completionHandler)
{
System.Diagnostics.Debug.WriteLine("interval");
WEBSITEFUNCTIONS kf = new WEBSITEFUNCTIONS();
kf.doCheck();
completionHandler(UIBackgroundFetchResult.NewData);
}
Perform Fetch is just straight up NEVER called. I need some consistency (being one minute off is no big deal... but several hours will not do). I let it run and it just straight up never worked. I've read lots on how PerformFetch works, and I don't think it'll give me the critical response time that the user needs.
UserNotifications:
New to iOS 10, is the ability to have repeating notifications. However this repeats the same notification.
var trigger = UNTimeIntervalNotificationTrigger.CreateTrigger(60, true);
var requestID = "sampleRequest";
var request = UNNotificationRequest.FromIdentifier(requestID, content, trigger);
UNUserNotificationCenter.Current.AddNotificationRequest(request, (err) =>
{
if (err != null)
{
// Do something with error...
}
});
Push Alerts:
My own server
I could setup a server that does the checking and then sends a message to the Firebase Cloud Messaging to send a message to the user about the new items. I have approximately 500 active users on the Android version, if they check 5 different pages every 5 minutes, at 90 kbs a check, that's about half a gig of bandwidth an hour.
So the cons are:
Excessive bandwidth usage will make my home internet
a lot slower
I will need to secure it myself
Power outages can sometimes last for days, leaving end users out of the loop
Their server could boot off my machine at any given
moment, I could get a new IP address from my ISP if that happened... assuming they allow that
Using my shared hosting, setup a cronjob every 15 minutes
I can setup a cronjob to do an alert every 15 minutes. It's not the fastest, but way better than relying on the first option (as it just straight up never gets called)
Once again, I'm at the mercy that their server doesn't kick me off. The app completely breaks if they do this.
Shared hosting might cut me off for putting too much strain on their servers (Hostgator claims unlimited bandwidth, I'm not sure if they'd like me doing that)

Two threads working on the same list

I'm working on a P2P application in C#.
It's a file transfer with a file splitting, and text chat.
On a client there are 2 threads, 1 for listening, 1 for sending.
When i send a file, it's first split into let's say 10 pieces, these 10 pieces are added to a send queue in the client, it then starts sending file chunk 1.
But now i want to send a message through the same pipe.
My idea is then to insert that message into the send list before file chunk 2.
What kind of threading do i need for 2 threads to work on the same list?
I have accounted for the objects being received this way.
My initial idea for the send function was something along these lines:
public void Send()
{
while (IsConnected())
{
if (unSentObjects.Count > 1)
{
Task sendTask = new Task(() => SendObj(unSentObjects[0]));
sendTask.Start();
}
}
}

You could use a Synchronization Object such as a mutex to prevent race conditions or simultaneous write/read to same file. Basically only 1 thread will be able to access the object.
If the data is global to the threads and they are all once process, you can use the synchronization object simply to signal when to use global shared data and when to not use it. Other than that using the shared global data is exactly the same, you are just trafficking the use of it.

Problems getting newly created thread to send outputs to asp:panel in ASP.NET C#

I'm creating a file processor for use in an intranet.
I described it in another question - ERR_EMPTY_RESPONSE when processing a large number of files in ASP.Net using C#
Now, as suggested on above question's answer, I'm trying to use threads to execute the file processing task.
But there is a problem. I need the newly created thread to write feedbacks to a component in page (asp:panel, or div, or whatever). Those feedbacks would be results from several database operations.
The application reads those txts, interprets each line of it, and insert data in database. Each line inserted in database must return a feedback, like "registry 'regname' inserted successfully", or "i got problems inserting registry 'regname' in file 'filename', skipping to next registry".
I did test with something very simple:
protected void DoImport()
{
try
{
MainBody.Style.Add(HtmlTextWriterStyle.Cursor, "wait");
int x = 0;
while (x < 10000)
{
ReturnMessage(String.Format("Number {0}<hr />", x), ref pnlConfirms);
x++;
}
}
catch (Exception ex)
{
ReturnMessage(String.Format("<font style='color:red;'><b>FATAL ERROR DURING DATA IMPORT</b></font><br /><br /><font style='color:black;'><b>Message:</b></font><font style='color:orange;'> {0}</font><br />{1}", ex.Message, ex.StackTrace), ref pnlErrors);
}
finally
{
MainBody.Style.Add(HtmlTextWriterStyle.Cursor, "default");
}
}
This function is called from Page_Load, and fills an asp:panel called "pnlConfirms" with a row of numbers, but all at once, on load.
I changed it to:
protected void DoImport()
{
try
{
MainBody.Style.Add(HtmlTextWriterStyle.Cursor, "wait");
ThreadPool.QueueUserWorkItem(new WaitCallback(DoWork));
}
catch (Exception ex)
{
ReturnMessage(String.Format("<font style='color:red;'><b>FATAL ERROR DURING DATA IMPORT</b></font><br /><br /><font style='color:black;'><b>Message:</b></font><font style='color:orange;'> {0}</font><br />{1}", ex.Message, ex.StackTrace), ref pnlErrors);
}
finally
{
MainBody.Style.Add(HtmlTextWriterStyle.Cursor, "default");
}
}
private void DoWork(Object stateInfo)
{
int x = 0;
while (x < 10000)
{
ReturnMessage(String.Format("Number {0}<hr />", x), ref pnlConfirms);
x++;
}
}
And both uses this function:
public void ReturnMessage(string message, ref Panel panel, bool reset = false)
{
if (reset)
{
panel.Controls.Clear();
}
Label msg = new Label();
msg.Attributes.Add("width", "100%");
msg.Text = message;
panel.Controls.Add(msg);
}
I need ThreadPool.QueueUserWorkItem(new WaitCallback(DoWork)); to fill those asp:panels with feedbacks - like insertion errors and warnings.
My code already has those feedbacks under try...catch statements, but they're not getting output to any asp:panel from threadpool (it works when invoked directly from DoImport() function, like in the first example I posted).
I'm doing something very wrong, but I can't find out what (and I'm researching this for almost 2 weeks). Please, help!

In ASP.NET, when a browser requests a page, that page is rendered and sent to the browser as soon as its processing finishes, so the browser will show the page as it's finally rendered.
According to your code you're trying to render a page, show a wait cursor, and expect it's shown on the browser and then, the cursor is changed by a default cursor. As I explained, independently from using or not additional threads, the page won't be sent to the browser until it's completely rendered. So you'l never see the wait cursor on the client side.
The easiest wait to get what you're trying to do is to use web services (traditional .asmx or WCF) and AJAX (jquery os ASP.NET AJAX).
1) create a web service that does the processing
2) create a page which is sent to the browser, and, using javascript (jQuery or ASP.NET AJAX) make a call to the web service, and show something to let the user know that the request is being processed. (a wait cursor, or even better an animated gif)
3) when the process finishes, your javascript will get the responde from the web service, and you can update the page to let the user know the process has finished.
if you don't have experience on javascript, you can make most of this task using:
ScriptManager which can be used to create a javascript web service proxy for your client side (other interesting article) and is required for the rest of the controls
some javascript (or jquery) which can be use to update the "process running/ process finished hints" on the client side. I.e. when the call to the web service ends, you can use javascript to update the page using DOM, or load a new page or the same page with an special parameter to show the result of the process
In this way you can do what you want:
1) show a page in a state that shows the process is running
2) show the same, or other page, in a state that shows the end of the process
The trick is comunicating the browser with the server, and this can only be done using some of the available ajax techniques.
Another typical technique is using jQuery.ajax, like explained in encosia.com
According to the OP message, the process of all the files would be so slow that it would tiemout the web service call. If this is the case, you can use this solution:
1) Create a web service that process one (or a batch) of the pending files, and returns at least the number of pending files when it finishes the processing of the current file (or batch).
2) from the client side (javascript), call the web service. When it finishes, update the page showing the number of pending files, and, if this number is greater than zero, call the web service again.
3) when the call to the web service returns 0 pending files, you can update the page to show the work is finished, and don't call it any more.
If you process all the files at once, there will be no feedback on the client side, and there will also be a timeout. Besides, IIS can decide to stop the working thread which is making the work. IIS does this for several reasons.
A more reliable solution, but harder to implement, is:
1) implement a Windows Service, that does the file processing
2) implement a web service that returns the number of pending files (you can communicate the Windows Service and Web App indirectly using the file system, a database table or something like that)
3) use a timer (ajax timer, or javascript setInterval) from your web page to poll the server every N seconds using the web service, until the number of pending files is 0.
An even harder way to do this is hosting a WCF service in your Windows Service, instead of the indirect communication between your web app and windows service. This case is much more complicated because you need to use threads to do the work, and attend the calls to the wcf service. If you can use indirect communitacion it's much easier to implemente. The dtabse table is a simple and effective solution: your working process updates a row a table whenever it process a file, and the web service reads the progress state from this table.
There are many different soultions for a not so simple problem.

You are starting new thread (or more precise running your code on one of free threads in thread pool)and not waiting for results in main thread. Something like Thread.Join (if you would use manual thread creation) or other synchronization mechanism as events need to be used if you want to go this route.
The question you've linked to suggests using asynchronous pages which you are not doing. You would start processing request, kick off the task and release the thread, when the task is finished you complete request.
Side note: consider simply doing all conversion on main thread that handles request. Unless you expect slow I/O to complete the task moving CPU work from one thread to another may not produce significant gains. Please measure performance of your current solution and confirm that it does not meet performance goals you have set up for your application. (this does not apply if you doing it for fun/educational purposes).

network sessions and sending files

Background
Hi.
I write a program that analyzes the packets for specific words contained therein. I need to analyze outgoing email, jabber, ICQ. If the words are found, the packet is blocked.I did it, but I have a problem with the files and sending email through the web.
Problems
Simple code:
while (Ndisapi.ReadPacket(hNdisapi, ref Request))
{
// some work
switch (protocol)
{
//....
case "HTTP":
// parse packet(byte[])
HTTP.HttpField field = HTTP.ParseHttp(ret);
if (field != null && field.Method == HTTP.HttpMethod.POST)
{
// analyze packet and drop if needed
DoWork();
}
}
The problem is the following. For example, I attach to email the file of 500 KB. The file will be split approximately in 340 packets. In the code above, DoWork() only for first packet will be executed.
Ok, then I need to restore session completely and pass whole session to DoWork(). I did it. But I can't wait while session is finished, because other packet( http, arp, all packets) will be suspended (And after a couple of minutes the Internet is disconnected).
Therefore, the first question:
How to solve this problem (may be advice for design program)?
Now the email, suppose this code:
switch (protocol)
{
//....
case "HTTP":
// parse packet(byte[])
var httpMimeMessage = Mime.Parse(ret);
// analyze packet and drop if needed
DoSomeWork();
break;
}
For example, we are looking for word "Finance". Then, if we open any website and there will be a word finance then packet is blocked.
Second question: How do I determine that this is the e-mail?
Thanks and sorry for my English.

To be able to analyze more than one packet/stream at the same time, you'll need to refactor your solution to use threading or some other form of multitasking and since your task appears to be both compute and io-intensive, you'll probably want to take a hard look at how to leverage event-handling at the operating system level (select, epoll, or the equivalent for your target platform).
And to answer your second question regarding email, you'll need to be able to identify and track the tcp session used to deliver email messages from client to server, assuming the session hasn't been encrypted.
As I'm sure you already know, the problem you're trying to solve is a very complicated one, requiring very specialized skills like realtime programming, deep knowledge of networking protocols, etc.
Of course, there are several "deep packet inspection" solutions out there already that do all of this for you, (typically used by public companies to fulfill regulatory requirements like Sarbanes-Oxley), but they are quite expensive.

Threading using AJAX

When the user clicks on a link to generate report I make an AJAX call which generates a pdf file in the background.Now the files are huge running upto 10mb or more.So it takes some time.In the mean time the user should be able to navigate other links as if nothing has happened.So I need to implement in such a way that the pdf generation process gets started & user doesn't have to wait for the process to finish.Is this possible?I am using AJAX Pro with c# with dot net framework 2.0
The problem here is that as soon as the AJAX activity begins the browser enters into a hung stage & the user has to wait although he clicks on a different link.

I would probably create a 'queue' or an 'inbox' for the user ...
start your pdf generation routine with a ThreadPool.QueueUserWorkItem (you would also need to modify your generation method to output to their inbox)
then on each http request check that inbox and notify the user of the item ... you can always poll the server on an interval or somthing

Sure, but once the user navigates to another page, the Javascript that is waiting for the Ajax response is no longer running, so that request is lost. You'd have to either find a way to keep that page open (using frames or exclusively Ajaxified navigiation), or find a way to store the response and notify the user of its completion on the next page view. For instance, storing a session variable that indicates that the operation is completed, or storing it in a database with (perhaps) an "unread" boolean value.

You can have asynchronous Ajax call with which you can do other tasks while response objects returns from the Ajax page.
Here is some example, testAjax.aspx is the Ajax page here :
http_request.onreadystatechange = function() { alertContents(http_request); };
http_request.open('GET', 'testAjax.aspx?', true);
http_request.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
http_request.send(null);
function alertContents(http_request)
{//debugger;
if (http_request.readyState == 4)
{
if (http_request.status == 200)
{
var vResult;
vResult=http_request.responseText;
//Write your logic after successful Ajax call here.
}
else
{
alert('There was a problem with the request.');
}
}
}