How to handle multi user and client refresh

[szlamany]

I've got a system where tasks get loaded and assigned to staff members.

I'm thinking of how I would like to somehow refresh a client page for a staff member if a new task gets assigned to that staff member. Some clerical people will be loading and assigning tasks to staff members.

How have you all handled this type of refresh in a webby environment. I'm fully jQuery and Ajax so I've got the tools...

[sapator]

There is an MVC thingy I cannot recall right now that is like a messenger but we don't want to use that I guess(?).
Can't recall the name.
But how about a timer refresh on a web service to check for new data? As I haven't done anything similar this is how I would do I if there was no other solution.
Seems logical with a simple 0-1 for new task

[szlamany]

How often would you hit a service like that before it became overwhelming?

[kfcSmitty]

Something like this would typically be achieved by long-polling.

Something like this should work:

function checkForChanges(){
   setTimeout(function(){
      $.ajax({ 
		url: "whatever", 
		success: function(data){
        		//either refresh your page or modify the display
			
        		checkForChanges(); //call the method again to ensure it is constantly polling
      		}, 
		dataType: "json"
	});
  }, 30000);
})();

This will recursively call the server every 30 seconds to check if anything has changed. If you're able to use HTML5 websockets or other technologies, there are also other, better, options available.

This post goes into some detail about it.

[sapator]

How often would you hit a service like that before it became overwhelming?

We are talking about a 0-1 in a new data so, I don't know. How often can we hit a service with that request?
I don't think it will ever become overwhelming but you are better in SQL than I am so I guess you can answer that yourself.

[szlamany]

I'm finally getting back to working on this...

Lately I've been making use of the Application class - saving information in it during long running requests so that other requests can grab it.

For instance - when a long running report starts in a web service - and while that request is still running - I can have the browser make AJAX hits back to the server to see how many pages are done.

Class looks like this:

    Public Class ApplicationMessage
        Private am_httpContext As System.Web.HttpContext
        Private am_sGuid As String
        Private am_appMsgType As String
        Private am_suppressMS As Integer = 0
        Private am_startTime As DateTime = Nothing
        Sub New(appMsgType As String, httpContext As System.Web.HttpContext, sGuid As String, initMessage As String)
            am_httpContext = httpContext
            am_sGuid = sGuid
            am_appMsgType = appMsgType
            am_startTime = Date.Now
            am_suppressMS = 0
            With am_httpContext.Application
                .Lock()
                .Add(am_appMsgType & ":" + am_sGuid, initMessage)
                .UnLock()
                Debug.Print(am_appMsgType & ": " & initMessage & " " & am_startTime.ToString())
            End With
        End Sub
        Public Function SendMessage(amMessage As String, Optional amOverride As Boolean = False) As Boolean
            Dim nowTime As DateTime = DateTime.Now
            Dim msDiff As TimeSpan = nowTime - am_startTime
            If Not amOverride AndAlso am_suppressMS > 0 AndAlso msDiff.TotalMilliseconds < am_suppressMS Then
                Debug.Print(am_appMsgType & ": " & amMessage & " " & Date.Now.ToString() & "** suppressed")
            Else
                With am_httpContext.Application
                    .Lock()
                    .Item(am_appMsgType & ":" + am_sGuid) = amMessage
                    Debug.Print(am_appMsgType & ": " & amMessage & " " & Date.Now.ToString())
                    .UnLock()
                End With
                am_startTime = nowTime
            End If
            Return True
        End Function

.
.
.
        Public Function SetSuppressMS(amSuppress As Integer) As Integer
            am_suppressMS = amSuppress
            Return am_suppressMS
        End Function
    End Class

And it's called like this

    Private _rptMsg As ApplicationMessage

    Sub New(httpContext As System.Web.HttpContext, sGuid As String)
        _httpContext = httpContext
        _sGuid = sGuid
        _rptMsg = New ApplicationMessage("acsReport", _httpContext, _sGuid, "Initiated")
    End Sub
.
.
.
_rptMsg.SendMessage("PrintReport:Started")
.
.
.
_rptMsg.SendMessage("PrintReport:Pages Completed: " + prtAddPage.ToString())
_rptMsg.SetSuppressMS(1000)

Then in another web method - one that is called every one or two seconds - I check this Application...Item and return it in a JSON string.

            If ctrloption = "acscheck" Then
                Dim strMessageText As String = ""
                With Application
                    .Lock()
                    strMessageText = .Item("acsReport:" + sguid).ToString()
                    Debug.WriteLine(strMessageText & " " & Date.Now.ToString())
                    .UnLock()
                End With
                .NewObject("acscheck", True)
                .Seperate()
                .NewObject("messagetext", strMessageText)
                .Seperate()
                strMessage = "acsCheck Done"
            End If

I just recently added that SetSuppress method so I can stop myself from filling this Application ITEM too frequently. I thought that could be a bad thing with lots of people hitting the server and running reports.

I'm also using the Application...Item() list to store security facts about users logged into my web app.

Now I'm thinking I can add more here - like the STATE of certain tables based on UPDATE's across the board.

Am I getting too crazy with the use of the Application class? Anyone crash into limits here - scalability??

[sapator]

Personally I haven't really used the application a lot. Not sure about locking and unlocking but I guess you know what you are doing.
I am marking this down for more investigation when I have the time( currently super busy with the seat rules and stuff).
But thanks you gave me something to think about.

[Lightning]

You should use SignalR, it is created for this kind of situation

[sapator]

I have suggested the same thing to szlamany in another thread but now I tend to disagree with my suggestion.
After all SignalR is merely a copycat emulation of true JS web service calls.
It's something (not quite of course) like an ol' updatepanel when you didn't quite got Jquery.
And of course MVC (hate MVC).

[szlamany]

You should use SignalR, it is created for this kind of situation

Why do you say SignalR - what does it give you??

I've already got the Ajax/JavaScript part handled in the browser with other notifications I'm doing. That seems lightweight and probably as simple as I can keep it.

The folllowing starts a report running and then does the initial call for a "check" of the results.

ctrlWebService("acsprint=" + rptSproc, ctrlval1, ctrlval2, ctrlval3, strCT, source);
g_printCycle = 1000;
setTimeout(function () {
    ctrlWebService("acscheck", "", "", "", strCT, []);
}, g_printCycle);

and when that ajax request completes it sets up another one - with a slowing increasing delay.

if (g_printOn) {
    if (g_printCycle < 3000) {
        g_printCycle += 500;
    }
    setTimeout(function () {
        ctrlWebService("acscheck", "", "", "", "", []);
    }, g_printCycle);
} else {
    printMenuClear(sender);
}

Back on the server side I'm using the Application class to share information between different POST's and more importantly, make thread safe with .Lock()/.Unlock(). Not sure of the scalability here.

I'm about to finish the code for this and get it into test with a user. I'll post back with my findings.

Any other ideas/thoughts anyone can suggest - thanks!