I am using MVC 2, I have view which simply displays label with current time on it.
I want to update this View(label) every 5 seconds so time will update. I am using below (taken from here) but doesn't seem to be working.
public ActionResult Time()
{
var waitHandle = new AutoResetEvent(false);
ThreadPool.RegisterWaitForSingleObject(
waitHandle,
// Method to execute
(state, timeout) =>
{
// TODO: implement the functionality you want to be executed
// on every 5 seconds here
// Important Remark: This method runs on a worker thread drawn
// from the thread pool which is also used to service requests
// so make sure that this method returns as fast as possible or
// you will be jeopardizing worker threads which could be catastrophic
// in a web application. Make sure you don't sleep here and if you were
// to perform some I/O intensive operation make sure you use asynchronous
// API and IO completion ports for increased scalability
ViewData["Time"] = "Current time is: " + DateTime.Now.ToLongTimeString();
},
// optional state object to pass to the method
null,
// Execute the method after 5 seconds
TimeSpan.FromSeconds(5),
// Set this to false to execute it repeatedly every 5 seconds
false
);
return View();
}
Thanks for help in advance!
What you are doing won't work as once the initial response is sent to the client, the client will no longer be listening for data from your server for that request. What you want to do is have the client initiate a new request every 5 seconds, then simply return the data for each request. One way to do this is with a refresh header.
public ActionResult Time()
{
this.HttpContext.Response.AddHeader( "refresh", "5; url=" + Url.Action("time") );
return View();
}
You need to put your recurring loop on the client side so that it reloads the page every five seconds.
One way, using Javascript:
<script>setTimeout("window.location.reload();",5000);</script>
The code you provided, runs at server, and when a page (View in this case) is sent to the client, the server will forgot it! You should create a client side code for refreshing the page every 5 seconds. You can use a header command (refresh) or a script:
<script>
setTimeout("window.location.reload();", /* time you want to refresh in milliseconds */ 5000);
</script>
But if you just want to refresh the page for updating the Time, I never suggest you to refresh page completely. Instead, you can create a javascript function, to tick every 5 seconds, and calculate the current time and update the label.
Related
I'm developing MVC3 based web application, which at one point needs to cache large amount of data from some external database. Process takes about 10-30 min (depending on a traffic) so I put it in BackgroundWorker. When you click particular button on the webpage, using ajax it just access other method in controller, depending on the returned value proper information is displayed on user interface.
Controller:
if (IsDbLocked())
{
return this.Json(new
{
success = false,
message = "There is already an update requested by other user on the way."
});
}
this.model.DataUpdateBegin();
return this.Json(new { success = true });
Model:
public void DataUpdateBegin()
{
var backgroundWorker = new BackgroundWorker
{
WorkerSupportsCancellation = false,
WorkerReportsProgress = true
};
backgroundWorker.DoWork += this.DataUpdateWorkerDoWork;
backgroundWorker.ProgressChanged += this.DataUpdaterWorkerProgressChanged;
backgroundWorker.RunWorkerCompleted += this.DataUpdaterWorkerRunWorkerCompleted;
if (this.DataUpdateLockDb(true))
{
backgroundWorker.RunWorkerAsync();
}
}
Now when I do update, UI still freezes. While debuging controller I can see, that it starts BackgroundWorker and instantly continues to return statement (with success = true), but then it just finishes, and nothing else happens (returned message never reaches webpage).
I can see page from other browser/user and everything works ok, but this particular thread is locked for several minutes (not entire 10-30 min, as it's get unlocked after about 5 min - timeout?)
My question is, what I did wrong and how to fix it. I expect backgroundWorker to just run in the background, and free user to move around page wherever he wish. Also making an entry in database and making some external application just fetch it and do all the work (in real background) is not an option for me.
Do not use Background worker like this. Yes, the work will be done within another thread, but still in scope of that web request. Web requests are not ment to be alive for 30 minutes, there are plenty of things that can go wrong (timeouts, app pool restart, other IIS behaviour..)
If you have this type of long-running task, you should do it in some worker - windows service, maybe console application, etc. and from web you just start it (console) or set it to be done (message queue, azure queue)
Also, i hope you are not locking database (you method IsDbLocked()) for 30 minutes? Just do your import in transaction and use proper isolation level (read commited) so DB work normally all the time and the changes are there instantly when import finishes.
I'm developing MVC3 based web application
... so I put it in BackgroundWorker
BackgroundWorker is designed to work with Windows (forms) application; to achieve similar in web application, use Task.Factory.StartNew or Thread (more primitive)
This question already has answers here:
Warn user before leaving web page with unsaved changes
(17 answers)
Closed 9 years ago.
I am currently working on a website in aspx, where I need to detect and record if a user is about to leave the site.
It will need to capture if possible all of the following, if the user:
clicks on the browser Back or Forward buttons
clicks on the browser close button
clicks on the tab close button
navigates to a new website
If it's remotely possible, change the requirement, because it will lead to a less-than-ideal user experience.
On at least some browsers, you can do a synchronous ajax request from the onbeforeunload handler to send information to your server that the user is leaving the page:
window.onbeforeunload = function() {
$.ajax({
url: "/path/to/page",
data: {/* ...stuff... */,
async: false // <== Option is being removed soon
});
};
The reason I say it's a bad user experience is that since the ajax call is synchronous, it holds them up, and fairly intrusively on some browsers (the whole thing locks up while waiting for the request to complete). This is also why it may well not be reliable cross-browser.
The jQuery team is removing the async option from ajax at some point. It's still there in the underlying XMLHttpRequest object, so when that happens you can use that directly.
The fact the user left the site is already apparent from the web server logs, although you can't tell how long they spent on the final page. If that "how long did they spend on the final page" is really vital information, rather than holding them up when they leave (and relying on something that may not be entirely reliable cross-browser), you could use a background "ping" while they're still on the page. It would probably be best to do the pings further and further apart over time.
So for instance, when the page loads:
(function($) {
var SECOND = 1000;
var MINUTE = 60000;
var arrived = +new Date();
var pingTimes = {
0: 10 * SECOND, // Every 10 seconds in first minute
1: 30 * SECOND, // Every 30 seconds in second minute
2: 45 * SECOND, // Every 45 seconds in third minute
other: 60 * SECOND, // Every minute otherwise
long: 10 * MINUTE // Every 10 minutes if they've been here a long time
};
nextPing();
function ping() {
$.ajax({
url: "/path/to/ping/page",
method: "POST",
success: nextPing,
error: nextPing
});
}
function nextPing() {
var elapsed, pingTime;
// Get the # of full minutes they've been here
elapsed = Math.floor((new Date() - arrived) / MINUTE);
// If it's been a long time, use `pingTimes.long`.
// Otherwise, use the time from the table or the default.
pingTime = elapsed > 15 * MINUTE ? pingTimes.long : (pingTimes[elapsed] || pingTimes.other);
setTimeout(ping, pingTime);
}
})(jQuery);
I am working on an assignment in asp.net to send notification email to users at specific intervals.
But the problem is that since the server is not privately owned i cannot implement a windows service on it.
Any ideas?
There's no reliable way to achieve that. If you cannot install a Windows Service on the host you could write a endpoint (.aspx or .ashx) that will send the email and then purchase on some other site a service which will ping this endpoint at regular intervals by sending it HTTP request. Obviously you should configure this endpoint to be accessible only from the IP address of the provider you purchase the service from, otherwise anyone could send an HTTP request to the endpoint and trigger the process which is probably undesirable.
Further reading: The Dangers of Implementing Recurring Background Tasks In ASP.NET.
There are several ways to get code executing on an interval that don't require a windows service.
One option is to use the Cache class - use one of the Insert overloads that takes a CacheItemRemovedCallback - this will be called when the cache item is removed. You can re-add the cache item with this callback again and again...
Though, the first thing you need to do is contact the hosting company and find out if they already have some sort of solution for you.
You could set up a scheduled task on the server to invoke a program with the desired action.
You can always use a System.Timer and create a call at specific intervals. What you need to be careful is that this must be run one time, eg on application start, but if you have more than one pools, then it may run more times, and you also need to access some database to read the data of your actions.
using System.Timers;
var oTimer = new Timer();
oTimer.Interval = 30000; // 30 second
oTimer.Elapsed += new ElapsedEventHandler(MyThreadFun);
oTimer.Start();
private static void MyThreadFun(object sender, ElapsedEventArgs e)
{
// inside here you read your query from the database
// get the next email that must be send,
// you send them, and mark them as send, log the errors and done.
}
why I select system timer:
http://msdn.microsoft.com/en-us/magazine/cc164015.aspx
more words
I use this in a more complex class and its work fine. What are the points that I have also made.
Signaling the application stop, to wait for the timer to end.
Use mutex and database for synchronize the works.
Easiest solution is to exploit global.asax application events
On application startup event, create a thread (or task) into a static singleton variable in the global class.
The thread/task/workitem will have an endless loop while(true) {...} with your "service like" code inside.
You'll also want to put a Thread.Sleep(60000) in the loop so it doesn't eat unnecessary CPU cycles.
static void FakeService(object obj) {
while(true) {
try {
// - get a list of users to send emails to
// - check the current time and compare it to the interval to send a new email
// - send emails
// - update the last_email_sent time for the users
} catch (Exception ex) {
// - log any exceptions
// - choose to keep the loop (fake service) running or end it (return)
}
Thread.Sleep(60000); //run the code in this loop every ~60 seconds
}
}
EDIT Because your task is more or less a simple timer job any of the ACID type concerns from an app pool reset or other error don't really apply, because it can just start up again and keep trucking along with any data corruption. But you could also use the thread to simply execute a request to an aspx or ashx that would hold your logic.
new WebClient().DownloadString("http://localhost/EmailJob.aspx");
I have webpage with a button. when user pressing on button he get email with the current time. i need to send him another message after 60 sec async .. [he can still press the button how many times he wants]
how can i do it ?
after looking it up here is the answer
// Wait X Sec and then try to send message
System.Timers.Timer t = new System.Timers.Timer();
t.Interval = Convert.ToDouble(ConfigurationManager.AppSettings["timer"]);
t.Elapsed += delegate { /*your function here */};
t.Start();
t.AutoReset = false; // do it once
You can do it in the client side, as #Holystream suggested, but that will fail if the user leaves your page in thsoe 60 seconds, let alone close the browser.
If you don't want to create your own queuing mechanism, you can try using the Windows Scheduler. Just create a task that will access a URL in your application that will send that email. It'll work with you don't have a lot of such requests, and if the minute is not absolutely crucial (you can miss it a little, the scheduler isn't designed for such resolutions).
You should store data for schedule in DB with schedule time-stamp.
If user press button multiple times that time you can validate in DB if a scheduled email is already exists for the criteria ignore it.
You need to set Cron Job (Scheduler) service to call you page which will send emails from the data in DB if scheduled time is elapsed.
Based on accuracy you need, you need to set shorter duration for Cron Job to send emails.
If you want to set own scheduler service one good C# library is http://csharp-source.net/open-source/job-schedulers/quartz-net.
Hope this helps.
I am attempting to improve the stability of the web dashboard I have created. I have noticed that the main cause of getting into a bad state is when the user moves too quickly and requests get cut short.
For instance, I have the following javascript:
//When a resize occurs a lot of handling needs to happen to convert the user's action into
//a visibly-pleasing result. In addition, the server has to be spoken with in order to save the controls.
function OnClientResizing(pane, eventArgs) {
eventArgs.set_cancel(true);
var parameters = new Array();
parameters.push("Resize");
parameters.push(pane.get_id());
parameters.push(eventArgs.get_delta());
__doPostBack(pane.get_splitter()._uniqueID, parameters);
}
This function passes the hard work back to the server, so that it can calculate the appropriate ways to resize the controls on the page during resizes. This takes X seconds. If the user then resizes the page again before X seconds has elapsed -- I enter into a bad state. Either the old request gets cut off prematurely, or the new one runs at the same time. Either way, controls become mishapen on the page.
As such, I would like to queue future resizes, or play around with canceling current requests. I read that the best way to do something like this is to simply set a flag outside the scope of this function. I can do that, but I am not sure how to detect the end of a doPostBack. Am I supposed to change the javascript variable from the server-side somehow in PageRequestManager - EndRequest?
Cheers
First off, don't let your server participate in UI resize algorithms. Do that entirely client side. You can send resulting data to the server at any time, but don't make a real-time UI positioning depend upon a server response. That should be handled client-side with CSS or javascript logic.
Second off, if your code can't handle two ajax calls in flight at the same time, then your options are as follows:
Fix your code so it can handle sequential ajax responses in flight at the same time.
Cancel/ignore the first ajax response the moment you send a second one so that you ignore the response from the first and wait for the response from the second.
Prevent a second ajax request until the first one completes. I wouldn't suggest queueing them because that's just going to lead to an even worse user experience.
The details of how to do 1, 2 or 3 depend upon how your code works which you have not yet shared.
The easiest is option 3). That can be done with just a global flag. Just define a global variable, set it to true when you start an ajax call and clear it when the ajax call completes (in a completion function):
var ajaxInFlight = false; // global declaration
function OnClientResizing(pane, eventArgs) {
if (ajaxInFlight) return; // do nothing if ajax call already in flight
ajaxInFlight = true;
eventArgs.set_cancel(true);
var parameters = new Array();
parameters.push("Resize");
parameters.push(pane.get_id());
parameters.push(eventArgs.get_delta());
__doPostBack(pane.get_splitter()._uniqueID, parameters);
}
function postBackCompletionHandler(id, parms) {
ajaxInFlight = false; // clear global flag, ajax call done
// ... rest of your function here
}
You will also have to make sure that error conditions are handled so that the global flag is reset if the ajax call fails for any reason.