Develop Reference

C# Calling method every minute at 55 second mark

I've been given a task to write a program to count how many page views are requested from our site. My current approach is to get data from google analytics Real Time API, which works to my suprise.
My problem is that to get pageviews every minute I need to poll data from google API twice (cause it returns sum of last 29 minutes + a value from a timer that resets every minute). After I set up 'the point of reset', lets just say, on a 55th second every minute, I poll data on 56th and later on at 53th second, which gives me relatively good estimation of new users / page views requested.
So this is my current approach:
static System.Timers.Timer myTimer = new System.Timers.Timer();
myTimer.AutoReset = false;
myTimer.Interval = interval();
myTimer.Elapsed += myTimer_Elapsed2;
myTimer.Start();
static double interval()
{
return 1000 - DateTime.Now.Millisecond;
}
static void myTimer_Elapsed2(object sender, System.Timers.ElapsedEventArgs e)
{
if (DateTime.Now.Second == (resetPoint.Second - 1) % 60 && warden)
{
DoStuff(); //mostly inserting google API data to database
}
else if (DateTime.Now.Second == (resetPoint.Second + 1) % 60) //so we dont get riddiculous 60 and above
{
//I get some data here, to later use it in DoStuff - mostly to calculate the gap between later
}
myTimer.Interval = interval(); //Because DoStuff() takes about 0.5 sec to execute, i need to recalibrate
myTimer.Start();
}
And it works really well, until it stops after about 2 hours, for now I have no idea why (program runs, just timer doesn't do its work anymore).
How do I make it stable for long periods of time? Best case scenario would be to run it for months without intervention.
# I edited to give a better sense what I'm actually doing
#END CREDITS
I ended up using two timers, each running in a one minute circle. And a database writing sometimes crashed and I didn't handle the corresponding exception properly. Log told me that google API functions from time to time tend to retrieve data a bit longer, which led to multiple Threading.Event calls and made my database data handling throw an exception hence stopping the timer.
I tried to use Quartz approach but its lack of human-friendly howto made me abandon this library.

You should really look into using Quartz.net for scheduling events on a reliable basis. Using a timer for scheduling is asking for stuff like race conditions, event skips and database deadlocks.
http://www.quartz-scheduler.net/ allows you to schedule events at precise intervals, independant of when your code starts or stops.
An example on how you use it: This will build a trigger that will fire at the top of the next hour, then repeat every 2 hours, forever:
trigger = TriggerBuilder.Create()
.WithIdentity("trigger8") // because group is not specified, "trigger8" will be in the default group
.StartAt(DateBuilder.EvenHourDate(null)) // get the next even-hour (minutes and seconds zero ("00:00"))
.WithSimpleSchedule(x => x
.WithIntervalInHours(2)
.RepeatForever())
// note that in this example, 'forJob(..)' is not called
// - which is valid if the trigger is passed to the scheduler along with the job
.Build();
scheduler.scheduleJob(trigger, job);
http://www.quartz-scheduler.net/documentation/quartz-2.x/tutorial/simpletriggers.html has a few examples. I really URGE you to use it, since it will severely simplify development.

The .NET timer is reliable. That is, it won't just stop working randomly for no apparent reason.
Most likely, something in your timer event handler is throwing an exception, which is not surfaced because System.Timers.Timer squashes exceptions. As the documentation states:
The Timer component catches and suppresses all exceptions thrown by event handlers for the Elapsed event. This behavior is subject to change in future releases of the .NET Framework.
That bit about the behavior being "subject to change" has been there since at least .NET 2.0.
What I think is happening is that the timer calls your event handler. The event handler or one of the methods it calls throws an exception, and the timer just drops it on the floor because you don't handle it.
You need to put an exception handler in your myTimer_Elapsed2 method so that you can at least log any exceptions that crop up. With the information provided from the exception log, you can probably identify what the problem is.
Better yet, stop using System.Timers.Timer. Use System.Threading.Timer instead.
Finally, there's no way that your code as written will reliably give you a timer tick at exactly 55 seconds past the minute, every minute. The timer isn't exact. It will be off by a few milliseconds each minute. Over time, it's going to start ticking at 54 seconds (or maybe 56), and then 53 (or 57), etc. If you really need this to tick reliably at 55 seconds past the minute, then you'll need to reset the timer after every minute, taking into account the current time.
I suspect that your need to check every minute at exactly the 55 second mark is overkill. Just set your timer to tick every minute, and then determine the exact elapsed time since the last tick. So one "minute" might be 61 or 62 seconds, and another might be 58 or 59 seconds. If you store the number of requests and the elapsed time, subsequent processing can smooth the bumps and give you a reliable requests-per-minute number. Trying to gather the data on exact one-minute boundaries is going to be exceedingly difficult, if even possible with a non-real-time operating system like Windows.

How to prevent loops in JavaScript that crash the browser or Apps?

I am creating a live editor in Windows 8.1 App using JavaScript. Almost done with that, but the problem is whenever I run such bad loops or functions then it automatically hangs or exits.
I test it with a loop such as:( It just a example-user may write its loop in its own way..)
for(i=0;i<=50000;i++)
{
for(j=0;j<5000;j++){
$('body').append('hey I am a bug<br>');
}
}
I know that this is a worst condition for any app or browser to handle that kind of loop. So here I want that if user uses such a loop then how I handle it, to produce their output?
Or if its not possible to protect my app for that kind of loop, if it is dangerous to my app so I alert the user that:
Running this snippet may crash the app!
I have an idea to check the code by using regular expressions if code have something like for(i=0;i<=5000;i++) then the above alert will show, how to do a Regex for that?
Also able to include C# as back-end .

Unfortunately, without doing some deep and complex code analysis of the edited code, you'll not be able to fully prevent errant JavaScript that kills your application. You could use, for example, a library that builds an abstract syntax tree from JavaScript and not allow code execution if certain patterns are found. But, the number of patterns that could cause an infinite loop are large, so it would not be simple to find, and it's likely to not be robust enough.
In the for example, you could modify the code to be like this:
for(i=0;!timeout() && i<=50000;i++)
{
for(j=0;!timeout() && j<5000;j++){
$('body').append('hey I am a bug<br>');
}
}
I've "injected" a call to a function you'd write called timeout. In there, it would need to be able to detect whether the loop should be aborted because the script has been running too long.
But, that could have been written with a do-while, so that type of loop would need to be handled.
The example of using jQuery for example in a tight loop, and modifying the DOM means that solutions that trying to isolate the JavaScript into a Web Worker would be complex, as it's not allowed to manipulate the DOM directly. It can only send/receive "string" messages.
If you had used the XAML/C# WebView to host (and build) the JavaScript editor, you could have considered using an event that is raised called WebView.LongRunningScriptDetected. It is raised when a long running script is detected, providing the host the ability to kill the script before the entire application becomes unresponsive and is killed.
Unfortunately, this same event is not available in the x-ms-webview control which is available in a WinJS project.

I've got 2 solutions:
1.
My first solution would be defining a variable
startSeconds=new Date().getSeconds();.
Then, using regex, I'm inserting this piece of code inside the nested loop.
;if(startSecond < new Date().getSeconds())break;
So, what it does is each time the loop runs, it does two things:
Checks if startSecond is less than current seconds new Date().getSeconds();.
For example, startSecond may be 22. new Date().getSeconds() may return 24.Now, the if condition succeeds so it breaks the loop.
Mostly, a non dangerous loop should run for about 2 to 3 seconds
Small loops like for(var i=0;i<30;i++){} will run fully, but big loops will run for 3 to 4 seconds, which is perfectly ok.
My solution uses your own example of 50000*5000, but it doesn't crash!
Live demo:http://jsfiddle.net/nHqUj/4
2.
My second solution would be defining two variables start, max.
Max should be the maximum number of loops that you are willing to run. Example 1000.
Then, using regex, I'm inserting this piece of code inside the nested loop.
;start+=1;if(start>max)break;
So, what it does is each time the loop runs, it does two things:
Increments the value of start by 1.
Checks whether start is greater than the max. If yes, it breaks the loop.
This solution also uses your own example of 50000*5000, but it doesn't crash!
Updated demo:http://jsfiddle.net/nHqUj/3
Regex I'm using:(?:(for|while|do)\s*\([^\{\}]*\))\s*\{([^\{\}]+)\}

One idea, but not sure what is your editor is capable of..
If some how you can understand that this loop may cause problem(like if a loop is more than 200 times then its a issue) and for a loop like that from user if you can change the code to below to provide the output then it will not hang. But frankly not sure if it will work for you.
var j = 0;
var inter = setInterval( function(){
if( j<5000 ){
$('#test').append('hey I am a bug<br>');
++j;
} else {
clearInterval(inter);
}
}, 100 );

Perhaps inject timers around for loops and check time at the first line. Do this for every loop.
Regex: /for\([^{]*\)[\s]*{/
Example:
/for\([^{]*\)[\s]*{/.test("for(var i=0; i<length; i++){");
> true
Now, if you use replace and wrap the for in a grouping you can get the result you want.
var code = "for(var i=0; i<length; i++){",
testRegex = /(?:for\([^{]*\)[\s]*{)/g,
matchReplace = "var timeStarted = new Date().getTime();" +
"$1" +
"if (new Date().getTime() - timeStarted > maxPossibleTime) {" +
"return; // do something here" +
"}";
code.replace(textRegex, matchReplace);

You cannot find what user is trying to do with a simple regex. Lets say, the user writes his code like...
for(i=0;i<=5;i++)
{
for(j=0;j<=5;j++){
if(j>=3){
i = i * 5000;
j = j * 5000;
}
$('body').append('hey I am a bug<br>');
}
}
Then with a simple regex you cannot avoid this. Because the value of i is increased after a time period. So the best way to solve the problem is to have a benchmark. Say, your app hangs after continuos processing of 3 minutes(Assume, until your app hits 3 minutes of processing time, its running fine). Then, whatever the code the user tries to run, you just start a timer before the process and if the process takes more than 2.5 minutes, then you just kill that process in your app and raise a popup to the user saying 'Running this snippet may crash the app!'... By doing this way you dont even need a regex or to verify users code if it is bad...
Try this... Might help... Cheers!!!

Let's assume you are doing this in the window context and not in a worker. Put a function called rocketChair in every single inner loop. This function is simple. It increments a global counter and checks the value against a global ceiling. When the ceiling is reached rocketChair summarily throws "eject from perilous code". At this time you can also save to a global state variable any state you wish to preserve.
Wrap your entire app in a single try catch block and when rocket chair ejects you can save the day like the hero you are.

How to run a timer at the TOP of each second? (when millis = 000)

In my application, I have used the number of System.Threading.Timer and set this timer to fire every 1 second. My application execute the thread at every 1 second but it execution of the millisecond is different.
In my application i have used the OPC server & OPC group .one thread reading the data from the OPC server (like one variable changing it's value & i want to log this moment of the changes values into my application every 1 s)
then another thread to read this data read this data from the first thread every 1s & second thread used for store data into the MYSQL database .
in this process when i will read the data from the first thread then i will get the old data values like , read the data at 10:28:01.530 this second then i will get the information of 10:28:00.260 this second.so i want to mange these threads the first thread worked at 000 millisecond & second thread worked at 500 millisecond. using this first thread update the data at 000 second & second thread read the data at 500 millisecond.
My output is given below:
10:28:32.875
10:28:33.390
10:28:34.875
....
10:28:39.530
10:28:40.875
However, I want following results:
10:28:32.000
10:28:33.000
10:28:34.000
....
10:28:39.000
10:28:40.000
How can the timer be set so the callback is executed at "000 milliseconds"?

First of all, it's impossible. Even if you are to schedule your 'events' for a time that they are fired few milliseconds ahead of schedule, then compare millisecond component of the current time with zero in a loop, the flow control for your code could be taken away at the any given moment.
You will have to rethink your design a little, and not depend on when the event would fire, but think of the algorithm that will compensate for the milliseconds delayed.
Also, you won't have much help with the Threading.Timer, you would have better chance if you have used your own thread, periodically:
check for the current time, see what is the time until next full second
Sleep() for that amount minus the 'spice' factor
do the work you have to do.
You'll calculate your 'spice' factor depending on the results you are getting - does the sleep finishes ahead or behind the schedule.
If you are to give more information about your apparent need for having event at exactly zero ms, I could help you get rid of that requirement.
HTH

I would say that its impossible. You have to understand that switching context for cpu takes time (if other process is running you have to wait - cpu shelduler is working). Each CPU tick takes some time so synchronization to 0 milliseconds is impossible. Maybe with setting high priority of your process you can get closer to 0 but you won't achive it ever.

IMHO it will be impossible to really get a timer to fire exactly every 1sec (on the milisecond) - even in hardcore assembler this would be a very hard task on your normal windows-machine.

I think first what you need to do: is to set right dueTime for a timer. I do it so:
dueTime = 1000 - DateTime.Now.Milliseconds + X; where X - is serving for accuracy and you need select It by testing. Then Threading.Timer each time It ticks running on thread from CLR thread pool and, how tests show - this thread is different each time. Creating threads slows timer, because of this you can use WaitableTimer, which always will be running at the same thread. Instead of WaitableTimer you can using Thread.Sleep method in such way:
Thread.CurrentThread.Priority = Priority.High; //If time is really critical
Thread.Sleep (1000 - DateTime.Now + 50); //Make bound = 1s
while (SomeBoolCondition)
{
Thread.Sleep (980); //1000 ms = 1 second, but something ms will be spent on exit from Sleep
//Here you write your code
}
It will be work faster then a timer.

.NET Timers, do they fire at the exact interval or after processing + interval

So a simple enough question really.
How exactly does the interval for System.Timers work?
Does it fire 1 second, each second, regardless of how long the timeout event takes or does it require the routine to finish first and then restarts the interval?
So either:
1 sec....1 sec....1 sec and so on
1 sec + process time....1 sec + process time....1 sec + process time and so on
The reason I ask this is I know my "processing" takes much less than 1 second but I would like to fire it every one second on the dot (or as close as).
I had been using a Thread.Sleep method like so:
Thread.Sleep(1000 - ((int)(DateTime.Now.Subtract(start).TotalMilliseconds) >= 1000 ? 0 : (int)(DateTime.Now.Subtract(start).TotalMilliseconds)));
Where start time is registered at start of the routine. The problem here is that Thread.Sleep only works in milliseconds. So my routine could restart at 1000ms or a fraction over like 1000.0234ms, which can happen as one of my routines takes 0ms according to "TimeSpan" but obviously it has used ticks/nanoseconds - which would then mean the timing is off and is no longer every second. If I could sleep by ticks or nanoseconds it would be bang on.
If number 1 applies to System.Timers then I guess I'm sorted. If not I need some way to "sleep" the thread to a higher resolution of time i.e ticks/nanoseconds.
You might ask why I do an inline IF statement, well sometimes the processing can go above 1000ms so we need to make sure we don't create a minus figure. Also, by the time we determine this, the ending time has changed slightly - not by much, but, it could make the thread delay slightly longer causing the entire subsequent sleeping off.
I know, I know, the time would be negligible... but what happens if the system suddenly stalled for a few ms... it would protect against that in this case.
Update 1
Ok. So I didn't realise you can put a TimeSpan in as the timing value. So I used the below code:
Thread.Sleep(TimeSpan.FromMilliseconds(1000) - ((DateTime.Now.Subtract(start).TotalMilliseconds >= 1000) ? TimeSpan.FromMilliseconds(0) : DateTime.Now.Subtract(start)));
If I am right, this should then allow me to repeat the thread at exactly 1 second - or as close as the system will allow.

IF you have set AutoReset = true; then your theory 1 is true, otherwise you would have to deal with it in code – see the docuementation for Timer on MSDN.

Progress Bar in a Winform application , Increment Progress Bar till a query is executed on a database

I am connecting to a mysql database online from my local C# .NET Winform application. I want that till the application connects to the online database, a Progress Bar is displayed , and as soon as the database connection is established, the progress bar should also complete incrementing.
please help with code.
how do i get the time taken by the application to connect to the online database , and then set that time as INTERVAL for the progress bar?

Why don't you change ProgressBar Style to marque a line before Query Start's Execution ,than on end you can Change ProgressBar Style in Block's and Give Progressbar.Value = 100; .

If i read that correctly, you would like to have a progress bar continually fill over and over until a connection with the database is established (since it is unknown how long a connection could take prior to completion)
If this is the case you can use a timer/backgroundworker to do this pretty easy.
Sudo code:
Timer a= new Timer();
a.Tick += TickMethod;
a.interval = 2;
BackgroundWorker b = new BackgroundWorker();
b.DoWork += BackgroundMethod();
b.WorkComplete += WorkDone();
void Start()
{
a.Start();
b.RunAsync();
}
void TickMethod()
{
if(progressBar.Value == progressBar.Max)
progressBar.Value = 0;
progresssBar.Step();
}
void BackgroundMethod(object s, Args e)
{
MakeConnection();
}
void WorkDone()
{
a.Stop();
progressBar.Value = progressBar.Max();
}
I'm sorry if thats not what you are looking for.

The "proper" way to use a progress bar for an operation that will take an indetermine time is to set it into Marquee mode. This shows the bar with an animated "shine" effect to show that something is happening, but does not show an actual progress bar (as you don't know how long it will take, you can't estimate a percentage complete). Once you have connected, you can then set the progressbar's Value to its Max so that it moves to 100%.
An alternative approach was used in some versions of IE while fetching web pages. This showed a progress bar that slowly incremented towards 100% over a long period (a predetermined time frame long enough to cover the worst case scenario - e.g. in your case you might choose 30 seconds as that is often the timeout period used to fail a connection anyway). When the connection is finally made, you then advance the bar to 100%. THis gives the impression of progress being made while you're waiting, and as long as your estimate of the worst case scenarion is reasonable, this will give good results.
However, note that .net progress bars don't jump immediately to a new value - they animate so as to "grow" towards the requested value, so if it has to go from 0% to 100% it will take a second or two before it actually displays 100%. This can mean that (for example) your window closes while the progress bar is only showing a value like 20%, which is highly irritating as it makes the user think that it failed in some way. There are two solutions to this:
1) Make your application pause (e.g. Sleep the thread) for a "long enough period" that you are sure the progress bar will reach 100%. This adds an extra delay of several seconds to the end of your operation, and the time needed can be rather unpredictable, so it's not a great solution, especially if the database fetch is often quick.
2) Force the progress bar to "jump" to 100% rather than slowly growing towards 100%. You can do this by setting Value = Max; Value = Max-1; Value = Max. When the progress bar is asked to go "backwards" in this way (to Max-1) it doesn't animate, but immediately updates to show the requested value.