Hugoware

The product of a web developer with a little too much caffeine

Posts Tagged ‘Threading

Keep Your Website Alive (Don’t Let IIS Recycle Your Website)!

with 2 comments

Have you ever opened a page for one of your websites and it lags for awhile before it finally shows a page but then all of your following requests are quick? If you were to look up the problem you’d find that often it ends up having to do with IIS meeting an idle time limit and shuts down your site. There is even some software you can purchase to fix the problem for you.

But who wants to spend money on something like that? Especially when we can solve this ourselves — even for Hosted Environments!

Stayin’ Alive — (ack! bad pun again!)

If you happened to check out that software above then you can probably glean what it does just from the title. I’d rather not devote my personal machine to something like that so lets see if we can’t approach this from an alternative route.

private static void _SetupRefreshJob() {

    //remove a previous job
    Action remove = HttpContext.Current.Cache["Refresh"] as Action;
    if (remove is Action) {
        HttpContext.Current.Cache.Remove("Refresh");
        remove.EndInvoke(null);
    }

    //get the worker
    Action work = () => {
        while (true) {
            Thread.Sleep(60000);
            //TODO: Refresh Code (Explained in a moment)
        }
    };
    work.BeginInvoke(null, null);

    //add this job to the cache
    HttpContext.Current.Cache.Add(
        "Refresh",
        work,
        null,
        Cache.NoAbsoluteExpiration,
        Cache.NoSlidingExpiration,
        CacheItemPriority.Normal,
        (s, o, r) => { _SetupRefreshJob(); }
        );
}

If we place this bit of code in the Global.asax and call it when Application_Start() is raised, we can basically start a job that keeps our website alive. You could just as easily use a Thread to host the refresh method but for this example we simply used an Action delegate (but if you are using an earlier version of .NET then you might HAVE to use a Thread to do this).

Once our application starts the refresh job is also started and is saved to the cache. In this example we’re using 60 seconds, but you can change this to be as often as you like.

So How Can We Keep It Fresh?

So how about an example of some code we can use? Here is a simple example that could keep our website alive. Replace the //TODO: in the example above with something like the following.

WebClient refresh = new WebClient();
try {
    refresh.UploadString("http://www.website.com/", string.Empty);
}
catch (Exception ex) {
    //snip...
}
finally {
    refresh.Dispose();
}

This snippet uses a WebClient to actually make an HTTP call to our website, thus keeping the site alive! We could do any number of things from this code like updating local data or get information from external resource. This can be used to keep our site alive and our content refreshed, even if we’re using a Hosted Environment!

It is worth nothing that might not actually need to do an HTTP call back to your website. It is possible that using any method will keep your website from being killed off (but I haven’t tested it yet so let me know what happens if you try it). This example, however, has been tested and works quite well with my provider.

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Written by hugoware

August 19, 2009 at 2:34 am

Simulate Threading Using Javascript

with 9 comments

One of the cool things about .NET is how easy it is to create more than one thread for your application to run on. On a recent project I had to make many calls to different web services on our network. They were all identical, but each call took quite awhile, roughly around 2 or 3 seconds each.

Instead of doing one at a time, I created 10 separate threads and then merged the results together. Instead of taking around 20 seconds, the calls were reduced to the length of the slowest call. (Web Services also have an Asynchronous method to call a service, so that is an alternative as well).

So What Does This Have To Do With Javascript?

In Javascript, any long running process will cause a noticeable lag for a user. Buttons won’t respond, links don’t do anything, the screen may even turn white — clearly not the user experience we want to deliver.

Recently I was experimenting with joining records using jLinq. jLinq was doing fairly well with the records I was using – I had about 850 records to join against a handful (about 10) of other records. The process finished in around 250ms to 500ms. I was pretty satisfied — until I tried a different set of records…

A different set of records, around 90, crippled the browser. After about 8 seconds the browser finally released itself and we were back in business. Yikes.

Simulating A Thread

So what are the options here? Well unless someone has built threading into Javascript then we’re forced to come with a more creative solution — enter setTimeout.

If you’ve read some of my blog posts before, you know I’m a big fan of enclosures. Using Javascript we can take advantage of both enclosures and setTimeout to try and simulate threading and reduce the time a browser is locked up.

So let’s say we’re working with a really large loop, say around 500,000 records – What can we do? One idea is to break up the work into smaller, more manageable chunks.


//loops through an array in segments
var threadedLoop = function(array) {
	var self = this;
	
	//holds the threaded work
	var thread = {
		work: null,
		wait: null,
		index: 0,
		total: array.length,
		finished: false
	};
	
	//set the properties for the class
	this.collection = array;
	this.finish = function() { };
	this.action = function() { throw "You must provide the action to do for each element"; };
	this.interval = 1;
	
	//set this to public so it can be changed
	var chunk = parseInt(thread.total * .005);
	this.chunk = (chunk == NaN || chunk == 0) ? thread.total : chunk;
	
	
	//end the thread interval
	thread.clear = function() {
		window.clearInterval(thread.work);
		window.clearTimeout(thread.wait);
		thread.work = null;	
		thread.wait = null;
	};
	
	//checks to run the finish method
	thread.end = function() {
		if (thread.finished) { return; }
		self.finish();
		thread.finished = true;
	};
	
	//set the function that handles the work
	thread.process = function() {
		if (thread.index >= thread.total) { return false; }
	
		//thread, do a chunk of the work
		if (thread.work) {
			var part = Math.min((thread.index + self.chunk), thread.total);
			while (thread.index++ < part) {
				self.action(self.collection&#91;thread.index&#93;, thread.index, thread.total);
			}					
		}
		else {
		
			//no thread, just finish the work
			while(thread.index++ < thread.total) {
				self.action(self.collection&#91;thread.index&#93;, thread.index, thread.total);
			}	
		}
		
		//check for the end of the thread
		if (thread.index >= thread.total) { 
			thread.clear(); 
			thread.end();
		}
		
		//return the process took place
		return true;
		
	};
	
	//set the working process
	self.start = function() {
		thread.finished = false;
		thread.index = 0;
		thread.work = window.setInterval(thread.process, self.interval);
	};
	
	//stop threading and finish the work
	self.wait = function(timeout) {

		//create the waiting function
		var complete = function() {
			thread.clear();
			thread.process();
			thread.end();
		};
		
		//if there is no time, just run it now
		if (!timeout) {
			complete();
		}
		else {
			thread.wait = window.setTimeout(complete, timeout);
		}
	};

};

// Note: this class is not battle-tested, just personal testing on large arrays

This example class allows us to pass in a loop and then supply a few actions for us to use on each pass. The idea here is that if we do a section, pause for the browser to catch up, and then resume work.

How exactly do you use this? Well let’s just say we have a really large loop of strings we’re wanting to compare…

var array = [];
for (var i = 0; i < 500000; i++) { array.push("this is some long string"); } [/sourcecode] That's a lot of work to check all those - Let's move it into our new class we created... [sourcecode language='javascript'] //create our new class var work = new threadedLoop(array); //create the action to compare each item with work.action = function(item, index, total) { var check = (item == "this is some long string comparison to slow it down"); document.body.innerHTML = "Item " + index + " of " + total; }; //another action to use when our loop is done work.finish = function(thread) { alert("Thread finished!"); }; //and start our 'thread' work.start(); [/sourcecode] If you run this test in a browser, you'll see that our page is updated as each pass of the array is completed. This way our browser remains 'responsive' to a degree, but continues to process our work in the background. This code allows you to set a few additional properties as well as an additional function.

  • chunk: The number of records to loop through on each interval. The default is numberOfRecords * 0.005.
  • interval: The number of milliseconds to wait between passes. The default is 1. A longer value gives the browser more time to recover, but makes the loop take longer.
  • wait([timeout]): Waits the number of milliseconds before canceling the thread and blocking the browser until the work finishes. If no time is provided, as in left blank, the waiting starts immediately.

Threading Possibilities?

It’s always amazing to see what enclosures can do – I’m not so sure how simple this same creation would be in Javascript without them. With a little bit of code we can create a half-way decent attempt at creating an asynchronous experience for our user, even if we have a lot of work to do.

Could your heavy client side scripts benefit from ‘threading’?

Written by hugoware

July 10, 2009 at 6:05 am