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Communication With a Background Thread in ASP.NET |
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This tutorial shows how to spin up a background thread to perform work not related to processing a web request. This example has a lot of moving parts. The first part is a custom HttpModule that launches a process in a background thread:
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public void Init(HttpApplication context)
{
Thread t = new Thread(BkgProcess.DoWork);
t.Start(context.Application);
} |
And of course a DoWork method that does something. In this case I am generating a random number between 1000 and 10000. This number is used as a value to put the thread to sleep or a random delay. It is also being used to set a value that is stored in the site’s application context. |
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public static void DoWork(object _app)
{
HttpApplicationState app = (HttpApplicationState)_app;
if (null != app)
{
int curVal = 1000;
if (null == app["curVal"])
{
app["curVal"] = curVal;
}
int i = 0;
while (true)
{
Random rnd1 = new Random(curVal);
curVal = rnd1.Next(1000, 10000);
lock (app["curVal"])
{
app["curVal"] = curVal;
}
Thread.Sleep(curVal);
i++;
if (i > 100)
{
break;
}
}
}
} |
There are a couple of things that need to be explained about this method. First it accepts an object _app. It is cast to an HttpApplicationState object, which is accessed in the module’s Init method from the current HttpContext.Next when the random value is stored in the application context it is locked, which prevents a potential overwrite by another thread.In this demo it is not a real concern, but in the real world it will be in most cases.Another thing I did was add a counter to keep this loop from running forever. I did this for demo purposes only.I am into JQuery and AJAX lately, so that is what we will do for this demo. All the HTML for the page is a simple H1 title and an empty paragraph. This paragraph will be used to hold the randomly generated value from the background thread:
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<h1>Background Value</h1>
<p id="curVal"></p>
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The AJAX for the demon uses the .ajax method of the JQuery framework to call a generic HttpHandler, with a success option that sets the content of the paragraph above. I also added a little pulsing feature (fadeIn and fadeOut). |
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$(document).ready(function() {
GetValue();
});
function GetValue(){
$('#curVal').fadeOut(750);
$.ajax({
type: "GET",
url: "GetCurrentValue.ashx",
dataType: "text",
success: function(curVal) {
$('#curVal').html('The current value is: ' + curVal);
$('#curVal').fadeIn(750);
var retryInt = setTimeout("GetValue()", 2500);
},
error: function(curVal) {
$('DIV').innerHTML = "error " + curVal;
}
});
}
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The Generic HttpHandler accesses the random value from the application context and writes it to the Request for the ajax call to consume. |
public void ProcessRequest(HttpContext context)
{
context.Response.ContentType = "text/plain";
if (null != context.Application["curVal"])
{
context.Response.Write(context.Application["curVal"]);
}
else
{
context.Response.Write("1");
}
context.Response.Flush();
context.Response.End();
}
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