Schedule your web tasks with WebTaskScheduler

WebTaskScheduler user guide in ASP.NET

• Download WebTaskScheduler_bin - 6.94 KB
• Download WebTaskScheduler_demo - 11.84 KB
• Download WebTaskScheduler_src - 27.13 KB

Read WebTaskScheduler user guide in ASP.NET in my site

Introduction

Desktop applications is very different form web applications in task scheduling. The problem of web applications is lack of a process to schedule their tasks. ASP.NET provides some technologies one of which I used to create task scheduler for web applications. I have used Caching techniques.

Easy Use

Please follow these steps:

1. Add a reference to SalarSoft.WebTaskScheduler.dll assembly in your project.
2. A callback method will be needed, so write it like following example:

C#

static void MyTask_CallBack(WebTaskEventArgs e)
{
 // Enter your codes here
}

VB.NET

Shared Sub MyTask_Callback(ByVal e As WebTaskEventArgs)
 ' Enter your codes here
End Sub

This callback method has an argument of WebTaskEventArgs type. This method will be called when the task is executed.

3. To run a task you need to add it. The following example adds a task that will run every weekend.

C#

WebTaskScheduler.Add("MyTask", MyTask_CallBack, TaskExecutePeriod.Weekly);

In VB.NET the codes are a bit longer. Here is a VB.NET example:

VB.NET

Sub AddMyTask()

 'Line 1
 Dim onMytaskCallBack As WebTaskExecuteCallback

 'Line 2
 onMytaskCallBack = New WebTaskExecuteCallback(AddressOf MyTask_CallBack)

 'Line 3
 WebTaskScheduler.Add("MyTask", onMytaskCallBack, TaskExecutePeriod.Weekly)
End Sub

On the first line we defined a variable of WebTaskExecuteCallback type. On the second line we created a new instance of WebTaskExecuteCallback type to the variable, and on the third line we added the task to the class.

4. Please apply steps 2 and 3 in the Global.asax file in ApplicationStart event. That's it.

Features

• How to add a new task with ADD method

Add method is used to add a new task. Here are three ways it is defined:

Method 1:
WebTaskScheduler.Add( String , WebTaskExecuteCallback , Integer  )


Method 2:
WebTaskScheduler.Add( String , WebTaskExecuteCallback , TaskExecutePeriod )


Method 3:
WebTaskScheduler.Add( String , WebTaskExecuteCallback , TimeSpan )

The two first arguments of these overloads have same behavior.

The first argument "key" which its type is string: Specifies the name of the task. This name should be unique. This key may be used for future operations.

The second argument "callback" which its type is WebTaskExecuteCallback: Specifies the callback method. This method will run if the task is executed. The method with WebTaskExecuteCallback type has a WebTaskEventArgs type of argument which has been described at the bottom of the page.

The third argument of Method 1, "DaysPeriod", which its type is integer: Specifies intervals between the execution of the tasks. If it is set to 10, the task will run after 10 days.

The third argument of Method 2, "period", which its type is TaskExecutePeriod: Specifies the type of the task execution intervals. The value can be one of None , EveryNoon , Daily , Weekly , TwoWeekly or Monthly. For example if the value sets to Weekly, the task will run every weekends.

The third argument of Method 3, "customPeriod", which its type is TimeSpan: Through this, the task will run after the specified time. For example if the value is set to 45 minutes, the task will run after 45 minutes of adding the method call.

• Deleting a task

The Remove method can be used to remove a task. Here is its definition:

Method 1:
Remove(string key)

Method 2:
Remove(WebTaskItem)

The first method accepts the key of the task. The second method accepts the task item which its type is "WebTaskItem".

• Getting Details of a Task

The GetItem method returns the existing task item.

GetItem( string )
Returns WebTaskItem

This method has an argument that is the key of the task which is defined in Add method. This method will return WebTaskItem.

• Synchronous Access

There are two methods to lock and unlock the access to WebTaskScheduler instance.
This is an advanced option to prevent threads from multiple access to methods. With these methods only one thread can have access to the class and the other threads will wait for the current thread to finish.

Here are theirs the definition:

Method 1:
Lock()

Method 2:
Lock( wait )

Method 3:
Unlock()

Call Lock method to lock the access, and call Unlock method to unlock the access.
The second method has an argument that specifies Wait option to check if there is another thread that uses the instance; if the value is set to false and there is another thread working with the class, the method will throw an exception.

Important: Please use try..finally block when you're going to use these methods.

Here is an example:

C#:

WebTaskScheduler.Lock();
try
{
    WebTaskScheduler.Add("MyTask", MyTask_CallBack, 1);
}
finally
{
    WebTaskScheduler.Unlock();
}

VB.NET:

WebTaskScheduler.Lock()
Try
 Dim onMytaskCallBack As WebTaskExecuteCallback
 onMytaskCallBack = New WebTaskExecuteCallback(AddressOf MyTask_CallBack)
 WebTaskScheduler.Add("MyTask", onMytaskCallBack, TaskExecutePeriod.Weekly)
Finally
 WebTaskScheduler.Unlock()
End Try

• TaskExecutePeriod

Name	Decription
None	Executes the task immediately (not recommended)
EveryNoon	Executes the task every noon
Daily	Executes the task every night
Weekly	Executes the task every weekend at night
TwoWeekly	Executes the task every two weeks at night
Monthly	Executes the task every month at night
ShamsiWeekly	Executes the task every week at night using Persian dates
ShamsiTwoWeekly	Executes the task every two weeks at night using Persian dates
ShamsiMonthly	Executes the task every month at night using Persian dates

• WebTaskEventArgs

This class has two properties: "TaskItem" and "CanContinue".
CanContinue specifies whether the task can run again next time or not. If it is set to false the task will be removed after execution. The default value is true.
TaskItem specifies the task item which its type is WebTaskItem. This can be modified in callback.

Some tips

1. Important: In your ASP.NET site, always add your tasks in Application_Start event of Global.asax.
2. The added tasks are not stored on the disk, so they will be removed if the web application shuts down or restarts.
3. The WebTaskScheduler is accessible from everywhere in your site. Just add the assembly reference to your application!

That's all!

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Dailybackup is not working Amitsp 0:01 3 May '09   hello i m using this as daily backup,but it is not working. code is below WebTaskScheduler.Lock(); try { WebTaskScheduler.Add("DailyBackup", DailyBackup_CallBack, TaskExecutePeriod.Daily); } finally { WebTaskScheduler.Unlock(); } waiting for your reply Amitsp Sign In·View Thread·PermaLink Re: Dailybackup is not working SalarSoft 5:06 3 May '09   That "DailyBackup_CallBack" will run every day at 23:59 Because ASP.net worker shuts down the application if there is not request, be sure that you have enough visitors. specially when that process is going to run if so the code will run successfully. www.softprojects.org Sign In·View Thread·PermaLink interesting. Jason Witty 14:12 3 Apr '08   Interesting and smart concept. but i would not recommend it to schedule anything that really really needs to run. When I have a process I need to execute that needs to be executed in the same memory space as a web application. (within the same application pool of a web site). I will usually just create a generic handler or web service that I can hit to execute a RPC. If security is a concern wse provides an easy to use framework to implement security. A Programmers Journal RSS Sign In·View Thread·PermaLink Re: interesting. SalarSoft 22:06 16 Apr '08   This tool is based on caching technique. So it inherits the caching limitations. It is clear that the cache is only available during application running and the cache will destroy if application close. So the tasks will destroy too. Yes, you're right that we can't use this for very serious jobs but still its useful for various jobs. I supposed that this will useful for backup operations, removing temporary uploaded files, mail sending like newsletters and etc. Sign In·View Thread·PermaLink What happens when no one is visiting? Thomas Eyde 4:05 3 Apr '08   This may solve the scheduling problem, assuming the scheduler will continue to run after a serious error, or after the last session timed out. The web application will unload automatically when the last session dies. Will the scheduler continue to run? Or does it die together with the web application? Sign In·View Thread·PermaLink Re: What happens when no one is visiting? SalarSoft 22:03 16 Apr '08   Nothing will happen if your site keeps running. And this tool will continue working even any serious *exception* happens. The application will die if there is no visitor and the cache too. This tool uses caching technique so it won't work after application died. This is caching issue. In designing I supposed that the tool will used in a site with enough daily visit. And I think this thought is clear that we don't need task scheduling in a site without visitor! Sign In·View Thread·PermaLink Re: What happens when no one is visiting? Thomas Eyde 0:38 17 Apr '08   Thanks. I thought the scheduler would die as well. And I never thought of it that way, that scheduling isn't that important on a site without visitors. However, I am not quite sold on that concept, yet. I still feel the scheduler should work in isolation, and it would be nice to have it running at night when no one is visiting. But when there's no alternative, this is a good one. Sign In·View Thread·PermaLink

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