HTTP Modules


Scheduler

The Scheduler in DotNetNuke is a mechanism that enables developers to schedule tasks to run at defined intervals. It is implemented using the Provider pattern; therefore, it can easily be replaced without modifying core code. Creating a scheduled task is a fairly simple process. First, though, it's important to understand which types of tasks are suitable for the Scheduler.

Because the Scheduler is run under the context of the web application, it is prone to the same types of application recycles as a web application. In a web-hosting environment, it is a common practice to conserve resources by recycling the worker process for a site periodically. When this happens, the Scheduler stops running. Therefore, the tasks run by the Scheduler do not run 24 hours a day, 7 days a week. They are executed according to a defined schedule, but they can only be triggered when the worker process is alive. For this reason, you cannot specify that a task should run every night at midnight. It is not possible in the web environment to meet this type of use case. Instead, you can specify how often a task is run by defining the execution frequency for each task. The execution frequency is defined as every x minutes/ hours/days.

To create a scheduled task, you must create a class that inherits from DotNetNuke.Services.Scheduling .SchedulerClient. This class must provide a constructor and a DoWork method. An example of a scheduled task is shown in Listing 8-9. This sample scheduled task will move all event log files to a folder named with the current date. By configuring this scheduled task to run once per day, the log files will be automatically archived daily, which keeps the log file sizes manageable.

Listing 8-9: Scheduled Task Example

image from book
 Public Class ArchiveEventLog     Inherits DotNetNuke.Services.Scheduling.SchedulerClient     Public Sub New(ByVal objScheduleHistoryItem As _         DotNetNuke.Services.Scheduling.ScheduleHistoryItem)         MyBase.new()         Me.ScheduleHistoryItem = objScheduleHistoryItem    'REQUIRED     End Sub     Public Overrides Sub DoWork()         Try             'notification that the event is progressing             'this is optional             Me.Progressing()    'OPTIONAL             'get the directory that logs are written to             Dim LogDirectory As String             LogDirectory = Common.Globals.HostMapPath + "Logs\"             'create a folder with today's date             Dim FolderName As String             FolderName = LogDirectory + Now.Month.ToString + "-" + _                 Now.Day.ToString + "-" + Now.Year.ToString + "\"             If Not IO.Directory.Exists(FolderName) Then                 IO.Directory.CreateDirectory(FolderName)             End If             'get the files in the log directory             Dim s As String()             s = IO.Directory.GetFiles(LogDirectory)             'loop through the files             Dim i As Integer             For i = 0 To s.Length - 1                 Dim OldFileInfo As New IO.FileInfo(s(i))                 'move all files to the new folder except the file                 'used to store pending log notifications                 If OldFileInfo.Name <> _                     "PendingLogNotifications.xml.resources" Then                     Dim NewFileName As String                     NewFileName = FolderName + OldFileInfo.Name                     'check to see if the new file already exists                     If IO.File.Exists(NewFileName) Then                         Dim errMessage As String                         errMessage = "An error occurred archiving " + _                             "log file to " + _                             NewFileName + ".  The file already exists."                         LogException(New _                             BasePortalException(errMessage))                     Else                         IO.File.Move(OldFileInfo.FullName, NewFileName)                         Me.ScheduleHistoryItem.AddLogNote("Moved " + _                             OldFileInfo.FullName + _                                 " to " + FolderName + _                                 OldFileInfo.Name + ".")      'OPTIONAL                     End If             End If         Next         Me.ScheduleHistoryItem.Succeeded = True    'REQUIRED         Catch exc As Exception 'REQUIRED            Me.ScheduleHistoryItem.Succeeded = False 'REQUIRED            Me.ScheduleHistoryItem.AddLogNote(String.Format(_                "Archiving log files failed.", _                exc.ToString))    'OPTIONAL             'notification that we have errored             Me.Errored(exc)    'REQUIRED             'log the exception             LogException(exc)   'OPTIONAL         End Try     End Sub End Class 
image from book

After the class has been compiled into the bin directory, the task can be scheduled from the Scheduling module under the Host page (see Chapter 6 for details). It is important to include each of the lines of code in Listing 8-9 that is labeled REQUIRED. These collectively ensure both the exception handling and schedule management are handled uniformly throughout all scheduled tasks.




Professional DotNetNuke 4.0 (c) Open Source Web Application Framework for ASP. NET 4.0
Professional DotNetNuke 4: Open Source Web Application Framework for ASP.NET 2.0 (Programmer to Programmer)
ISBN: 0471788163
EAN: 2147483647
Year: 2006
Pages: 182

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