Programming Windows Services with Microsoft Visual Basic 2008 : Writing a New Thread Method, Monitoring with Multiple Threads

1. Writing a New Thread Method

Modify your existing ThreadFunc to match the code shown in Listing 1.

Listing 1. Updates to the current thread method.

Private Sub ThreadFunc() While Not m_ThreadAction.StopThread If Not m_ThreadAction.Pause Then Try For Each TextFile As String In My.Computer.FileSystem.GetFiles( _ My.Resources.IncomingPath, _ FileIO.SearchOption.SearchTopLevelOnly, "*.txt") If m_ThreadAction.Pause Or m_ThreadAction.StopThread Then Exit For End If Try WriteLogEvent(My.Resources.ThreadMessage + TextFile, _ THREAD_INFO, EventLogEntryType.Information, My.Resources.Source) Catch ex As Exception WriteLogEvent(My.Resources.ThreadErrorMessage + Now.ToString, _ THREAD_ERROR, EventLogEntryType.Error, My.Resources.Source) End Try Next Catch fio As IOException WriteLogEvent(My.Resources.ThreadIOError + Now.ToString, _ THREAD_ABORT_ERROR, EventLogEntryType.Error, My.Resources.Source) Catch tab As ThreadAbortException 'this must be listed first as Exception is the master catch 'Clean up thread here WriteLogEvent(My.Resources.ThreadAbortMessage + Now.ToString, _ THREAD_ABORT_ERROR, EventLogEntryType.Error, My.Resources.Source) Catch ex As Exception WriteLogEvent(My.Resources.ThreadErrorMessage + Now.ToString, _ THREAD_ERROR, EventLogEntryType.Error, My.Resources.Source) End Try End If If Not m_ThreadAction.StopThread Then Thread.Sleep(THREAD_WAIT) End If End While End Sub

The code in Listing 1 searches for any text files in the IncomingPath without looking in any subdirectories. After it finds a file it attempts to log an event using the text name and the standard message.

Note

You must remember to set the constant IncomingPath to the directory you created, otherwise the path will not exist and your query will always fail with an IOException.

Install and Verify

Now you need to recompile the new code, remove the old service, and install the new tutorials.exe.

Start the service. If that directory has no .txt files, you won’t see any entries in the Application log. However, if you were to create or copy .txt files into the directory while the service was still running, not only would you see entries in the Application log, but you would also see them duplicated every five seconds, which is the sleep time. As you remove, delete, add, and create .txt files in your temp file directory, you will see new entries about every five seconds in the Application log.

Note

Remember to stop the current service before continuing so that you do not fill the Application log with unwanted events.

2. Monitoring with Multiple Threads

We have successfully created a multithreaded polling service, which can be very useful, if you had to monitor more than one directory; for example, you could either have one thread monitor all the directories, or you could create multiple threads, using one per directory. You could also create a pool of threads, monitoring not only file system directories but also FTP folders and MSMQ queues so you could make sure that the proper thread handles the correct source and processing occurs correctly.

Expanding Processing

For this example, we will expand the service. We will monitor the incoming directory for files and then move these files to a newly created output directory. Although we don’t process these files directly, the local service might be able to move files and then have another application process them after they are moved to the output directory. We are merely emulating the creation and pre-processing move to another application’s processing folder.

Creating the Code

Create the code by following these steps:

1.	Start by creating another folder, which we will call “outgoing.” I create mine in the c:\temp directory, which is where the incoming folder is.
2.	Add another resource entry called OutgoingPath and set its value to c:\temp\outgoing.
3.	Add another set of InstanceId values in the modTutorial file.
4.	In the modService.vb module file, add the following constant directly below the THREAD_INFO constant: Public Const FILE_WRITE_INFO As Integer = 3000
5.	We also want to add a new error const under the existing definitions, as shown in the following code: Public Const FILE_WRITE_ERROR As Integer = 3001

Modifying the <ThreadFunc> Method

We need to modify the current <ThreadFunc> method so that instead of only logging an eventlog entry, it will move the file to the new output folder. We will modify the code as shown in Listing 2.

Listing 2. Modifications to the Thread method.

Private Sub ThreadFunc() While Not m_ThreadAction.StopThread If Not m_ThreadAction.Pause Then Try For Each TextFile As String In _ My.Computer.FileSystem.GetFiles( _ My.Resources.IncomingPath, _ FileIO.SearchOption.SearchTopLevelOnly, "*.txt") If m_ThreadAction.Pause Or m_ThreadAction.StopThread Then Exit For End If Try Dim FileOutput As String = My.Resources.OutgoingPath + "\" + My.Computer.FileSystem.GetName(TextFile) My.Computer.FileSystem.MoveFile(TextFile, FileOutput) WriteLogEvent(My.Resources.ThreadMessage + TextFile, THREAD_INFO, EventLogEntryType.Information, My.Resources.Source) Catch ex As Exception WriteLogEvent(My.Resources.ThreadErrorMessage + Now.ToString, THREAD_ERROR, EventLogEntryType.Error, My.Resources.Source) End Try Next Catch fio As IOException WriteLogEvent(My.Resources.ThreadIOError + Now.ToString, THREAD_ABORT_ERROR, EventLogEntryType.Error, My.Resources.Source) Catch tab As ThreadAbortException 'this must be listed first as Exception s the master catch 'Clean up thread here WriteLogEvent(My.Resources.ThreadAbortMessage + Now.ToString, THREAD_ABORT_ERROR, EventLogEntryType.Error, My.Resources.Source) Catch ex As Exception WriteLogEvent(My.Resources.ThreadErrorMessage + Now.ToString, THREAD_ERROR, EventLogEntryType.Error, My.Resources.Source) End Try End If If Not m_ThreadAction.StopThread Then Thread.Sleep(THREAD_WAIT) End If End While End Sub End Try

We are going to continue to use My Object to move the file from its current location to the OutgoingPath resource setting.

After the file is written to the output folder we log an event to the eventlog as we did in the previous version. If an exception occurs, we write an event that covers the error.

Installation and Verification

Before we compile and install the new service, we need to make one more change. The Local Service account (which we’ve been using for the service) doesn’t by default have the proper authority to write to the Outgoing directory, and we must fix this.

Changing the StartUp Account

In Solution Explorer, double-click ProjectInstaller.vb. Select the ServiceProcessInstaller1 control, right-click, and select Properties. Change the Account property from LocalService to LocalSystem. Save and then build the project.

Note

You could grant the Local Service account Modify permissions to both the incoming and outgoing folders instead of using the Local System account.

Install the newly created service and start it. Open Windows Explorer and click the c:\temp\incoming directory. In the right-hand pane, right-click, and choose New Text Document—or you could copy one or more existing text files into this folder from another location. Click in the white space to save the file. Within five seconds the file should disappear. The file will appear in your outgoing directory, and you should see a 2003 event in the Application log for each file that you created.