Process StandardOutput and StandardError on seperate threads.

[mwazir]

Hi all,

I have reposted this question from dotnet.general as I have been advised
that this is a more appropriate forum for this question. Apologies for the
repost.

I have a process thats starts in my application and only terminates when my
application is terminated. I want to write the output and the errors of this
process to a seperate log file. In order to do this, I spawned two threads.

My code looks something like this

' Starting the process
oProcessStartInfo = New ProcessStartInfo()
With oProcessStartInfo
.FileName = strFilename
.Arguments = strArguments
.UseShellExecute = False
.CreateNoWindow = True
.RedirectStandardOutput = True
.RedirectStandardError = True
End With
oProcess = Process.Start(oProcessStartInfo)


' Starting the threads
oOutputThread = New Thread(AddressOf ReadStdOut)
oErrorThread = New Thread(AddressOf ReadStdError)
With oOutputThread
.Name = "StandardOutput"
.Priority = ThreadPriority.BelowNormal
.Start()
End With

With oErrorThread
.Name = "StandardError"
.Priority = ThreadPriority.BelowNormal
.Start()
End With

Private Sub ReadStdOut()
' Has to run in a seperate thread
' ReadtoEnd will work only if the process is getting terminated.
Dim str As String = oProcess.StandardOutput.ReadLine
Try
Do While str.Length >= 0
If str.Length <> 0 Then
Me.oLog.WriteLog("Standard Output : " & str) ' Writes to
a log file.
End If
str = oProcess.StandardOutput.ReadLine
Loop
Catch
Return
End Try
End Sub

I have a similair ReadStdError function and both share the same instance of
the logging class.
When writing in the log class I implement ReadWriteLock

ReadWriteLock.AcquireWriterLock(System.Threading.Timeout.Infinite)
Try
With oStreamWriter
.BaseStream.Seek(0, SeekOrigin.End)
.WriteLine(sDate & " : " & sMessage)
End With
Finally
ReadWriteLock.ReleaseWriterLock() ' Release the write lock.
End Try


I would like to know if this is the best approach. It works well for me.
However I felt that if I have an infinite loop while reading the standard
output stream, my application would be memory and process intensive and that
hasnt been the case. So I am a bit curious to know why it hasnt been
intensive.

Couple of additional points (not sure of its impact to my question)
- The process doesnt has a irregular stream of data coming from Standard
Output and its not very oft occuring.
- The StandardError by its very nature also doesnt have regular data coming
from it unless there is a real issue. I dont expect any errors if my setups
are correct.
- The Do While Loop should constantly be checking ReadLine - and thats my
real concern

Greateful for any thoughts you may have. I am a complete greenhorn in
threading.

Regards,
Wazir

 

[Lifeng Lu]

You don't have to worry about this. A thread could cause problems if it is
continuely doing something without going to sleep mode. For example, if you
have a loop to check a value of a variable, and exits until it changes. It
will cause problems because the thread will consume the CPU and does
nothing.
In your case, your thread will sleep when there is nothing to read when you
call ReadLine. The thread would wake up and run until something ready to
read...

Thanks