how to decrease CPU usage when using multiple threads VB.net? - vb.net

Question

I am using vb.net , .NetFramework 2.0 .
My application gets live stock prices from google and updates stocks in database each 10 seconds.
I get this code for multithreading. When application starts updating stocks in database(about 200 stocks) , the update takes up to 3 seconds but it increase CPU usage from 10 % to 70 % or 80 %.
What is the best way to to update database without getting CPU increase to high level?
I observed that all threads works at the same time. how to make each thread wait until the second ends?
This is my code. The problem is in function updateThreaded2().
Please I need quick help. Thanks
Public Function Update2(ByVal l As SortableBindingList(Of NewStockList)) As Long
res = 0
UThread = New System.Threading.Thread(AddressOf UpdateThreaded2)
If Me.URunning = True Then
Else
Try
Me.URunning = True
Interlocked.Exchange(Me.UCount, 0) 'threadsafe method of assigning static value
Interlocked.Exchange(Me.UDone, 0) 'threadsafe method of assigning static value
UThread.Priority = Threading.ThreadPriority.BelowNormal
UThread.IsBackground = True
UThread.Start(l)
Return 0
Catch ex As Exception
End Try
End If
End Function
Private Sub UpdateThreaded2(ByVal l As SortableBindingList(Of NewStockList))
Dim i As Integer = 0
Dim threadcount As Integer = Math.Min(Me.MaxThreads, Me.Stocks.Count)
Dim threads(threadcount - 1) As SUTC
Try
While i < Me.Stocks.Count
For j As Integer = 0 To threadcount - 1
If threads(j) Is Nothing Then
If i < Me.Stocks.Count Then
threads(j) = New SUTC(Me.Stocks(i), Me.DefaultService, AdjustSplits, Use20Minutes, l)
threads(j).Thread.Priority = Threading.ThreadPriority.BelowNormal
threads(j).Thread.IsBackground = True
threads(j).Thread.Start()
i += 1
End If
ElseIf threads(j).UpdateState = 0 Then
If i < Me.Stocks.Count Then
SecUpd(j) = Me.Stocks(i).symbol
threads(j) = New SUTC(Me.Stocks(i), Me.DefaultService, AdjustSplits, Use20Minutes, l)
threads(j).Thread.Priority = Threading.ThreadPriority.BelowNormal
threads(j).Thread.IsBackground = True
threads(j).Thread.Start()
i += 1
End If
End If
Next
Dim running As Boolean = True
While running
For j As Integer = 0 To threadcount - 1
If threads(j).UpdateState = 0 Then
Thread.Sleep(10)
running = False
SecUpd(j) = ""
Interlocked.Increment(UDone) 'threadsafe method of incrementing a variable by 1
Interlocked.Exchange(UCount, UCount + threads(j).UpdateCount) 'Threadsafe method for assigning a value
End If
Next
End While
End While
Dim pending As Integer = threadcount
Dim tempcount As Integer = 0
Dim oldcount As Integer = UCount
While pending > 0
pending = threadcount
tempcount = 0
For i = 0 To threadcount - 1
If threads(i).UpdateState = 0 Then
SecUpd(i) = ""
pending -= 1
tempcount += threads(i).UpdateCount
Thread.Sleep(10)
End If
Next
Interlocked.Exchange(UDone, Me.Stocks.Count - pending) 'Threadsafe method for assigning a value
Interlocked.Exchange(UCount, oldcount + tempcount) 'Threadsafe method for assigning a value
End While
Me.URunning = False
Catch ex As System.Threading.ThreadAbortException 'handle abort correctly
Dim pending As Integer = threadcount
Dim tempcount As Integer = 0
Dim oldcount As Integer = UCount
While pending > 0
pending = threadcount
tempcount = 0
For i = 0 To threadcount - 1
If threads(i).UpdateState = 0 Then
SecUpd(i) = ""
pending -= 1
tempcount += threads(i).UpdateCount
End If
Next
Interlocked.Exchange(UDone, Me.Stocks.Count - pending) 'Threadsafe method for assigning a value
Interlocked.Exchange(UCount, oldcount + tempcount) 'Threadsafe method for assigning a value
End While
End Try
End Sub

Answer 1

This is fantastically simplified, but threads by their nature will run at the same time (if possible and depending to some extent on the whim of the OS). If you want less going on simultaneously, use fewer threads. In your case, since you want the jobs done sequentially, you really only want one thread.
The best approach, as mentioned, is to create a background worker that runs on a single background thread. There's usually a queue to which you submit jobs in a thread-safe way from the foreground thread. The thread proc typically runs in an infinite loop, processing each job in the queue, and going to sleep waiting for new jobs when there are none.