How to decrease CPU usage when using multiple threads?

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

When the market is opened, stock prices changed every 500 ms . You can see this change on google finance.
I figured as much, but my thoughts are that if you can somehow find a way to make your program more event driven, then it may be possible to reduce unnecessary looping...
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