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Throttling - Managing Application Performance

, 1 Apr 2009
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Implement throttling in appplications to manage performance.

Introduction

Often, an application is developed that interacts with an external host/application. A situation arises that the application needs to control/throttle the rate at which messages are being sent out or read/received from the external host. It could be a messaging application or a repetitive call to perform a function.

This article would like to address that scenario. It is a spin off from what I have been working on and have been looking to optimize the performance of.

Background

Some scenarios where this could be useful are:

  1. Send messages to another host/application at a controlled rate, e.g., 50 messages/second.
  2. Read messages from a queue (MQ queue or otherwise) at a controlled rate in a non-blocking processing environment, so that the load on your application is controlled.

Using the code

The abstract (MustInherit) class ProcessGovernor manages the throttling. A new class (clsTestGiov) can be defined by extending (inheriting) ProcessGovernor and implementing a "trigger".

setThrottle is for setting the number of calls/reads to be done in 30 seconds. If setThrottle is uninitialized, it runs without throttling.

//
// Process Governor
//

Public MustInherit Class ProcessGovernor
    '--------------------------------------------------- Constants
    Private Const cTIMESLOT As Short = 30
    '--------------------------------------------------- Params
    Dim objName As String
    '--------------------------------------------------- Throttle Params
    Private timeSlot As Short
    Private shtTotMsg As Short
    Private shtMaxMsg As Short = -1
    '--------------------------------------------------- Throttle Timers
    Dim objTimer As TimerCallback
    Dim CallBackTimer As Timer
    Private evntRead As AutoResetEvent
    '--------------------------------------------------- Process Loop
    Private blnReadyStatus As Boolean

     Public Sub New() 
        timeSlot = GetTimeSlot()
        shtMaxMsg = -1
        objTimer = New TimerCallback(AddressOf RestartTrigger)
        CallBackTimer = New Timer(objTimer, Nothing, _
                            TimeSpan.FromSeconds(2), _
                            TimeSpan.FromSeconds(0))
        Me.evntRead = New AutoResetEvent(False)
    End Sub
    
      Public MustOverride Sub Trigger() 

     Public Sub SetThrottle(ByVal shtCount As Short) 
        Try
            If Not IsNumeric(shtCount) Then
                Exit Sub
            End If
            If (shtCount < 1) Or (shtCount > Short.MaxValue) Then
                shtMaxMsg = -1
            Else
                shtMaxMsg = shtCount
            End If
        Catch ex As Exception
            shtMaxMsg = -1
        End Try
    End Sub

     Public Function GetThrottle() As Short  
        Return shtMaxMsg
    End Function

    Public Sub SetName(ByVal strName As String)
        objName = strName
    End Sub

    Public Function GetName() As String
        Return objName
    End Function

    Public Sub StartGovr()
        blnReadyStatus = True
        While blnReadyStatus
            If shtMaxMsg <> -1 Then
                If timeSlot <> GetTimeSlot() Then
                    timeSlot = GetTimeSlot()
                    shtTotMsg = 1
                Else
                    shtTotMsg += 1
                End If
                If shtTotMsg > shtMaxMsg Then
                    CallBackTimer.Change(GetTimeSlotExpiry() * 1000, 0)
                    evntRead.WaitOne()
                Else
                    Trigger()
                End If
            Else
                Trigger()
            End If
        End While
    End Sub

    Public Sub StopGovr()
        If blnReadyStatus Then
            blnReadyStatus = False
        End If
    End Sub

    Public Sub ShutDownGovr()
        blnReadyStatus = False
        CallBackTimer.Dispose()
        objTimer = Nothing
        evntRead = Nothing
    End Sub

    Private Sub RestartTrigger(ByVal inpObjState As Object)
        CallBackTimer.Change(System.Threading.Timeout.Infinite, 0)
        evntRead.Set()
    End Sub

    Private Function GetTimeSlot() As Short
        Return (Now.Hour * 60 + Now.Minute) * 10 + Int(Now.Second / cTIMESLOT)
    End Function

    Private Function GetTimeSlotExpiry() As Short
        Return (cTIMESLOT - (Now.Second Mod cTIMESLOT))
    End Function

    Protected Overrides Sub Finalize()
        blnReadyStatus = False
        If Not objTimer Is Nothing Then
            objTimer = Nothing
        End If
        If Not CallBackTimer Is Nothing Then
            CallBackTimer.Change(Threading.Timeout.Infinite, 0)
            CallBackTimer.Dispose()
        End If
        If Not evntRead Is Nothing Then
            evntRead.Reset()
            evntRead = Nothing
        End If
    End Sub

End Class


//
// Class to  implement Governor/Throttle 
// 
Public Class clsTestGov  
    Inherits ProcessGovernor
    '--------------------------------------------------- Throttle Params
    Dim objProcessor As clsProcessor
    Public Sub New(ByVal inProcessor As HostProcessor)
        MyBase.New()
        objProcessor = inProcessor
    End Sub
    Public Overrides Sub Trigger()
        objProcessor.QueMsg(KapitiHost.GetMessage)
        Thread.Sleep(100)
    End Sub
End Class

//
// Start Processing using the Governor. 
// Note that the Governor is started in a separate thread 
//
Public Class clsProcessor
  
    '-------------------------------------------------- Governor
    Private objGovernor As ProcessGovernor
    Dim t As Thread
     Public Sub New()
        objGovernor = New clsTestGov (Me)
        //
        // Set throttle to 50 messages in 30 seconds
        //
        objGovernor.SetThrottle(50)
    End Sub
    Public Sub StartListeningGov()
        Try
            t = New Threading.Thread(New _
                Threading.ThreadStart(AddressOf objGovernor.StartGovr))
            t.Start()
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
    End Sub
    Public Sub StopListeningGov()
        objGovernor.ShutDownGovr()
        Try
            t.Abort()
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
        t.Join()
        t = Nothing
    End Sub
End Class

To implement, associate the clsTestGov in a parent class (clsProcessor) and call the method "StartGovr" on a new thread. Set the throttle (the number of calls) to 30 seconds.

Points of interest

Callback timers and WaitHandles are extremely useful, and a good understanding of them opens up your choices while designing a system.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

About the Author

Roji Jacob
Acette Technologies FZ LLC, Dubai Internet City
United Arab Emirates United Arab Emirates
I have been working mainly on messaging applications (Banking/Cards) and gained insight/experience into system integration, online messaging. Presently on "SMS Banking" where message processing at the server side is a challenge and constant refactoring to optimise the performance is the challenge.

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