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vb.net threading question

Posted on 2011-02-23
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Last Modified: 2012-06-27
I'm trying to ensure that I'm using synclock correctly.

I have the following class

public class MyThreadTest
   private MyLockObject as new Object
   private lstOrgs as new List(of Org)
   Private AllergyUpdateThreadPool(MaxAllergyUpdateThreads) As Thread
   Private VendorCount as integer


   Public sub New()
          Dim x As Integer
                For x = 0 To UBound(AllergyUpdateThreadPool) - 1
                    AllergyUpdateThreadPool(x) = New Thread(AddressOf UpdateAllergy)
                    AllergyUpdateThreadPool(x).Name = "DrFirstAllergyUpdateThread #" + CStr(x)
                    ' AllergyUpdateThreadPool(x).Start()
                Next
     end sub


   public sub StartThreads(VendorList as list (of Org))
       dim x as integer
        SyncLock (MySyncLock)
                lstOrgs .Clear()
                LoadVendorList(VendorList)
                VendorCount = -1
          End SyncLock
           For x = 0 To UBound(AllergyUpdateThreadPool) - 1
                        AllergyUpdateThreadPool(x).Start()
            Next
end sub


 Private Sub UpdateAllergy()
          SyncLock (MySyncLock)
                        ' v = OperationQueue.Dequeue()
                        If VendorCount = lVendors.Count - 1 Then
                            VendorCount = 0
                        Else
                            VendorCount += 1
                        End If
                        v = lVendors(VendorCount)
               End SyncLock

                 'Do some work
end sub
           


In Main form
Dim  t as new MyThreadTest
Dim MyVendorList as new List (of Org)

'Load vendor list

t.StartAllergyUpdateProcess(MyVendorList)



Questions
1. Does this look like a safe approach for using the MyLockObject object for multiple threads in this class? Is it declared correctly or does it need to be a shared or protected variable?
2. Any other areas of concern (Note. this is a simplified version of what I'm doing)
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Question by:rutledgj
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4 Comments
 
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Accepted Solution

by:
Mike Tomlinson earned 2000 total points
ID: 34962300
The SyncLock portion will work just fine.  You would need it to be Shared if your List was shared and being used across multiple instances of MyThreadTest.  Since everything is contained within this class it will work as expected.

The counter logic, though, looks off to me.  If you pass in an empty list then both VendorCount and (lVendors.Count - 1) would be -1.  In that case you set VendorCount = 0 and then attempt to access the List at that Index which of course would cause an exception since the List is empty.
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Author Comment

by:rutledgj
ID: 34962454
Thanks, You are right about the empty list. I will add a check for that.

One other question if you don't mind. I aslo will be using a database class to perform database activities within the thread.

Should the database class be instantiated within the UpdateAllergy function (One dbOps object for each thread) or can I declare it once within the whole class and each thread use the same connection?
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LVL 86

Expert Comment

by:Mike Tomlinson
ID: 34962506
I'm not a DB guy but it seems to me that you should have just one instance for the class that all the threads share.  You may need to place calls to the DB within SyncLock blocks to make sure they don't write over each other.
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Author Closing Comment

by:rutledgj
ID: 34962767
Ok. thanks. I think I'll post another question specifically for that.
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