Question

I have inherited some code below that works fine, the only problem is, I want to be able to limit the number of threads that run at any one time, at the moment I have around 8-10 jobs that run in parallel, I want to limit the number of threads to maybe 3 or 4 at any time, is this possible with the code below without too many changes?

Public Sub threading_Example()

 Dim threadList As New List(Of Thread)

 For n = 0 To numJobs 'about 8-10 normally

     Dim new_job As New System.Threading.Thread(New System.Threading.ParameterizedThreadStart(AddressOf do_Job))
     Dim job As New Job

     'job.stuff = stuff

     newJob.Start(job)
     threadList.Add(new_job)

 Next

 For Each t As Thread In threadList
     t.Join()
 Next

End Sub

Public Sub do_Job(ByVal job As Object)
   'do task 
End Sub

Answer 1

Try to use Semaphore for example:

ReadOnly Sem As New Semaphore(3, 4)

    Sub Main()

        Dim threadList As New List(Of Thread)
        Dim numJobs As Integer
        For n = 0 To numJobs

            Dim new_job As New System.Threading.Thread(New System.Threading.ParameterizedThreadStart(AddressOf do_Job))

            new_job.Start()
            threadList.Add(new_job)

        Next

        For Each t As Thread In threadList
            t.Join()
        Next


    End Sub


    Public Sub do_Job(ByVal job As Object)

        Sem.WaitOne()
        'only 3 or 4 threads at time can do task
        Sem.Release()
    End Sub