VB.NET Technology

Synchronization is needed in thread when we have multiple threads that share data, we need to provide synchronized access to the data. We have to deal with synchronization issues related to concurrent access to variables and objects accessible by multiple threads at the same time.

Imports System.Threading
Module Module1
    Class Program
        Shared Sub Main()
            Console.WriteLine("----->  Multiple Threads ---->")
            Dim p As New Printer()
            Dim Threads As Thread() = New Thread(2) {}
            For i As Integer = 0 To 2
                Threads(i) = New Thread(New ThreadStart(AddressOf p.PrintNumbers))
                Threads(i).Name = "Child " & i
            Next
            For Each t As Thread In Threads
                t.Start()
            Next
            Console.ReadLine()
        End Sub
    End Class
    Class Printer
        Public Sub PrintNumbers()
            For i As Integer = 0 To 4
                Thread.Sleep(100)
                Console.Write(i & ",")
            Next
            Console.WriteLine()
        End Sub
    End Class
End Module

Why we use Lock keyword

lock(object) is used to synchronize the shared object.

Syntax

SyncLock objecttobelocked
	objecttobelocked.somemethod()
End SyncLock

objecttobelocked is the object reference which is used by more than one thread to call the method on that object.
The lock keyword requires us to specify a token (an object reference) that must be acquired by a thread to enter within the lock scope.

Using of Monitor- The lock scope actually resolves to the Monitor class after being processed by the VB.Net compiler. Lock keyword is just a notation for Imports System.Threading.Monitor class.

Imports System.Threading
Imports System.Threading.Monitor
Module Module1
    Class Program
        Shared Sub Main(ByVal arg As String())
            Console.WriteLine(" ----->  Multiple Threads  ----->")
            Dim p As New Printer()
            Dim Threads As Thread() = New Thread(2) {}
            For i As Integer = 0 To 2
                Threads(i) = New Thread(New ThreadStart(AddressOf p.PrintNumbers))
                Threads(i).Name = "Child " & i
            Next
            For Each t As Thread In Threads
                t.Start()
            Next
            Console.ReadLine()
        End Sub
    End Class
    Class Printer
        Public Sub PrintNumbers()
            Monitor.Enter(Me)
            Try
                For i As Integer = 0 To 4
                    Thread.Sleep(100)
                    Console.Write(i & ",")
                Next
                Console.WriteLine()
            Finally
                Monitor.[Exit](Me)
            End Try
        End Sub
    End Class
End Module