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Imports System.Threading
Module Module1
Class Account
Dim thisLock As New Object
Dim balance As Integer
Dim r As New Random()
Public Sub New(ByVal initial As Integer)
balance = initial
End Sub
Public Function Withdraw(ByVal amount As Integer) As Integer
' This condition will never be true unless the SyncLock statement
' is commented out:
If balance < 0 Then
Throw New Exception("Negative Balance")
End If
' Comment out the SyncLock and End SyncLock lines to see
' the effect of leaving out the SyncLock keyword.
SyncLock thisLock
If balance >= amount Then
Console.WriteLine("Balance before Withdrawal : " & balance)
Console.WriteLine("Amount to Withdraw : -" & amount)
balance = balance - amount
Console.WriteLine("Balance after Withdrawal : " & balance)
Return amount
Else
' Transaction rejected.
Return 0
End If
End SyncLock
End Function
Public Sub DoTransactions()
For i As Integer = 0 To 99
Withdraw(r.Next(1, 100))
Next
End Sub
End Class
Sub Main()
Dim threads(10) As Thread
Dim acc As New Account(1000)
For i As Integer = 0 To 9
Dim t As New Thread(New ThreadStart(AddressOf acc.DoTransactions))
threads(i) = t
Next
For i As Integer = 0 To 9
threads(i).Start()
Next
End Sub
End Module