Understanding Threads using Visual Basic 2005 - Part 1
page 5 of 7
by Abhishek Kumar Singh
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Implementing thread lock using SyncLock

This time we will move delegate method DoAction to a separate class for better understanding. We will modify the code inside DoAction to use lock features. Let’s add a class CThread in the application and add the DoAction method in it. In this example to use SyncLock in it what we are going to do is just to put all lines of code in DoAction method to be placed between SyncLock Me and End SyncLock constructs. The complement class code is given below.

Listing 7 – Implementing SyncLock (locking feature) in thread delegate method

Public Class CThread
  Public Sub DoAction()
    SyncLock Me
    Console.WriteLine("{0} : {1} : To sleep now...", _
      Threading.Thread.CurrentThread.ManagedThreadId, Now.ToString())
    Console.WriteLine("{0} : {1} : is woke up...", _
      Threading.Thread.CurrentThread.ManagedThreadId, Now.ToString())
    End SyncLock
  End Sub
End Class

So we also need minor modification in the Main(). We just need to create object of class CThread in Main() and set thread start delegate method DoAction with class object. The code of Main() is given below.

Listing 8 – Code for Main method of the application

Sub Main()
  Dim oCThread As New CThread()
  Console.WriteLine("{0} : {1} : Main thread started...", _
    Threading.Thread.CurrentThread.ManagedThreadId, Now.ToString())
  Dim oThOneMethod As Threading.ThreadStart = _
    New Threading.ThreadStart(AddressOf oCThread.DoAction)
  Dim oThTwoMethod As Threading.ThreadStart = _
    New Threading.ThreadStart(AddressOf oCThread.DoAction)
  Dim oTh1 As Threading.Thread = New Threading.Thread(oThOneMethod)
  Dim oTh2 As Threading.Thread = New Threading.Thread(oThTwoMethod)
  Console.WriteLine("{0} : {1} : Main thread finishing...", _
    Threading.Thread.CurrentThread.ManagedThreadId, Now.ToString())
End Sub

Run the application (CTRL+F5). You should see output window like:

Figure 3 – Console output of the application with SyncLock uses

If you look the output carefully you can see that even if thread 3 has gone to sleep for 5 seconds, thread 4 could not enter the SyncLock section. In fact thread 4 just waits at the beginning of SyncLock till previous thread (# 3 here) leaves the SyncLock section. When thread 3 woke up and comes out of SyncLock section, thread 4 resumes its execution. In the same way, if there would have been more thread like # 5,6,7 etc, all would have gone into a thread queue and processed one by one with the rule that only one thread can enter into the SyncLock at a time.

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User Comments

Title: Thread   
Name: Pari
Date: 2012-10-16 4:02:22 AM
very helpful
Title: Enginer   
Name: Didier Fonseca
Date: 2010-11-10 4:46:13 PM
Thanks,very good and easy to understand tutorial
Title: dig deeper   
Name: rs
Date: 2008-06-09 10:47:16 AM
nice introduction in synchronization. next thing that comes up comparing different solutions is rating them. how do they differ (e.g. in performance) and which is suitable for what kind of problem ...
Title: thanks   
Name: Abhishek Singh
Date: 2008-06-06 6:50:45 AM
thanks to all of you!
Title: Vey Good Article   
Name: Babita
Date: 2008-06-05 3:23:22 AM
Very useful article about thread.
Title: Good one   
Name: Soumya
Date: 2008-06-03 2:52:33 AM
Very helpful definitions and examples.
Title: nice article   
Name: rupesh
Date: 2008-06-03 2:40:32 AM
Very nice article about thread

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