Using Monitor Class For Thread Synchronization


While developing a multithreaded application it is very important to maintain synchronization between multiple calls to the same method. Consider for example that you have a function that writes to a file. If at the same time multiple threads call this function it is bound to throw an exception as previous method call is yet to finish with the file. To avoid such situations you can use Monitor class.

Namespaces Involved

Following namespaces are involved in our example:
  • System
  • System.Threading
  • System.IO
  • System.Text

Using Monitor class

Monitor class can synchronize method calls using its Enter and Exit methods. Following code shows how these methods work:
Dim fs As FileStream = New FileStream
("C:\Temp\SyncTest.txt", FileMode.Append)
Dim t As Thread = Thread.CurrentThread
fs.Write(Encoding.ASCII.GetBytes(t.Name & vbCrLf), 
0, t.Name.Length + 2)
Dim i As Integer
For i = 0 To 10000
   fs.Write(Encoding.ASCII.GetBytes(i & ","),
   0, i.ToString().Length + 1)
Here, we called Monitor.Enter method at the start of the method followed by our code that writes into a file. Once the writing operation is complete we call Monitor.Exit method. This ensures that till the time one thread is executing the function any other thread can not execute the same function. You can easily check what happens if you do not use Monitor class by simply commenting these two lines.

Bipin Joshi is an independent software consultant, trainer, author, and meditation teacher. He has been programming, meditating, and teaching for 25+ years. He conducts instructor-led online training courses in ASP.NET family of technologies for individuals and small groups. He is a published author and has authored or co-authored books for Apress and Wrox press. Having embraced the Yoga way of life he also teaches Ajapa Yoga to interested individuals. To know more about him click here.

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Posted On : 02 November 2002

Tags : .NET Framework VB.NET C# Components Multithreading