Using Monitor Class For Thread Synchronization

Introduction

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:
Monitor.Enter(Me)
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)
Next
fs.Close()
Monitor.Exit(Me)
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 and trainer by profession specializing in Microsoft web development technologies. Having embraced the Yoga way of life he is also a yoga mentor, meditation teacher, and spiritual guide to his students. He is a prolific author and writes regularly about software development and yoga on his websites. He is programming, meditating, writing, and teaching for over 27 years. To know more about his private online courses on ASP.NET and meditation go here and here.

Posted On : 02 November 2002


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