Home > Articles


Setting Up Global Objects with the global.asax File

ASP.NET uses a special file, called global.asax, to establish any global objects that your Web application uses. The .asax extension denotes an application file rather than .aspx for a page file.

Each ASP.NET application can contain at most one global.asax file. The file is compiled on the first page hit to your Web application. ASP.NET is also configured so that any attempts to browse to the global.asax page directly are rejected.

Listing 3.8 shows a global.asax file that you can use to make a more complete hit counter.

Listing 3.8  global.asax: Event Handlers for the Application and Session Objects

 1: <%@ language="VB" %>
 2: <script runat="server">
 3: Sub Application_Start(Sender As Object, e As EventArgs)
 5:   Application("Hits") = 0
 6:   Application("Sessions") = 0
 7:   Application("TerminatedSessions") = 0
 9: End Sub
11: `The BeginRequest event is fired for every hit 
12: `to every page in the site.
13: Sub Application_BeginRequest(Sender As Object, e As EventArgs)
15:   Application.Lock()
16:   Application("Hits") = Application("Hits") + 1
17:   Application.UnLock()
19: End Sub
21: Sub Session_Start(Sender As Object, e As EventArgs)
23:   Application.Lock()
24:   Application("Sessions") = Application("Sessions") + 1
25:   Application.UnLock()
27: End Sub
29: Sub Session_End(Sender As Object, e As EventArgs)
31:   Application.Lock()
32:   Application("TerminatedSessions") = _
33:     Application("TerminatedSessions") + 1
34:   Application.UnLock()
36: End Sub
38: Sub Application_End(Sender As Object, e As EventArgs)
40:   `Write out our statistics to a log file
41:   `...code omitted...
43: End Sub
44: </script>

ANALYSIS   The global.asax file in Listing 3.8 contains event handlers for the Session and Application objects. Each event handler has the same signature as the Page_Load event handler.

The code in Listing 3.8 handles three Application object-related events: Start (Lines 3-9), End (Lines 38-43), and BeginRequest (Lines 13-19). Start and End are called when the Web application starts and ends, respectively. BeginRequest is called for every page hit that the site receives. Listing 3.8 updates the total number of hits in this event.

The Session Start (Lines 21-27)and End (Lines 29-36)events are handled in the middle of the listing. These two events count how many different Web users have accessed the site.

You can write a simple page to utilize the statistics that Listing 3.8 tracks. Listing 3.9 shows a page that writes out the results of the hit-counting code in the global.asax file. Figure 3.5 shows the statistics page after a few hits.

Figure 3.5 The Statistics page after some traffic.

Listing 3.9  Statistics.aspx: The Results of the Tracking in the global.asax File

<%@ page language="VB" %>
<h2> Statistics for the Test Web Application </h2>
Total hits: <% Response.Write(Application("Hits").ToString()) %> <br>

Total sessions: <% Response.Write(Application("Sessions")) %> <br>

Expired sessions: 
  <% Response.Write(Application("TerminatedSessions")) %> <br>


If the global.asax file is modified, the Web application is restarted on the next page hit and the global.asax file is recompiled.

Adding Objects to the global.asax File

To use global objects in your ASP.NET application, add the <object> tag in the global.asax file for each one. The <object> tag has an optional attribute called scope, which determines if the added object will be created on-the-fly, associated with the Application object, or associated with the Session object.

To explore the <object> tag, let's create a simple class that stores and retrieves strings. The sample is going to associate an object of this class with the Application object in the global.asax file, so the class must be thread-safe. The term thread-safe means that many client threads can access the class at the same time without any data corruption. Because ASP.NET uses one thread per page, ensuring that the class is thread-safe is critical if multiple users browse the site at the same time.

Understanding Threads

What's a thread? To answer, let's review processes first. All Windows applications are processes that run on your computer. Processes contain their own code and memory space, and can interact with computer peripherals, such as the screen or the network card. ASP.NET runs as a process, and it executes your code, of course.

Each process contains one or more threads. A thread is like a process or an individual program, because it also executes a certain set of code. However, a thread is a "lightweight" version of a process. Threads live inside processes, and use a process's memory. The Windows operating system gives each thread a small amount of time to execute and quickly switches between threads so that it seems like more than one thread is executing at the same time. For all practical intents, the threads are running at the same time.

Because threads use their parent process's memory, they can potentially change the same object (in memory) at the same time. For two threads, A and B, thread A might add 10 to the counter object. Thread B might subtract 10 from the counter. If the two threads are switched on and off by the operating system in an "unlucky" way, the counter object could contain a scrambled result.

When each ASP.NET page is being processed, it gets its own thread. If more than one user accesses the Web site at the same time, many threads will appear even if both users are accessing the same ASP.NET page.

To prevent threads (and ASP.NET pages) from interfering with each other when accessing the same object, use the technique in the example that follows.

To make the class thread-safe, use the Synchronized method of the base collection class, Hashtable. This class is shown in Listing 3.10.

Listing 3.10  MyClass.vb: Implementing a Class to Store and Retrieve Strings in a Thread-Safe Way

Imports System
Imports System.Collections

Namespace TestApplication 

  public class MyClass1 
    private m_col As Hashtable 
    `m_colSync will be a thread-safe container for m_col
    private m_colSync As Hashtable 

    Public Sub New() 
        m_col = new Hashtable()
        m_colSync = Hashtable.Synchronized(m_col)
    End Sub

    Public Sub AddItem(Name As String, Value As String) 
        m_colSync(Name) = Value
    End Sub

    Public Function GetItem(Name As String) As String
       return m_colSync(Name)
    End Function

  End Class

End Namespace

`note: use "vbc /out:bin\myclass.dll /t:library myclass.cs /r:system.dll"
`      to compile with the command line utility

Note that the DLL file is placed in the bin directory off the project directory. The next step is to add this object to the global.asax file with the <object> tag. A short global.asax file that does this follows:

<object id="MyStringCollection" runat="server"
        class="TestApplication.MyClass1" scope="Application" />

The id attribute tells ASP.NET what to call our object when it's used later. The class attribute can be used to specify COM objects in addition to .NET components, but by using their ProgID.

If the listing omitted the scope attribute, a new object is created on-the-fly for every page that uses the StringCollection object.

Let's write a sample page that uses StringCollection. Listing 3.11 shows just such a page.

Listing 3.11  UseObject.aspx: Using the Global Object

<%@ language="VB" %>
<script runat="server">
Sub Page_Load(Sender As Object, e As EventArgs)

  MyStringCollection.AddItem("FirstUser", "Joe Smith")

End Sub
The name of the first user is 
   <% Response.Write(MyStringCollection.GetItem("FirstUser")) %>

Putting Code Behind the global.asax File

If you use Visual Studio. NET to create your Web project, it will use the code behind feature of ASP.NET for global.asax. The code behind file that is generated is named global.asax.vb, when using the Visual Basic compiler. To use code behind in global.asax manually, use the Application directive instead of the Page directive, like this:

<@ Application Inherits="MyApplication.GlobalClass" %>

Listing 3.12 shows a code behind example for the global.asax file.

Listing 3.12  GlobalClass.vb: Implementing the Code for the global.asax File

Namespace MyApplication

  Imports System
  Imports System.Web
  Imports System.Web.SessionState

  Public class GlobalClass
      Inherits System.Web.HttpApplication
     protected Sub Session_Start(Sender As Object, e As EventArgs)
       Response.Write("Session started <br>")
     End Sub
  End Class
`note: use "vbc /out:bin\globalclass.dll /t:library globalclass.cs /r:system.dll"
`      to compile with the command line utility

End Namespace


You can mix code behind and the <object> tag in the global.asax file.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020