Home > Articles > Programming > Windows Programming

This chapter is from the book

Rule 2-9: Avoid ActiveX EXEs Except for Simple, Small-Scale Needs

When you create a new project in VB, you are presented with a list of project types from which to choose: Standard EXE, ActiveX EXE, ActiveX DLL, ActiveX Control, Addin, IIS Application, and so forth. The ActiveX project types are used when you want to create a COM server—a set of classes in a DLL or EXE that can be activated using COM. If your goal is a user-interface component, select ActiveX Control. However, if your goal is a traditional object-oriented, non-user interface component, then you should select either ActiveX DLL or ActiveX EXE. But which one?

The answer depends on two factors: the type of COM activation you desire, and whether you plan to use MTS or COM+. Let's review the three types of COM activation: in-process, local, and remote. An in-process activation means the COM object resides in the same process as the client that created the object. In this case, you must create an ActiveX DLL project, and the resulting DLL must be installed on the client's machine. Both local and remote COM activation represent out-of-process activation, in which the object resides in a process separate from the client—on either the same machine (local) or a different one (remote). With this scenario you have a choice. You can create an ActiveX EXE project, and the resulting EXE serves as a stand-alone process for hosting your objects, or you can create an ActiveX DLL and configure it to run within MTS or COM+ as a server process.

In-process objects are much more efficient, because calls are typically 10 to 100 times faster than calls out of process. The trade-off is that out-of-process objects offer

  • Fault isolation (object can crash without crashing the client, and vice versa)

  • Separate security identity (object runs under an identity separate from the client)

  • Multi-threaded behavior (clients can concurrently activate objects/execute calls)

  • The ability to run objects on a machine separate from the clients

The last is perhaps the most important, because it enables the construction of distributed, multi-tier applications. Assuming you want out-of-process activation, the question is should you use ActiveX EXEs or should you turn to MTS/COM+?

In short, VB's ActiveX EXEs are designed to support small-scale needs. They provide basic out-of-process activation, nothing more. On the other hand, MTS and COM+ support large-scale designs, in addition to providing a host of other services: security, resource sharing, distributed transactions, and configuration/process management. When in doubt, the general consensus is to use MTS or COM+, because you never know when you may need to handle additional clients, share resources among your objects, or implement security. However, if your needs are simple, then VB's ActiveX EXEs are a viable option. Because Chapter 3 focuses entirely on MTS and COM+, we discuss ActiveX EXEs here.

VB's ActiveX EXEs enable you to build multi-threaded server applications with relative ease. Like many features of VB, multi-threading is presented through the IDE with the utmost consideration for productivity. In this case, your ActiveX EXE's threading strategy is determined by two option buttons and a text box, not by coding. These Threading Model settings are found in your project's properties, under the General tab as shown in Figure 2.20.

Figure 2.20 Project properties for an ActiveX EXE

An ActiveX EXE is compiled to follow one of three threading model approaches. The default is Thread Pool of 1 (shown in Figure 2.20), which gives you a single-threaded application. This means that a single-thread is shared by all objects living in this server process, and thus only one client request can be processed at a time. Although this type of server consumes very few resources, it should be used only when you are supporting a single client.

The second approach is Thread per Object, which represents the other end of the threading spectrum. Now, instead of one thread, every object has its own thread.25 The result is maximum concurrency, because no client request blocks that of another. However, even though the server process supports an unlimited number of concurrent clients, does it maximize throughput? Not likely. At some point, the rising number of threads begins to hurt performance, because the operating system spends more time switching from one thread to another than it does letting a thread run. Thus, if you want to maximize both concurrency and throughput, you need to either scale up (add more hardware to the existing machine) or scale out (add more machines and load balance). You'll also need to cap the size of the thread pool—the motivation for the third approach.

The third (and best) approach for multi-threading is a thread pool more than 1. The idea is to limit concurrency by restricting the number of threads, thereby guaranteeing some base amount of throughput as the load on your server process increases. For example, Figure 2.21 shows a VB ActiveX EXE compiled with a thread pool of 3. The threads are depicted as circles with arrowheads, and each thread is assigned to a single apartment within the process (hence the term single-threaded apartment, or STA). When VB objects are created, they are likewise assigned to an apartment, and remain in that apartment until they are destroyed. Although the ActiveX EXE can support an unlimited number of objects (and hence an unlimited number of clients), in this example only three client requests can be processed concurrently. In particular, note that clients 1 and 2 have objects assigned to the same thread. Thus, if both submit a request (i.e., make a method call) at the same time, one request is processed and the other is blocked.

Figure 2.21 ActiveX EXE server with four clients and a thread pool of 3

The idea of a fixed-size thread pool is not unique to VB. MTS and COM+ also take this approach: MTS 2.0 on WinNT has a thread pool of 100, whereas COM+ (i.e., MTS 3.0) on Windows 2000 has a thread pool per processor ranging in size from 7 to 10. Notice that the size of the pool was reduced significantly in COM+, acknowledging the tension between concurrency and throughput.

Even though their thread pooling strategies are the same, note that MTS and COM+ provide a more sophisticated implementation, yielding better performance than VB's ActiveX EXEs. MTS and COM+ provide other distinct advantages as well. For example, consider the problem of objects trying to share data such as configuration information or a set of database records. In VB, the standard approach is to use global variables declared in a BAS module. However, in an ActiveX EXE, global variables are not truly global: A BAS module is replicated so that each apartment has its own copy. The result is that "global" variables are global only within an apartment. 26 This implies that you must use an alternative mechanism to share state, such as a file or database, or the memory-based Shared Property Manager within MTS and COM+.

With regard to security, VB's ActiveX EXEs rely on COM's security model. Using the dcomcnfg utility, you can configure the identity under which an ActiveX EXE runs, as well as who may start up, access, and configure the EXE. This also applies to the authentication level (frequency of authentication and network packet integrity/privacy).

In summary, ActiveX EXEs provide a quick-and-dirty mechanism for outof-process COM activation, and thus are a basis for application designs requiring fault isolation, security, concurrency, or distributed processing. However, keep in mind that Microsoft is moving away from ActiveX EXEs, and is encouraging developers to build ActiveX DLLs and to let MTS or COM+ serve as your EXE. This allows Microsoft to provide services that are difficult to implement yourself, and the ability to evolve these services without the need for you to recompile your code. Applications based on MTS and COM+ will scale, offer better concurrency and resource sharing, allow more flexible configuration of the server, and yield faster time-to-market for multi-tier systems. In the end, you'll spend your time more productively, working on business logic rather than infrastructure.

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.

Overview


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.

Surveys

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.

Newsletters

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.

Security


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

Children


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

Marketing


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.

Choice/Opt-out


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.

Links


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