Home > Articles > Programming > Windows Programming

The Common Language Runtime: Overview of the Runtime Environment

📄 Contents

  1. Introduction to the Runtime
  2. Starting a Method
  3. Summary
  • Print
  • + Share This
Kevin Burton provides a brief overview of the framework under which managed code runs in this sample chapter from .NET Common Language Runtime Unleashed. Learn the rules for loading an assembly and starting execution of a method.
This sample chapter is excerpted from .NET Common Language Runtime Unleashed, by Kevin Burton.
This chapter is from the book

In This Chapter

  • Introduction to the Runtime

  • Starting a Method

At a high level, the CLR is simply an engine that takes in IL instructions, translates them into machine instructions, and executes them. This does not mean that the CLR is interpreting the instructions. This is just to say that the CLR forms an environment in which IL code can be executed. For this to work efficiently and portably, the execution engine must form a runtime environment that is both efficient and portable. Efficiency is key; if the code does not run quickly enough, all of the other features of the system become moot.

Portability is important because of the number of processors and devices on which the CLR is slated to run. For a long time, Microsoft and Intel seemed to be close partners. Microsoft more or less picked the Intel line of processors to run the software that the company produced. This allowed Microsoft to build and develop software without worrying about supporting multiple CPU architectures and instructions. The company didn't have to worry about shipping a Motorola 68XXX version of the software because it was not supported. Limiting the scope of processor support became a problem as Win16 gave way to Win32. (No APIs were called Win16, but this is the name I will give the APIs that existed before Win32.) Building software that took advantage of the features of a 32-bit CPU remained somewhat backward compatible with older Win16 APIs and proved to be a major undertaking. With Win64 on the horizon, Microsoft must realize that it cannot continue to "port" all of its software with each new CPU that is released if it wants to stay alive as a company. Microsoft is trying to penetrate the mobile phone, hand-held, and tablet markets that are powered by a myriad of different processors and architectures. Too much software is produced at Microsoft for it to continue to produce a CPU-bound version.

The answer to the problem of base address and data size (Win32 versus Win64) and to the problem of providing general portability to other processors came in the form of the runtime environment, or the Common Language Runtime. Without going into the details of the specific instructions that the CLR supports (this is done in Chapter 5, "Intermediate Language Basics"), this chapter details the architecture of the runtime that goes into making a managed application run.

Introduction to the Runtime

Before .NET, an executable (usually a file with an .exe suffix), was the application. In other words, the application was contained within one file. To make the overall system run more efficiently, the application would elect to use code that was shared (usually a file with a .dll suffix). If the program elected to use shared code, you could either use an import library (a file that points function references to the DLL that is associated with the import library), or you could load the DLL explicitly at runtime (using LoadLibrary, LoadLibraryEx, and GetProcAddress). With .NET, the unit of execution and deployment is the assembly. Execution usually begins with an assembly that has an .exe suffix. The application can use shared code by importing the assembly that contains the shared code with an explicit reference. (You can add the reference via the "Add References" node in Visual Studio .NET or include it via a command-line switch /r). The application can also explicitly load an assembly with Assembly.Load or Assembly.LoadFrom.

Note

Before going further, you need to learn definitions of some of the terms:

  • Assembly—The assembly is the primary unit of deployment within the .NET Framework. Within the base class libraries is a class that encapsulates a physical assembly appropriately named Assembly. When this book refers to the class or an instance of the class, it will be denoted as Assembly. This class exists in the System namespace. An assembly can contain references to other assemblies and modules. Chapter 4, "The Assembly," contains more detailed information about assemblies.

  • Module—A module is a single file that contains executable content. An assembly can encapsulate one or more modules; a module does not stand alone without an assembly referring to it. Similar to assembly, a class exists in the base class library that encapsulates most of the features of a module called Module. When this book refers to Module, it is referring to the class in the base class library. This class exists in the System namespace.

  • AppDomain—An application domain has been referred to as a lightweight process. Before .NET, isolation was achieved through separate processes through assistance from the OS and the supporting hardware. If one process ran amok, then it would not bring down the whole system, just that process. Because types are so tightly controlled with the .NET Framework, it is possible to have a mechanism whereby this same level of isolation can occur within a process. This mechanism is called the application domain, or AppDomain. As with modules and assemblies, a class in the base class library encapsulates many of the features and functionality of an application domain called AppDomain. This class exists in the System namespace. When this book refers to the class, it will be called AppDomain.

  • IL or MSIL—IL stands for Intermediate Language, and MSIL stands for Microsoft Intermediate Language. IL is the language in which assemblies are written. It is a set of instructions that represent the code of the application. It is intermediate because it is not turned in to native code until needed. When the code that describes a method is required to run, it is compiled into native code with the JIT compiler. Chapter 5 contains information about individual IL instructions.

  • JIT—JIT stands for Just-In-Time. This term refers to the compiler that is run against IL code on an as-needed basis.

After the code is "loaded," execution of the code can begin. This is where the old (pre-.NET) and the new (.NET) start to diverge significantly. In the case of unmanaged code, the compiler and linker have already turned the source into native instructions, so those instructions can begin to execute immediately. Of course, this means that you will have to compile a separate version of the code for every different native environment. In some cases, because it is undesirable to ship and maintain a separate version for every possible native environment, only a compatible version is compiled and shipped. This leads to a lowest common denominator approach as companies want to ship software that can be run on as wide a range of environments as possible. Currently, few companies ship programs that target environments that have an accelerated graphics engine. Not only would the manufacturer need to ship a different program for each graphics accelerator card, but a different program also would need to be developed for those cases where a graphics accelerator was lacking. Other examples of hardware environments in which specific optimizations could be taken advantage of would be disk cache, memory cache, high-speed networks, multiple CPUs, specialized hardware for processing images, accelerated math functions, and so forth. In numerous other examples, compiling a program ahead of time either results in a highly optimized yet very specific program, or an unoptimized and general program.

One of the first steps that the CLR takes in running a program is checking the method that is about to be run to see whether it has been turned into native code. If the method has not been turned into native code, then the code in the method is Just-In-Time compiled (JITd). Delaying the compilation of a method yields two immediate benefits. First, it is possible for a company to ship one version of the software and have the CLR on the CPU where the program is installed take care of the specific optimizations that are appropriate for the hardware environment. Second, it is possible for the JIT compiler to take advantage of specific optimizations that allow the program to run more quickly than a general-purpose, unmanaged version of the program. Systems built with a 64-bit processor will have a "compatibility" mode that allows 32-bit programs to run unmodified on the 64-bit CPU. This compatibility mode will not result in the most efficient or fastest possible throughput, however. If an application is compiled into IL, it can take advantage of the 64-bit processing as long as a JIT engine can target the new 64-bit processor.

The process of loading a method and compiling it if necessary is repeated until either all of the methods in the application have been compiled or the application terminates. The rest of this chapter explores the environment in which the CLR encloses each class method.

  • + Share This
  • 🔖 Save To Your Account

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