Intermediate Language IL and Just-In-Time JIT Compilation Metadata
3.7 Intermediate Language IL and Just-In-Time JIT Compilation
All compilers that target the CLR compile source code to Intermediate Language IL, also known as Common Intermediate Language CIL. IL is a machine language that is not tied to any specific machine. Microsoft designed it from scratch to support the CLIs programming concepts. The CLI specifies that all CLR implementations can compile or interpret IL on the machine on which the CLR is running. If the IL is compiled versus interpreted, compilation can occur at either of two times: • Immediately prior to a method in the application being executed • At deployment time In the first case, each method is compiled only when it is actually needed. After the method is compiled, subsequent calls bypass the compilation mechanism and call the compiled code directly. The compiled code is not saved to disk, so if the application is stopped and restarted, the compilation must occur again. This is known as just-in-time JIT compilation and is the most common scenario. In the second case, the application is compiled in its entirety at deployment time. IL is saved to .exe and .dll files. When such a file containing IL is executed, the CLR knows how to invoke the JIT compiler and execute the resulting code. Note that on the Microsoft Windows platforms, IL is always compiled—never interpreted.3.8 Metadata
Source code consists of some constructs that are procedural in nature and others that are declarative in nature. An example of a procedural construct is: someObject.SomeMember = 5 This is procedural because it compiles into executable code that performs an action at runtime. Namely, it assigns the value 5 to the SomeMember member of the someObject object. In contrast, here is a declarative construct: Dim someObject As SomeClass This is declarative because it doesnt perform an action. It states that the symbol someObject is a variable that holds a reference to an object of type SomeClass. In the past, declarative information typically was used only by the compiler and did not compile directly into the executable. In the CLR, however, declarative information is everything The CLR uses type and signature information to ensure that memory is always referenced in a safe way. The JIT compiler uses type and signature information to resolve method calls to the appropriate target code at JIT compile time. The only way for this to work is for this declarative information to be included alongside its associated procedural information. Compilers that target the CLR therefore store both procedural 118 and declarative information in the resulting .exe or .dll file. The procedural information is stored as IL, and the declarative information is stored as metadata. Metadata is just the CLIs name for declarative information. The CLI has a mechanism that allows programmers to include arbitrary metadata in compiled applications. This mechanism is known as custom attributes and is available in Visual Basic .NET. Custom attributes were discussed in detail in Chapt er 2 .3.9 Memory Management and Garbage Collection
Parts
» VB.NET - (O'Reilly) Programming Visual Basic NET
» What Is the Microsoft .NET Framework?
» hello, world An Example Visual Basic .NET Program
» Hello, Windows An Example Visual Basic .NET Program
» Hello, Browser An Example Visual Basic .NET Program
» Source Files Identifiers The Visual Basic .NET Language
» Numeric Literals String Literals Character Literals
» Date Literals Boolean Literals Nothing Summary of Literal Formats
» Custom Types Collections Types
» The Namespace Statement The Imports Statement
» Symbolic Constants Scope The Visual Basic .NET Language
» Access Modifiers Assignment The Visual Basic .NET Language
» Unary Operators Arithmetic Operators
» Relational Operators Operators and Expressions
» String-Concatenation Operators Bitwise Operators
» Logical Operators Operator Precedence
» Call Exit Branching Statements
» Goto If RaiseEvent Branching Statements
» Return Select Case Branching Statements
» For Each Iteration Statements
» Object Instantiation and New Constructors
» Handling Events Inheritance Classes
» Passing arrays as parameters
» Variable-length parameter lists Main method
» Implementing interface methods Overriding inherited methods
» Overloading Overloading inherited methods
» The MyBase Keyword Nested Classes Destructors
» Interfaces The Visual Basic .NET Language
» Enumerations The Visual Basic .NET Language
» Exceptions The Visual Basic .NET Language
» Delegates The Visual Basic .NET Language
» Using Events and Delegates Together
» Creating Custom Attributes Attributes
» Standard Modules Conditional Compilation
» Summary The Visual Basic .NET Language
» Common Language Infrastructure CLI and Common Language Runtime CLR
» Global Assembly Cache GAC Comparison of Assemblies, Modules, and Namespaces
» Application Domains Common Language Specification CLS
» Intermediate Language IL and Just-In-Time JIT Compilation Metadata
» Finalize Memory Management and Garbage Collection
» Dispose Memory Management and Garbage Collection
» A Brief Tour of the .NET Framework Namespaces
» Configuration File Format Configuration
» Configuration Section Groups The appSettings Section
» Adding event handlers Creating a Form in Code
» Handling Form Events Windows Forms I: Developing Desktop Applications
» Relationships Between Forms Windows Forms I: Developing Desktop Applications
» Merging Menus MDI Applications
» Detecting MDI Child Window Activation
» Component Attributes Windows Forms I: Developing Desktop Applications
» The Graphics Class 2-D Graphics Programming with GDI+
» The Pen Class 2-D Graphics Programming with GDI+
» The Brush Class 2-D Graphics Programming with GDI+
» System colors The Color Structure
» Alpha Blending 2-D Graphics Programming with GDI+
» Antialiasing 2-D Graphics Programming with GDI+
» The PrintPageEventArgs Class Printing
» The OnBeginPrint and OnEndPrint Methods Choosing a Printer
» The PageSettings Class Printing
» The PrinterSettings Class Printing
» Page Setup Dialog Box Print Preview
» Summary Windows Forms I: Developing Desktop Applications
» The Button Class The CheckBox Class The ComboBox Class
» The DateTimePicker Class The GroupBox Class The ImageList Class
» The Label Class The LinkLabel Class
» The ListBox Class Common Controls and Components
» The ListBox.ObjectCollection Class
» The ListView Class Common Controls and Components
» The MonthCalendar Class Common Controls and Components
» The Panel Class The PictureBox Class
» The RadioButton Class Common Controls and Components
» The TextBox Class The Timer Class
» Other Controls and Components
» Control Events Windows Forms II: Controls, Common Dialog Boxes, and Menus
» The Anchor Property Form and Control Layout
» Controlling dock order The Dock Property
» The Splitter control The Dock Property
» ColorDialog FontDialog OpenFileDialog Common Dialog Boxes
» PageSetupDialog PrintDialog PrintPreviewDialog SaveFileDialog
» Adding Menus in the Visual Studio .NET Windows Forms Designer
» Programmatically Creating Menus Menus
» Building Controls from Other Controls
» Building Controls That Draw Themselves Building Nonrectangular Controls
» Summary Windows Forms II: Controls, Common Dialog Boxes, and Menus
» Setting control properties using attributes Adding event handlers
» AutoEventWireup Handling Page Events
» The Button control Web Controls
» The CheckBox control The DropDownList control
» The Image control The Label control
» The ListBox control Web Controls
» The RadioButton control Web Controls
» The Table control Web Controls
» The TextBox control Web Controls
» Other web controls Web Controls
» HTML Controls Handling Control Events
» Programmatically Instantiating Controls More About Server Controls
» More About Validation-Control Tag Attributes
» Using Validation-Control Properties Providing a Summary View of Validation Failures
» Performing Custom Validation Adding Validation
» Using Directives to Modify Web Page Compilation
» The Server Object ASP.NET Objects: Interacting with the Framework
» The Application Object The Session Object The Cache Object The Request Object
» The Response Object ASP.NET Objects: Interacting with the Framework
» Discovering Browser Capabilities ASP.NET and Web Forms: Developing Browser-Based Applications
» The Session Object Maintaining State
» The Application Object Maintaining State
» Session and Application Startup and Shutdown global.asax Compiles to a Class
» Adding Global Objects Application-Level Code and global.asax
» ASP.NET authorization Authorization
» Windows NTFS authorization Code-access authorization
» IUSR_ComputerName Impersonation Accessing Network Resources
» User Controls Designing Custom Controls
» Creating a custom server control using Visual Studio .NET
» Creating a custom server control in code Using a custom server control in Visual Studio .NET
» Summary ASP.NET and Web Forms: Developing Browser-Based Applications
» The WebService Attribute The WebMethod Attribute
» Testing a Web Service with a Browser
» Consuming a Web Service in Visual Studio .NET
» Consuming a Web Service in Notepad
» Synchronous Versus Asynchronous Calls
» Web-Service Descriptions Web-Service Discovery
» Limitations of Web Services Summary
» A Brief History of Universal Data Access Managed Providers
» Connecting to a SQL Server Database
» Connecting to an OLE DB Data Source
» The DataSet Class Finding Tables
» Finding Column Values Finding Column Definitions Changing, Adding, and Deleting Rows
» Writing Updates Back to the Data Source
» Relations Between DataTables in a DataSet
» The DataSets XML Capabilities
» Binding a DataSet to a Windows Forms DataGrid
» Binding a DataSet to a Web Forms DataGrid
» Typed DataSets ADO.NET: Developing Database Applications
» Reading Data Using a DataReader
Show more