W4156: COMS Advanced Software Engineering
Prof. Gail Kaiser [e-mail] http://york.cs.columbia.edu/classes/cs4156/
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.NET and Component Services
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What is .NET?
An object-oriented general purpose software development platform with multi-language
interoperability
Common Language Infrastructure (CLI) Common Type System Common Intermediate Language Common Language Specification common Virtual Execution Environment common XML metadata representation
CLI specification is an ECMA standard (originally
European Computer Manufacturers Association,
http://www.ecma-international.org/)
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Overview of the CLI
A file format A common type system An extensible metadata system An intermediate language Access to the underlying platform A factored base class library
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File Format
Based on Common Object File Format (predecessor to ELF on Unix but a variant still used for Windows) Code represented as MSIL (Microsoft Intermediate Language) instructions Metadata stored in read-only area Methods include a descriptive header
Stack frame size Types of local variables and parameters Pinned variable information Exception handler table
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Common Type System
Spans large number of languages Object-oriented in flavor Supports procedural and functional languages, too Includes value types ("structs"), pointers and by-reference values Subset for wide reach
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Metadata System
Self-description for assemblies (components)
Includes referenced assemblies Allows crypto-strong names Records version information Security boundary
Self-description for types
Name and defining assembly Member information (fields, methods, etc.)
Extensible through custom attributes Stored in file along with code
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Intermediate Language
Simple stack machine model Typeless opcodes (add, not add.int32)
Signed and unsigned via opcode, not type Rich set of conversion operations
Tail calls, virtual dispatch, call via function pointer, exception handling Typed variable argument lists, dynamically typed pointers Objects, vectors, strings, integers, floats built-in
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Access to Platform
Metadata describes managed and unmanaged interface Marshaling is automatic for many types Custom marshaling can be specified Platform-specific transformations are possible (ANSI <-> Unicode, etc.) Platform-specific calling conventions can be specified
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Factored Class Library
Designed for cross-language use Factored to allow minimal footprint and minimal hardware requirements (minimal base is always present) File format independent of factorization Intended to be platform-neutral Three layers: kernel, basic language, additional functionality
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Methodology
Define Kernel
Fixes file format Hand-picked classes and methods
Define Basic Language
Minimal hardware support required Most common language features (including those required for C#) Depends on classes defined in Kernel
Package each advanced function separately
Implemented a la carte by runtime vendors Required a la carte by developers
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Languages and Packages
C#
Requires Kernel, Basic Language and Extended Numerics
ECMAScript
Requires above plus Reflection
ISO C++
Requires Kernel, Basic Language, Extended Numerics, and NonCLS
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Scenario-based System Design
Scenario Minimal C# Program Ex: Connected C# Application Required Packages Kernel Kernel, Basic Language Kernel, Basic Language, Common DT, Networking Kernel, Basic Language, Common DT, Advanced DT, Networking, XML, IO, Collections
Core Execution Engine
Minimal .Net Execution
Core Execution Engine
Base Language
C# Program Execution
Core Execution Engine
Base Language
Common Data Types
Networking
Example: Connected C# App
Ex: Connected XML C# Application
Core Execution Engine
Base Language
Common Data Types
Advanced Data Types
Networking
XML
Standard IO
Collections
Example: Advanced C# App
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Categories of Packages
Classes grouped into packages Packages grouped into five categories
Miscellaneo us High Level Programming Abstract OS Interfaces Common Programming Utilities EE Functionality
Core Execution Engine Base Language Development Time Classes
Not In Buckets
Asynch Support
Advanced XML
Remoting
XML
Globalization
High Level Programming
Security
Standard IO
Networking
Threading
Abstract OS Interfaces
Serialization
Regular Expressions
Extended Numerics
Common Data Types
Advanced Data Types
Collections
Common Programming Utilities
GC
Hosting
Unmanaged
Reflection
Non-CLS Support
EE Functionality
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Abstract OS Interface
Platform-independent operating system functionality Networking
System.Net.*
Security
System.IsolatedStorage, System.Security, ...
Standard I/O
System.Console, System.IO, System.Text, ...
Threading
System.Threading, ...
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Common Programming Utilities
Classes that support typical programming patterns Common Data Types
System.DateTime, System.Text.StringBuilder, etc.
Advanced Data Types
System.BitConverter, System.URI, ...
Collections
System.Collections
Extended Numerics
System.Decimal, System.Double, etc.
Regular Expressions
System.Text.RegularExpressions.*
Serialization
System.Runtime.Serialization.*, etc.
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High-Level Programming
"Advanced" programming patterns Asynchronous Programming
System.AsyncCallback, System.IAsyncResult
Globalization
System.Globalization.*, System.Resources.*, etc.
Remoting
System.Runtime.Remoting.*
XML
System.Xml.* (parsing and generation)
Advanced XML
System.Xml.Xsl.*, System.Xml.XPath.*
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Execution Environment Functionality
Revealing underlying operations to programming languages GC
System.WeakReference, System.WeakReferenceException
Hosting
System.OperatingSystem, etc.
NonCLS
System.ArgIterator, etc.
Reflection
System.Reflection.*, etc.
Unmanaged
System.Runtime.InteropServices, etc.
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Miscellaneous
Kernel, Basic Language, and support for developers Kernel
1, 2, and 4 byte integers, arrays, string, object, etc.
Basic Language Support
System.EventHandler, System.IFormattable, System.Type, etc.
Development Time
System.Diagnostics.*, System.Runtime.CompilerServices.*
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CLI Summary
A file format A common type system An extensible metadata system An intermediate language Access to the underlying platform A factored base class library
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Back to: What is .NET?
Common Language Runtime (CLR) is Microsoft's implementation of CLI Compilers for C#, VB.NET and C++ turn source code into MSIL that runs on CLR Extensive Framework Class Libraries, supporting windows GUI development (Windows Forms), database access (ADO.NET), web development (ASP.NET), web services, XML, etc. Other implementations of CLI: Mono, DotGNU
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Why do they call it ".NET"?
"I don't know what they were thinking. They certainly weren't thinking of people using search tools. It's meaningless marketing nonsense." [Andy McMullan]
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How do multiple languages interoperate?
A compiler from any language compiles an application into MSIL (also referred to as CIL Common Intermediate Language) The compiler also generates metadata in XML on information the types and named entities (classes, methods, fields, etc.) defined and used in the application At runtime, the CIL code is Just-in-Time (JIT) compiled into the target platform's native code The CLR uses the metadata to perform runtime checks for type-safety and security ("managed code")
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Common Language Runtime
Execution Model
Source code
VB Compiler Assembly C# Compiler Assembly C++ Compiler Assembly
MSIL
Ngen
Common Language Runtime JIT Compiler
Native code
Managed Code CLR Services
Managed CLR Code
Managed Code
Unmanaged Code
Operating System Services
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What does "managed" mean?
Managed code: .NET provides several core run-time services to the programs that run within it, e.g., exception handling and security - for these services to work, the code must provide a minimum level of information to the runtime Managed data: Data that is allocated and freed by the .NET runtime's garbage collector Managed classes: A C++ class can be marked with the __gc keyword - then memory for instances of the class are managed by the garbage collector and the class can interoperate with classes written in other CLR languages, e.g., inherit from a VB class (also restrictions, e.g., a managed class can only inherit from one base class)
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What is an "assembly"?
A logical .exe or .dll, can be an application (with a main entry point) or a library Consists of one or more files (dlls, exes, html files, etc), and represents a group of resources, type definitions, implementations of those types, and references to other assemblies These resources, types and references are described in a block of data called a manifest -part of the assembly making it self-describing Assemblies often referred to as "components"
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More on Assemblies
The identity of a type is the assembly that houses it combined with the type name: if assembly A exports a type called T, and assembly B exports a type called T, .NET sees these as two completely different types (separate from .NET namespaces) Many of the security restrictions are enforced at the assembly boundary Also unit of versioning (version number consists of 4 parts, convention is major.minor.build.revision) Produced by compiler (single module) or linker (multiple modules)
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Private vs. Shared Assemblies
A private assembly is normally used by a single application, and is stored in the application's directory A shared assembly is intended to be used by multiple applications, and is normally stored in the global assembly cache (GAC) but can be stored elsewhere Assemblies find each other (outside the GAC) by searching directory paths
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Attributes
Metadata attributes attach some data to a class or method, which can be accessed via reflection, e.g., [serializable] Context attributes provide an interception mechanism whereby instance activation and method calls can be pre- and/or postprocessed Analogous to use of Java annotations in EJB 3.0
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Remoting
Send messages along channels, e.g., TCP or HTTP Multiple serialization formats, e.g., SOAP (for HTTP) or binary (for TCP, similar to DCOM) Distributed garbage collection of objects is managed by "leased based lifetime" when that time expires the object is disconnected from the .NET runtime remoting infrastructure unless in the interim renewed by a successful call from the client to the object (or explicit renewal by client)
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Remote Invocations
SingleCall: Each incoming request from a client is serviced by a new object Singleton: All incoming requests from clients are processed by a single server object Client-activated object: Same as stateful (D)COM, whereby the client receives a reference to the remote object and holds that reference (thus keeping the remote object alive) until it is finished with it
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So Where's the Component Services?
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So Where's the Component Services?
COM+ (and Web Services)
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Recall COM+ Services
Transactions Role-base security Queued components Loosely coupled events Just-in-time activation Object pooling ...
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.NET Serviced Components
COM+ services can be used by .NET components derived from the ServicedComponent class using the System.EnterpriseServices namespace Must be registered with the COM+ catalog Can also use COM+ services outside components (Windows 2003 only)
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