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Code-Reuse A Historic Perspective
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Transcript of Code-Reuse A Historic Perspective
Code-Reuse A Historic Perspective
Yingcai Xiao
Want to know?
Why we have to write programs to run a computer?
Why an error in a program is called a bug?
Why there are so many programming languages?
What is a computer? (From a programmer’s point of view).
How do those languages support code reuse?
Programming a Computer
Programming a Computer
Types of ComputersAnalog: Analog Device, 1.2345678Digital: Binary Device, 0 or 1
Programming a ComputerWiring: Hardware, Bug, AdaCoding: Software
Modern Computers: Voneumann Machines• Run stored programs (code reuse) to process
stored data.• Components: Memory, IO, CPU, Secondary
Storage.
What is a program and what is programming?
Programs: stored instructions for data processing.
Programming
= Data Structures + Algorithms
Professor Donald E. Knuth
http://www-cs-faculty.stanford.edu/~knuth/
What is a program from a computer’s point of view?
Programs: • Stored binary opcodes• Different types of computers have
different opcodes • Opcodes are not reusable on different
types computers • Programs in binary codes are not reusable
on different types of computers
How data are stored on a computer?
Bits (0/1) and bytes (0-255):
Short Int (2 bytes):
0 0 0 0 0 0 1 0
0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0
Endian (byte ordering): little (Intel), big (Moterola, Sun), bi (DEC Alpha, MIPS), big-to-bi (Sun SPARK v9)
Is data reusable?
0 1 0 0 0 0 0 1
No, in general.
Is data saved on one type of computers reusable on another type of computers?
Yes, for ASCII text or any type of a byte in size.
‘A’ (65)
ASCII text (ISO/IEC 8859-1) is platform-independent.
What is a program and what is programming?
Programs: stored binary opcodes
Punch Card Programming:
punch card machines
converts instructions typed into binary codes (0 no hole, 1 hole) on a stack of cards.
Programming Languages
Assembly Languages
• English-like: load, add, save
• Assembler: a program that translates code written in an assembly language into opcodes.
• Assembly languages are machine-dependent. An assembly language is only valid for a specific CPU architecture.
• Programs written in an assembly language are machine-dependent and not reusable on a different types of CPU architectures.
High-level Programming Languages
• English-like: if, for, switch, …
• Compiler: a program that translates code written in a high-level programming language into opcodes. The input is called the source code and output is called the object code (.obj).
• Object-codes and executables are machine-dependent.• High-level languages are machine-independent.
• Linker: a program that links object codes together to make an executable (.exe).
High-level Programming Languages
• Binary codes are reusable as libraries on computers of the same architecture. (compile-time sharing).
• Object codes (from different high-level programming languages) can be put together to make a library (.lib).
• Libraries (.lib and .dll) are machine-dependent.
• A dynamically-linked library (.dll) can be shared by all programs on the same computer and by all the running processes on the same computer (run-time sharing).
• Libraries and object files on a computer are linked together to form an executable. (compile-time sharing of binary code).
High-level Programming Languages
• The header files contain the header (not the implementation) of user defined data types and related methods (functions), i.e., describe what’s in the library.
• To use a library, one needs to include the header files (.h) for the library in the source code.
• The compiler use the information in the header files to make type checking.
• Before compilation, the preprocessor of the compiler copies everything in the header files into the source code and generate an intermediate (.I) file.
High-level Programming Languages
• Source codes written in a high-level programming language are reusable on different types of computers.
• Binary codes (.obj, .lib, .dll, .exe) compiled from a high-level programming language are reusable on the computers of the same architecture but not reusable on computers of different architecture.
Traditional Compilation
Source File (.cpp)
Intermediate File (.I)
Object File (.obj)
Binary File (.exe)
Preprocessing
Compilation
Linking
Common Binary Code?(Binary Code Reuse Cross System Architectures)
Traditional Compilation
Source Code for Language 1
Language 1 Compiler on OS1
Binary Code for OS1
OS1
Source Code for Language 1
Language 1 Compiler on OS2
Binary Code for OS2
OS2
OS-Independent Code: Intermediate Languages
The trend to support machine-independent binary code is to compile the source code into the binary format of an intermediate language.
And to provide an interpreter for the intermediate language on each OS to translate the binary code of the intermediate language into the native binary code of the OS.
OS-Independent Compilation: Intermediate Language
Source Code for Language 1
Language 1 Compiler on OS1
Intermediate Binary Code for Language1
OS1
Intermediate Code Interpreter OS1
OS2
Language 1 Compiler on OS2
Binary Code for OS2Binary Code for OS1
Intermediate Code Interpreter OS2
Java Intermediate Language: Java Bytecode
Java Source Code (.java)
Java Compiler (javac) on OS1
Java Bytecode (.class)
OS1
Java Interpreter on OS1 (java)
OS2
Java Compiler (javac) on OS2
Binary Code for OS2Binary Code for OS1
Java Interpreter on OS2 (java)
Program statements are interpreted one at a time during the run-time.
JIT Compiler
An interpreter interprets intermediate code one line at a time. Slow execution.
A JIT (Just-In-Time) compiler compiles the complete code all at once just into native binary code before execution. Faster execution.
JIT Complier: Java Bite Code Compiler
Java Source Code (.java)
Java Compiler (javac) on OS1
Java Bytecode (.class)
OS1
Java JIT Compiler on OS1
OS2
Java Compiler (javac) on OS2
Binary Code for OS2Binary Code for OS1
Java JIT Compiler on OS2
All programming statements are compiled at compile time.
.NET OS-Platform-Independence
MSIL: Microsoft Intermediate Language (Used by .NET)
Source Code for Language 1
Language 1 Compiler on OS1
MSIL Code
OS1
MSIL JIT Compiler on OS1
OS2
Language 1 Compiler on OS2
Binary Code for OS2Binary Code for OS1
MSIL JIT Compiler on OS2
JIT Compilation in .NET
All MSIL code are JIT-compiled to native binary code before execution. No run-time interpretation, faster execution.
A Common Language?(Source Code Reuse Cross Languages)
.NET CTS/CLR
.NET Common Language Runtime
To make .NET language independent, CLR (Common Language Runtime) is defined as the runtime environment.
CLR defines CTS (Common Type System) which should be followed by all languages to be used in the .NET framework.
The code that follows CTS standard and runs through CLR is called managed code.
Ex. multiple inheritance is allowed in C++ but not allowed in Managed C++ since CTS doesn’t support it.
.NET Language-Independence
CLR: Common Language Runtime
Source Code for Language 1
Language 1 Compiler on OS1
MSIL Code Confirming CTS (Managed Code)
OS1
CLR on OS1
OS2
Language 2 Compiler on OS2
Binary Code for OS2Binary Code for OS1
CLR on OS2
Source Code for Language 2
.NET Architecture for Language and Platform Independence(fan-in and fan-out on MSIL)
Source Code for Language 1
Language 1 Compiler on OS1
OS1
CLR for OS1
OS2
Language 2 Compiler on OS2
Binary Code for OS2Binary Code for OS1
CLR for OS2
Source Code for Language 2
MSIL Code Confirming CTS (Managed Code)
CLI (Common Language Infrastructure)
CLR/CTS for Everyone?
CLI : Common Language Infrastructure
A specification defines an environment for multiple high-level languages to be used on different computer platforms.
Created by Microsoft based on .NET, standardized by MS, Intel, HP and others, ratified by ECMA and ISO.
.NET is an implementation of CLI for desktop systems.
.NET Compact Framework is an implementation of CLI for portable devices.
Open Source implementations: Mono development platform (Novell), Portable .NET (dotGNU)
CLI (Common Language Infrastructure) SpecificationOpen Architecture for Language and Platform Independent Programming
Source Code for Language 1
Language 1 Compiler on OS1
OS1
CLR for OS1
OS2
Language 2 Compiler on OS2
Binary Code for OS2Binary Code for OS1
CLR for OS2
Source Code for Language 2
CIL (Common Intermediate Language) Code
Confirming CTS (Common Type System)
Run-time Binary Code Sharing
Cross the Internet
Web Services
Libraries shared over the Internet at run-time.
Service interfaces specify what the services can do (contracts).
Service interfaces are defined in WSDL (Web Service Description Language)
UDDI Registry: Universal Description, Discovery, and Integration. (yellow page)
Access Standard:
SOAP: Simple Object Access Protocol
Architecture of Web Services
Programming Client 1
Programming
Client 2
Web Service 1
UDDI Registry 1
WSDL Interface 1
UDDI Registry 2
Web Service 2 WSDL Interface 2
SOAP
SOAP
WEB
Web Service Example
.NET Passport (one login for the whole Internet)
www.passport.com (run by Microsoft)
www.ubid.com (An online auction shop using Passport web service)
Windows Live (one location to get all you need from the Internet)
http://get.live.com/ (run by Microsoft)
Windows Live ID is replacing Passport ID.
Code Reuse Tools by Microsoft
MFC: code reuse within an application (process)
COM: Component Object Model, code reuse across applications (processes)
DCOM: Distributed COM, code reuse across systems
COM+: Internet-based Enterprise COM, code reuse across the Internet
.NET: COM+ 2.0, all COM+ services are available in .NET, even those not in managed code, interoperable with COM-based applications
A Common Language for the Internet?
A Common Language for the Internet
ASCII text (ISO/IEC 8859-1) is platform-independent.
=> HTTP (Hyper Text Transport Protocol)
=> Recognizable by all types of computers. (World Wide Web)
=> Everything is presented as text including data and programs.
Tim Berners-Lee
=> HTML (Hyper Text Markup Language)
A Common Language for the Internet
=> XML (eXtensible Markup Language), HTML-based
=> SOAP (Simple Object Access Protocol), HTML-based
=> WSDL (Web Service Description Language), HTML-based