1、5.1 Operating System ConceptsModule 5: Threads線程線程Overview 綜述綜述Benefits 益處益處User and Kernel Threads 用戶和內核線程用戶和內核線程Multithreading Models 多線程模型多線程模型Solaris 2 Threads Solaris 2線程線程Java Threads Java線程線程5.2 Operating System ConceptsResponsiveness 響應響應Resource Sharing 資源共享資源共享Economy經濟性經濟性Utilization of M

2、P Architectures MP體系結構的運用體系結構的運用Benefits益處益處5.3 Operating System ConceptsSingle and Multithreaded Processes單個和多線程進程單個和多線程進程5.4 Operating System ConceptsMultithreads exampleA www server5.5 Operating System ConceptsMultithreads exampleA www server5.6 Operating System ConceptsMulti-ThreadingWhy limit o

3、urselves to a single thread? Think of a web server that must service a large stream of requests If only have one thread, can only process one request at a time What to do when reading a file from disk?Multi-threading model Each process can have multiple threads Each thread has a private stackTRegist

4、ers are also private All threads of a process share the code and heapTObjects to be shared across multiple threads should be allocated on the heap5.7 Operating System ConceptsMulti-Threading (cont)Implementation Each thread is described by a thread-control block (TCB) A TCB typically containsTThread

5、 IDTSpace for saving registersTPointer to thread-specific data not on stackObservation Although the model is that each thread has a private stack, threads actually share the process address space Theres no memory protection! Threads could potentially write into each others stack5.8 Operating System

6、ConceptsProcess Address Space RevisitedOSCodeGlobalsStackHeapOSCodeGlobalsStackHeapStack(a) Single-threaded address space(b) Multi-threaded address space5.9 Operating System ConceptsUser Threads用戶線程用戶線程Thread Management Done by User-Level Threads Library由用戶級線程庫進行管理的線程由用戶級線程庫進行管理的線程Examples例子例子- POSI

7、X Pthreads- Mach C-threads- Solaris threads5.10 Operating System ConceptsKernel Threads內核線程內核線程Supported by the Kernel由內核支持由內核支持Examples例子例子- Windows 95/98/NT - Solaris- Digital UNIX5.11 Operating System ConceptsUser vs. Kernel ThreadsAdvantages of user threads Performance: low-cost thread operation

8、s (do not require crossing protection domains) Flexibility: scheduling can be application specific Portability: user thread library easy to portDisadvantages of user threads If a user-level thread is blocked in the kernel, the entire process (all threads of that process) are blocked Cannot take adva

9、ntage of multiprocessing (the kernel assigns one process to only one processor)5.12 Operating System ConceptsUser vs. Kernel Threadsprocessprocessoruserthreadsthreadschedulingprocessschedulingkernelthreadsthreadschedulingkerneluserprocessorthreadsthreadsprocessscheduling5.13 Operating System Concept

10、sUser vs. Kernel ThreadsNo reason why we shouldnt have bothMost systems now support kernel threadsUser-level threads are available as linkable librarieskernelthreadsprocessoruserthreadsthreadschedulingthreadschedulingkerneluserprocessscheduling5.14 Operating System ConceptsMultithreading Models多線程模型

11、多線程模型Many-to-One多對一多對一One-to-One一對一一對一Many-to-Many 多對多多對多5.15 Operating System ConceptsMany-to-One多對一多對一Many User-Level Threads Mapped to Single Kernel Thread.多個用戶級線程映像進單個內核線程多個用戶級線程映像進單個內核線程Used on Systems That Do Not Support Kernel Threads. 用于不支持內核線程的系統中用于不支持內核線程的系統中5.16 Operating System ConceptsM

12、any-to-one Model多對一模型多對一模型5.17 Operating System ConceptsOne-to-One一對一一對一Each User-Level Thread Maps to Kernel Thread.每個用戶級線程映像進內核線程每個用戶級線程映像進內核線程Examples- Windows 95/98/NT- OS/25.18 Operating System ConceptsOne-to-one Model一對一模型一對一模型5.19 Operating System ConceptsMany-to-many Model多對多模型多對多模型5.20 Oper

13、ating System ConceptsPthreadsa POSIX standard (IEEE 1003.1c) API for thread creation and synchronization.API specifies behavior of the thread library, implementation is up to development of the library.Common in UNIX operating systems.5.21 Operating System ConceptsSolaris 2 Threads Solaris 2線程線程5.22

14、 Operating System ConceptssolarisUnix 的發展分支的發展分支4.XBSD是由加州大學貝克萊分校計算機系統研究組開發的。該研是由加州大學貝克萊分校計算機系統研究組開發的。該研究組也發布究組也發布BSD NET1和和BSD NET2版，它們包含了版，它們包含了4.XBSD系統系統公眾可用源代碼。公眾可用源代碼。SVRX是是AT& T的系統的系統V的簡稱。的簡稱。XPG3是是X/Open可移植性指南的第三次發行本的簡稱。可移植性指南的第三次發行本的簡稱。ANSI C是是C程序設程序設計語言的計語言的ANSI標準。標準。POSIX.1是是Unix類系統界面的

15、類系統界面的IEEE和和ISD標標準。準。 5.23 Operating System ConceptsSolaris Process Solaris 線程線程5.24 Operating System ConceptsLinux ThreadsLinux refers to them as tasks rather than threads.Thread creation is done through clone() system call.Clone() allows a child task to share the address space of the parent task (

16、process)5.25 Operating System ConceptsJava Threads Java線程線程Java Threads May be Created by: Java線程可如下創建：線程可如下創建： Extending Thread class 擴充線程類擴充線程類 Implementing the Runnable interface 實現可運行接口實現可運行接口5.26 Operating System ConceptsExtending the Thread Class線程類型的擴展線程類型的擴展class Worker1 extends Threadpublic

17、 void run() System.out.println(“I am a Worker Thread”);5.27 Operating System ConceptsCreating the Thread創建線程創建線程public class Firstpublic static void main(String args) Worker runner = new Worker1();runner.start();System.out.println(“I am the main thread”);5.28 Operating System ConceptsThe Runnable In

18、terface可運行接口可運行接口public interface Runnablepublic abstract void run();5.29 Operating System ConceptsImplementing the Runnable Interface可運行接口的實現可運行接口的實現class Worker2 implements Runnablepublic void run() System.out.println(“I am a Worker Thread”);5.30 Operating System ConceptsCreating the Thread創建線程創建線

19、程public class Secondpublic static void main(String args) Runnable runner = new Worker2();Thread thrd = new Thread(runner);thrd.start();System.out.println(“I am the main thread”);5.31 Operating System ConceptsJava Thread ManagementJava線程的管理線程的管理suspend() suspends execution of the currently running th

20、read.掛起掛起 - 暫停當前線程的運行暫停當前線程的運行sleep() puts the currently running thread to sleep for a specified amount of time. 睡眠睡眠 - 讓當前線程入睡一段指定的時間讓當前線程入睡一段指定的時間resume() resumes execution of a suspended thread. 恢復恢復 - 再執行被掛起的線程再執行被掛起的線程stop() stops execution of a thread. 停止停止 - 停止一個線程的執行停止一個線程的執行5.32 Operating System ConceptsJava Thread States Java線程狀態線程狀態 5.33 Operating System ConceptsProducer Consumer Problem生產著消費者問題生產著消費者問題public class Server public Server() MessageQueue mailBox = new MessageQueue(); Producer producerThread = new Producer(mailBox); Consumer con