Operating Systems. Chapter 4 Threads. Lei Duan

Transcription

1 Operating Systems Chapter 4 Threads Lei Duan leiduan@scu.edu.cn

2 Agenda 4.1 Processes and Threads 4.2 Types of Threads 4.3 Multicore and Multithreading 4.4 Summary /49

3 Agenda 4.1 Processes and Threads Introduction Multithreading Thread Functionality 4.2 Types of Threads 4.3 Multicore and Multithreading 4.4 Summary /49

4 Introduction Resource ownership ( 资源所有权 ) A process includes a virtual address space to hold the process image (Recall what is process image?) A process may be allocated control or ownership of resources Scheduling/execution ( 调度 / 执行 ) The execution of a process follows an execution path that may be interleaved with other processes A process is the entity that is scheduled and dispatched by the OS These two characteristics are treated independently by the operating system /49

5 Introduction The unit of dispatching is referred to as a thread or lightweight process ( 调度的单位称为线程或轻量进程 ) The unit of resource ownership is referred to as a process or task ( 资源所有权的单位称为进程或者任务 ) /49

6 Introduction Threads run within application Multiple tasks with the application can be implemented by separate threads Update display Fetch data Spell checking Answer a network request Process creation is heavy-weight while thread creation is light-weight Can simplify code, increase efficiency Kernels are generally multithreaded /49

7 Agenda 4.1 Processes and Threads Introduction Multithreading Thread Functionality 4.2 Types of Threads 4.3 Multicore and Multithreading 4.4 Summary /49

8 Single-Thread ( 单线程 ) Single-threaded approach refers to the traditional approach of a single thread of execution per process, in which the concept of a thread is not recognized ( 单线程指一个进程中只有一个线程在执行的传统方法, 线程的概念并不明确 ) MS-DOS supports a single thread ( 单进程 单线程 ) Some UNIX supports multiple user processes but only supports one thread per process ( 多进程, 每个进程单线程 ) /49

9 Multithreading ( 多线程 ) Multithreading refers to the ability of an OS to support multiple threads of execution within a single process ( 指操作系统支持在一个进程中执行多个线程的能力 ) Windows, Solaris, Linux, Mach, and OS/2 support multiple threads /49

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11 In a multithreaded environment Process: Unit of Resource allocation and Unit of Protection ( 资源分配和保护的单位 ) Have a virtual address space ( 虚拟地址空间 ) which holds the process image (code, data, stack and PCB) Protected access to processors, memory, other processes ( 与其他进程通信 ), files, and I/O resources Contains one or more threads /49

12 Thread: Unit of Scheduling/Execution ( 调度执行的单位 ) Each thread has: An execution state (running, ready, etc.) A saved thread context when not running Has an execution stack Some per-thread static storage for local variables Access to the memory and resources of its process all threads of a process share this /49

13 Distinction Between Threads and Processes From the Point of View of Process Management ( 从进程管理的角度看线程和进程 ) /49

14 Distinction Between Threads and Processes From the Point of View of Process Management ( 从进程管理的角度看线程和进程 ) All of the threads of a process share the state and resources of that process /49

15 Distinction Between Threads and Processes From the Point of View of Process Management ( 从进程管理的角度看线程和进程 ) They reside in the same address space and have access to the same data /49

16 Distinction Between Threads and Processes From the Point of View of Process Management ( 从进程管理的角度看线程和进程 ) When one thread alters an item of data in memory, other threads see the results if and when they access that item /49

17 Distinction Between Threads and Processes From the Point of View of Process Management ( 从进程管理的角度看线程和进程 ) If one thread opens a file with read privileges, other threads in the same process can also read from that file /49

18 Benefits of Threads 1. Takes less time to create a new thread than a process 2. Less time to terminate a thread than a process 3. Less time to switch between two threads within the same process 4. Since threads within the same process share memory and files, they can communicate with each other without invoking the kernel /49

19 Benefits of Threads 1. Takes less time to create a new thread than a process 2. Less time to terminate a thread than a process 3. Less time to switch between two threads within the same process 4. Since threads within the same process share memory and files, they can communicate with each other without invoking the kernel It is far more efficient to do so as a collection of threads rather than a collection of separate processes /49

20 Threads are Affected by Many Process Action Suspending a process involves suspending all threads of the process since all threads share the same address space ( 挂起进程会挂起该进程的所有线程 ) Termination of a process, terminates all threads within the process ( 终止进程会终止该进程的所有线程 ) /49

21 Threads are Affected by Many Process Action Suspending a process involves suspending all threads of the process since all threads share the same address space ( 挂起进程会挂起该进程的所有线程 ) Termination of a process, terminates all threads within the process ( 终止进程会终止该进程的所有线程 ) Because all threads in a process share the same address space /49

22 Agenda 4.1 Processes and Threads Introduction Multithreading Thread Functionality 4.2 Types of Threads 4.3 Multicore and Multithreading 4.4 Summary /49

23 Thread States Operations associated with a change in thread state Spawn ( 派生 ) Spawn another thread Block ( 阻塞 ) Unblock ( 解除阻塞 ) Finish Deallocate register context and stacks /49

24 Thread States Suspending a process involves suspending all threads of the process Whether the blocking of a thread results in the blocking of the entire process? /49

25 Thread States Suspending a process involves suspending all threads of the process Whether the blocking of a thread results in the blocking of the entire process? Clearly, some of the flexibility and power of threads is lost if the one blocked thread blocks an entire process user-level threads kernel-level threads /49

26 Remote Procedure Call Using Single Thread The results are obtained in sequence, The program has to wait for a response from each server in turn /49

27 Remote Procedure Call Using Threads /49

28 Agenda 4.1 Processes and Threads 4.2 Types of Threads User-Level and Kernel-Level Thread Other Arrangements 4.3 Multicore and Multithreading 4.4 Summary /49

29 User-Level and Kernel-Level Threads Two broad categories of thread implementation: user-level threads (ULTs) kernel-level threads (KLTs) are also referred to as kernel-supported threads or lightweight processes /49

30 Pure User-Level Threads (ULT, 用户级线程 ) Multithread implemented by a threads library All thread management is done by the application The kernel is not aware of the existence of threads & scheduling is done on a process basis a package of routines for ULT management /49

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32 Kernel-Level Threads ( 内核级线程 ) All of the work of thread management is done by the kernel Kernel maintains context information for the process and the threads Scheduling is done on a thread basis /49

33 Advantages of ULT compared to KLT Less overhead of thread switches all of the thread management data structures are within the user address space of a single process mode switches do not required Scheduling can be application specific the scheduling algorithm can be tailored to the application without disturbing the underlying OS scheduler ULTs can run on any operating system the threads library is a set of application-level functions shared by all applications /49

34 Disadvantages of ULT compared to KLT One thread is blocked, all other threads of the process are blocked A multithreaded application cannot take advantage of multiprocessing A kernel assigns one process to only one processor at a time Ways to work around these drawbacks: writing an application as multiple processes rather than multiple threads. greater overhead Jacketing: convert a blocking system call into a nonblocking system call /49

35 Advantages of KLT compared to ULT Overcomes the two principal drawbacks of the ULT Multiple threads in one process can simultaneously run on multiple processors One threads blocked cannot make the other threads within the same process blocked Kernel routines themselves can be multithreaded /49

36 Disadvantages of KLT compared to ULT The principal disadvantage is that thread switch requires mode switches ( 模式切换 ) to the kernel the transfer of control from one thread to another within the same process requires a mode switch to the kernel /49

37 Combined Approaches Thread creation is done in the user space Bulk of scheduling and synchronization of threads within application The multiple ULTs from a single application are mapped onto some (smaller or equal) number of KLTs Example is Solaris /49

38 Agenda 4.1 Processes and Threads 4.2 Types of Threads User-Level and Kernel-Level Thread Other Arrangements 4.3 Multicore and Multithreading 4.4 Summary /49

39 Relationship Between Threads and Processes /49

40 Agenda 4.1 Processes and Threads 4.2 Types of Threads 4.3 Multicore and Multithreading Performance of Software on Multicore Application Example: Valve Game Software 4.4 Summary /49

41 Amdahl s law The law assumes a program in which a fraction (1 - f) of the execution time involves code that is inherently serial and a fraction f that involves code that is infinitely parallelizable with no scheduling overhead /49

42 Overhead by multicore organization If only 10% of the code is inherently serial ( f = 0.9), running the program on a multicore system with eight processors yields a performance gain of only a factor of /49

43 Overhead by multicore organization software typically incurs overhead as a result of communication and distribution of work to multiple processors and cache coherence overhead /49

44 DBMS and DB applications are one area in which multicore systems can be used effectively Servers typically handle numerous relatively independent transactions in parallel /49

45 Applications benefit directly from the ability to scale throughput with the number of cores Multithreaded native applications a small number of highly threaded processes Multiprocess applications many single-threaded processes Java applications JVM is a multithreaded process that provides scheduling and memory management for Java applications Multiinstance applications running multiple instances of the application in parallel /49

46 Agenda 4.1 Processes and Threads 4.2 Types of Threads 4.3 Multicore and Multithreading Performance of Software on Multicore Application Example: Valve Game Software Self study 4.4 Summary /49

47 Agenda 4.1 Processes and Threads 4.2 Types of Threads 4.3 Multicore and Multithreading 4.4 Summary /49

48 Exercise Problems 4.2, 4.9 Name your homework as following rule: OS_StudentID_name_n.doc (n 为当章节序号 ) E.g.: OS_95002_ 张三 _3.doc Submit to TA ( 晏力 ) Mailbox: roy18@126.com Deadline: April 13th, 23: /49

49 Any Question? Thank you! /49