Advanced Operating Systems

Transcription

1 Advanced Operating Systems Welcome to this course, in Fall Semester Main TextBooks 1- Tanenbaum s book 2- Chow s Book 3- Singhal s Book Other extra references: 1- Attieh s book 2- Lynch s book OS2-Sharif University of Technology - Sem ; R. Jalili 1

2 Advanced Operating Systems Assistants: to be announced. Evaluation: Mid-Term Exam Project Review Paper Final Exam The course Home page and Mailing-list Office Hours: Sunday and Tuesday 8-9 2

3 1 Introduction to Distributed Systems and Distributed Operating Systems (DOSs) (From Tanenbaum s Book) 3

4 Definition of a Distributed System (1) A distributed system is: A collection of independent computers that appears to its users as a single coherent system. 4

5 Definition of a Distributed System (2) 1.1 A distributed system organized as middleware. Note that the middleware layer extends over multiple machines. OS2-Sharif University of Technology - Sem ; R. Jalili 5

6 Goals in DSs Connecting Users and Resources Transparency Openness Scalability Will be discussed in the next slides. 6

7 Transparency in Distributed Systems Transparency Access Location Migration Relocation Replication Concurrency Failure Persistence Description Hide differences in data representation and how a resource is accessed Hide where a resource is located Hide that a resource may move to another location Hide that a resource may be moved to another location while in use Hide that a resource may be shared by several competitive users Hide that a resource may be shared by several competitive users Hide the failure and recovery of a resource Hide whether a (software) resource is in memory or on disk Different forms of transparency in a distributed system. OS2-Sharif University of Technology - Sem ; R. Jalili 7

8 Degree of Transparency Is transparency good anytime and everywhere? Tradeoff between transparency and performance. - Updating a replicated database! 8

9 Openness Offering services based on standards. Services are specified through interfaces, described in IDL (Interface Definition Language) Interoperability: two implementations of a system to co-exist and work together; or multiple systems developed by different vendors to be able to work with each other. Portability: An application developed to work on A can be executed on another system B. Separating policy from mechanism 9

10 Scalability Definition of an scalable system? 3 different dimensions Size: Adding more users and resources to the system. Geography: Users and resources can lie far apart. Administration: Many administration organization! 10

11 Scalability Obstacles Concept Centralized services Centralized data Centralized algorithms Example A single server for all users A single on-line telephone book Doing routing based on complete information Examples of scalability limitations. OS2-Sharif University of Technology - Sem ; R. Jalili 11

12 Scalability Solutions 1. Hiding communication latencies: try to avoid waiting for responses to remote service requests Use Asynchronous Communication Many applications cannot run on an asynch communication system Next slide example. 2. Distribution: DNS as example 3. Replication: Caching and consistency! 12

13 Scaling Techniques (1) 1.4 The difference between letting: a) a server or b) a client check forms as they are being filled OS2-Sharif University of Technology - Sem ; R. Jalili 13

14 Scaling Techniques (2) 1.5 An example of dividing the DNS name space into zones. OS2-Sharif University of Technology - Sem ; R. Jalili 14

15 Hardware Concepts 1.6 Different basic organizations and memories in distributed computer systems OS2-Sharif University of Technology - Sem ; R. Jalili 15

16 Multiprocessors A bus-based multiprocessor. 1.7 Memory is Coherent. The bus is overloaded. Caching: hit-rate? Scalability? 16

17 Software Concepts System Description Main Goal DOS NOS Middleware Tightly-coupled operating system for multiprocessors and homogeneous multicomputers Loosely-coupled operating system for heterogeneous multicomputers (LAN and WAN) Additional layer atop of NOS implementing general-purpose services Hide and manage hardware resources Offer local services to remote clients Provide distribution transparency An overview of DOS (Distributed Operating Systems) NOS (Network Operating Systems) Middleware 17

18 Uniprocessor Operating Systems Separating applications from operating system code through a microkernel

19 Multiprocessor Operating Systems (1) A monitor to protect an integer against concurrent access. monitor Counter { private: int count = 0; public: int value() { return count;} void incr () { count = count + 1;} void decr() { count = count 1;} } 19

20 Multiprocessor Operating Systems (2) A monitor to protect an integer against concurrent access, but blocking a process. monitor Counter { private: int count = 0; int blocked_procs = 0; condition unblocked; public: int value () { return count;} void incr () { if (blocked_procs == 0) count = count + 1; else signal (unblocked); } void decr() { if (count ==0) { blocked_procs = blocked_procs + 1; wait (unblocked); blocked_procs = blocked_procs 1; } else count = count 1; } } 20

21 Multicomputer Operating Systems (1) General structure of a multicomputer operating system Message Passing 1.14 OS2-Sharif University of Technology - Sem ; R. Jalili 21

22 Distributed Shared Memory Systems (1) a) Pages of address space distributed among four machines b) Situation after CPU 1 references page 10 c) Situation if page 10 is read only and replication is used 22

23 DSM An Interesting Scenario! False sharing of a page between two independent processes False Sharing! 23

24 Network Operating System (1) General structure of a network operating system

25 Network Operating System (2) Two clients and a server in a network operating system

26 Network Operating System (3) Different clients may mount the servers in different places

27 Positioning Middleware General structure of a distributed system as middleware

28 Middleware and Openness 1.23 In an open middleware-based distributed system, the protocols used by each middleware layer should be the same, as well as the interfaces they offer to applications. 28

29 Comparison between Systems Item Distributed OS Multiproc. Multicomp. Network OS Middlewarebased OS Degree of transparency Very High High Low High Same OS on all nodes Yes Yes No No Number of copies of OS 1 N N N Basis for communication Shared memory Messages Files Model specific Resource management Global, central Global, distributed Per node Per node Scalability No Moderately Yes Varies Openness Closed Closed Open Open 29

30 Clients and Servers General interaction between a client and a server

31 An Example Client and Server (1) The header.h file used by the client and server. 31

32 An Example Client and Server (2) A sample server. 32

33 An Example Client and Server (3) 1-27 b A client using the server to copy a file. 33

34 Application Layering:Processing Level The general organization of an Internet search engine into three different layers

35 Multitiered Architectures (1) Alternative client-server organizations (a) (e)

36 Multitiered Architectures (2) An example of a server acting as a client

37 Modern Architectures An example of horizontal distribution of a Web service