CSSE 444: Concurrent

1
CSSE 444 Concurrent Distributed Systems

• Dr. Yingwu Zhu
• Office ENGR 530 Phone [phone] Email
  zhuy_at_seattleu.edu
• Web http//fac-staff.seattleu.edu/zhuy

2
Brief Bio

• PhD in CSE, University of Cincinnati, 2005
• MS., BS. in CS, Huazhong University of Science
  Technology
• MCSE (Microsoft Certified Software Engineer)
• 3-year Software Engineer and Project Manager in
  industry
• Publications papers in top Journals and
  Conferences
• http//fac-staff.seattleu.edu/zhuy
• Research Peer-to-peer(P2P) systems,
  file/storage systems, distributed systems,
  networking
• Teaching Data Structures, C/C, Advanced
  topics in OS, Concurrent Distributed Systems

3
What can you learn in this course?

• Two main threads
• Basic concepts in distributed systems
• Communications, naming, reliability,
  availability, consistency, security, etc.
• Practical projects in network programming
  (TCP/UDP), http client/server models, processes
  and threads communications

4
Syllabus

• Access the syllabus on my homepage

5
OITLNX Account

• OITLNX will be the server where you do the
  programming assignments/projects
• If you do NOT have an account, contact HelpDesk
  ASAP!
• Programming related docs in my website

6
My Questions?

• Q1 Do you have experiences in socket
  programming?
• Q2 Do you have experiences in process
  communications?
• Q3 Do you have experiences in thread
  programming?
• Q4 Do you have knowledge in computer networks?

7
My Office Hours

• 130-230PM MWF
• Or Anytime as long as I am in office (Generally I
  am in office every week day ?)

8
Introduction

• Chapter 1

9
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.
• Two aspects
• Hardware machines are autonomous
• Software Users think it is a single system

10
Definition of a Distributed System (2)
1.1
A distributed system organized as
middleware.Note that the middleware layer
extends over multiple machines.
11
Goals of Distributed Systems

• Connecting users and resources
• Access remote resources, e.g., files, printers,
  etc
• Share local resources with other users in a
  controlled way
• Transparency
• Hide that fact that processes and resources are
  physically distributed across multiple computers
• Different forms of transparency

12
Transparency in a Distributed System
Transparency Description
Access Hide differences in data representation and how a resource is accessed
Location Hide where a resource is located
Migration Hide that a resource may move to another location
Relocation Hide that a resource may be moved to another location while in use
Replication Hide that a resource is replicated
Concurrency Hide that a resource may be shared by several competitive users
Failure Hide the failure and recovery of a resource
Persistence Hide whether a (software) resource is in memory or on disk
Different forms of transparency in a distributed
system.
13
Openness

• Definition A system that offers services
  according to standard rules that describe the
  syntax and semantics of those services
• Interoperability
• Portability

14
Scalability

• How to measure scalability of a system?
• By system size scale to more users and resources
  added to the system
• By geography geographically scalable in that
  users and resources are distributed across the
  Internet
• By administration administratively scalable,
  spanning many independent administrative
  organizations

15
Scalability Problems
Concept Example
Centralized services A single server for all users
Centralized data A single on-line telephone book
Centralized algorithms Doing routing based on complete information
Examples of scalability limitations.
16
Scaling Techniques (1)
1.4

• The difference between letting
• a server or
• a client check forms as they are being filled

17
Scaling Techniques (2)
1.5
An example of dividing the DNS name space into
zones.
18
Hardware Concepts
1.6
Different basic organizations and memories in
distributed computer systems
19
Multiprocessors (1)
1.7

• A bus-based multiprocessor.

20
Multiprocessors (2)
1.8

1. A crossbar switch
2. An omega switching network

21
Homogeneous Multicomputer Systems
1-9

1. Grid
2. Hypercube

22
Software Concepts
System Description Main Goal
DOS Tightly-coupled operating system for multi-processors and homogeneous multicomputers Hide and manage hardware resources
NOS Loosely-coupled operating system for heterogeneous multicomputers (LAN and WAN) Offer local services to remote clients
Middleware Additional layer atop of NOS implementing general-purpose services Provide distribution transparency

• An overview of
• DOS (Distributed Operating Systems)
• NOS (Network Operating Systems)
• Middleware

23
Uniprocessor Operating Systems
1.11

• Separating applications from operating system
  code through
• a microkernel.

24
Multiprocessor Operating Systems (1)
monitor Counter private int count
0 public int value() return count void
incr () count count 1 void decr()
count count 1

• A monitor to protect an integer against
  concurrent access.

25
Multiprocessor Operating Systems (2)
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

• A monitor to protect an integer against
  concurrent access, but
• blocking a process.

26
Multicomputer Operating Systems (1)
1.14

• General structure of a multicomputer operating
  system

27
Multicomputer Operating Systems (2)
1.15

• Alternatives for blocking and buffering in
  message passing.

28
Multicomputer Operating Systems (3)
Synchronization point Send buffer Reliable comm. guaranteed?
Block sender until buffer not full Yes Not necessary
Block sender until message sent No Not necessary
Block sender until message received No Necessary
Block sender until message delivered No Necessary

• Relation between blocking, buffering, and
  reliable communications.

29
Distributed Shared Memory Systems (1)

1. Pages of address space distributed among four
   machines
2. Situation after CPU 1 references page 10
3. Situation if page 10 is read only and replication
   is used

30
Distributed Shared Memory Systems (2)
1.18

• False sharing of a page between two independent
  processes.

31
Network Operating System (1)
1-19

• General structure of a network operating system.

32
Network Operating System (2)
1-20

• Two clients and a server in a network operating
  system.

33
Network Operating System (3)
1.21

• Different clients may mount the servers in
  different places.

34
Positioning Middleware
1-22

• General structure of a distributed system as
  middleware.

35
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.

36
Comparison between Systems
Item Distributed OS Distributed OS Network OS Middleware-based OS
Item Multiproc. Multicomp. Network OS Middleware-based 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

• A comparison between multiprocessor operating
  systems, multicomputer operating systems, network
  operating systems, and middleware based
  distributed systems.

37
Clients and Servers
1.25

• General interaction between a client and a server.

38
An Example Client and Server (1)

• The header.h file used by the client and server.

39
An Example Client and Server (2)

• A sample server.

40
An Example Client and Server (3)
1-27 b

• A client using the server to copy a file.

41
Processing Level
1-28

• The general organization of an Internet
  search engine into three different layers

42
Multitiered Architectures (1)
1-29

• Alternative client-server organizations (a) (e).

43
Multitiered Architectures (2)
1-30

• An example of a server acting as a client.

44
Modern Architectures
1-31

• An example of horizontal distribution of a Web
  service.