Chapter 4.1 Message Passing Communication

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Chapter 4.1Message Passing Communication

• Prepared by
• Karthik V Puttaparthi
• kputtaparthi1_at_student.gs
  u.edu

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OUTLINE

• Interprocess Communication
• Message Passing Communication
• Basic Communication Primitives
• Message Design Issues
• Synchronization and Buffering
• References

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INTERPROCESS COMMUNICATION

• Processes executing concurrently in the operating
  system may be either independent or cooperating
  processes.
• Reasons for providing an environment that allows
  process cooperation.
• 1) Information Sharing
• Several users may be interested in the
  same piece of information.
• 2) Computational Speed up
• Process can be divided into sub tasks
  to run faster, speed up can be achieved if the
  computer has multiple processing elements.
• 3) Modularity
• Dividing the system functions into
  separate processes or threads.
• 4) Convenience
• Even an individual user may work on
  many tasks at the same time.

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COMMUNICATION MODELS

• Cooperating processes require IPC
  mechanism that allow them to exchange data and
  information. Communication can take place either
  by Shared memory or Message passing Mechanisms.
• Shared Memory
• 1) Processes can exchange information by
• reading and writing data to the shared region.
• 2) Faster than message passing as it can be
• done at memory speeds when within a computer.
• 3) System calls are responsible only to establish
• shared memory regions.
• Message Passing
• Mechanism to allow processes to communicate and
• synchronize their actions without sharing the
  same
• address space and is particularly useful in
  distributed

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Message Passing Communication

• Messages are collection of data objects and their
  structures
• Messages have a header containing system
  dependent control information and a message body
  that can be fixed or variable size.
• When a process interacts with another, two
  requirements
• have to be satisfied.
• Synchronization and Communication.
• Fixed Length
• Easy to implement
• Minimizes processing and storage overhead.
• Variable Length
• Requires dynamic memory allocation, so
• fragmentation could occur.

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Basic Communication Primitives

• Two generic message passing primitives for
  sending and receiving messages.
• send (destination, message)
• receive (source, message) source
  or dest process name, link, mailbox, port
• Addressing - Direct and Indirect
• 1) Direct Send/ Receive communication primitives
• Communication entities can be addressed by
  process names (global process identifiers)
• Global Process Identifier can be made unique
  by concatenating the network host address with
  the locally generated process id. This scheme
  implies that only one direct logical
  communication path exists between any pair of
  sending and receiving processes.
• Symmetric Addressing Both the processes have to
  explicitly name in the communication primitives.
• Asymmetric Addressing Only sender needs to
  indicate the recipient.
  
  

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• 2) Indirect Send/ Receive communication
  primitives
• Messages are not sent directly from sender
  to receiver, but sent to shared data structure.
• Multiple clients might
  request services
• 
  from one of multiple
  servers. We use mail boxes.
• Abstraction of a finite size FIFO queue
  maintained by kernel.

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Synchronization and Buffering

• These are the three typical combinations.
• 1) Blocking Send, Blocking Receive
• Both receiver and sender are blocked
  until the message is delivered. (provides tight
  synchronization between processes)
• 2) Non Blocking Send, Blocking Receive
• Sender can continue the execution after
  sending a message, the receiver is blocked until
  message arrives. (most useful combination)
• 3) Non Blocking Send, Non Blocking Receive
• Neither party waits.

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Message Synchronization Stages

• Sender source network
  destination receiver
• 1 2 message
  3
  4 request
• 8
  7 ack
  6
  5 reply
• Message passing depends on Synchronization at
  several points.
• When sending a message to remote destination, the
  message is passed to sender system kernel which
  transmits it to communication network.
• Non blocking Send 18
• Sender process
  is released after message has been composed and
  copied into senders kernel.

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Message Design Issues

• Synchronization
• Blocking vs. Non-blocking
• Addressing
• Direct
• Indirect
• Message transmission
• Through value
• Through reference
• Format
• Content
• Length
• Fixed
• Variable
• Queuing discipline
• FIFO
• Priority

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The Producer Consumer Problem

• The producer-consumer problem illustrates the
  need for synchronization in systems where many
  processes share a resource. In the problem, two
  processes share a fixed-size buffer. One process
  produces information and puts it in the buffer,
  while the other process consumes information from
  the buffer. These processes do not take turns
  accessing the buffer, they both work
  concurrently. Herein lies the problem. What
  happens if the producer tries to put an item into
  a full buffer? What happens if the consumer tries
  to take an item from an empty buffer?

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Producer
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Consumer
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Pipe Socket APIs

• More convenient to the users and to the system if
  the communication is achieved through a well
  defined set of standard APIs.
• Pipe
• Pipes are implemented with finite size, FIFO byte
  stream buffer maintained by the kernel.
• Used by 2 communicating processes, a pipe serves
  as unidirectional communication link so that one
  process can write data into tail end of pipe
  while another process may read from head end of
  the pipe.
• Pipe is created by a system call which returns 2
  file descriptors, one for reading and another for
  writing.
• Pipe concept can be extended to include messages.
• For unrelated processes, there is need to
  uniquely identify a pipe since pipe descriptors
  cannot be shared. So concept of Named pipes.
• With a unique path name, named pipes can be
  shared among disjoint processes across different
  machines with a common file system.

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SOCKETS

• A Socket is a communication end point of a
  communication link managed by the transport
  services.
• It is not feasible to name a communication
  channel across different domains.
• A Communication channel can be visualized
  as a pair of 2 communication endpoints.
• Sockets have become most popular message passing
  API.
• Most recent version of the Windows Socket
  which is developed by WinSock Standard Group
  which has 32 companies (including Microsoft) also
  includes a SSL (Secure Socket Layer) in the
  specification.
• The goal of SSL is to provide
• Privacy in socket communication by using
  symmetric cryptographic data encryption.
• Integrity in socket data by using message
  integrity check.
• Authenticity of servers and clients by
  using asymmetric public key cryptography.

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References

• Operating System Concepts, Silberschatz, Galvin
  and Gange 2002
• Sameer Ajmani Automatic Software Upgrades for
  Distributed Systems'' Ph.D. dissertation, MIT,
  Sep. 2004
• Message passing information from The University
  of Edinburgh
• MPI-2 standards beyond the message-passing
  modelLusk, E.Massively Parallel Programming
  Models, 1997. Proceedings. Third Working
  Conference on12-14 Nov. 1997 Page(s)43 - 49
  Digital Object Identifier 10.1109/MPPM.1997.71596
  0
• A. N. Bessani, M. Correia, J. S. Fraga, and L. C.
  Lung. Sharing memory between Byzantine processes
  using policy-enforced tuple spaces. In
  Proceedings of the 26th International Conference
  on Distributed Computing Systems, July 2006
• A multithreaded message-passing system for high
  performance distributed computing
  applicationsPark, S.-Y. Lee, J. Hariri,
  S.Distributed Computing Systems, 1998.
  Proceedings. 18th International Conference
  on26-29 May 1998 Page(s)258 - 265 Digital
  Object Identifier 10.1109/ICDCS.1998.679521
• A message passing standard for MPP and
  workstations J. J. Dongarra, S. W. Otto, M. Snir,
  and D. Walker, CACM, 39(7), 1996, pp. 84-90
• N. Alon, M. Merrit, O. Reingold, G. Taubenfeld,
  and R. Wright. Tight bounds for shared memory
  systems acessed by Byzantine processes.
  Distributed Computing, 18(2)99109, 2005

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References

• Lessons for massively parallel applications on
  message passing computersFox, G.C.Compcon
  Spring '92. Thirty-Seventh IEEE Computer Society
  International Conference, Digest of Papers.24-28
  Feb. 1992 Page(s)103 - 114 Digital Object
  Identifier 10.1109/CMPCON.1992.186695
• An analysis of message passing systems for
  distributed memory computersClematis, A.
  Tavani, O.Parallel and Distributed Processing,
  1993. Proceedings. Euromicro Workshop on27-29
  Jan. 1993 Page(s)299 - 306 Digital Object
  Identifier 10.1109/EMPDP.1993.336388
• An analysis of message passing systems for
  distributed memory computersClematis, A.
  Tavani, O.Parallel and Distributed Processing,
  1993. Proceedings. Euromicro Workshop on27-29
  Jan. 1993 Page(s)299 - 306 Digital Object
  Identifier 10.1109/EMPDP.1993.336388

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Thank You!