Lecture Operating systems: A concept-based approach (2/e): Chapter 10 - Dhananjay M. Dhamdhere

  
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Chapter 10: 
Message Passing

Dhamdhere: Operating Systems—
A Concept­Based Approach, 2 ed

Slide No: 1
Copyright © 2008


Message passing preliminaries

•  The sender process names the destination process and provides the message
•  The destination process specifies an area in which the message should be put

  

Chapter 10: 
Message Passing

Dhamdhere: Operating Systems—
A Concept­Based Approach, 2 ed

Slide No: 2
Copyright © 2008

Issues in message passing

•

Naming of processes
* Direct and indirect naming
 Direct: Process names are specified in send / receive
commands
 Indirect: Process names are inferred by the kernel
* Symmetric and asymmetric naming
 Symmetric: Both sender and receiver processes specify each
other’s names
 Asymmetric: Receiving process does not specify name of a
sender process

  

Chapter 10: 
Message Passing

Dhamdhere: Operating Systems—
A Concept­Based Approach, 2 ed

Slide No: 3
Copyright © 2008


Issues in message passing

•

Method for transferring messages
* Process executing a receive command is blocked until a message is
delivered
* The sender process may or may not be blocked until delivery
 Synchronous message passing: sender is blocked
» Simplifies message passing, saves memory
 Asynchronous message passing: sender is not blocked
* Order in which messages are delivered
* Handling of exceptions like non-existing processes, undeliverable
messages

  

Chapter 10: 
Message Passing

Dhamdhere: Operating Systems—
A Concept­Based Approach, 2 ed

Slide No: 4
Copyright © 2008


Issues in message passing

•

Kernel responsibilities

– Buffering of messages
* Kernel builds an interprocess message control block (IMCB)
* IMCB is stored in an appropriate data structure
 The message may be stored in IMCB or separately

– Blocking and unblocking of processes
* May be performed using event control blocks (ECBs)

  

Chapter 10: 
Message Passing

Dhamdhere: Operating Systems—
A Concept­Based Approach, 2 ed

Slide No: 5
Copyright © 2008


Interprocess message control block (IMCB)

  

Chapter 10: 
Message Passing

Dhamdhere: Operating Systems—
A Concept­Based Approach, 2 ed

Slide No: 6
Copyright © 2008


Lists of IMCBs pending delivery of messages

  

Chapter 10: 
Message Passing

Dhamdhere: Operating Systems—
A Concept­Based Approach, 2 ed

Slide No: 7
Copyright © 2008


Symmetric naming and blocking sends

(a) A process executes send and destination process has not executed receive
(b) A process executes receive and sender process has not executed send

  

Chapter 10: 
Message Passing

Dhamdhere: Operating Systems—
A Concept­Based Approach, 2 ed

Slide No: 8
Copyright © 2008


Symmetric naming and blocking sends

  

Chapter 10: 
Message Passing

Dhamdhere: Operating Systems—
A Concept­Based Approach, 2 ed

Slide No: 9
Copyright © 2008


Symmetric naming and blocking sends

  

Chapter 10: 
Message Passing

Dhamdhere: Operating Systems—
A Concept­Based Approach, 2 ed

Slide No: 10

Copyright © 2008


Mailbox

  

•  A mailbox has a name and is a repository of messages
•  Processes connect to a mailbox and send / receive messages from it

Chapter 10: 
Message Passing

Dhamdhere: Operating Systems—
A Concept­Based Approach, 2 ed

Slide No: 11
Copyright © 2008


Mailbox

•

Benefits of using a mailbox
– Anonimity of receiver
* A sender process need not know identity of receiver process

– Classification of messages
* A process can use numerous mailboxes, one for each kind of

message

  

Chapter 10: 
Message Passing

Dhamdhere: Operating Systems—
A Concept­Based Approach, 2 ed

Slide No: 12
Copyright © 2008


Use of mailboxes

•  An airline reservations process uses three mailboxes
─ book, enquire, receive
  
•  This way it can process cancellations followed by bookings followed by queries

Chapter 10: 
Message Passing

Dhamdhere: Operating Systems—
A Concept­Based Approach, 2 ed

Slide No: 13
Copyright © 2008

Message passing in Unix

  

    Pipe           Message queue                         Socket

•  A pipe is a FIFO mechanism, message queue is analogous to a mailbox
•  Socket is one end of a communication path in a Unix domain or  in the
   Internet domain
Chapter 10: 
Message Passing

Dhamdhere: Operating Systems—
A Concept­Based Approach, 2 ed

Slide No: 14
Copyright © 2008


Reservations server in Unix 5.4

•  Cancellation, booking and enquiry messages are assigned types 1, 2 and 3 resp
•  The msgrcv call returns a cancellation message, if present
  
•  If no cancellation messages exist, it returns a bookings message, if present, or
   an enquiry message
Chapter 10: 
Message Passing

Dhamdhere: Operating Systems—
A Concept­Based Approach, 2 ed

Slide No: 15
Copyright © 2008


Message passing in Windows

•

Overview of Windows features
– Local procedure call (LPC) for message passing between
processes located in the same computer
* Provides three types of message passing
 Small and large messages are sent using ports, where a port is
like a mailbox
» Small messages are stored in the port, large messages are
stored in section objects
 Quick LPC: A server creates a thread for each client. This
thread and the client use event pair objects to synchronize

  

Chapter 10: 
Message Passing

Dhamdhere: Operating Systems—
A Concept­Based Approach, 2 ed

Slide No: 16
Copyright © 2008