1. CS533 Concepts of Operating Systems On the Duality of Operating System Structures
Hugh Lauer
Xerox Corporation
Roger Needham
Cambridge University
Presented by Thanh Dang
Acknowledgements: Yahia Mahmoud, Jonathan Walpole

2. CS533 - Concepts of Operating Systems
What the paper is about?
CS533 - Concepts of Operating Systems

3. CS533 - Concepts of Operating Systems
Outlines
Concepts
Duality: What “=“ means?
Operating System Structures
Messasge-oriented vs. procedure-oriented
Observations on duality
Duality mapping
Logically identical
Identical performance
Implications
Comments
CS533 - Concepts of Operating Systems

4. CS533 - Concepts of Operating Systems
Duality (Optimization): The solution of one is also the solution of another.
Two systems are dual if they
From outside
Are logically identical to each other
Have identical performance.
From inside
Have primitives defined by one can be mapped directly into the other
Have Primitive operations of one are as efficient as the other
CS533 - Concepts of Operating Systems

5. Are operating systems dual?
CS533 - Concepts of Operating Systems

6. Models of operating systems
How do processes communicate and synchronize?
Message passing : Message-oriented model
Small number of big processes
Explicit message channels
Identification of the context of execution with processes
Shared memory : Procedure-oriented system
Large number of small processes
Direct sharing and interlocking of data
Identification of the context of execution with functions
CS533 - Concepts of Operating Systems

7. Message-oriented system
Synchronization: Message queue
Data passed by reference
Peripheral devices are processes
Static context, no global naming
Process creation and deletion are difficult
CS533 - Concepts of Operating Systems

8. Message-oriented model
CS533 - Concepts of Operating Systems

9. Message-oriented model
CS533 - Concepts of Operating Systems

10. Message-oriented model
Messages, message identifiers
Message channels, message ports
SendMessage[ messageChannel, messageBody ]
returns[ messageId ]
AwaitReply[ messageId ] returns [ messageBody ]
WaitForMessage[ set of messagePort ] returns [ messageBody, messageld, messagePort ]
SendReply[ messageId, messageBody ]
Process declaration
CreateProcess
CS533 - Concepts of Operating Systems

11. Procedure-oriented system
Synchronization: process waiting for lock
Data shared among processes
“interrupts” from peripheral devices – locks or shared data
Global naming
Process creation and deletion are cheap
CS533 - Concepts of Operating Systems

12. Procedure-oriented model
CS533 - Concepts of Operating Systems

13. Procedure-oriented model
CS533 - Concepts of Operating Systems

14. Procedure-oriented model
Procedures, process identifiers
Procedure call facilities, synchronous and asynchronous
processld <- FORK procedureName[ parameterList ]
[ resultList ] <- JOIN processld
Modules and monitors
Module instantiation with NEW and START
Condition variables
WAIT conditionVariable
SIGNAL condition Variable
CS533 - Concepts of Operating Systems

15. CS533 - Concepts of Operating Systems
Duality: The solution of one is also the solution of another.
Two systems are duality if
From outside
Logically identical to each other
Identical performance.
From inside
Primitives defined by one can be mapped directly into the other one
Primitive operations of one is as efficient as the dual model.
CS533 - Concepts of Operating Systems

16. Observation 1: Duality Mapping
Message-oriented system
Procedure-oriented system
Processes, CreateProcess
message channels message
message ports
SendMessage; AwaitReply (immediate)
SendMessage;... AwaitReply (delayed)
SendReply
main message loop
arms of the case statement selective
waiting for messages
monitors, NEW/START External
procedure identifiers ENTRY
procedure identifiers simple
procedure call
FORK; . . .JOIN
RETURN (from procedure) monitor
lock, ENTRY attribute
ENTRY procedure declarations
condition variables, WAIT, SIGNAL
CS533 - Concepts of Operating Systems

17. Observation 2: Logically identical
Control structures are directly translated
No algorithms are changed
No data structures are replaced
Semantic content is invariant
Logic of the program is preserved
CS533 - Concepts of Operating Systems

18. Observation 3: Identical performance
Performance P = E + S + Q
E: Execution time of the program
Same data structure, same operations
S: System call overhead
Method calls = message sends
Process switching can be equally fast
Virtual memory and paging can be equally fast
Q: Queuing and waiting time
Message queuing = lock queuing
CS533 - Concepts of Operating Systems

19. CS533 - Concepts of Operating Systems
Outlines
Concepts
Duality: What “=“ means?
Operating System Structures
Messasge-oriented vs. procedure-oriented
Duality
Program Similarity
Performance
Implications
Comments
CS533 - Concepts of Operating Systems

20. CS533 - Concepts of Operating Systems
Implications
No model is inherently preferable
Choosing one or another depends on
Machine structure
Not application
CS533 - Concepts of Operating Systems

21. CS533 - Concepts of Operating Systems
Other comments
Empirical analysis but refer to only a few practical operating systems
Informal arguments, not sure if formal and rigorous proof is possible
A mechanism which has no dual: Good or Bad?
Unclear if it is still true when we have a zoo of operating systems nowadays – empirical data is different. Has time already proved if they are correct?
CS533 - Concepts of Operating Systems