Transcript Operating System organization

A Brief Discussion on
Operating System Organization
CS-3013 & CS-502,
Summer 2006
Operating System Organization
1
The “THE” Operating System
System Operator
User Programs
I/O Management
Operator-Process Communication
Memory Management
Processes & Semaphores
Dijkstra, E. W., “The Structure of the ‘THE’-Multiprogramming System,”
Communications of ACM, vol.11, pp. 341-346, May 1968. (.pdf)
CS-3013 & CS-502,
Summer 2006
Operating System Organization
2
Operating System Organizations
• The literature in operating systems is full
of papers of simple, elegant systems like
this one
• Simple
• Easy to build and maintain by small teams
• Very instructive for study
• Limited usefulness
CS-3013 & CS-502,
Summer 2006
Operating System Organization
3
Question
• In a typical system, how do the layers or
components talk to each other?
• Answer: one of two ways
• Messages between processes
• Procedure/function calls between “modules”
CS-3013 & CS-502,
Summer 2006
Operating System Organization
4
Message-based systems
• Processes are isolated from each other –
separate address spaces, etc.
• IPC primitives
• Send Message (socket, content)
• Wait For Message (socket, &content)
• Requests, results, and status encoded in
message contents
• Static processes to manage resources,
create abstractions and layers
CS-3013 & CS-502,
Summer 2006
Operating System Organization
5
Message-based systems –
Typical Resource Manager
<internal data for managing resource>
while (true) {
ReceiveMessage (socket, &content)
switch (content.action) {
case action1: <do something & reply>
case action2: <do something else>
case action3: <hold pending some event>
case action4: <release previously held
action & reply>
...
}
}
CS-3013 & CS-502,
Summer 2006
Operating System Organization
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E.g., File Manager
void File_Manager(socket fileSocket) {
<internal data for managing files>
while (true) {
ReceiveMessage (fileSocket, &content)
switch (content.action) {
case write: <start or queue write operation>
case seek: <start or queue disk arm motion>
case read: <start or queue read operation>
case writeDone: <return acknowledgement>
case readDone: <return result of
previously started read operation>
...
}
}
}
CS-3013 & CS-502,
Summer 2006
Operating System Organization
7
Message-based systems
(continued)
• Resource manager
• Infinite loop
• Created at system start-up, assigned fixed sockets
• Effectively a critical section – one request or
activity is handled at a time
• Maintains internal data structures for queuing up
requests that cannot be replied to immediately
• No sharing of data with requesting processes
• Status information encoded in message content
• Reply to specific socket of requester
CS-3013 & CS-502,
Summer 2006
Operating System Organization
8
Message-based systems
(continued)
• Requested actions encapsulated in function – e.g.,
void read(file f, char *p, int len) {
socket s = new(socket);
content c = {f, readAction,len, s};
content r = {char c[len]);
SendMessage(fileManager, c);
WaitForMessage(s, &r);
strcpy(r.c, p, len);
}
• Examples
• MACH (Carnegie Mellon University)
• Mac OS-X
CS-3013 & CS-502,
Summer 2006
Operating System Organization
9
Procedure/Monitor-based
systems
• Resource Manager represented as a Monitor –
e.g.,
monitor class file {
<internal data for managing files>
void read(file f, char *p, int len);
void write(file f, char *p, int len);
void seek(file f, position);
...
}
• Requester makes direct function calls to monitor
• Implies monitor is same address space
CS-3013 & CS-502,
Summer 2006
Operating System Organization
10
Process/Monitor systems
• Resource manager
• Static object with functions; created at start-up
• Effectively a critical section – one request or
activity is handled at a time
• Maintains internal data structures for queuing up
requests that cannot be replied to immediately
• Shared address space, but internal data hidden
from requesters
• Status maintained in stack of requesting process
• Examples
• Pilot
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Summer 2006
Operating System Organization
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Requested Actions
• Monitor function calls look just like calls to
encapsulating functions in Message
system – E.g.,
– void read(file f, char *p, int len);
• May either send a message or enter a monitor!
• Caller does not know the difference
CS-3013 & CS-502,
Summer 2006
Operating System Organization
12
Observation
• There is really no fundamental difference
between systems organized by messages
and those organized by monitors
• Choice depends upon what is available in
underlying system
• Shared or separate address spaces
• Language support for monitor discipline
•…
Lauer, H.C. and Needham, R.M., “On the Duality of
Operating System Structures,” Operating Systems
Review, vol 13, #2, April 1979, pp. 3-19. (.pdf)
CS-3013 & CS-502,
Summer 2006
Operating System Organization
13
Next Topic
CS-3013 & CS-502,
Summer 2006
Operating System Organization
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