Section notes for 16 January 2007

Sections 101/102/103

GSI: Thomas Kho <cs162-ta@inst.eecs.berkeley.edu> / <tkho@eecs>

Based on notes by Hakim Weatherspoon and Karl Chen

Agenda

1. Introductions
2. Logistics
3. What is an OS?
4. HW1
5. CVS
   

• About me
  
• About you

Class logistics

• TA: Thomas Kho <cs162-ta@inst.eecs.berkeley.edu> or <tkho@eecs>
• Section notes: http://inst.eecs.berkeley.edu/~cs162-ta/
• Office hours: Tuesday 3-4, Thursday 4-6, 751 Soda, or by appointment.
• Class account forms distributed next week IN DISCUSSION
  
• Please use newsgroup for most things: ucb.class.cs162 (and search it via Google Groups!)
• Section 101 to be cancelled, please move to another discussion
  
• Textbook (use it as a reference; lecture notes are most important), 2 readers (Nachos + technical papers, available at Northside Copy Central)
  
• Homeworks (including taking lecture notes)
  
• 3 midterms, review before each midterm
  
• Nachos
• 4 projects, with have extra sessions for project overview
• Good experience
• Don't procrastinate!
• Why Java

• Great system, easy to use, makes OS development experimentation much easier than hacking a real OS 
• Runs on UNIX, Mac, Windows, etc - very portable
• Please, do not print the Nachos code, use your Reader!
• We will be using Java! 
• Mainly need to understand basics of language, classes, etc. (not all of the crazy APIs)
• You will not be using Java threads (directly) - so don't really need to understand them either
• Java/Nachos is on course web page - please download and read!

• Groups:
• Up to 5, extra credit for 1-2
• Peer evaluations - serious!
• Make groups now; email me (or post on newsgroup) for help

Projects Comments

• Plan realistic TIME in your project for: 
1. analysis
2. design
3. implementation
4. testing
5. documentation
• Not necessarily in the order above!

• START EARLY! You may have problems with getting Nachos, CVS, etc. working, especially first time
• Check due times - not always midnight - use 'submit' program
• You get a total of 5 slip days during the semester rounded up to next full day (so 12:00 midnight counts as 1 day if due at 11:59 the day before) No excuses for late work after you use your slip days!
• 'glookup' program to look up your grades

Project Phases

1. Design Document
• Example design documents available on web page
2. Design Meetings  - 15-20 minute design meeting with group, everyone in group MUST attend. Sign up online in a couple of weeks
3. Turn in code using 'submit'
4. Turn in group evaluations and final design docs usually the day after

CVS (CVS overview below)

• Groups must use CVS for sharing code during projects (and why not documentation)
• Great way to manage the project (and also serves to back up everything you do!)
• Short tutorial on CVS on course webpage

What is an OS?
• Coordinator
    • Resource allocation & management => concurrency (CPU, I/O)
    • Sharing & protection
• Extended machine
    • "Nice interface"
        • Standard functions - POSIX
    • File system
    • VM
    • Etc.

Program vs Process
------------------
• Play vs Script

Homework 1
==========

Event-driven simulation
• Event list
• Events: start job, stop job
• Each event on event list contains event time
• Advance clock to next event -- don't "tick"

• Get started on RR
• Will go over other scheduling algorithms (overview)
• Order: SRPT, SJF, SET, RR, FCFS

Generating hyperexponential random numbers
• R = new java.util.Random()
• U = R.nextDouble()
• exprand = (0.20)(-ln(U))

• U = R.nextDouble()
• if U < .8: exprand(0.20) else if U < .95 ...

Quick CVS Primer (also see http://inst.eecs.berkeley.edu/~cs162/fa06/Nachos/cvs.html)

• Basic model: Single REPOSITORY which stores the "master" version of the code, as well as all previous versions
• Users do NOT edit anything in the repository - rather, they "check out" a copy of the files, and edit that copy
• After making changes, you "commit" the changes back to the repository
• Other users only see those changes if they do an "update"

Basic CVS usage

• Repository will be created by each project group - stay tuned
• Repository should be readable ONLY to members of your group - so we will assign UNIX groups to you

1) Set your CVSROOT environment variable to point to the repository:

     setenv CVSROOT <repository dir>

   If you want to check the files out from a remote machine (say, over

   ssh), then you would use the following instead: 

      setenv CVSROOT cs162@torus:/home/ff/cs162/repository

      setenv CVS_RSH ssh

2) Check out a local copy of the files you want to edit. For example, to

   modify your project's Nachos code, you might do:

        cvs co nachos

   This will create a "nachos" directory with all of the Nachos code

   in it.

3) Edit your local copy of the files.

4) Commit the changes back to the repository:

        cvs commit

   This will start up an editor for you to enter a log entry describing

   your changes. PLEASE enter a descriptive entry of the changes you

   made -- this will make tracking changes a lot easier.

   Note that you cannot commit changes unless your local files are

   up to date: that is, that you have been editing the most recent copy.

   See next step...

5) For other users to see the changes, they need to do:

cvs update -d

   which will update their local files to be in sync with the repository.

   If there are conflicts (that is, someone else edited the same file

   while you were in the process of editing it), you will be notified at

   this point and given a chance to fix the conflict.

To add a file or directory to the repository, just do:

        cvs add filenames...

After 'cvs add' you need to 'cvs commit' for the addition to take

effect. 

Also: 'cvs import' to add a whole tree (e.g. the nachos code for the first

time):

  cvs import <tree-root> <placeholder> <placeholder>

To remove a file, first remove it from your local copy:

        rm filename

Then remove it from the CVS repository:

        cvs remove filename

        cvs commit

Other features: 

  - Can check out copy of code as it looked at a given time

      cvs co -D "yesterday" nachos

      cvs co -D "02/03/03 8:00" nachos

  - Can tag a version of the file for later use:

      cvs tag working1

      cvs co -r working1 nachos

  - Can look at changes:

      cvs log

      cvs diff -D "yesterday"

      cvs diff -r 1.3 foo.java

IMPORTANT CAVEATS:

Note that CVS does not allow you to rename files - you need to "remove"

the file and then "add" the file under the new name. In general it's

best not to rename files, since this loses all of the editing history

for that file.

Also note that CVS does not allow you to remove or rename directories

once they have been added to the repository. THIS IS VERY IMPORTANT!! Do

not add directories to the repository temporarily - you can never get

rid of them. This is a real drawback to CVS, but it's something you just

have to live with.