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Programming Assignment 1 P1: A Process Manager (Pman) Solution
1 Goals
This assignment is designed to help you:
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get familiar with C programming,
get familiar with system calls related to process management,
get familiar with the process control block (PCB).
You are required to implement your solution in C (other languages are not allowed). Your work
will be tested on linux.csc.uvic.ca.
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Note: linux.csc.uvic.ca is a particular machine at the UVic Department of Computer Sci-
ence. It does not mean \any Linux machine" at UVic. Even more importantly, it does not mean any
\Unix-like" machine, such as a Mac OS X machine|many students have developed their programs
for their Mac OS X laptops only to nd that their code works di erently on linux.csc.uvic.ca
resulting in a substantial loss of marks.
You can remote access linux.csc.uvic.ca by ssh username@linux.csc.uvic.ca. SSH clients
are available for a wide variety of operating systems including Linux, Mac OS and Windows.
Be sure to study the man pages for the various systems calls and functions suggested in this
assignment. The system calls are in Section 2 of the man pages, so you should type (for example):
$ man 2 waitpid
2 Schedule
In order to help you nish this programming assignment on time, the schedule of this assignment
has been synchronized with both the lectures and the tutorials. There are three tutorials arranged
during the course of this assignment.
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Tutorial No.
Tutorial
Milestones
First
P1 spec go-through, design hints, system calls
design and code skeleton
Second
more on system programming and testing
alpha code done
Third
nal testing and last-minute help
nal deliverable
28 3 Requirements
29 3.1 Prompt for user input
Your PMan needs to show the prompt for user input. For example, when you run PMan by type in
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linux.csc.uvic.ca:/home/user$ ./PMan
It prompts
PMan:
for user input.
3.2 Background Execution of Programs
PMan allows a program to be started in the background|that is, the program is running, but PMan
continues to accept input from the user. You will implement a simpli ed version of background
execution that supports executing processes in the background.
If the user types: bg cat foo.txt, your PMan will start the command cat with the argument
foo.txt in the background. That is, the program will execute and PMan will also continue to
execute and give the prompt to accept more commands.
The command bglist will have PMan display a list of all the programs currently executing in
the background, e.g.,:
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/home/user/a1/foo
/home/user/a1/foo Total background jobs: 2
In this case, there are 2 background jobs, both running the program foo, the rst one with
process ID 123 and the second one with 456.
Your PMan needs to support the following commands:
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The command bgkill pid will send the TERM signal to the job with process ID pid to terminate that job.
The command bgstop pid will send the STOP signal to the job pid to stop (temporarily) that job.
The command bgstart pid will send the CONT signal to the job pid to re-start that job (which has been previously stopped).
See the man page for the kill() system call for details.
Your PMan must indicate to the user when background jobs have terminated. Read the man
page for the waitpid() system call. You are suggested to use the WNOHANG option.
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59 3.3 Status of Process
Your PMan needs to support a command pstat pid to list the following information related to
process pid, where pid is the Process ID.
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comm : The lename of the executable, in parentheses. This is visible whether or not the executable is swapped out.
state : One of the following characters, indicating process state: R (Running), S (Sleeping in an interruptible wait), D (Waiting in uninterruptible disk sleep), Z (Zombie), T (Stopped (on a signal) or (before Linux 2.6.33) trace stopped ), t (Tracing stop (Linux 2.6.33 onward)), W (Paging (only before Linux 2.6.0)), X (Dead (from Linux 2.6.0 onward)), x (Dead (Linux 2.6.33 to 3.13 only)), K (Wakekill (Linux 2.6.33 to 3.13 only)), W (Waking (Linux 2.6.33 to
3.13 only)), P (Parked (Linux 3.9 to 3.13 only)).
utime: Amount of time that this process has been scheduled in user mode, measured in clock ticks (divide by sysconf( SC CLK TCK)). This includes guest time, guest time (time spent running a virtual CPU, see below), so that applications that are not aware of the guest time eld do not lose that time from their calculations.
stime: Amount of time that this process has been scheduled in kernel mode, measured in clock ticks (divide by sysconf( SC CLK TCK)).
rss: Resident Set Size: number of pages the process has in real memory. This is just the pages which count toward text, data, or stack space. This does not include pages which have not been demand-loaded in, or which are swapped out.
voluntary ctxt switches: Number of voluntary context switches (since Linux 2.6.23).
nonvoluntary ctxt switches: Number of involuntary context switches (since Linux 2.6.23).
If process pid does not exist, PMan returns an error like:
Error: Process 1245 does not exist.
In the above example, 1245 is the pid value.
To summarize, your PMan should support the following commands: bg, bglist, bgkill,
bgstop, bgstart, and pstat. If the user types an unrecognized command, an error message is
given by PMan, e.g.,
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PMan: ttest
PMan: ttest: command not found
89 4 Deliveries and Marking Scheme
For your nal submission of each assignment you are required to submit your source code to connex
dropbox. You should include a readme le to tell TA how to compile and run your code. TAs are not
supposed to x the bugs, either in your source code or in your make le. If following your readme
le, the TAs cannot compile and run your code, you may get a zero mark for the assignment.
The marking scheme is as follows:
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Components
Weight
Make le
5
Error handling
10
bg
10
bglist
10
bgkill
10
95
bgstop
10
bgstart
15
pstat
20
Code style
5
Readme.txt
5
Total Weight
100
96 5 Odds and Ends
97 5.1 Implementation Hints
1. Use fork() and execvp() so that the parent process accepts user input and the child process
executes arbitrary commands.
2. Use a data structure (e.g., a linked list) to record the background processes.
3. Use the nproc pseudo- le system to nd out the information required by pstat. Note that
nproc is not a real le system, because all les have a size zero. The les just include a pointer
to process control block (PCB) in the OS kernel. Due to this reason, never try to write
anything into nproc!
5.2 Warning
Since you will use fork() in your assignment, it is important that you do not create a fork()
bomb, which easily eats up all the pid resources allocated to you. If this happens, you cannot log
into your account any more, even from a di erent machine. Both the instructor and the TAs cannot
help you out. You have to go to IT support asking them to kill your buggy process. Clearly, IT
support will not be happy if many students ask for such a help.
To avoid the mishap, you MUST use ulimit -u in bash to nd out the default max number
of user processes allocated to you (it is normally 50), and reduce this number to a safe value. For
instance, if the default max number of user processes is 50, you can use
% ulimit -u 35
to reduce this number to 35. Therefore, even if your code has a bug and has created a fork()
bomb, you still have unused 15 processes left and you can log in from a di erent machine to kill
the buggy process.
Please take this warning seriously!
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119 5.3 Compilation
You’ve been provided with a Makefile that builds the sample code (in p1s.tar.gz). It takes care
of linking-in the GNU readline library for you. The sample code shows you how to use readline()
to get input from the user, only if you choose to use the readline library.
5.4 Helper Programs
5.4.1 inf.c
This program takes two parameters:
tag: a single word which is printed repeatedly
interval: the interval, in seconds, between two printings of the tag
The purpose of this program is to help you with debugging background processes. It acts a trivial
background process, whose presence can be \felt" since it prints a tag (speci ed by you) every few
seconds (as speci ed by you). This program takes a tag so that even when multiple instances of it
are executing, you can tell the di erence between each instance.
This program considerably simpli es the programming of PMan which deals with re-starting,
stopping, and killing programs.
5.4.2 args.c
This is a very trivial program which prints out a list of all arguments passed to it.
This program is provided so that you can verify that your PMan passes all arguments supplied
on the command line|often, people have o -by-1 errors in their code and pass one argument less.
5.5 Code Quality
We cannot specify completely the coding style that we would like to see but it includes the following:
1. Proper decomposition of a program into subroutines (and multiple source code les when
necessary)|A 500 line program as a single routine won’t su ce.
2. Comment|judiciously, but not profusely. Comments also serve to help a marker, in addition
to yourself. To further elaborate:
(a) Your favorite quote from Star Wars or Douglas Adams’ Hitch-hiker’s Guide to the Galaxy
does not count as comments. In fact, they simply count as anti-comments, and will result
in a loss of marks.
(b) Comment your code in English. It is the o cial language of this university.
3. Proper variable names|leia is not a good variable name, it never was and never will be.
4. Small number of global variables, if any. Most programs need a very small number of global
variables, if any. (If you have a global variable named temp, think again.)
5. The return values from all system calls and function calls listed in the assignment
speci cation should be checked and all values should be dealt with appropriately.
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153 5.6 Plagiarism
This assignment is to be done individually. You are encouraged to discuss the design of your solution
with your classmates, but each person must implement their own assignment.
Your markers will submit the code to an automated plagiarism detection program.
We add archived solutions from previous semesters (a few years worth) to the plagia-
rism detector, in order to catch \recycled" solutions.
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The End
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