Programming Assignment #3 Solution

Multiprocessing and File Statistics

 

A Unix systems programmer has the ability to fork/exec  binaries, to establish  pipes for synchronous communication between the processes executing those binaries,  and to use signals for asynchronous interaction between  those  processes.  This  permits  her to “reuse”  small utilities  to produce  more complex  functions.    This  is particularly useful  when  there  is no  source  available  for the  small utilities.

 

 

Components

 

 

This  assignment requires  that you  build  a  five process  system from  three  relatively  small  pro- grams.

 

 

The totalsize Program

 

The totalsize program  expects that its standard input  is a list of file names separated by “whites- pace”  (see the  isspace(3) manual  page).   For  all regular  files whose name  are  on its  stdin,  it computes  the total  size of all those files it can access. That total  size is sent to its standard output as a nicely formatted integer (a string  that looks like an integer,  actually). For example, suppose a directory  contains  the following files (the  -lu option  requests  a long directory  listing with time of last access shown):

 



-rwxr-xr-x
1
kearns
wheel
24576
Feb
23
13:51
a.out
-rw-r--r--
2
kearns
wheel
612
Feb
21
13:51
fileinfo.c
-rw-r--r--
2
kearns
wheel
612
Feb
21
13:51
link.c
lrwxrwxrwx
1
kearns
wheel
10
Feb
23
14:20
symlink.c - fileinfo.c
 
 
% ls -lu total 27

 

 

 

 

 

 

Below we show  the  invocation  of totalsize assuming  that the  above  directory  is the  current working directory:

 

% echo ". .. a.out fileinfo.c link.c symlink.c" | ./totalsize

25188

 

This  indicates  that there  are  25118 bytes  of storage  tied  up  in the  regular  files in the  list.   The directories  . and  .. are  not  regular  files; fileinfo.c, link.c, and  symlink.c all refer to  the same regular  file (the  first two are hard  links, and the last is a symbolic link).

If  the  UNITS environment  variable  has  value  "K" or  "k" when  totalsize is invoked,  then  the total  size of the named  regular  files in kilobytes is printed  as an integer  (truncate, don’t round  up) followed by the string  “kB.”

 

% export UNITS=K

% echo ". .. a.out fileinfo.c link.c symlink.c" | ./totalsize

24kB

% export UNITS=bogus

% echo ". .. a.out fileinfo.c link.c symlink.c" | ./totalsize

25188

 

If the  TSTALL environment variable  looks like a positive  non-zero integer,  then  totalsize should sleep for that many seconds before inputting a file name.

 

If the TMOM environment variable looks like a positive non-zero integer, then totalsize should treat the value as a pid and signal that pid with a SIGUSR1 after it has produced  all of its output

 

 

The accessed Program

 

Like totalsize, the  accessed program  takes  a list  of file names  on its  standard input.   It  also takes  a mandatory argument. The program  must  be invoked as

 

accessed num

 

where num is an integer.  If num is positive, accessed outputs, on its standard output, those regular files to which it has access which have not been accessed for num days.  For example, assuming that it is about  3 p.m.  on February 23:

 

% echo ". .. a.out fileinfo.c link.c symlink.c" | ./accessed 1 link.c

% echo ". .. a.out fileinfo.c link.c symlink.c" | ./accessed 5

%

 

When there  are multiple  links to a file, any (single) link will do as the name of the file.

 

If num is negative,  accessed outputs, on its standard output, those  regular  files to which it has access which have been  accessed within  num  days.   Again,  assuming  that it  is about  3 p.m.   on February 23:

 

% echo ". .. a.out fileinfo.c link.c symlink.c" | accessed -1 a.out

% echo ". .. a.out fileinfo.c link.c symlink.c" | accessed -5 a.out

link.c

 

A value of 0 for the integer argument is invalid.  A value that is too large or too small (i.e., negative)

to be represented on the system is also invalid.

 

The  Driver Program, report

 

The report program  will be responsible for creating  and interconnecting the other processes of this multiprocess  computation.

 

• It takes  a list of filenames on its stdin.

 

• It  creates  four  child  processes,  two  execute  the  totalsize binary  and  two  the  accessed

binary.

 

• Pipes  must  be established  so that report feeds the  file names  read  on its  stdin onto  the

stdin of both children  running  accessed.

 

• Pipes must be established  to bind the stdout of each accessed process onto the stdin of an associated  totalsize binary.

 

• Pipes must  be established  so that report can read the stdout of both totalsize children.

 

• The report program accepts a mandatory non-zero positive integer, num, as its first command line argument.  The  integer  specifies a duration in days.   The  first  accessed process  will essentially  be invoked as

 

accessed num

 

The second will essentially  be invoked as

 

accessed -num

 

The  net  effect is that the  first  accessed process should  output those  files which  have  not been accessed in num days.  The  second should output those  files which have been accessed in num days.

 

• It  accepts  an  optional  -k as  a  command  line  argument  that causes  it  to  display  all  size information  in kilobytes.

 

• It accepts an optional  -d as a command  line option.  If -d is asserted  the next command  line argument must  be a positive  non-zero integer  that specifies the  number  of seconds that the totalsize processes sleep before inputting a file name.

 

• After  writing  the  last  file name  onto  its  output pipes,  it  enters  a non- terminating loop in which it sleeps for 1 second and outputs an asterisk  on its standard output.

 

• Upon receipt  of a SIGUSR1 signal, it exits the loop, reads the output of the first totalsize process, and outputs a nicely formatted message.  It prints  a separator line (perhaps  hyphens or asterisks).   It  then  outputs a message incorporating the  stdout  of the  second totalsize process.

 

• On termination, no garbage  files or orphan  processes should be left on the system.

 

The  following figure shows how a running  system  should  appear.The heavy  lines connecting  the processes represent pipe-based  communication.

 

 

file list
0
0
accessed
1
0     totalsize     1
 
 

report
 
 
 
 
 
 
output
1
0
accessed
1
0
totalsize
1
 

 

 

In the context  of our example,  here are some executions  of the system:

 

% echo ". .. a.out fileinfo.c link.c symlink.c" | report 1 -d 2

******

A total of 612 bytes are in regular files not accessed for 1 days.

----------

A total of 24576 bytes are in regular files accessed within 1 days.

 

% echo ". .. a.out fileinfo.c link.c symlink.c" | report 5 -k

A total of 0kB are in regular files not accessed for 5 days.

----------

A total of 24kB are in regular files accessed within 5 days.

 

Note that the exact  number  of asterisks  is roughly proportional to the delay (if any).    1

 

 

 

Notes

 

 

The totalsize and accessed programs  must  be able to run as stand-alone binaries.  We will test them  in stand-alone mode before testing  the full-blown system  of five processes.

 

The TA will look at your source code to make sure you follow the termination protocol as specified (i.e.,  that one of the  totalsize processes  signals  report to  pull  it  out  of the  asterisk-printing loop).  You are well advised to make your source code neat  and readable.

 

You must  use the  fork() system  call and  any  of the  variants of the  exec() system  call/library function  that you choose.  This  implies that you may not  use the  system() and  popen() library functions  (or similar)  in this assignment.

 

All information  about  a file can  be obtained  from the  stat() system  call.  I will have  a special mini-lecture  on the use of stat() and computations that involve real time.

 

 

Due

 

 

The submission  deadline  is 11:59pm on Tuesday,  February 28.

 

You must structure your system to have three source files, report.c, totalsize.c, and accessed.c. Follow these steps to submit:

 

 tar zcvf system.tgz report.c totalsize.c accessed.c

This produces  a gzipped (compressed)  “tarball” consisting of your three  source files.

 

2.  gpg -r CSCI415 --sign -e system.tgz

This signs and encrypts  your gzipped tarball so the TA can retrieve  the submission.

 

3.  mv system.tgz.gpg ~; chmod 644 ~/system.tgz.gpg

This moves your submission  to your home directory  and protects  it so that it can be copied by the TA.