16. Inter-process communications

Make 16_IPC directory. Code must reside here.

Use lecture examples and modify them

0. processes

   • ps -ef / pstree / ps axu (BSD-style format) / ps xf (BSD style own process only)

   • pidof program

   • ls /proc

   • kill proc / kill -STOP proc / kill -HUP proc (use two terminals)

1. proc.c that waits forever, periodically printfs it's PID via getpid and increased counter. A parameter defines timeout between printfs

   • ./proc 5 printfs once a 5 seconds (using sleep something like

     26475: 0
     26475: 1
     26475: 2
     …

2. killn.c to send a signal

   • use /bin/kill -l | head -16 and edit it's output to create signal names array

     • challenge: use sed s/regexp/replacement/ to eliminate handwork (spoiler here: /bin/kill -l | head -16 | sed 's/\(.*\)/"\1",/ )

     • much uglier version that does all:

       /bin/kill -l | head -16 | sed 's/\(.*\)/"\1",/;1s/^/char *names[]={"NONE", /;$s/,$/};/' | tr '\n' ' '

   • ./killn PID NAME sends PID process signal NAME

   • see kill

   • use perror if error occurred

   • print "No such signal" if NAME isn't found and returns 1 instead of 0

   • try to ./killn running proc 4, non-existent process, foreign process

3. Copy proc.c to catch.c and modify it, adding a signal handler

   • ./catch 5 SIGNAL_NAME1 SIGNAL_NAME2 … should print corresponded signals' description (via strsignal) when catching a signal instead of falling off (still printing messages once a 5 seconds)

     • note not all signals can be handled

        1 $ ./catch 5 INT ABRT SEGV
        2 26775: 0
        3 ^C[Caught: Interrupt]26775: 1
        4 26775: 2
        5 [Caught: Segmentation fault]26775: 3
        6 26775: 4
        7 26775: 5
        8 [Caught: Aborted]26775: 6
        9 26775: 7
       10 Illegal instruction
       11 $
     

        1 $ kill -SEGV 26775
        2 $ kill -ABRT 26775
        3 $ kill -ILL 26772
     

4. Join catch.c with child-control program from lecture, name the result childctl.c.

   • ./childctl timeout signalQ signal1 … signaln should:

     • print a message once in timeout seconds

     • catch signal1 … signaln and print message

     • peacefully exit when got signalQ

H/W

Modify last program to:

• Exit after getting signalQ three times

• Check every syscall return values on error state