Howto check for other instances in C and kill already running ones

Karl Godt · 04-25-2013, 06:06 PM

In bash I would write something like this :

Code:

full_progname=`readlink -e "$0"`
base_progname="${full_progname##*/}"
ALL_PIDS=`pidof "$base_progname"`
pid_program=$$
PIDS_TO_KILL=`echo "$ALL_PIDS" | tr ' ' '\n' | grep -v -w "$pid_program"`
for a_pid in $PIDS_TO_KILL
do
kill -9 $a_pid
done

I have a line in C as

Code:

system("kill `pidof freememapplet | grep ' ' | cut -f 2 -d ' '`");

or

Code:

system("FREEMEMPIDS=`pidof -o $$ -o %PPID freememapplet`;for PiD in $FREEMEMPIDS;do kill $PiD;done");

which works as long as the new instance has a higher pid number as the former instance . $$ and %PPID also refer apparently to the system() call, not to the program .

/* The program "freememapplet" is a Puppy Linux specific tray application . */

These variables I am able to compute already :

Code:

char* PROGRAMNAME = argv[0];
pid_t pid;
int MYPID = getpid();
extern char *__progname;
printf("%s" " " "%s" "\n", PROGRAMNAME, __progname);
printf("%d" " " "%d" "\n", pid, MYPID );

sundialsvcs · 04-25-2013, 06:13 PM

What you should do is to attempt to lock a file (or some global named semaphore of some kind), and terminate if you can't get it ... because it means that there's another instance out there already running.

If you attempt to have one process "murder its rivals," there are all sorts of timing-hole problems associated with that (in addition to blood 'n guts .. very messy). But a process can atomically deduce that "it's not alone."