In C how can i have only one instance of it running



mayank

Hi ...

Not having a coding example handy, but you
could do a system( ps ) [on my box this
( ps -Ac --no-headers | grep your_progs_name )
would provide the desired information] and
terminate if it's already running?

Cheers,
Tink

It maybe a bit of a workaround, but could you make your program create a certain file as soon as it starts in /tmp or /var/run. And check before if the file exists, and if it does exit (as not to start another instance).

A good way to do this, is to open the file from the start of the program and not closing it anywhere. Instead delete (unlink) it immediately after opening.
The file will then be deleted when the program exits, or when it's killed. This way the file will also be deleted if the program is killed some day. And also it wouldn't matter is another program tries to delete it, while your program is running.

Instead of creating a lock file, I believe a better method
(under UNIX) is to use a semaphore -- with options that
the starting program creates a semaphore and that the
semaphore will allow only one program to increment it.
Dying program will clear its increment, so it will automagically
make the next program startup possible.
The SEM_UNDO option should be used for auto-clear of the
semop() increment on process exit.

Another possibility is indeed to create a file with the
pid of the process in it.
Any other process may open this file and check if the
process with given pid is still running. If not, it will remove
the file and will re-create it with own pid.
To avoid theoretically possible startup of more than one
process "at the *same* time", one should provide an
exclusive lock to the file.

-z

Thanks all for the answers and providing help


mayank johri