Re: New library: libpidfile.

From: Pawel Jakub Dawidek (pjd_at_FreeBSD.org)
Date: 08/24/05

  • Next message: Yar Tikhiy: "Re: New library: libpidfile." 
    Date: Wed, 24 Aug 2005 01:18:48 +0200
To: Peter Jeremy <PeterJeremy@optushome.com.au>

    On Tue, Aug 23, 2005 at 07:42:26PM +1000, Peter Jeremy wrote:
    +> On Tue, 2005-Aug-23 10:17:58 +0200, Pawel Jakub Dawidek wrote:
    +> >In my first concept (when it was part of libutil) I allocated memory
    +> >to store needed informations, because I didn't wanted to use preallocated
    +> >memory (someone linking libutil doesn't have to use pidfile
    +> >functionality).
    +>
    +> Since there's an initialisation function, why not just malloc whatever
    +> memory you need? You can either store the pointer in a local static
    +> or have pidfile_open() return it as an opaque pointer that the user
    +> has to pass into other pidfile_XXX functions.

    I added a handle, so now it goes like this:

            struct pidfh *pfh;
            pid_t otherpid, childpid;

            pfh = pidfile_open("/var/run/daemon.pid", 0644, &otherpid);
            if (pfh == NULL) {
                    if (errno == EEXIST)
                            errx(EXIT_FAILURE, "Daemon already running, pid: %d.", otherpid);
                    /* If we cannot create pidfile from other reasons, only warn. */
                    warn("Cannot open or create pidfile");
            }

            if (daemon(0, 0) == -1) {
                    warn("Cannot daemonize");
                    pidfile_remove(pfh);
                    exit(EXIT_FAILURE);
            }

            pidfile_write(pfh);

            for (;;) {
                    /* Do work. */
                    childpid = fork();
                    switch (childpid) {
                    case -1:
                            syslog(LOG_ERR, "Cannot fork(): %s.", strerror(errno));
                            break;
                    case 0:
                            pidfile_close(pfh);
                            /* Do child work. */
                            break;
                    default:
                            syslog(LOG_INFO, "Child %d started.", childpid);
                            break;
                    }
            }

            pidfile_remove(pfh);
            exit(EXIT_SUCCESS);

    I can't use atexit(3) anymore to remove pidfile, but I like it this way
    better, anyway.

    +> >It also now has 4 functions, which makes it a good candidate of small,
    +> >nice, lightweight library:)
    +>
    +> IMHO, 4 functions is too small. I would prefer to have a smaller
    +> number of larger libraries and think this belongs in an existing
    +> library - eg libutil. Whilst this may form a nice lightweight
    +> library, if everyone wrote small, lightweight libraries, linking
    +> an application would require a mile-long command line.

    I talked about this with few more guys and they agree it should be a
    part of libutil, so I moved it there.

    +> Can I suggest two enhancements:
    +> 1) Allow NULL to be passed to pidfile_open() to indicate that the
    +> pidfile should be in /var/run/PROCESS_NAME.pid (and/or if the
    +> name doesn't include any '/' then default to /var/run)

    I implemented NULL behaviour, but I'm not sure about the second thing.
    I'd like to avoid it.

    +> 2) Write a wrapper function that calls pidfile_open() and if it's
    +> successful, exec's the rest of the command line.

    There is simlar wrapper: lockf(1), so I'll not duplicate functionality,
    but I changed daemon(8) to use pidfile(3).

    Thanks for all suggestions. 

    -- 
Pawel Jakub Dawidek                       http://www.wheel.pl
pjd@FreeBSD.org                           http://www.FreeBSD.org
FreeBSD committer                         Am I Evil? Yes, I Am!

  • Next message: Yar Tikhiy: "Re: New library: libpidfile."

    Relevant Pages