Code as Exemplar

Reasons

Strategy

Example: tail -f (NetBSD)

        while ((ch = getopt(argc, argv, "b:c:fn:r")) != -1)
                switch(ch) {
                [...]
                case 'f':
                        fflag = 1;
                        break;
                }

[...]

        for (;;) {
                while ((ch = getc(fp)) != EOF)
                        if (putchar(ch) == EOF)
                                oerr();
                [...]
                if (!fflag)
                        break;
                /*
                 * We pause for one second after displaying any data that has
                 * accumulated since we read the file.  Since sleep(3) takes
                 * eight system calls, use select() instead.
                 */
                second.tv_sec = 1;
                second.tv_usec = 0;
                if (select(0, NULL, NULL, NULL, &second) == -1)
                        err(1, "select: %s", strerror(errno));
                clearerr(fp);
        }

Example: tail -f (FreeBSD)

        if (fflag) {
                kq = kqueue();
                if (kq < 0)
                        err(1, "kqueue");
                action = ADD_EVENTS;
        }
        for (;;) {
                while ((ch = getc(fp)) != EOF)
                        if (putchar(ch) == EOF)
                                oerr();
[...]
                if (! fflag)
                        break;
                clearerr(fp);

                switch (action) {
                case ADD_EVENTS:
                        n = 0;
                        ts.tv_sec = 0;
                        ts.tv_nsec = 0;

                        if (Fflag && fileno(fp) != STDIN_FILENO) {
                                EV_SET(&ev[n], fileno(fp), EVFILT_VNODE,
                                    EV_ADD | EV_ENABLE | EV_CLEAR,
                                    NOTE_DELETE | NOTE_RENAME, 0, 0);
                                n++;
                        }
                        EV_SET(&ev[n], fileno(fp), EVFILT_READ,
                            EV_ADD | EV_ENABLE | EV_CLEAR, 0, 0, 0);
                        n++;

                        if (kevent(kq, ev, n, NULL, 0, &ts) < 0) {
                                action = USE_SLEEP;
                        } else {
                                action = USE_KQUEUE;
                        }
                        break;
kqueue, kevent - kernel event notification mechanism

Creative Commons License  Last change: Saturday, March 13, 2004 12:46 am
 Unless otherwise expressly stated, all original material on this page created by Diomidis Spinellis is licensed under a Creative Commons Attribution-Share Alike 3.0 Greece License.