source: BAORadio/libindi/v1.0.1/eventloop.c@ 674

#if 0
    INDI
    Copyright (C) 2003 Elwood C. Downey

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Lesser General Public
    License as published by the Free Software Foundation; either
    version 2.1 of the License, or (at your option) any later version.

    This library is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public
    License along with this library; if not, write to the Free Software
    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA

#endif

/* suite of functions to implement an event driven program.
 *
 * callbacks may be registered that are triggered when a file descriptor
 *   will not block when read;
 *
 * timers may be registered that will run no sooner than a specified delay from
 *   the moment they were registered;
 *
 * work procedures may be registered that are called when there is nothing
 *   else to do;
 *
 #define MAIN_TEST for a stand-alone test program.
 */

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>
#include <time.h>
#include <sys/types.h>
#include <sys/time.h>
#include <unistd.h>

#include "eventloop.h"

/* info about one registered callback.
 * the malloced array cback is never shrunk, entries are reused. new id's are
 * the index of first unused slot in array (and thus reused like unix' open(2)).
 */
typedef struct {
    int in_use;                         /* flag to mark this record is active */
    int fd;                             /* fd descriptor to watch for read */
    void *ud;                           /* user's data handle */
    CBF *fp;                            /* callback function */
} CB;
static CB *cback;                       /* malloced list of callbacks */
static int ncback;                      /* n entries in cback[] */
static int ncbinuse;                    /* n entries in cback[] marked in_use */
static int lastcb;                      /* cback index of last cb called */

/* info about one registered timer function.
 * the entries are kept sorted by decreasing time from epoch, ie,
 *   the next entry to fire is at the end of the array.
 */
typedef struct {
    double tgo;                         /* trigger time, ms from epoch */
    void *ud;                           /* user's data handle */
    TCF *fp;                            /* timer function */
    int tid;                            /* unique id for this timer */
} TF;
static TF *timef;                       /* malloced list of timer functions */
static int ntimef;                      /* n entries in ntimef[] */
static int tid;                         /* source of unique timer ids */
#define EPOCHDT(tp)                     /* ms from epoch to timeval *tp */  \
        (((tp)->tv_usec)/1000.0 + ((tp)->tv_sec)*1000.0)

/* info about one registered work procedure.
 * the malloced array wproc is never shrunk, entries are reused. new id's are
 * the index of first unused slot in array (and thus reused like unix' open(2)).
 */
typedef struct {
    int in_use;                         /* flag to mark this record is active */
    void *ud;                           /* user's data handle */
    WPF *fp;                            /* work proc function function */
} WP;
static WP *wproc;                       /* malloced list of work procedures */
static int nwproc;                      /* n entries in wproc[] */
static int nwpinuse;                    /* n entries in wproc[] marked in-use */
static int lastwp;                      /* wproc index of last workproc called*/

static void runWorkProc (void);
static void callCallback(fd_set *rfdp);
static void checkTimer();
static void oneLoop(void);
static void deferTO (void *p);

/* inf loop to dispatch callbacks, work procs and timers as necessary.
 * never returns.
 */
void
eventLoop()
{
        /* run loop forever */
        while (1)
            oneLoop();
}

/* allow other timers/callbacks/workprocs to run until time out in maxms
 * or *flagp becomes non-0. wait forever if maxms is 0.
 * return 0 if flag did flip, else -1 if never changed and we timed out.
 * the expected usage for this is for the caller to arrange for a T/C/W to set
 *   a flag, then give caller an in-line way to wait for the flag to change.
 */
int
deferLoop (int maxms, int *flagp)
{
        int toflag = 0;
        int totid = maxms ? addTimer (maxms, deferTO, &toflag) : 0;

        while (!*flagp) {
            oneLoop();
            if (toflag)
                return (-1);    /* totid already dead */
        }

        if (totid)
            rmTimer (totid);
        return (0);
}

/* allow other timers/callbacks/workprocs to run until time out in maxms
 * or *flagp becomes 0. wait forever if maxms is 0.
 * return 0 if flag did flip, else -1 if never changed and we timed out.
 * the expected usage for this is for the caller to arrange for a T/C/W to set
 *   a flag, then give caller an in-line way to wait for the flag to change.
 */
int
deferLoop0 (int maxms, int *flagp)
{
        int toflag = 0;
        int totid = maxms ? addTimer (maxms, deferTO, &toflag) : 0;

        while (*flagp) {
            oneLoop();
            if (toflag)
                return (-1);    /* totid already dead */
        }

        if (totid)
            rmTimer (totid);
        return (0);
}

/* register a new callback, fp, to be called with ud as arg when fd is ready.
 * return a unique callback id for use with rmCallback().
 */
int
addCallback (int fd, CBF *fp, void *ud)
{
        CB *cp;

        /* reuse first unused slot or grow */
        for (cp = cback; cp < &cback[ncback]; cp++)
            if (!cp->in_use)
                break;
        if (cp == &cback[ncback]) {
            cback = cback ? (CB *) realloc (cback, (ncback+1)*sizeof(CB))
                          : (CB *) malloc (sizeof(CB));
            cp = &cback[ncback++];
        }

        /* init new entry */
        cp->in_use = 1;
        cp->fp = fp;
        cp->ud = ud;
        cp->fd = fd;
        ncbinuse++;

        /* id is index into array */
        return (cp - cback);
}

/* remove the callback with the given id, as returned from addCallback().
 * silently ignore if id not valid.
 */
void
rmCallback (int cid)
{
        CB *cp;

        /* validate id */
        if (cid < 0 || cid >= ncback)
            return;
        cp = &cback[cid];
        if (!cp->in_use)
            return;

        /* mark for reuse */
        cp->in_use = 0;
        ncbinuse--;
}

/* register a new timer function, fp, to be called with ud as arg after ms
 * milliseconds. add to list in order of decreasing time from epoch, ie,
 * last entry runs soonest. return id for use with rmTimer().
 */
int
addTimer (int ms, TCF *fp, void *ud)
{
        struct timeval t;
        TF *tp;

        /* get time now */
        gettimeofday (&t, NULL);

        /* add one entry */
        timef = timef ? (TF *) realloc (timef, (ntimef+1)*sizeof(TF))
                      : (TF *) malloc (sizeof(TF));
        tp = &timef[ntimef++];

        /* init new entry */
        tp->ud = ud;
        tp->fp = fp;
        tp->tgo = EPOCHDT(&t) + ms;

        /* insert maintaining sort */
        for ( ; tp > timef && tp[0].tgo > tp[-1].tgo; tp--) {
            TF tmptf = tp[-1];
            tp[-1] = tp[0];
            tp[0] = tmptf;
        }

        /* store and return new unique id */
        return (tp->tid = ++tid);
}

/* remove the timer with the given id, as returned from addTimer().
 * silently ignore if id not found.
 */
void
rmTimer (int timer_id)
{
        TF *tp;

        /* find it */
        for (tp = timef; tp < &timef[ntimef]; tp++)
            if (tp->tid == timer_id)
                break;
        if (tp == &timef[ntimef])
            return;

        /* bubble it out */
        for (++tp; tp < &timef[ntimef]; tp++)
            tp[-1] = tp[0];

        /* shrink list */
        timef = (TF *) realloc (timef, (--ntimef)*sizeof(TF));
}

/* add a new work procedure, fp, to be called with ud when nothing else to do.
 * return unique id for use with rmWorkProc().
 */
int
addWorkProc (WPF *fp, void *ud)
{
        WP *wp;

        /* reuse first unused slot or grow */
        for (wp = wproc; wp < &wproc[nwproc]; wp++)
            if (!wp->in_use)
                break;
        if (wp == &wproc[nwproc]) {
            wproc = wproc ? (WP *) realloc (wproc, (nwproc+1)*sizeof(WP))
                          : (WP *) malloc (sizeof(WP));
            wp = &wproc[nwproc++];
        }

        /* init new entry */
        wp->in_use = 1;
        wp->fp = fp;
        wp->ud = ud;
        nwpinuse++;

        /* id is index into array */
        return (wp - wproc);
}


/* remove the work proc with the given id, as returned from addWorkProc().
 * silently ignore if id not found.
 */
void
rmWorkProc (int wid)
{
        WP *wp;

        /* validate id */
        if (wid < 0 || wid >= nwproc)
            return;
        wp = &wproc[wid];
        if (!wp->in_use)
            return;

        /* mark for reuse */
        wp->in_use = 0;
        nwpinuse--;
}

/* run next work procedure */
static void
runWorkProc ()
{
        WP *wp;

        /* skip if list is empty */
        if (!nwpinuse)
            return;

        /* find next */
        do {
            lastwp = (lastwp+1) % nwproc;
            wp = &wproc[lastwp];
        } while (!wp->in_use);

        /* run */
        (*wp->fp) (wp->ud);
}

/* run next callback whose fd is listed as ready to go in rfdp */
static void
callCallback(fd_set *rfdp)
{
        CB *cp;

        /* skip if list is empty */
        if (!ncbinuse)
            return;

        /* find next */
        do {
            lastcb = (lastcb+1) % ncback;
            cp = &cback[lastcb];
        } while (!cp->in_use || !FD_ISSET (cp->fd, rfdp));

        /* run */
        (*cp->fp) (cp->fd, cp->ud);
}

/* run the next timer callback whose time has come, if any. all we have to do
 * is is check the last entry in timef[] because it is sorted in decreasing
 * order of time from epoch to run, ie, last entry runs soonest.
 */
static void
checkTimer()
{
        struct timeval now;
        double tgonow;
        TF *tp;

        /* skip if list is empty */
        if (!ntimef)
            return;

        gettimeofday (&now, NULL);
        tgonow = EPOCHDT (&now);
        tp = &timef[ntimef-1];
        if (tp->tgo <= tgonow) {
            ntimef--;                   /* pop then call */
            (*tp->fp) (tp->ud);
        }
}

/* check fd's from each active callback.
 * if any ready, call their callbacks else call each registered work procedure.
 */
static void
oneLoop()
{
        struct timeval tv, *tvp;
        fd_set rfd;
        CB *cp;
        int maxfd, ns;

        /* build list of callback file descriptors to check */
        FD_ZERO (&rfd);
        maxfd = -1;
        for (cp = cback; cp < &cback[ncback]; cp++) {
            if (cp->in_use) {
                FD_SET (cp->fd, &rfd);
                if (cp->fd > maxfd)
                    maxfd = cp->fd;
            }
        }

        /* determine timeout:
         * if there are work procs
         *   set delay = 0
         * else if there is at least one timer func
         *   set delay = time until soonest timer func expires
         * else
         *   set delay = forever
         */
        if (nwpinuse > 0) {
            tvp = &tv;
            tvp->tv_sec = tvp->tv_usec = 0;
        } else if (ntimef > 0) {
            struct timeval now;
            double late;
            gettimeofday (&now, NULL);
            late = timef[ntimef-1].tgo - EPOCHDT (&now);        /* ms late */
            if (late < 0)
                late = 0;
            late /= 1000.0;                                     /* secs late */
            tvp = &tv;
            tvp->tv_sec = (long)floor(late);
            tvp->tv_usec = (long)floor((late - tvp->tv_sec)*1000000.0);
        } else
            tvp = NULL;

        /* check file descriptors, timeout depending on pending work */
        ns = select (maxfd+1, &rfd, NULL, NULL, tvp);
        if (ns < 0) {
            perror ("select");
            exit(1);
        }
        
        /* dispatch */
        checkTimer();
        if (ns == 0)
            runWorkProc();
        else
            callCallback(&rfd);
}

/* timer callback used to implement deferLoop().
 * arg is pointer to int which we set to 1
 */
static void
deferTO (void *p)
{
        *(int*)p = 1;
}

#if defined(MAIN_TEST)
/* make a small stand-alone test program.
 */

#include <unistd.h>
#include <sys/time.h>

int mycid;
int mywid;
int mytid;

int user_a;
int user_b;
int counter;

void
wp (void *ud)
{
        struct timeval tv;

        gettimeofday (&tv, NULL);
        printf ("workproc @ %ld.%03ld %d %d\n", 
                (long)tv.tv_sec, (long)tv.tv_usec/1000, counter, ++(*(int*)ud));
}

void
to (void *ud)
{
        printf ("timeout %d\n", (int)ud);
}

void
stdinCB (int fd, void *ud)
{
        char c;

        if (read (fd, &c, 1) != 1) {
            perror ("read");
            exit(1);
        }

        switch (c) {
        case '+': counter++; break;
        case '-': counter--; break;

        case 'W': mywid = addWorkProc (wp, &user_b); break;
        case 'w': rmWorkProc (mywid); break;

        case 'c': rmCallback (mycid); break;

        case 't': rmTimer (mytid); break;
        case '1': mytid = addTimer (1000, to, (void *)1); break;
        case '2': mytid = addTimer (2000, to, (void *)2); break;
        case '3': mytid = addTimer (3000, to, (void *)3); break;
        case '4': mytid = addTimer (4000, to, (void *)4); break;
        case '5': mytid = addTimer (5000, to, (void *)5); break;
        default: return;        /* silently absorb other chars like \n */
        }

        printf ("callback: %d\n", ++(*(int*)ud));
}

int
main (int ac, char *av[])
{
        (void) addCallback (0, stdinCB, &user_a);
        eventLoop();
        exit(0);
}

#endif