eventloop.c

#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 <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/time.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 */
    ntimef--;
    if (ntimef == 0)
    {
        free(timef);
        timef = NULL;
        return;
    }
    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");
        return;
    }

    /* 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");
        return;
    }

    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