src/lib/lwp/sel.c

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/*
 *  Empire - A multi-player, client/server Internet based war game.
 *  Copyright (C) 1994-2007, Dave Pare, Jeff Bailey, Thomas Ruschak,
 *                           Ken Stevens, Steve McClure
 *  Copyright (C) 1991-3 Stephen Crane
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program 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 General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 *  ---
 *
 *  See files README, COPYING and CREDITS in the root of the source
 *  tree for related information and legal notices.  It is expected
 *  that future projects/authors will amend these files as needed.
 *
 *  ---
 *
 *  sel.c: arrange to block on read/write file descriptors using lwp
 * 
 *  Known contributors to this file:
 *     Dave Pare, 1994
 *     Markus Armbruster, 2007
 */

#include <config.h>

#include <errno.h>
#include <sys/time.h>
#include <time.h>
#include <unistd.h>
#include "lwp.h"
#include "lwpint.h"
#include "prototypes.h"

/* Largest fd in LwpReadfds, LwpWritefds */
static int LwpMaxfd;

/* Number of file descriptors in LwpReadfds, LwpWritefds */
static int LwpNfds;

/* File descriptors waited for in lwpSleepFd() */
static fd_set LwpReadfds, LwpWritefds;

/* Map file descriptor to thread sleeping in lwpSleepFd() */
static struct lwpProc **LwpFdwait;

/* Threads sleeping in lwpSleepUntil(), in no particular order */
static struct lwpQueue LwpDelayq;

/* The thread executing lwpSelect() */
static struct lwpProc *LwpSelProc;      

void
lwpInitSelect(struct lwpProc *proc)
{
    LwpMaxfd = 0;
    LwpNfds = 0;
    FD_ZERO(&LwpReadfds);
    FD_ZERO(&LwpWritefds);
    LwpFdwait = calloc(FD_SETSIZE, sizeof(struct lwpProc *));
    LwpDelayq.head = 0;
    LwpDelayq.tail = 0;
    LwpSelProc = proc;
}

void
lwpSleepFd(int fd, int mask)
{
    lwpStatus(LwpCurrent, "sleeping on fd %d for %d", fd, mask);

    if (CANT_HAPPEN(fd > FD_SETSIZE))
        return;
    if (LwpFdwait[fd] != 0) {
        lwpStatus(LwpCurrent,
                  "multiple sleeps attempted on file descriptor %d", fd);
        return;
    }
    if (mask & LWP_FD_READ)
        FD_SET(fd, &LwpReadfds);
    if (mask & LWP_FD_WRITE)
        FD_SET(fd, &LwpWritefds);

    LwpNfds++;

    if (LwpMaxfd == 0 && LwpDelayq.head == 0) {
        /* select process is sleeping until first waiter arrives */
        lwpStatus(LwpCurrent, "going to resched fd %d", fd);
        lwpReady(LwpSelProc);
    }
    lwpStatus(LwpCurrent, "going to wait on fd %d", fd);
    if (fd > LwpMaxfd)
        LwpMaxfd = fd;
    LwpFdwait[fd] = LwpCurrent;
    LwpCurrent->fd = fd;
    lwpReschedule();
}

static void
lwpWakeupFd(struct lwpProc *proc)
{
    if (proc->fd < 0)
        return;

    lwpStatus(proc, "awakening; was sleeping on fd %d", proc->fd);
    FD_CLR(proc->fd, &LwpReadfds);
    FD_CLR(proc->fd, &LwpWritefds);
    LwpNfds--;
    LwpFdwait[proc->fd] = 0;
    proc->fd = -1;
    lwpReady(proc);
}

void
lwpWakeupSleep(void)
{
    time_t now;
    struct lwpQueue save;
    struct lwpProc *proc;

    if (LwpDelayq.head) {
        now = time(NULL);
        save.tail = save.head = 0;
        while (NULL != (proc = lwpGetFirst(&LwpDelayq))) {
            if (now >= proc->runtime) {
                lwpStatus(proc, "sleep done");
                lwpReady(proc);
            } else {
                lwpAddTail(&save, proc);
            }
        }
        LwpDelayq = save;
    }
}

void
lwpWakeup(struct lwpProc *proc)
{
    if (proc->fd >= 0)
        lwpWakeupFd(proc);
    else if (proc->runtime != (time_t)-1) {
        proc->runtime = 0;
        lwpWakeupSleep();
    }
}

int
lwpSleepUntil(time_t until)
{
    int res;

    lwpStatus(LwpCurrent, "sleeping for %ld sec",
              (long)(until - time(NULL)));
    LwpCurrent->runtime = until;
    if (LwpMaxfd == 0 && LwpDelayq.head == 0) {
        /* select process is sleeping until first waiter arrives */
        lwpReady(LwpSelProc);
    }
    lwpAddTail(&LwpDelayq, LwpCurrent);
    lwpReschedule();
    res = LwpCurrent->runtime ? 0 : -1;
    LwpCurrent->runtime = (time_t)-1;
    return res;
}

/*ARGSUSED*/
void
lwpSelect(void *arg)
{
    struct lwpProc *us = LwpCurrent;
    fd_set readmask;
    fd_set writemask;
    int n;
    int fd;
    time_t now;
    time_t delta;
    struct lwpProc *proc;
    struct timeval tv;

    lwpStatus(us, "starting select loop");
    FD_ZERO(&readmask);
    FD_ZERO(&writemask);
    while (1) {
        while (1) {
            if (LwpNfds)
                break;
            if (LwpDelayq.head)
                break;
            /* wait for someone to lwpSleepFd or lwpSleepUntil */
            LwpMaxfd = 0;
            lwpStatus(us, "no fds or sleepers, waiting");
            lwpReschedule();
        }
        tv.tv_sec = 1000000;
        tv.tv_usec = 0;
        if (LwpDelayq.head) {
            time(&now);
            proc = LwpDelayq.head;
            for (; proc != 0; proc = proc->next) {
                delta = proc->runtime - now;
                if (delta < tv.tv_sec)
                    tv.tv_sec = delta;
            }
            if (tv.tv_sec < 0)
                tv.tv_sec = 0;
        }
        lwpStatus(us, "selecting; sleep %ld secs", tv.tv_sec);

        memcpy(&readmask, &LwpReadfds, sizeof(fd_set));
        memcpy(&writemask, &LwpWritefds, sizeof(fd_set));
        n = select(LwpMaxfd + 1, &readmask, &writemask, NULL, &tv);
        if (n < 0) {
            if (errno != EINTR) {
                logerror("select failed (%s)", strerror(errno));
                exit(1);
            }
            /* go handle the signal */
            lwpReady(us);
            lwpReschedule();
            continue;
        }

        lwpWakeupSleep();
        if (n > 0) {
            /* file descriptor activity */
            for (fd = 0; fd <= LwpMaxfd; fd++) {
                if (LwpFdwait[fd] == 0)
                    continue;
                if (FD_ISSET(fd, &readmask)) {
                    lwpStatus(LwpFdwait[fd], "input ready");
                    lwpWakeupFd(LwpFdwait[fd]);
                    continue;
                }
                if (FD_ISSET(fd, &writemask)) {
                    lwpStatus(LwpFdwait[fd], "output ready");
                    lwpWakeupFd(LwpFdwait[fd]);
                    continue;
                }
            }
        }
        lwpStatus(us, "fd dispatch completed");
        lwpReady(LwpCurrent);
        lwpReschedule();
    }
    /*NOTREACHED*/
}

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