select.c

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Author : Nick Mathewson
Date : 2009-06-24 22:39:03
Hash : b99254ac
Message : Activate fd events in a pseudorandom order on older backends. New backends like poll and kqueue and so on add fds to the queue in the order that they are triggered. But the select backend currently activates low-numbered fds first, whereas the poll and win32 backends currently favor whatever fds have been on for the longest. This is no good for fairness. svn:r1327
select.c
/*	$OpenBSD: select.c,v 1.2 2002/06/25 15:50:15 mickey Exp $	*/

/*
 * Copyright 2000-2002 Niels Provos <provos@citi.umich.edu>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <sys/types.h>
#ifdef HAVE_SYS_TIME_H
#include <sys/time.h>
#else
#include <sys/_time.h>
#endif
#ifdef HAVE_SYS_SELECT_H
#include <sys/select.h>
#endif
#include <sys/queue.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#ifdef CHECK_INVARIANTS
#include <assert.h>
#endif

#include "event.h"
#include "event-internal.h"
#include "evsignal.h"
#include "log.h"

#ifndef howmany
#define        howmany(x, y)   (((x)+((y)-1))/(y))
#endif

struct selectop {
	int event_fds;		/* Highest fd in fd set */
	int event_fdsz;
	fd_set *event_readset_in;
	fd_set *event_writeset_in;
	fd_set *event_readset_out;
	fd_set *event_writeset_out;
	struct event **event_r_by_fd;
	struct event **event_w_by_fd;
};

static void *select_init	(struct event_base *);
static int select_add		(void *, struct event *);
static int select_del		(void *, struct event *);
static int select_dispatch	(struct event_base *, void *, struct timeval *);
static void select_dealloc     (struct event_base *, void *);

const struct eventop selectops = {
	"select",
	select_init,
	select_add,
	select_del,
	select_dispatch,
	select_dealloc,
	0
};

static int select_resize(struct selectop *sop, int fdsz);

static void *
select_init(struct event_base *base)
{
	struct selectop *sop;

	/* Disable select when this environment variable is set */
	if (getenv("EVENT_NOSELECT"))
		return (NULL);

	if (!(sop = calloc(1, sizeof(struct selectop))))
		return (NULL);

	select_resize(sop, howmany(32 + 1, NFDBITS)*sizeof(fd_mask));

	evsignal_init(base);

	return (sop);
}

#ifdef CHECK_INVARIANTS
static void
check_selectop(struct selectop *sop)
{
	int i;
	for (i = 0; i <= sop->event_fds; ++i) {
		if (FD_ISSET(i, sop->event_readset_in)) {
			assert(sop->event_r_by_fd[i]);
			assert(sop->event_r_by_fd[i]->ev_events & EV_READ);
			assert(sop->event_r_by_fd[i]->ev_fd == i);
		} else {
			assert(! sop->event_r_by_fd[i]);
		}
		if (FD_ISSET(i, sop->event_writeset_in)) {
			assert(sop->event_w_by_fd[i]);
			assert(sop->event_w_by_fd[i]->ev_events & EV_WRITE);
			assert(sop->event_w_by_fd[i]->ev_fd == i);
		} else {
			assert(! sop->event_w_by_fd[i]);
		}
	}

}
#else
#define check_selectop(sop) do { (void) sop; } while (0)
#endif

static int
select_dispatch(struct event_base *base, void *arg, struct timeval *tv)
{
	int res, i, j;
	struct selectop *sop = arg;

	check_selectop(sop);

	memcpy(sop->event_readset_out, sop->event_readset_in,
	       sop->event_fdsz);
	memcpy(sop->event_writeset_out, sop->event_writeset_in,
	       sop->event_fdsz);

	res = select(sop->event_fds + 1, sop->event_readset_out,
	    sop->event_writeset_out, NULL, tv);

	check_selectop(sop);

	if (res == -1) {
		if (errno != EINTR) {
			event_warn("select");
			return (-1);
		}

		evsignal_process(base);
		return (0);
	} else if (base->sig.evsignal_caught) {
		evsignal_process(base);
	}

	event_debug(("%s: select reports %d", __func__, res));

	check_selectop(sop);
	i = random() % (sop->event_fds+1);
	for (j = 0; j <= sop->event_fds; ++j) {
		struct event *r_ev = NULL, *w_ev = NULL;
		if (++i >= sop->event_fds+1)
			i = 0;

		res = 0;
		if (FD_ISSET(i, sop->event_readset_out)) {
			r_ev = sop->event_r_by_fd[i];
			res |= EV_READ;
		}
		if (FD_ISSET(i, sop->event_writeset_out)) {
			w_ev = sop->event_w_by_fd[i];
			res |= EV_WRITE;
		}
		if (r_ev && (res & r_ev->ev_events)) {
			event_active(r_ev, res & r_ev->ev_events, 1);
		}
		if (w_ev && w_ev != r_ev && (res & w_ev->ev_events)) {
			event_active(w_ev, res & w_ev->ev_events, 1);
		}
	}
	check_selectop(sop);

	return (0);
}


static int
select_resize(struct selectop *sop, int fdsz)
{
	int n_events, n_events_old;

	fd_set *readset_in = NULL;
	fd_set *writeset_in = NULL;
	fd_set *readset_out = NULL;
	fd_set *writeset_out = NULL;
	struct event **r_by_fd = NULL;
	struct event **w_by_fd = NULL;

	n_events = (fdsz/sizeof(fd_mask)) * NFDBITS;
	n_events_old = (sop->event_fdsz/sizeof(fd_mask)) * NFDBITS;

	if (sop->event_readset_in)
		check_selectop(sop);

	if ((readset_in = realloc(sop->event_readset_in, fdsz)) == NULL)
		goto error;
	sop->event_readset_in = readset_in;
	if ((readset_out = realloc(sop->event_readset_out, fdsz)) == NULL)
		goto error;
	sop->event_readset_out = readset_out;
	if ((writeset_in = realloc(sop->event_writeset_in, fdsz)) == NULL)
		goto error;
	sop->event_writeset_in = writeset_in;
	if ((writeset_out = realloc(sop->event_writeset_out, fdsz)) == NULL)
		goto error;
	sop->event_writeset_out = writeset_out;
	if ((r_by_fd = realloc(sop->event_r_by_fd,
		 n_events*sizeof(struct event*))) == NULL)
		goto error;
	sop->event_r_by_fd = r_by_fd;
	if ((w_by_fd = realloc(sop->event_w_by_fd,
		 n_events * sizeof(struct event*))) == NULL)
		goto error;
	sop->event_w_by_fd = w_by_fd;

	memset((char *)sop->event_readset_in + sop->event_fdsz, 0,
	    fdsz - sop->event_fdsz);
	memset((char *)sop->event_writeset_in + sop->event_fdsz, 0,
	    fdsz - sop->event_fdsz);
	memset(sop->event_r_by_fd + n_events_old, 0,
	    (n_events-n_events_old) * sizeof(struct event*));
	memset(sop->event_w_by_fd + n_events_old, 0,
	    (n_events-n_events_old) * sizeof(struct event*));

	sop->event_fdsz = fdsz;
	check_selectop(sop);

	return (0);

 error:
	event_warn("malloc");
	return (-1);
}


static int
select_add(void *arg, struct event *ev)
{
	struct selectop *sop = arg;

	if (ev->ev_events & EV_SIGNAL)
		return (evsignal_add(ev));

	check_selectop(sop);
	/*
	 * Keep track of the highest fd, so that we can calculate the size
	 * of the fd_sets for select(2)
	 */
	if (sop->event_fds < ev->ev_fd) {
		int fdsz = sop->event_fdsz;

		if (fdsz < sizeof(fd_mask))
			fdsz = sizeof(fd_mask);

		while (fdsz <
		    (howmany(ev->ev_fd + 1, NFDBITS) * sizeof(fd_mask)))
			fdsz *= 2;

		if (fdsz != sop->event_fdsz) {
			if (select_resize(sop, fdsz)) {
				check_selectop(sop);
				return (-1);
			}
		}

		sop->event_fds = ev->ev_fd;
	}

	if (ev->ev_events & EV_READ) {
		FD_SET(ev->ev_fd, sop->event_readset_in);
		sop->event_r_by_fd[ev->ev_fd] = ev;
	}
	if (ev->ev_events & EV_WRITE) {
		FD_SET(ev->ev_fd, sop->event_writeset_in);
		sop->event_w_by_fd[ev->ev_fd] = ev;
	}
	check_selectop(sop);

	return (0);
}

/*
 * Nothing to be done here.
 */

static int
select_del(void *arg, struct event *ev)
{
	struct selectop *sop = arg;

	check_selectop(sop);
	if (ev->ev_events & EV_SIGNAL)
		return (evsignal_del(ev));

	if (sop->event_fds < ev->ev_fd) {
		check_selectop(sop);
		return (0);
	}

	if (ev->ev_events & EV_READ) {
		FD_CLR(ev->ev_fd, sop->event_readset_in);
		sop->event_r_by_fd[ev->ev_fd] = NULL;
	}

	if (ev->ev_events & EV_WRITE) {
		FD_CLR(ev->ev_fd, sop->event_writeset_in);
		sop->event_w_by_fd[ev->ev_fd] = NULL;
	}

	check_selectop(sop);
	return (0);
}

static void
select_dealloc(struct event_base *base, void *arg)
{
	struct selectop *sop = arg;

	evsignal_dealloc(base);
	if (sop->event_readset_in)
		free(sop->event_readset_in);
	if (sop->event_writeset_in)
		free(sop->event_writeset_in);
	if (sop->event_readset_out)
		free(sop->event_readset_out);
	if (sop->event_writeset_out)
		free(sop->event_writeset_out);
	if (sop->event_r_by_fd)
		free(sop->event_r_by_fd);
	if (sop->event_w_by_fd)
		free(sop->event_w_by_fd);

	memset(sop, 0, sizeof(struct selectop));
	free(sop);
}
kc3-lang/libevent/select.c

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kc3-lang/libevent /select.c
