select.c

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Author : Nick Mathewson
Date : 2009-05-27 15:35:00
Hash : cdaca02c
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:r1318
select.c
/*	$OpenBSD: select.c,v 1.2 2002/06/25 15:50:15 mickey Exp $	*/

/*
 * Copyright 2000-2007 Niels Provos <provos@citi.umich.edu>
 * Copyright 2007-2009 Niels Provos and Nick Mathewson
 *
 * 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 "event-config.h"
#endif

#include <sys/types.h>
#ifdef _EVENT_HAVE_SYS_TIME_H
#include <sys/time.h>
#else
#include <sys/_time.h>
#endif
#ifdef _EVENT_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>
#include <assert.h>

#include "event-internal.h"
#include "evsignal-internal.h"
#include "log-internal.h"
#include "evmap-internal.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;
};

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

const struct eventop selectops = {
	"select",
	select_init,
	select_add,
	select_del,
	select_dispatch,
	select_dealloc,
	0, /* doesn't need reinit. */
	EV_FEATURE_FDS,
	0,
};

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

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

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

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

	evsig_init(base);

	return (sop);
}

#ifdef CHECK_INVARIANTS
static void
check_selectop(struct selectop *sop)
{
	/* nothing to be done here */
}
#else
#define check_selectop(sop) do { (void) sop; } while (0)
#endif

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

	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);
		}

		evsig_process(base);
		return (0);
	} else if (base->sig.evsig_caught) {
		evsig_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) {
		if (++i >= sop->event_fds+1)
			i = 0;
		res = 0;
		if (FD_ISSET(i, sop->event_readset_out))
			res |= EV_READ;
		if (FD_ISSET(i, sop->event_writeset_out))
			res |= EV_WRITE;

		if (res == 0)
			continue;

		evmap_io_active(base, i, res);
	}
	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;

	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 = mm_realloc(sop->event_readset_in, fdsz)) == NULL)
		goto error;
	sop->event_readset_in = readset_in;
	if ((readset_out = mm_realloc(sop->event_readset_out, fdsz)) == NULL)
		goto error;
	sop->event_readset_out = readset_out;
	if ((writeset_in = mm_realloc(sop->event_writeset_in, fdsz)) == NULL)
		goto error;
	sop->event_writeset_in = writeset_in;
	if ((writeset_out = mm_realloc(sop->event_writeset_out, fdsz)) == NULL)
		goto error;
	sop->event_writeset_out = writeset_out;

	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);

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

	return (0);

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


static int
select_add(struct event_base *base, int fd, short old, short events, void *p)
{
	struct selectop *sop = base->evbase;
	(void) p;

	assert((events & EV_SIGNAL) == 0);
	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 < fd) {
		int fdsz = sop->event_fdsz;

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

		while (fdsz <
		    (howmany(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 = fd;
	}

	if (events & EV_READ)
		FD_SET(fd, sop->event_readset_in);
	if (events & EV_WRITE)
		FD_SET(fd, sop->event_writeset_in);
	check_selectop(sop);

	return (0);
}

/*
 * Nothing to be done here.
 */

static int
select_del(struct event_base *base, int fd, short old, short events, void *p)
{
	struct selectop *sop = base->evbase;
	(void)p;

	assert((events & EV_SIGNAL) == 0);
	check_selectop(sop);

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

	if (events & EV_READ)
		FD_CLR(fd, sop->event_readset_in);

	if (events & EV_WRITE)
		FD_CLR(fd, sop->event_writeset_in);

	check_selectop(sop);
	return (0);
}

static void
select_dealloc(struct event_base *base)
{
	struct selectop *sop = base->evbase;

	evsig_dealloc(base);
	if (sop->event_readset_in)
		mm_free(sop->event_readset_in);
	if (sop->event_writeset_in)
		mm_free(sop->event_writeset_in);
	if (sop->event_readset_out)
		mm_free(sop->event_readset_out);
	if (sop->event_writeset_out)
		mm_free(sop->event_writeset_out);

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

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kc3-lang/libevent /select.c
