poll.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
poll.c
/*	$OpenBSD: poll.c,v 1.2 2002/06/25 15:50:15 mickey Exp $	*/

/*
 * Copyright 2000-2003 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
#include <sys/queue.h>
#include <poll.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"

struct pollop {
	int event_count;		/* Highest number alloc */
	int nfds;                       /* Size of event_* */
	int fd_count;                   /* Size of idxplus1_by_fd */
	struct pollfd *event_set;
	struct event **event_r_back;
	struct event **event_w_back;
	int *idxplus1_by_fd; /* Index into event_set by fd; we add 1 so
			      * that 0 (which is easy to memset) can mean
			      * "no entry." */
};

static void *poll_init	(struct event_base *);
static int poll_add		(void *, struct event *);
static int poll_del		(void *, struct event *);
static int poll_dispatch	(struct event_base *, void *, struct timeval *);
static void poll_dealloc	(struct event_base *, void *);

const struct eventop pollops = {
	"poll",
	poll_init,
	poll_add,
	poll_del,
	poll_dispatch,
	poll_dealloc,
    0
};

static void *
poll_init(struct event_base *base)
{
	struct pollop *pollop;

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

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

	evsignal_init(base);

	return (pollop);
}

#ifdef CHECK_INVARIANTS
static void
poll_check_ok(struct pollop *pop)
{
	int i, idx;
	struct event *ev;

	for (i = 0; i < pop->fd_count; ++i) {
		idx = pop->idxplus1_by_fd[i]-1;
		if (idx < 0)
			continue;
		assert(pop->event_set[idx].fd == i);
		if (pop->event_set[idx].events & POLLIN) {
			ev = pop->event_r_back[idx];
			assert(ev);
			assert(ev->ev_events & EV_READ);
			assert(ev->ev_fd == i);
		}
		if (pop->event_set[idx].events & POLLOUT) {
			ev = pop->event_w_back[idx];
			assert(ev);
			assert(ev->ev_events & EV_WRITE);
			assert(ev->ev_fd == i);
		}
	}
	for (i = 0; i < pop->nfds; ++i) {
		struct pollfd *pfd = &pop->event_set[i];
		assert(pop->idxplus1_by_fd[pfd->fd] == i+1);
	}
}
#else
#define poll_check_ok(pop)
#endif

static int
poll_dispatch(struct event_base *base, void *arg, struct timeval *tv)
{
	int res, i, j, msec = -1, nfds;
	struct pollop *pop = arg;

	poll_check_ok(pop);

	if (tv != NULL)
		msec = tv->tv_sec * 1000 + (tv->tv_usec + 999) / 1000;

	nfds = pop->nfds;
	res = poll(pop->event_set, nfds, msec);

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

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

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

	if (res == 0 || nfds == 0)
		return (0);

	i = random() % nfds;
	for (j = 0; j < nfds; j++) {
		struct event *r_ev = NULL, *w_ev = NULL;
		int what;
		if (++i == nfds)
			i = 0;
		what = pop->event_set[i].revents;

		if (!what)
			continue;

		res = 0;

		/* If the file gets closed notify */
		if (what & (POLLHUP|POLLERR))
			what |= POLLIN|POLLOUT;
		if (what & POLLIN) {
			res |= EV_READ;
			r_ev = pop->event_r_back[i];
		}
		if (what & POLLOUT) {
			res |= EV_WRITE;
			w_ev = pop->event_w_back[i];
		}
		if (res == 0)
			continue;

		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);
		}
	}

	return (0);
}

static int
poll_add(void *arg, struct event *ev)
{
	struct pollop *pop = arg;
	struct pollfd *pfd = NULL;
	int i;

	if (ev->ev_events & EV_SIGNAL)
		return (evsignal_add(ev));
	if (!(ev->ev_events & (EV_READ|EV_WRITE)))
		return (0);

	poll_check_ok(pop);
	if (pop->nfds + 1 >= pop->event_count) {
		struct pollfd *tmp_event_set;
		struct event **tmp_event_r_back;
		struct event **tmp_event_w_back;
		int tmp_event_count;

		if (pop->event_count < 32)
			tmp_event_count = 32;
		else
			tmp_event_count = pop->event_count * 2;

		/* We need more file descriptors */
		tmp_event_set = realloc(pop->event_set,
				 tmp_event_count * sizeof(struct pollfd));
		if (tmp_event_set == NULL) {
			event_warn("realloc");
			return (-1);
		}
		pop->event_set = tmp_event_set;

		tmp_event_r_back = realloc(pop->event_r_back,
			    tmp_event_count * sizeof(struct event *));
		if (tmp_event_r_back == NULL) {
			/* event_set overallocated; that's okay. */
			event_warn("realloc");
			return (-1);
		}
		pop->event_r_back = tmp_event_r_back;

		tmp_event_w_back = realloc(pop->event_w_back,
			    tmp_event_count * sizeof(struct event *));
		if (tmp_event_w_back == NULL) {
			/* event_set and event_r_back overallocated; that's
			 * okay. */
			event_warn("realloc");
			return (-1);
		}
		pop->event_w_back = tmp_event_w_back;

		pop->event_count = tmp_event_count;
	}
	if (ev->ev_fd >= pop->fd_count) {
		int *tmp_idxplus1_by_fd;
		int new_count;
		if (pop->fd_count < 32)
			new_count = 32;
		else
			new_count = pop->fd_count * 2;
		while (new_count <= ev->ev_fd)
			new_count *= 2;
		tmp_idxplus1_by_fd =
			realloc(pop->idxplus1_by_fd, new_count * sizeof(int));
		if (tmp_idxplus1_by_fd == NULL) {
			event_warn("realloc");
			return (-1);
		}
		pop->idxplus1_by_fd = tmp_idxplus1_by_fd;
		memset(pop->idxplus1_by_fd + pop->fd_count,
		       0, sizeof(int)*(new_count - pop->fd_count));
		pop->fd_count = new_count;
	}

	i = pop->idxplus1_by_fd[ev->ev_fd] - 1;
	if (i >= 0) {
		pfd = &pop->event_set[i];
	} else {
		i = pop->nfds++;
		pfd = &pop->event_set[i];
		pfd->events = 0;
		pfd->fd = ev->ev_fd;
		pop->event_w_back[i] = pop->event_r_back[i] = NULL;
		pop->idxplus1_by_fd[ev->ev_fd] = i + 1;
	}

	pfd->revents = 0;
	if (ev->ev_events & EV_WRITE) {
		pfd->events |= POLLOUT;
		pop->event_w_back[i] = ev;
	}
	if (ev->ev_events & EV_READ) {
		pfd->events |= POLLIN;
		pop->event_r_back[i] = ev;
	}
	poll_check_ok(pop);

	return (0);
}

/*
 * Nothing to be done here.
 */

static int
poll_del(void *arg, struct event *ev)
{
	struct pollop *pop = arg;
	struct pollfd *pfd = NULL;
	int i;

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

	if (!(ev->ev_events & (EV_READ|EV_WRITE)))
		return (0);

	poll_check_ok(pop);
	i = pop->idxplus1_by_fd[ev->ev_fd] - 1;
	if (i < 0)
		return (-1);

	/* Do we still want to read or write? */
	pfd = &pop->event_set[i];
	if (ev->ev_events & EV_READ) {
		pfd->events &= ~POLLIN;
		pop->event_r_back[i] = NULL;
	}
	if (ev->ev_events & EV_WRITE) {
		pfd->events &= ~POLLOUT;
		pop->event_w_back[i] = NULL;
	}
	poll_check_ok(pop);
	if (pfd->events)
		/* Another event cares about that fd. */
		return (0);

	/* Okay, so we aren't interested in that fd anymore. */
	pop->idxplus1_by_fd[ev->ev_fd] = 0;

	--pop->nfds;
	if (i != pop->nfds) {
		/* 
		 * Shift the last pollfd down into the now-unoccupied
		 * position.
		 */
		memcpy(&pop->event_set[i], &pop->event_set[pop->nfds],
		       sizeof(struct pollfd));
		pop->event_r_back[i] = pop->event_r_back[pop->nfds];
		pop->event_w_back[i] = pop->event_w_back[pop->nfds];
		pop->idxplus1_by_fd[pop->event_set[i].fd] = i + 1;
	}

	poll_check_ok(pop);
	return (0);
}

static void
poll_dealloc(struct event_base *base, void *arg)
{
	struct pollop *pop = arg;

	evsignal_dealloc(base);
	if (pop->event_set)
		free(pop->event_set);
	if (pop->event_r_back)
		free(pop->event_r_back);
	if (pop->event_w_back)
		free(pop->event_w_back);
	if (pop->idxplus1_by_fd)
		free(pop->idxplus1_by_fd);

	memset(pop, 0, sizeof(struct pollop));
	free(pop);
}
kc3-lang/libevent/poll.c

Commit

kc3-lang/libevent /poll.c
