bufferevent_pair.c

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Author : Nick Mathewson
Date : 2010-02-20 18:44:35
Hash : d3288293
Message : Provide consistent, tested semantics for bufferevent timeouts The different bufferevent implementations had different behavior for their timeouts. Some of them kept re-triggering the timeouts indefinitely; some disabled the event immediately the first time a timeout triggered. Some of them made the timeouts only count when the bufferevent was actively trying to read or write; some did not. The new behavior is modeled after old socket bufferevents, since they were here first and their behavior is relatively sane. Basically, each timeout disables the bufferevent's corresponding read or write operation when it fires. Timeouts are stopped whenever we suspend writing or reading, and reset whenever we unsuspend writing or reading. Calling bufferevent_enable resets a timeout, as does changing the timeout value.

bufferevent_pair.c

/*
 * Copyright (c) 2009 Niels Provos, 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.
 */

#include <sys/types.h>

#ifdef WIN32
#include <winsock2.h>
#endif

#include "event-config.h"

#include "event2/util.h"
#include "event2/buffer.h"
#include "event2/bufferevent.h"
#include "event2/bufferevent_struct.h"
#include "event2/event.h"
#include "defer-internal.h"
#include "bufferevent-internal.h"
#include "mm-internal.h"
#include "util-internal.h"

struct bufferevent_pair {
	struct bufferevent_private bev;
	struct bufferevent_pair *partner;
};


/* Given a bufferevent that's really a bev part of a bufferevent_pair,
 * return that bufferevent_filtered. Returns NULL otherwise.*/
static inline struct bufferevent_pair *
upcast(struct bufferevent *bev)
{
	struct bufferevent_pair *bev_p;
	if (bev->be_ops != &bufferevent_ops_pair)
		return NULL;
	bev_p = EVUTIL_UPCAST(bev, struct bufferevent_pair, bev.bev);
	EVUTIL_ASSERT(bev_p->bev.bev.be_ops == &bufferevent_ops_pair);
	return bev_p;
}

#define downcast(bev_pair) (&(bev_pair)->bev.bev)

static inline void
incref_and_lock(struct bufferevent *b)
{
	struct bufferevent_pair *bevp;
	_bufferevent_incref_and_lock(b);
	bevp = upcast(b);
	if (bevp->partner)
		_bufferevent_incref_and_lock(downcast(bevp->partner));
}

static inline void
decref_and_unlock(struct bufferevent *b)
{
	struct bufferevent_pair *bevp = upcast(b);
	if (bevp->partner)
		_bufferevent_decref_and_unlock(downcast(bevp->partner));
	_bufferevent_decref_and_unlock(b);
}

/* XXX Handle close */

static void be_pair_outbuf_cb(struct evbuffer *,
    const struct evbuffer_cb_info *, void *);

static struct bufferevent_pair *
bufferevent_pair_elt_new(struct event_base *base,
    int options)
{
	struct bufferevent_pair *bufev;
	if (! (bufev = mm_calloc(1, sizeof(struct bufferevent_pair))))
		return NULL;
	if (bufferevent_init_common(&bufev->bev, base, &bufferevent_ops_pair,
		options)) {
		mm_free(bufev);
		return NULL;
	}
	if (!evbuffer_add_cb(bufev->bev.bev.output, be_pair_outbuf_cb, bufev)) {
		bufferevent_free(downcast(bufev));
		return NULL;
	}

	_bufferevent_init_generic_timeout_cbs(&bufev->bev.bev);

	return bufev;
}

int
bufferevent_pair_new(struct event_base *base, int options,
    struct bufferevent *pair[2])
{
	struct bufferevent_pair *bufev1 = NULL, *bufev2 = NULL;
	int tmp_options;

	options |= BEV_OPT_DEFER_CALLBACKS;
	tmp_options = options & ~BEV_OPT_THREADSAFE;

	bufev1 = bufferevent_pair_elt_new(base, options);
	if (!bufev1)
		return -1;
	bufev2 = bufferevent_pair_elt_new(base, tmp_options);
	if (!bufev2) {
		bufferevent_free(downcast(bufev1));
		return -1;
	}

	if (options & BEV_OPT_THREADSAFE) {
		/*XXXX check return */
		bufferevent_enable_locking(downcast(bufev2), bufev1->bev.lock);
	}

	bufev1->partner = bufev2;
	bufev2->partner = bufev1;

	evbuffer_freeze(downcast(bufev1)->input, 0);
	evbuffer_freeze(downcast(bufev1)->output, 1);
	evbuffer_freeze(downcast(bufev2)->input, 0);
	evbuffer_freeze(downcast(bufev2)->output, 1);

	pair[0] = downcast(bufev1);
	pair[1] = downcast(bufev2);

	return 0;
}

static void
be_pair_transfer(struct bufferevent *src, struct bufferevent *dst,
    int ignore_wm)
{
	size_t src_size, dst_size;
	size_t n;

	evbuffer_unfreeze(src->output, 1);
	evbuffer_unfreeze(dst->input, 0);

	if (dst->wm_read.high) {
		size_t dst_size = evbuffer_get_length(dst->input);
		if (dst_size < dst->wm_read.high) {
			n = dst->wm_read.high - dst_size;
			evbuffer_remove_buffer(src->output, dst->input, n);
		} else {
			if (!ignore_wm)
				goto done;
			n = evbuffer_get_length(src->output);
			evbuffer_add_buffer(dst->input, src->output);
		}
	} else {
		n = evbuffer_get_length(src->output);
		evbuffer_add_buffer(dst->input, src->output);
	}

	if (n) {
		BEV_RESET_GENERIC_READ_TIMEOUT(dst);

		if (evbuffer_get_length(dst->output))
			BEV_RESET_GENERIC_WRITE_TIMEOUT(dst);
		else
			BEV_DEL_GENERIC_WRITE_TIMEOUT(dst);
	}

	src_size = evbuffer_get_length(src->output);
	dst_size = evbuffer_get_length(dst->input);

	if (dst_size >= dst->wm_read.low) {
		_bufferevent_run_readcb(dst);
	}
	if (src_size <= src->wm_write.low) {
		_bufferevent_run_writecb(src);
	}
done:
	evbuffer_freeze(src->output, 1);
	evbuffer_freeze(dst->input, 0);
}

static inline int
be_pair_wants_to_talk(struct bufferevent_pair *src,
    struct bufferevent_pair *dst)
{
	return (downcast(src)->enabled & EV_WRITE) &&
	    (downcast(dst)->enabled & EV_READ) &&
	    !dst->bev.read_suspended &&
	    evbuffer_get_length(downcast(src)->output);
}

static void
be_pair_outbuf_cb(struct evbuffer *outbuf,
    const struct evbuffer_cb_info *info, void *arg)
{
	struct bufferevent_pair *bev_pair = arg;
	struct bufferevent_pair *partner = bev_pair->partner;

	incref_and_lock(downcast(bev_pair));

	if (info->n_added > info->n_deleted && partner) {
		/* We got more data.  If the other side's reading, then
		   hand it over. */
		if (be_pair_wants_to_talk(bev_pair, partner)) {
			be_pair_transfer(downcast(bev_pair), downcast(partner), 0);
		}
	}

	decref_and_unlock(downcast(bev_pair));
}

static int
be_pair_enable(struct bufferevent *bufev, short events)
{
	struct bufferevent_pair *bev_p = upcast(bufev);
	struct bufferevent_pair *partner = bev_p->partner;

	incref_and_lock(bufev);

	if (events & EV_READ) {
		BEV_RESET_GENERIC_READ_TIMEOUT(bufev);
	}
	if ((events & EV_WRITE) && evbuffer_get_length(bufev->output))
		BEV_RESET_GENERIC_WRITE_TIMEOUT(bufev);

	/* We're starting to read! Does the other side have anything to write?*/
	if ((events & EV_READ) && partner &&
	    be_pair_wants_to_talk(partner, bev_p)) {
		be_pair_transfer(downcast(partner), bufev, 0);
	}
	/* We're starting to write! Does the other side want to read? */
	if ((events & EV_WRITE) && partner &&
	    be_pair_wants_to_talk(bev_p, partner)) {
		be_pair_transfer(bufev, downcast(partner), 0);
	}
	decref_and_unlock(bufev);
	return 0;
}

static int
be_pair_disable(struct bufferevent *bev, short events)
{
	if (events & EV_READ) {
		BEV_DEL_GENERIC_READ_TIMEOUT(bev);
	}
	if (events & EV_WRITE)
		BEV_DEL_GENERIC_WRITE_TIMEOUT(bev);
	return 0;
}

static void
be_pair_destruct(struct bufferevent *bev)
{
	struct bufferevent_pair *bev_p = upcast(bev);

	if (bev_p->partner) {
		bev_p->partner->partner = NULL;
		bev_p->partner = NULL;
	}

	_bufferevent_del_generic_timeout_cbs(bev);
}

static int
be_pair_flush(struct bufferevent *bev, short iotype,
    enum bufferevent_flush_mode mode)
{
	struct bufferevent_pair *bev_p = upcast(bev);
	struct bufferevent *partner;
	incref_and_lock(bev);
	if (!bev_p->partner)
		return -1;

	partner = downcast(bev_p->partner);

	if (mode == BEV_NORMAL)
		return 0;

	if ((iotype & EV_READ) != 0)
		be_pair_transfer(partner, bev, 1);

	if ((iotype & EV_WRITE) != 0)
		be_pair_transfer(bev, partner, 1);

	if (mode == BEV_FINISHED) {
		_bufferevent_run_eventcb(partner, iotype|BEV_EVENT_EOF);
	}
	decref_and_unlock(bev);
	return 0;
}

const struct bufferevent_ops bufferevent_ops_pair = {
	"pair_elt",
	evutil_offsetof(struct bufferevent_pair, bev),
	be_pair_enable,
	be_pair_disable,
	be_pair_destruct,
	_bufferevent_generic_adj_timeouts,
	be_pair_flush,
	NULL, /* ctrl */
};

kc3-lang/libevent/bufferevent_pair.c

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kc3-lang/libevent /bufferevent_pair.c