VILLASnode/lib/hooks/drop.c

/** Drop hook.
 *
 * @author Steffen Vogel <stvogel@eonerc.rwth-aachen.de>
 * @copyright 2017, Institute for Automation of Complex Power Systems, EONERC
 * @license GNU General Public License (version 3)
 *
 * VILLASnode
 *
 * 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 3 of the License, or
 * 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, see <http://www.gnu.org/licenses/>.
 *********************************************************************************/

/** @addtogroup hooks Hook functions
 * @{
 */

#include <villas/hook.h>
#include <villas/plugin.h>
#include <villas/stats.h>
#include <villas/node.h>
#include <villas/sample.h>

struct drop {
	struct sample *prev;
};

static int drop_start(struct hook *h)
{
	struct drop *d = (struct drop *) h->_vd;

	d->prev = NULL;

	return 0;
}

static int drop_stop(struct hook *h)
{
	struct drop *d = (struct drop *) h->_vd;

	if (d->prev)
		sample_put(d->prev);

	return 0;
}

static int drop_read(struct hook *h, struct sample *smps[], unsigned *cnt)
{
	int i, ok, dist;

	struct drop *d = (struct drop *) h->_vd;
	struct sample *prev, *cur = NULL;

	for (i = 0, ok = 0, prev = d->prev; i < *cnt; i++, prev = cur) {
		cur = smps[i];

		if (prev) {
			dist = cur->sequence - (int32_t) prev->sequence;
			if (dist <= 0) {
				cur->flags |= SAMPLE_IS_REORDERED;

				debug(10, "Dropping reordered sample: sequence=%u, distance=%d", cur->sequence, dist);
			}
			else
				goto ok;
		}
		else
			goto ok;

		continue;

ok:		/* To discard the first X samples in 'smps[]' we must
		 * shift them to the end of the 'smps[]' array.
		 * In case the hook returns a number 'ok' which is smaller than 'cnt',
		 * only the first 'ok' samples in 'smps[]' are accepted and further processed.
		 */

		smps[i] = smps[ok];
		smps[ok++] = cur;
	}

	if (cur)
		sample_get(cur);
	if (d->prev)
		sample_put(d->prev);

	d->prev = cur;

	*cnt = ok;

	return 0;
}

static int drop_restart(struct hook *h)
{
	struct drop *d = (struct drop *) h->_vd;

	if (d->prev) {
		sample_put(d->prev);
		d->prev = NULL;
	}

	return 0;
}

static struct plugin p = {
	.name		= "drop",
	.description	= "Drop messages with reordered sequence numbers",
	.type		= PLUGIN_TYPE_HOOK,
	.hook		= {
		.flags	= HOOK_BUILTIN | HOOK_NODE,
		.priority = 3,
		.read	= drop_read,
		.start	= drop_start,
		.stop	= drop_stop,
		.restart= drop_restart,
		.size	= sizeof(struct drop)
	}
};

REGISTER_PLUGIN(&p)

/** @} */