/* wg.c - Thread management tools modeled on
 * https://golang.org/pkg/sync/#WaitGroup
 *
 * Copyright (C) 2016  Luke Shumaker
 *
 * 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
 * (at your option) 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/>.
 */

#include <errno.h>
#include <error.h>
#include <stdlib.h> /* for EXIT_FAILURE */
#include <unistd.h>

#include "wg.h"

/* pthread_cond_t is overly complicated. Just use a self-pipe. */

void wg_init(struct wg *wg) {
	wg->count = 0;
	pthread_mutex_init(&wg->lock, NULL);
	int fds[2];
	if (pipe(fds) != 0)
		error(EXIT_FAILURE, errno, "pipe");
	wg->fd_wait = fds[0];
	wg->fd_signal = fds[1];
}

void wg_add(struct wg *wg, unsigned int n) {
	pthread_mutex_lock(&wg->lock);
	wg->count += n;
	pthread_mutex_unlock(&wg->lock);
}

void wg_sub(struct wg *wg, unsigned int n) {
	pthread_mutex_lock(&wg->lock);
	wg->count -= n;
	if (wg->count == 0)
		if (write(wg->fd_signal, " ", 1) < 1)
			error(EXIT_FAILURE, errno, "write");
	pthread_mutex_unlock(&wg->lock);
}

void wg_wait(struct wg *wg) {
	char b;
 retry:
	if (read(wg->fd_wait, &b, 1) == -1) {
		if (errno == EINTR)
			goto retry;
		error(EXIT_FAILURE, errno, "wg_wait");
	}
}