/* 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. */

static
void *wg_gc(void *wg_anon) {
	struct wg *wg = wg_anon;

	pthread_t thread;
	while (1) {
		ssize_t r = read(wg->fd_threads[0], &thread, sizeof(thread));
		if (r < 0) {
			if (errno == EINTR)
				continue;
			error(EXIT_FAILURE, errno, "wg_gc: read");
		} else if ((size_t)r < sizeof(thread)) {
			error(EXIT_FAILURE, 0, "wg_gc: read: only read %zd/%zu", r, sizeof(thread));
		}

		pthread_join(thread, NULL);

		int p;
		if ((p = pthread_mutex_lock(&wg->lock)) != 0)
			error(EXIT_FAILURE, p, "wg_gc: pthread_mutex_lock");
		wg->count--;
		if (wg->count == 0) {
			if ((p = pthread_mutex_unlock(&wg->lock)) != 0)
				error(EXIT_FAILURE, p, "wg_gc: pthread_mutex_unlock");
			return NULL;
		}
		if ((p = pthread_mutex_unlock(&wg->lock)) != 0)
			error(EXIT_FAILURE, p, "wg_gc: pthread_mutex_unlock");
	}
}

void wg_init(struct wg *wg) {
	wg->count = 0;
	int r;
	if ((r = pthread_mutex_init(&wg->lock, NULL)) != 0)
		error(EXIT_FAILURE, r, "wg_init: pthread_mutex_init");
	if (pipe(wg->fd_threads) != 0)
		error(EXIT_FAILURE, errno, "wg_init: pipe");
	if ((r = pthread_create(&wg->gc, NULL, wg_gc, (void*)wg)) != 0)
		error(EXIT_FAILURE, r, "wg_init: pthread_create");
}

void wg_add(struct wg *wg) {
	int r;
	if ((r = pthread_mutex_lock(&wg->lock)) != 0)
		error(EXIT_FAILURE, r, "wg_add: pthread_mutex_lock");
	wg->count++;
	if ((r = pthread_mutex_unlock(&wg->lock)) != 0)
		error(EXIT_FAILURE, r, "wg_add: pthread_mutex_unlock");
}

void wg_sub(struct wg *wg) {
	pthread_t thread = pthread_self();
	ssize_t r = write(wg->fd_threads[1], &thread, sizeof(thread));
	if (r < 0) {
		error(EXIT_FAILURE, errno, "wg_sub: write");
	} else if ((size_t)r < sizeof(thread)) {
		error(EXIT_FAILURE, 0, "wg_sub: only wrote %zd/%zu", r, sizeof(thread));
	}
}

void wg_wait(struct wg *wg) {
	int r;
	if ((r = pthread_join(wg->gc, NULL)) != 0)
		error(EXIT_FAILURE, r, "wg_wait: pthread_join");
	if (close(wg->fd_threads[1]) != 0)
		error(EXIT_FAILURE, errno, "wg_wait: close(fd_threads[1])");
	if (close(wg->fd_threads[0]) != 0)
		error(EXIT_FAILURE, errno, "wg_wait: close(fd_threads[0])");
	if ((r = pthread_mutex_destroy(&wg->lock)) != 0)
		error(EXIT_FAILURE, r, "wg_wait: pthread_mutex_destroy");
}