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Rewrite command queue handling. Each client still has a command queue,
but there is also now a global command queue. Instead of command queues
being dispatched on demand from wherever the command happens to be
added, they are now all dispatched from the top level server
loop. Command queues may now also include callbacks as well as commands,
and items may be inserted after the current command as well as at the end.

This all makes command queues significantly more predictable and easier
to use, and avoids the complex multiple nested command queues used by
source-file, if-shell and friends.

A mass rename of struct cmdq to a better name (cmdq_item probably) is
coming.

/* $OpenBSD: cmd-wait-for.c,v 1.15 2016/10/16 17:55:14 nicm Exp $ */

/*
 * Copyright (c) 2013 Nicholas Marriott <nicholas.marriott@gmail.com>
 * Copyright (c) 2013 Thiago de Arruda <tpadilha84@gmail.com>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF MIND, USE, DATA OR PROFITS, WHETHER
 * IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
 * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <sys/types.h>

#include <stdlib.h>
#include <string.h>

#include "tmux.h"

/*
 * Block or wake a client on a named wait channel.
 */

static enum cmd_retval cmd_wait_for_exec(struct cmd *, struct cmd_q *);

const struct cmd_entry cmd_wait_for_entry = {
	.name = "wait-for",
	.alias = "wait",

	.args = { "LSU", 1, 1 },
	.usage = "[-L|-S|-U] channel",

	.flags = 0,
	.exec = cmd_wait_for_exec
};

struct wait_item {
	struct cmd_q		*cmdq;
	TAILQ_ENTRY(wait_item)	 entry;
};

struct wait_channel {
	const char	       *name;
	int			locked;
	int			woken;

	TAILQ_HEAD(, wait_item)	waiters;
	TAILQ_HEAD(, wait_item)	lockers;

	RB_ENTRY(wait_channel)	entry;
};
RB_HEAD(wait_channels, wait_channel);
static struct wait_channels wait_channels = RB_INITIALIZER(wait_channels);

static int wait_channel_cmp(struct wait_channel *, struct wait_channel *);
RB_GENERATE_STATIC(wait_channels, wait_channel, entry, wait_channel_cmp);

static int
wait_channel_cmp(struct wait_channel *wc1, struct wait_channel *wc2)
{
	return (strcmp(wc1->name, wc2->name));
}

static enum cmd_retval	cmd_wait_for_signal(struct cmd_q *, const char *,
			    struct wait_channel *);
static enum cmd_retval	cmd_wait_for_wait(struct cmd_q *, const char *,
			    struct wait_channel *);
static enum cmd_retval	cmd_wait_for_lock(struct cmd_q *, const char *,
			    struct wait_channel *);
static enum cmd_retval	cmd_wait_for_unlock(struct cmd_q *, const char *,
			    struct wait_channel *);

static struct wait_channel	*cmd_wait_for_add(const char *);
static void			 cmd_wait_for_remove(struct wait_channel *wc);

static struct wait_channel *
cmd_wait_for_add(const char *name)
{
	struct wait_channel *wc;

	wc = xmalloc(sizeof *wc);
	wc->name = xstrdup(name);

	wc->locked = 0;
	wc->woken = 0;

	TAILQ_INIT(&wc->waiters);
	TAILQ_INIT(&wc->lockers);

	RB_INSERT(wait_channels, &wait_channels, wc);

	log_debug("add wait channel %s", wc->name);

	return (wc);
}

static void
cmd_wait_for_remove(struct wait_channel *wc)
{
	if (wc->locked)
		return;
	if (!TAILQ_EMPTY(&wc->waiters) || !wc->woken)
		return;

	log_debug("remove wait channel %s", wc->name);

	RB_REMOVE(wait_channels, &wait_channels, wc);

	free((void *)wc->name);
	free(wc);
}

static enum cmd_retval
cmd_wait_for_exec(struct cmd *self, struct cmd_q *cmdq)
{
	struct args     	*args = self->args;
	const char		*name = args->argv[0];
	struct wait_channel	*wc, wc0;

	wc0.name = name;
	wc = RB_FIND(wait_channels, &wait_channels, &wc0);

	if (args_has(args, 'S'))
		return (cmd_wait_for_signal(cmdq, name, wc));
	if (args_has(args, 'L'))
		return (cmd_wait_for_lock(cmdq, name, wc));
	if (args_has(args, 'U'))
		return (cmd_wait_for_unlock(cmdq, name, wc));
	return (cmd_wait_for_wait(cmdq, name, wc));
}

static enum cmd_retval
cmd_wait_for_signal(__unused struct cmd_q *cmdq, const char *name,
    struct wait_channel *wc)
{
	struct wait_item	*wi, *wi1;

	if (wc == NULL)
		wc = cmd_wait_for_add(name);

	if (TAILQ_EMPTY(&wc->waiters) && !wc->woken) {
		log_debug("signal wait channel %s, no waiters", wc->name);
		wc->woken = 1;
		return (CMD_RETURN_NORMAL);
	}
	log_debug("signal wait channel %s, with waiters", wc->name);

	TAILQ_FOREACH_SAFE(wi, &wc->waiters, entry, wi1) {
		wi->cmdq->flags &= ~CMD_Q_WAITING;

		TAILQ_REMOVE(&wc->waiters, wi, entry);
		free(wi);
	}

	cmd_wait_for_remove(wc);
	return (CMD_RETURN_NORMAL);
}

static enum cmd_retval
cmd_wait_for_wait(struct cmd_q *cmdq, const char *name, struct wait_channel *wc)
{
	struct client		*c = cmdq->client;
	struct wait_item	*wi;

	if (c == NULL || c->session != NULL) {
		cmdq_error(cmdq, "not able to wait");
		return (CMD_RETURN_ERROR);
	}

	if (wc == NULL)
		wc = cmd_wait_for_add(name);

	if (wc->woken) {
		log_debug("wait channel %s already woken (%p)", wc->name, c);
		cmd_wait_for_remove(wc);
		return (CMD_RETURN_NORMAL);
	}
	log_debug("wait channel %s not woken (%p)", wc->name, c);

	wi = xcalloc(1, sizeof *wi);
	wi->cmdq = cmdq;
	TAILQ_INSERT_TAIL(&wc->waiters, wi, entry);

	return (CMD_RETURN_WAIT);
}

static enum cmd_retval
cmd_wait_for_lock(struct cmd_q *cmdq, const char *name, struct wait_channel *wc)
{
	struct wait_item	*wi;

	if (cmdq->client == NULL || cmdq->client->session != NULL) {
		cmdq_error(cmdq, "not able to lock");
		return (CMD_RETURN_ERROR);
	}

	if (wc == NULL)
		wc = cmd_wait_for_add(name);

	if (wc->locked) {
		wi = xcalloc(1, sizeof *wi);
		wi->cmdq = cmdq;
		TAILQ_INSERT_TAIL(&wc->lockers, wi, entry);
		return (CMD_RETURN_WAIT);
	}
	wc->locked = 1;

	return (CMD_RETURN_NORMAL);
}

static enum cmd_retval
cmd_wait_for_unlock(struct cmd_q *cmdq, const char *name,
    struct wait_channel *wc)
{
	struct wait_item	*wi;

	if (wc == NULL || !wc->locked) {
		cmdq_error(cmdq, "channel %s not locked", name);
		return (CMD_RETURN_ERROR);
	}

	if ((wi = TAILQ_FIRST(&wc->lockers)) != NULL) {
		wi->cmdq->flags &= ~CMD_Q_WAITING;
		TAILQ_REMOVE(&wc->lockers, wi, entry);
		free(wi);
	} else {
		wc->locked = 0;
		cmd_wait_for_remove(wc);
	}

	return (CMD_RETURN_NORMAL);
}

void
cmd_wait_for_flush(void)
{
	struct wait_channel	*wc, *wc1;
	struct wait_item	*wi, *wi1;

	RB_FOREACH_SAFE(wc, wait_channels, &wait_channels, wc1) {
		TAILQ_FOREACH_SAFE(wi, &wc->waiters, entry, wi1) {
			wi->cmdq->flags &= ~CMD_Q_WAITING;
			TAILQ_REMOVE(&wc->waiters, wi, entry);
			free(wi);
		}
		wc->woken = 1;
		TAILQ_FOREACH_SAFE(wi, &wc->lockers, entry, wi1) {
			wi->cmdq->flags &= ~CMD_Q_WAITING;
			TAILQ_REMOVE(&wc->lockers, wi, entry);
			free(wi);
		}
		wc->locked = 0;
		cmd_wait_for_remove(wc);
	}
}