/*

 * iSCSI timeout & deferred work handling

 *

 * Copyright (C) 2004 Dmitry Yusupov, Alex Aizman

 * Copyright (C) 2014 Red Hat Inc.

 * maintained by open-iscsi@googlegroups.com

 *

 * 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 2 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.

 *

 * See the file COPYING included with this distribution for more details.

 */

#include <inttypes.h>

#include <time.h>

#include <sys/signalfd.h>

#include <assert.h>

#include <unistd.h>

#include "actor.h"

#include "log.h"

#include "list.h"

static LIST_HEAD(pend_list);

static LIST_HEAD(ready_list);

static volatile int poll_in_progress;

static uint64_t

actor_time_left(actor_t *thread, time_t current_time)

{

	if (current_time > thread->ttschedule)

		return 0;

	else

		return (thread->ttschedule - current_time);

}

#define time_after(a,b) \

	((int64_t)(b) - (int64_t)(a) < 0)

void

actor_init(actor_t *thread, void (*callback)(void *), void *data)

{

	INIT_LIST_HEAD(&thread->list);

	thread->state = ACTOR_NOTSCHEDULED;

	thread->callback = callback;

	thread->data = data;

}

void

actor_delete(actor_t *thread)

{

	log_debug(7, "thread %08lx delete: state %d", (long)thread,

			thread->state);

	switch(thread->state) {

	case ACTOR_WAITING:

		/* TODO: remove/reset alarm if we were 1st entry in pend_list */

		/* priority: low */

		/* fallthrough */

	case ACTOR_SCHEDULED:

		log_debug(1, "deleting a scheduled/waiting thread!");

		list_del_init(&thread->list);

		if (list_empty(&pend_list)) {

			log_debug(7, "nothing left on pend_list, deactivating alarm");

			alarm(0);

		}

		break;

	default:

		break;

	}

	thread->state = ACTOR_NOTSCHEDULED;

}

/*

 * Inserts actor on pend list and sets alarm if new item is

 * sooner than previous entries.

 */

static void

actor_insert_on_pend_list(actor_t *thread, uint32_t delay_secs)

{

	struct actor *orig_head;

	struct actor *new_head;

	struct actor *next_thread;

	orig_head = list_first_entry_or_null(&pend_list,

					     struct actor, list);

	/* insert new entry in sort order */

	list_for_each_entry(next_thread, &pend_list, list) {

		if (time_after(next_thread->ttschedule, thread->ttschedule)) {

			log_debug(7, "next thread %p due %lld", next_thread,

			  (long long)next_thread->ttschedule);

			log_debug(7, "new thread %p is before (%lld), inserting", thread,

			  (long long)thread->ttschedule);

			/* insert new thread before the next thread */

			__list_add(&thread->list, next_thread->list.prev, &next_thread->list);

			goto inserted;

		}

	}

	if (orig_head) {

		log_debug(7, "last thread %p due %lld", next_thread,

			  (long long)next_thread->ttschedule);

		log_debug(7, "new thread %p is after (%lld), inserting at tail", thread,

			  (long long)thread->ttschedule);

	}

	else

		log_debug(7, "new thread %p due %lld is first item on pend_list", thread,

			  (long long)thread->ttschedule);

	/* Not before any existing entries */

	list_add_tail(&thread->list, &pend_list);

inserted:

	new_head = list_first_entry(&pend_list, struct actor, list);

	if (orig_head != new_head) {

		int result = alarm(delay_secs);

		log_debug(7, "new alarm set for %d seconds, old alarm %d",

			  delay_secs, result);

	}

}

static void

actor_schedule_private(actor_t *thread, uint32_t delay_secs, int head)

{

	time_t current_time;

	struct timespec tv;

	if (clock_gettime(CLOCK_MONOTONIC_COARSE, &tv)) {

		log_error("clock_getime failed, can't schedule!");

		return;

	}

	current_time = tv.tv_sec;

	log_debug(7, "thread %p schedule: delay %u state %d",

		thread, delay_secs, thread->state);

	switch(thread->state) {

	case ACTOR_WAITING:

		log_error("rescheduling a waiting thread!");

		list_del(&thread->list);

		/* fall-through */

	case ACTOR_NOTSCHEDULED:

		INIT_LIST_HEAD(&thread->list);

		if (delay_secs == 0) {

			thread->state = ACTOR_SCHEDULED;

			if (head)

				list_add(&thread->list, &ready_list);

			else

				list_add_tail(&thread->list, &ready_list);

		} else {

			thread->state = ACTOR_WAITING;

			thread->ttschedule = current_time + delay_secs;

			actor_insert_on_pend_list(thread, delay_secs);

		}

		break;

	case ACTOR_SCHEDULED:

		// don't do anything

		break;

	case ACTOR_INVALID:

		log_error("BUG: Trying to schedule a thread that has not been "

			  "setup. Ignoring sched.");

		break;

	}

}

void

actor_schedule_head(actor_t *thread)

{

	actor_schedule_private(thread, 0, 1);

}

void

actor_schedule(actor_t *thread)

{

	actor_schedule_private(thread, 0, 0);

}

void

actor_timer(actor_t *thread, uint32_t timeout_secs, void (*callback)(void *),

	    void *data)

{

	actor_init(thread, callback, data);

	actor_schedule_private(thread, timeout_secs, 0);

}

void

actor_timer_mod(actor_t *thread, uint32_t new_timeout_secs, void *data)

{

	actor_delete(thread);

	thread->data = data;

	actor_schedule_private(thread, new_timeout_secs, 0);

}

/*

 * Execute all items that have expired.

 *

 * Set an alarm if items remain. Caller must catch SIGALRM and

 * then re-invoke this function.

 */

void

actor_poll(void)

{

	struct actor *thread, *tmp;

	uint64_t current_time;

	struct timespec tv;

	if (poll_in_progress) {

		log_error("recursive actor_poll() is not allowed");

		return;

	}

	if (clock_gettime(CLOCK_MONOTONIC_COARSE, &tv)) {

		log_error("clock_gettime failed, can't schedule!");

		return;

	}

	current_time = tv.tv_sec;

	/*

	 * Move items that are ripe from pend_list to ready_list.

	 * Actors are in sorted order of ascending run time, so

	 * stop at the first unripe entry.

	 */

	log_debug(7, "current time %" PRIu64, current_time);

	list_for_each_entry_safe(thread, tmp, &pend_list, list) {

		uint64_t time_left = actor_time_left(thread, current_time);

		if (time_left) {

			log_debug(7, "thread %08lx due %" PRIu64 ", wait %" PRIu64 " more",

				  (long)thread,

				  (uint64_t)thread->ttschedule, time_left);

			alarm(time_left);

			break;

		}

		/* This entry can be run now */

		list_del_init(&thread->list);

		log_debug(2, "thread %08lx was scheduled for "

			  "%" PRIu64 ", curtime %" PRIu64 " q_forw %p "

			  "&pend_list %p",

			  (long)thread, (uint64_t)thread->ttschedule,

			  current_time, pend_list.next, &pend_list);

		list_add_tail(&thread->list, &ready_list);

		assert(thread->state == ACTOR_WAITING);

		thread->state = ACTOR_SCHEDULED;

		log_debug(7, "thread %08lx now in ready_list",

			  (long)thread);

	}

	/* Disable alarm if nothing else pending */

	if (list_empty(&pend_list)) {

		log_debug(7, "nothing on pend_list, deactivating alarm");

		alarm(0);

	}

	poll_in_progress = 1;

	while (!list_empty(&ready_list)) {

		thread = list_first_entry(&ready_list, struct actor, list);

		list_del_init(&thread->list);

		if (thread->state != ACTOR_SCHEDULED)

			log_error("ready_list: thread state corrupted! "

				  "Thread with state %d in actor list.",

				  thread->state);

		thread->state = ACTOR_NOTSCHEDULED;

		log_debug(7, "exec thread %08lx callback", (long)thread);

		thread->callback(thread->data);

		log_debug(7, "thread %08lx done", (long)thread);

	}

	poll_in_progress = 0;

}