/*
 * Copyright 2010-2017, Tarantool AUTHORS, please see AUTHORS file.
 *
 * Redistribution and use in source and binary forms, with or
 * without modification, are permitted provided that the following
 * conditions are met:
 *
 * 1. Redistributions of source code must retain the above
 *    copyright notice, this list of conditions and the
 *    following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above
 *    copyright notice, this list of conditions and the following
 *    disclaimer in the documentation and/or other materials
 *    provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY <COPYRIGHT HOLDER> ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
 * <COPYRIGHT HOLDER> OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
 * THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */
#include "fiber_pool.h"
/**
 * Main function of the fiber invoked to handle all outstanding
 * tasks in a queue.
 */
static int
fiber_pool_f(va_list ap)
{
	struct fiber_pool *pool = va_arg(ap, struct fiber_pool *);
	struct cord *cord = cord();
	struct fiber *f = fiber();
	struct ev_loop *loop = pool->consumer;
	struct stailq *output = &pool->output;
	struct cmsg *msg;
	ev_tstamp last_active_at = ev_monotonic_now(loop);
	pool->size++;
restart:
	msg = NULL;
	while (!stailq_empty(output) && !fiber_is_cancelled()) {
		 msg = stailq_shift_entry(output, struct cmsg, fifo);

		if (f->caller == &cord->sched && ! stailq_empty(output) &&
		    ! rlist_empty(&pool->idle)) {
			/*
			 * Activate a "backup" fiber for the next
			 * message in the queue.
			 */
			f->caller = rlist_shift_entry(&pool->idle,
						      struct fiber,
						      state);
			f->caller->flags |= FIBER_IS_READY;
			assert(f->caller->caller == &cord->sched);
		}
		cmsg_deliver(msg);
		/*
		 * Normally fibers die after their function
		 * returns, and they call on_stop() triggers. The
		 * pool optimization interferes into that logic
		 * and a fiber doesn't die after its function
		 * returns. But on_stop triggers still should be
		 * called so that the pool wouldn't affect fiber's
		 * visible lifecycle.
		 */
		fiber_on_stop(f);
	}
	/** Put the current fiber into a fiber cache. */
	if (!fiber_is_cancelled() && (msg != NULL ||
	    ev_monotonic_now(loop) - last_active_at < pool->idle_timeout)) {
		if (msg != NULL)
			last_active_at = ev_monotonic_now(loop);
		/*
		 * Add the fiber to the front of the list, so that
		 * it is most likely to get scheduled again.
		 */
		rlist_add_entry(&pool->idle, fiber(), state);
		fiber_yield();
		goto restart;
	}
	pool->size--;
	fiber_cond_signal(&pool->worker_cond);

	return 0;
}

static void
fiber_pool_idle_cb(ev_loop *loop, struct ev_timer *watcher, int events)
{
	(void) events;
	struct fiber_pool *pool = (struct fiber_pool *) watcher->data;
	if (! rlist_empty(&pool->idle)) {
		struct fiber *f;
		/*
		 * Schedule the fiber at the tail of the list,
		 * it's the one most likely to have not been
		 * scheduled lately.
		 */
		f = rlist_shift_tail_entry(&pool->idle, struct fiber, state);
		fiber_call(f);
	}
	ev_timer_again(loop, watcher);
}

/** Create fibers to handle all outstanding tasks. */
static void
fiber_pool_cb(ev_loop *loop, struct ev_watcher *watcher, int events)
{
	(void) loop;
	(void) events;
	struct fiber_pool *pool = (struct fiber_pool *) watcher->data;
	/** Fetch messages */
	cbus_endpoint_fetch(&pool->endpoint, &pool->output);

	struct stailq *output = &pool->output;
	while (! stailq_empty(output)) {
		struct fiber *f;
		if (! rlist_empty(&pool->idle)) {
			f = rlist_shift_entry(&pool->idle, struct fiber, state);
			fiber_call(f);
		} else if (pool->size < pool->max_size) {
			f = fiber_new(cord_name(cord()), fiber_pool_f);
			if (f == NULL) {
				diag_log();
				break;
			}
			fiber_start(f, pool);
		} else {
			/**
			 * No worries that this watcher may not
			 * get scheduled again - there are enough
			 * worker fibers already, so just leave.
			 */
			say_warn("fiber pool size %d reached on endpoint %s",
				 pool->max_size, pool->endpoint.name);
			break;
		}
	}
}

void
fiber_pool_set_max_size(struct fiber_pool *pool, int new_max_size)
{
	pool->max_size = new_max_size;
}

void
fiber_pool_create(struct fiber_pool *pool, const char *name, int max_pool_size,
		  float idle_timeout)
{
	pool->consumer = loop();
	pool->idle_timeout = idle_timeout;
	rlist_create(&pool->idle);
	ev_timer_init(&pool->idle_timer, fiber_pool_idle_cb, 0,
		      pool->idle_timeout);
	pool->idle_timer.data = pool;
	ev_timer_again(loop(), &pool->idle_timer);
	pool->size = 0;
	pool->max_size = max_pool_size;
	stailq_create(&pool->output);
	fiber_cond_create(&pool->worker_cond);
	/* Join fiber pool to cbus */
	cbus_endpoint_create(&pool->endpoint, name, fiber_pool_cb, pool);
}

void
fiber_pool_destroy(struct fiber_pool *pool)
{
	/** Endpoint has connected pipes or unfetched messages */
	cbus_endpoint_destroy(&pool->endpoint, NULL);
	/**
	 * At this point all messages are started to execution because last
	 * cbus poison message was fired (endpoint_destroy condition).
	 * We won't to have new messages from cbus and can send wakeup
	 * to each idle fiber. In this case idle fiber can not fetch any
	 * new message and will exit. We adjust idle_timeout to.
	 */
	pool->idle_timeout = 0;
	struct fiber *idle_fiber;
	rlist_foreach_entry(idle_fiber, &pool->idle, state)
		fiber_wakeup(idle_fiber);
	/**
	 * Just wait on fiber exit condition until all fibers are done
	 */
	while (pool->size > 0)
		fiber_cond_wait(&pool->worker_cond);
	fiber_cond_destroy(&pool->worker_cond);
}

