/* fiber.c - fiber management and scheduling
 *
 * Copyright (C) 2009 Timo Teräs <timo.teras@iki.fi>
 * All rights reserved.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 or later as
 * published by the Free Software Foundation.
 *
 * See http://www.gnu.org/ for details.
 */
#include <errno.h>
#include <libtf/tf.h>
#include TF_UCTX_H

struct tf_scheduler {
	struct tf_list_head	run_q;
	struct tf_list_head	sleep_q;

	struct tf_fiber *	active_fiber;
	int			num_fibers;
};

/* FIXME: should be in thread local storage */
static struct tf_scheduler *__scheduler;

void *tf_fiber_create(tf_fiber_proc fiber_main, int private_size)
{
	struct tf_scheduler *sched = __scheduler;
	struct tf_fiber *fiber;

	fiber = tf_uctx_create(fiber_main, private_size);

	/* The initial references for caller and scheduler */
	*fiber = (struct tf_fiber) {
		.ref_count = 2,
		.queue_node = TF_LIST_INITIALIZER(fiber->queue_node),
	};

	tf_list_add_tail(&fiber->queue_node, &sched->run_q);
	sched->num_fibers++;

	return fiber->data;
}

void __tf_fiber_destroy(struct tf_fiber *fiber)
{
	tf_uctx_destroy(fiber);
}

void *tf_fiber_get(void *data)
{
	struct tf_fiber *fiber = container_of(data, struct tf_fiber, data);
	tf_atomic_inc(fiber->ref_count);
	return data;
}

void tf_fiber_put(void *data)
{
	struct tf_fiber *fiber = container_of(data, struct tf_fiber, data);
	if (tf_atomic_dec(fiber->ref_count) == 0)
		__tf_fiber_destroy(fiber);
}

static void run_fiber(void)
{
	struct tf_scheduler *sched = __scheduler;
	struct tf_fiber *schedf = container_of((void*) __scheduler, struct tf_fiber, data);
	struct tf_fiber *f;

	if (tf_list_empty(&sched->run_q))
		return;

	f = tf_list_first(&sched->run_q, struct tf_fiber, queue_node);
	tf_list_del(&f->queue_node);

	sched->active_fiber = f;
	switch (tf_uctx_transfer(schedf, f, 1)) {
	case EFAULT: /* Fiber is dead */
		tf_fiber_put(f->data);
		sched->num_fibers--;
		break;
	case EAGAIN: /* Yielded, reshedule */
		tf_list_add_tail(&f->queue_node, &sched->run_q);
		break;
	case EIO: /* Blocked, in sleep */
		tf_list_add_tail(&f->queue_node, &sched->sleep_q);
		break;
	default:
		TF_BUG_ON("bad scheduler call from fiber");
	}
}

int tf_main(tf_fiber_proc main_fiber)
{
	struct tf_uctx *ctx = alloca(sizeof(struct tf_uctx) + sizeof(struct tf_scheduler));
	struct tf_scheduler *sched = (struct tf_scheduler*) ctx->fiber.data;
	int stack_guard = STACK_GUARD;

	ctx->stack_guard = &stack_guard;
	*sched = (struct tf_scheduler){
		.run_q = TF_LIST_HEAD_INITIALIZER(sched->run_q),
		.sleep_q = TF_LIST_HEAD_INITIALIZER(sched->sleep_q),
	};
	__scheduler = sched;
	tf_fiber_put(tf_fiber_create(main_fiber, 0));
	do {
		run_fiber();
	} while (likely(sched->num_fibers));
	__scheduler = NULL;

	return 0;
}

int tf_schedule(int err)
{
	struct tf_scheduler *sched = __scheduler;
	struct tf_fiber *schedf = container_of((void*) __scheduler, struct tf_fiber, data);
	struct tf_fiber *f = sched->active_fiber;
	int r;

	r = tf_uctx_transfer(f, schedf, err);
	if (r == 1)
		return 0;

	return r;
}

void tf_kill(void *fiber)
{
}