metalsvm/include/metalsvm/semaphore.h

/* 
 * Copyright 2010 Stefan Lankes, Chair for Operating Systems,
 *                               RWTH Aachen University
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * This file is part of MetalSVM.
 */

/**
 * @author Stefan Lankes
 * @file include/metalsvm/semaphore.h
 * @brief semaphore functions definition
 */

#ifndef __SEMAPHORE_H__
#define __SEMAPHORE_H__

#include <metalsvm/string.h>
#include <metalsvm/semaphore_types.h>
#include <metalsvm/spinlock.h>
#include <metalsvm/errno.h>
#include <metalsvm/time.h>

#ifdef __cplusplus
extern "C" {
#endif

/** @brief Semaphore initialization
 *
 * Always init semaphores before use!
 *
 * @param s Pointer to semaphore structure to initialize
 * @param v Resource count
 *
 * @return
 * - 0 on success
 * - -EINVAL on invalid argument
 */
inline static int sem_init(sem_t* s, unsigned int v) {
	unsigned int i;

	if (BUILTIN_EXPECT(!s, 0))
		return -EINVAL;

	s->value = v;
	s->pos = 0;
	for(i=0; i<MAX_TASKS; i++)
		s->queue[i] = MAX_TASKS;
	spinlock_irqsave_init(&s->lock);

	return 0;
}

/** @brief Destroy semaphore
 * @return
 * - 0 on success
 * - -EINVAL on invalid argument
 */
inline static int sem_destroy(sem_t* s) {
	if (BUILTIN_EXPECT(!s, 0))
		return -EINVAL;

	spinlock_irqsave_destroy(&s->lock);

	return 0;
}

/** @brief Nonblocking trywait for sempahore
 *
 * Will return immediately if not available
 *
 * @return
 * - 0 on success (You got the semaphore)
 * - -EINVAL on invalid argument
 * - -ECANCELED on failure (You still have to wait)
 */
inline static int sem_trywait(sem_t* s) {
	int ret = -ECANCELED;

	if (BUILTIN_EXPECT(!s, 0))
		return -EINVAL;

	spinlock_irqsave_lock(&s->lock);
	if (s->value > 0) {
		s->value--;
		ret = 0;
	}
	spinlock_irqsave_unlock(&s->lock);

	return ret;
}

/** @brief Blocking wait for semaphore
 *
 * @param ms Timeout in milliseconds
 * @return 
 * - 0 on success
 * - -EINVAL on invalid argument
 * - -ETIME on timer expired
 */
inline static int sem_wait(sem_t* s, uint32_t ms) {
	task_t* curr_task = per_core(current_task);

	if (BUILTIN_EXPECT(!s, 0))
		return -EINVAL;

	if (!ms) {
next_try1:
		spinlock_irqsave_lock(&s->lock);
		if (s->value > 0) {
			s->value--;
			spinlock_irqsave_unlock(&s->lock);
		} else {
			s->queue[s->pos] = curr_task->id;
			s->pos = (s->pos + 1) % MAX_TASKS;
			block_current_task();
			spinlock_irqsave_unlock(&s->lock);
			reschedule();
			NOP2;
			goto next_try1;
		}

		return 0;
	} else {
		uint32_t ticks = (ms * TIMER_FREQ) / 1000;
		uint32_t remain = (ms * TIMER_FREQ) % 1000;

		if (ticks) {
			uint64_t deadline = get_clock_tick() + ticks;

next_try2:
			spinlock_irqsave_lock(&s->lock);
			if (s->value > 0) {
				s->value--;
				spinlock_irqsave_unlock(&s->lock);
				return 0;
			} else {
				if (get_clock_tick() >= deadline) {
					spinlock_irqsave_unlock(&s->lock);
					goto timeout;
				}
				s->queue[s->pos] = curr_task->id;
				s->pos = (s->pos + 1) % MAX_TASKS;
				set_timer(deadline);
				spinlock_irqsave_unlock(&s->lock);
				reschedule();
				NOP2;
				goto next_try2;
			}
		}

timeout:
		while (remain) {
			udelay(1000);
			remain--;

			if (!sem_trywait(s))
				return 0;
		}

		return -ETIME;
	}
}

/** @brief Give back resource 
 * @return
 * - 0 on success
 * - -EINVAL on invalid argument
 */
inline static int sem_post(sem_t* s) {
	if (BUILTIN_EXPECT(!s, 0))
		return -EINVAL;

	spinlock_irqsave_lock(&s->lock);
	if (s->value > 0) {
		s->value++;
		spinlock_irqsave_unlock(&s->lock);
	} else {
		unsigned int k, i;

		s->value++;
		i = s->pos;
		for(k=0; k<MAX_TASKS; k++) {
			if (s->queue[i] < MAX_TASKS) {
				wakeup_task(s->queue[i]);
				s->queue[i] = MAX_TASKS;
				break;
			}
			i = (i + 1) % MAX_TASKS;
		}
		spinlock_irqsave_unlock(&s->lock);
	}

	return 0;
}

#ifdef __cplusplus
}
#endif

#endif