mutex.h

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/*
 * Copyright (C) 2015 Kaspar Schleiser <kaspar@schleiser.de>
 *               2013, 2014 Freie Universität Berlin
 *
 * This file is subject to the terms and conditions of the GNU Lesser
 * General Public License v2.1. See the file LICENSE in the top level
 * directory for more details.
 */
 
#ifndef MUTEX_H
#define MUTEX_H
 
#include <stddef.h>
#include <stdint.h>
 
#include "kernel_defines.h"
#include "list.h"
#include "thread.h"
 
#ifndef __cplusplus
#include "irq.h"
#endif
 
#ifdef __cplusplus
extern "C" {
#endif
 
typedef struct {
    list_node_t queue;
} mutex_t;
 
typedef struct {
    mutex_t *mutex;     
    thread_t *thread;   
    uint8_t cancelled;  
} mutex_cancel_t;
 
#define MUTEX_INIT { { NULL } }
 
#define MUTEX_INIT_LOCKED { { MUTEX_LOCKED } }
 
#define MUTEX_LOCKED ((list_node_t *)-1)
static inline void mutex_init(mutex_t *mutex)
{
    mutex->queue.next = NULL;
}
 
static inline mutex_cancel_t mutex_cancel_init(mutex_t *mutex)
{
    mutex_cancel_t result = { mutex, thread_get_active(), 0 };
 
    return result;
}
 
int mutex_trylock_ffi(mutex_t *mutex);
 
static inline int mutex_trylock(mutex_t *mutex)
{
#ifdef __cplusplus
    return mutex_trylock_ffi(mutex);
#else
    unsigned irq_state = irq_disable();
    int retval = 0;
 
    if (mutex->queue.next == NULL) {
        mutex->queue.next = MUTEX_LOCKED;
        retval = 1;
    }
    irq_restore(irq_state);
    return retval;
#endif
}
 
#if (MAXTHREADS > 1) || DOXYGEN
void mutex_lock(mutex_t *mutex);
#else
static inline void mutex_lock(mutex_t *mutex)
{
    /* (ab)use next pointer as lock variable */
    volatile uintptr_t *lock = (void *)&mutex->queue.next;
 
    /* spin until lock is released (e.g. by interrupt).
     *
     * Note: since only the numbers 0 and 1 are ever stored in lock, this
     * read does not need to be atomic here - even while a concurrent write
     * is performed on lock, a read will still either yield 0 or 1 (so the old
     * or new value, which both is fine), even if the lock is read out byte-wise
     * (e.g. on AVR).
     */
    while (*lock) {}
 
    /* set lock variable */
    *lock = 1;
}
#endif
 
int mutex_lock_cancelable(mutex_cancel_t *mc);
 
#if (MAXTHREADS > 1) || DOXYGEN
void mutex_unlock(mutex_t *mutex);
#else
static inline void mutex_unlock(mutex_t *mutex)
{
    /* (ab)use next pointer as lock variable */
    mutex->queue.next = NULL;
}
#endif
 
void mutex_unlock_and_sleep(mutex_t *mutex);
 
void mutex_cancel(mutex_cancel_t *mc);
 
#ifdef __cplusplus
}
#endif
 
#endif /* MUTEX_H */