rte_rwlock.h

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/* SPDX-License-Identifier: BSD-3-Clause
 * Copyright(c) 2010-2014 Intel Corporation
 */

#ifndef _RTE_RWLOCK_H_
#define _RTE_RWLOCK_H_

#ifdef __cplusplus
extern "C" {
#endif

#include <rte_common.h>
#include <rte_atomic.h>
#include <rte_pause.h>

typedef struct {
    volatile int32_t cnt; 
} rte_rwlock_t;

#define RTE_RWLOCK_INITIALIZER { 0 }

static inline void
rte_rwlock_init(rte_rwlock_t *rwl)
{
    rwl->cnt = 0;
}

static inline void
rte_rwlock_read_lock(rte_rwlock_t *rwl)
{
    int32_t x;
    int success = 0;

    while (success == 0) {
        x = __atomic_load_n(&rwl->cnt, __ATOMIC_RELAXED);
        /* write lock is held */
        if (x < 0) {
            rte_pause();
            continue;
        }
        success = __atomic_compare_exchange_n(&rwl->cnt, &x, x + 1, 1,
                    __ATOMIC_ACQUIRE, __ATOMIC_RELAXED);
    }
}

static inline __rte_experimental int
rte_rwlock_read_trylock(rte_rwlock_t *rwl)
{
    int32_t x;
    int success = 0;

    while (success == 0) {
        x = __atomic_load_n(&rwl->cnt, __ATOMIC_RELAXED);
        /* write lock is held */
        if (x < 0)
            return -EBUSY;
        success = __atomic_compare_exchange_n(&rwl->cnt, &x, x + 1, 1,
                    __ATOMIC_ACQUIRE, __ATOMIC_RELAXED);
    }

    return 0;
}

static inline void
rte_rwlock_read_unlock(rte_rwlock_t *rwl)
{
    __atomic_fetch_sub(&rwl->cnt, 1, __ATOMIC_RELEASE);
}

static inline __rte_experimental int
rte_rwlock_write_trylock(rte_rwlock_t *rwl)
{
    int32_t x;

    x = __atomic_load_n(&rwl->cnt, __ATOMIC_RELAXED);
    if (x != 0 || __atomic_compare_exchange_n(&rwl->cnt, &x, -1, 1,
                  __ATOMIC_ACQUIRE, __ATOMIC_RELAXED) == 0)
        return -EBUSY;

    return 0;
}

static inline void
rte_rwlock_write_lock(rte_rwlock_t *rwl)
{
    int32_t x;
    int success = 0;

    while (success == 0) {
        x = __atomic_load_n(&rwl->cnt, __ATOMIC_RELAXED);
        /* a lock is held */
        if (x != 0) {
            rte_pause();
            continue;
        }
        success = __atomic_compare_exchange_n(&rwl->cnt, &x, -1, 1,
                    __ATOMIC_ACQUIRE, __ATOMIC_RELAXED);
    }
}

static inline void
rte_rwlock_write_unlock(rte_rwlock_t *rwl)
{
    __atomic_store_n(&rwl->cnt, 0, __ATOMIC_RELEASE);
}

static inline void
rte_rwlock_read_lock_tm(rte_rwlock_t *rwl);

static inline void
rte_rwlock_read_unlock_tm(rte_rwlock_t *rwl);

static inline void
rte_rwlock_write_lock_tm(rte_rwlock_t *rwl);

static inline void
rte_rwlock_write_unlock_tm(rte_rwlock_t *rwl);

#ifdef __cplusplus
}
#endif

#endif /* _RTE_RWLOCK_H_ */