rte_ticketlock.h

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/* SPDX-License-Identifier: BSD-3-Clause
 * Copyright(c) 2019 Arm Limited
 */

#ifndef _RTE_TICKETLOCK_H_
#define _RTE_TICKETLOCK_H_

#ifdef __cplusplus
extern "C" {
#endif

#include <rte_common.h>
#include <rte_lcore.h>
#include <rte_pause.h>
#include <rte_stdatomic.h>

typedef union {
    RTE_ATOMIC(uint32_t) tickets;
    struct {
        RTE_ATOMIC(uint16_t) current;
        RTE_ATOMIC(uint16_t) next;
    } s;
} rte_ticketlock_t;

#define RTE_TICKETLOCK_INITIALIZER { 0 }

static inline void
rte_ticketlock_init(rte_ticketlock_t *tl)
{
    rte_atomic_store_explicit(&tl->tickets, 0, rte_memory_order_relaxed);
}

static inline void
rte_ticketlock_lock(rte_ticketlock_t *tl)
{
    uint16_t me = rte_atomic_fetch_add_explicit(&tl->s.next, 1, rte_memory_order_relaxed);
    rte_wait_until_equal_16((uint16_t *)(uintptr_t)&tl->s.current, me,
        rte_memory_order_acquire);
}

static inline void
rte_ticketlock_unlock(rte_ticketlock_t *tl)
{
    uint16_t i = rte_atomic_load_explicit(&tl->s.current, rte_memory_order_relaxed);
    rte_atomic_store_explicit(&tl->s.current, i + 1, rte_memory_order_release);
}

static inline int
rte_ticketlock_trylock(rte_ticketlock_t *tl)
{
    rte_ticketlock_t oldl, newl;
    oldl.tickets = rte_atomic_load_explicit(&tl->tickets, rte_memory_order_relaxed);
    newl.tickets = oldl.tickets;
    newl.s.next++;
    if (oldl.s.next == oldl.s.current) {
        if (rte_atomic_compare_exchange_strong_explicit(&tl->tickets,
                (uint32_t *)(uintptr_t)&oldl.tickets, newl.tickets,
                rte_memory_order_acquire, rte_memory_order_relaxed))
            return 1;
    }

    return 0;
}

static inline int
rte_ticketlock_is_locked(rte_ticketlock_t *tl)
{
    rte_ticketlock_t tic;
    tic.tickets = rte_atomic_load_explicit(&tl->tickets, rte_memory_order_acquire);
    return (tic.s.current != tic.s.next);
}

#define TICKET_LOCK_INVALID_ID -1

typedef struct {
    rte_ticketlock_t tl; 
    RTE_ATOMIC(int) user; 
    unsigned int count; 
} rte_ticketlock_recursive_t;

#define RTE_TICKETLOCK_RECURSIVE_INITIALIZER {RTE_TICKETLOCK_INITIALIZER, \
                          TICKET_LOCK_INVALID_ID, 0}

static inline void
rte_ticketlock_recursive_init(rte_ticketlock_recursive_t *tlr)
{
    rte_ticketlock_init(&tlr->tl);
    rte_atomic_store_explicit(&tlr->user, TICKET_LOCK_INVALID_ID, rte_memory_order_relaxed);
    tlr->count = 0;
}

static inline void
rte_ticketlock_recursive_lock(rte_ticketlock_recursive_t *tlr)
{
    int id = rte_gettid();

    if (rte_atomic_load_explicit(&tlr->user, rte_memory_order_relaxed) != id) {
        rte_ticketlock_lock(&tlr->tl);
        rte_atomic_store_explicit(&tlr->user, id, rte_memory_order_relaxed);
    }
    tlr->count++;
}

static inline void
rte_ticketlock_recursive_unlock(rte_ticketlock_recursive_t *tlr)
{
    if (--(tlr->count) == 0) {
        rte_atomic_store_explicit(&tlr->user, TICKET_LOCK_INVALID_ID,
                 rte_memory_order_relaxed);
        rte_ticketlock_unlock(&tlr->tl);
    }
}

static inline int
rte_ticketlock_recursive_trylock(rte_ticketlock_recursive_t *tlr)
{
    int id = rte_gettid();

    if (rte_atomic_load_explicit(&tlr->user, rte_memory_order_relaxed) != id) {
        if (rte_ticketlock_trylock(&tlr->tl) == 0)
            return 0;
        rte_atomic_store_explicit(&tlr->user, id, rte_memory_order_relaxed);
    }
    tlr->count++;
    return 1;
}

#ifdef __cplusplus
}
#endif

#endif /* _RTE_TICKETLOCK_H_ */