spinlock.c

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#include "./spinlock.h"
 
static inline void cpu_relax(void) {
    __asm__ volatile("pause" ::: "memory");
    __asm__ volatile("" ::: "memory");
}
 
void spin_acquire(spinlock_t* lock) {
 
    uint16_t my_ticket =
        __atomic_fetch_add(&lock->next_ticket, 1, __ATOMIC_RELAXED);
 
    while (__atomic_load_n(&lock->now_serving, __ATOMIC_ACQUIRE) !=
           my_ticket) {
        cpu_relax();
    }
}
 
void spin_release(spinlock_t* lock) {
 
    uint16_t next =
        __atomic_load_n(&lock->now_serving, __ATOMIC_RELAXED) + 1;
 
    __atomic_store_n(&lock->now_serving, next, __ATOMIC_RELEASE);
}
 
bool spin_is_locked(const spinlock_t* lock) {
    uint16_t serving =
        __atomic_load_n(&lock->now_serving, __ATOMIC_RELAXED);
    uint16_t next = __atomic_load_n(&lock->next_ticket, __ATOMIC_RELAXED);
    return serving != next;
}