lock.c

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#include <core/system.h>
#include <sys/cpu.h>
#include <sys/lock.h>
 
static volatile uint32_t next_ticket, serving;
 
/* the CPU that holds the lock, or -1 */
static volatile int owner = -1;

void kernel_lock(void)
{
    uint32_t ticket = __atomic_fetch_add(&next_ticket, 1, __ATOMIC_RELAXED);
 
    while (__atomic_load_n(&serving, __ATOMIC_ACQUIRE) != ticket)
        arch_lock_spin();
 
    owner = curcpu()->id;
    arch_lock_taken();
}

void kernel_unlock(void)
{
    owner = -1;
    __atomic_store_n(&serving, serving + 1, __ATOMIC_RELEASE);
}

int kernel_lock_held(void)
{
    return owner == curcpu()->id;
}

int kernel_enter(void)
{
    if (kernel_lock_held())
        return 0;
 
    kernel_lock();
    return 1;
}

void kernel_leave(int took)
{
    if (took)
        kernel_unlock();
}