Another question I have is regarding _Atomic qualifiers. Since I'm not using any language-level operations that need to be atomic, and I would like for spin_lock's initialization of node not to be atomic (since no other thread will read those values), is it okay that I've left them out? Or is it illegal to cast a pointer to _Atomic?
(As an aside, the standard doesn't seem to require <stdatomic.h> in freestanding implementations, but GCC seems to provide it anyway. Am I missing something?)
Code: Select all
struct spinlock {
struct spinlock_node *tail;
};
struct spinlock_node {
struct spinlock_node *next;
bool locked;
};
static inline void spin_lock(struct spinlock *lock, struct spinlock_node *node) {
node->next = NULL;
node->locked = false;
struct spinlock_node *prev = atomic_exchange_explicit(&lock->tail, node, memory_order_acquire);
if (prev == NULL) {
return;
}
atomic_store_explicit(&prev->next, node, memory_order_relaxed);
while (!atomic_load_explicit(&node->locked, memory_order_acquire)) {
__asm__ volatile ("pause");
}
}
static inline void spin_unlock(struct spinlock *lock, struct spinlock_node *node) {
struct spinlock_node *next = atomic_load_explicit(&node->next, memory_order_relaxed);
if (next == NULL) {
struct spinlock_node *prev = node;
if (atomic_compare_exchange_strong_explicit(
&lock->tail, &prev, NULL, memory_order_release, memory_order_relaxed
)) {
return;
}
while ((next = atomic_load_explicit(&node->next, memory_order_relaxed)) == NULL) {
__asm__ volatile ("pause");
}
}
atomic_store_explicit(&next->locked, true, memory_order_release);
}
