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Lockfree usecount: deferring unlocks to the metaloop

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This allows us for easy temporary locks without additional burden of explicit cleanup.
This commit is contained in:
Maria Matejka
2024-03-05 13:57:11 +01:00
parent 422ecddaae
commit 622d406087
3 changed files with 60 additions and 5 deletions
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49
lib/lockfree.h
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@@ -14,6 +14,7 @@
#include "lib/rcu.h"
#include "lib/settle.h"
#include "lib/tlists.h"
#include "lib/io-loop.h"
#include <stdatomic.h>
@@ -57,7 +58,7 @@ static inline u64 lfuc_lock_revive(struct lfuc *c)
}
/**
* lfuc_unlock - decrease an atomic usecount
* lfuc_unlock_immediately - decrease an atomic usecount
* @c: the usecount structure
* @el: prune event list
* @ev: prune event itself
@@ -65,7 +66,7 @@ static inline u64 lfuc_lock_revive(struct lfuc *c)
* If the usecount reaches zero, a prune event is run to possibly free the object.
* The prune event MUST use lfuc_finished() to check the object state.
*/
static inline u64 lfuc_unlock(struct lfuc *c, event_list *el, event *ev)
static inline void lfuc_unlock_immediately(struct lfuc *c, event_list *el, event *ev)
{
/* Unlocking is tricky. We do it lockless so at the same time, the prune
* event may be running, therefore if the unlock gets us to zero, it must be
@@ -112,7 +113,49 @@ static inline u64 lfuc_unlock(struct lfuc *c, event_list *el, event *ev)
* RCU synchronization instead of a busy loop. */
rcu_read_unlock();
return uc - LFUC_IN_PROGRESS - 1;
// return uc - LFUC_IN_PROGRESS - 1;
}
extern _Thread_local struct lfuc_unlock_queue {
event e;
u32 pos;
struct lfuc_unlock_queue_block {
struct lfuc *c;
event_list *el;
event *ev;
} block[0];
} *lfuc_unlock_queue;
void lfuc_unlock_deferred(void *queue);
static inline void lfuc_unlock(struct lfuc *c, event_list *el, event *ev)
{
static u32 queue_items = 0;
if (queue_items == 0)
{
ASSERT_DIE((u64) page_size > sizeof(struct lfuc_unlock_queue) + sizeof(struct lfuc_unlock_queue_block));
queue_items = (page_size - OFFSETOF(struct lfuc_unlock_queue, block))
/ sizeof lfuc_unlock_queue->block[0];
}
if (!lfuc_unlock_queue || (lfuc_unlock_queue->pos >= queue_items))
{
lfuc_unlock_queue = alloc_page();
*lfuc_unlock_queue = (struct lfuc_unlock_queue) {
.e = {
.hook = lfuc_unlock_deferred,
.data = lfuc_unlock_queue,
},
};
ev_send_this_thread(&lfuc_unlock_queue->e);
}
lfuc_unlock_queue->block[lfuc_unlock_queue->pos++] = (struct lfuc_unlock_queue_block) {
.c = c,
.el = el,
.ev = ev,
};
}
/**