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// SPDX-License-Identifier: GPL-3.0-or-later
#include "rrdengine.h"
struct page_cache_descr *rrdeng_create_pg_cache_descr(struct rrdengine_instance *ctx)
{
struct page_cache_descr *pg_cache_descr;
pg_cache_descr = mallocz(sizeof(*pg_cache_descr));
rrd_stat_atomic_add(&ctx->stats.page_cache_descriptors, 1);
pg_cache_descr->page = NULL;
pg_cache_descr->flags = 0;
pg_cache_descr->prev = pg_cache_descr->next = NULL;
pg_cache_descr->refcnt = 0;
pg_cache_descr->waiters = 0;
assert(0 == uv_cond_init(&pg_cache_descr->cond));
assert(0 == uv_mutex_init(&pg_cache_descr->mutex));
return pg_cache_descr;
}
void rrdeng_destroy_pg_cache_descr(struct rrdengine_instance *ctx, struct page_cache_descr *pg_cache_descr)
{
uv_cond_destroy(&pg_cache_descr->cond);
uv_mutex_destroy(&pg_cache_descr->mutex);
freez(pg_cache_descr);
rrd_stat_atomic_add(&ctx->stats.page_cache_descriptors, -1);
}
/* also allocates page cache descriptor if missing */
void rrdeng_page_descr_mutex_lock(struct rrdengine_instance *ctx, struct rrdeng_page_descr *descr)
{
unsigned long old_state, old_users, new_state, ret_state;
struct page_cache_descr *pg_cache_descr = NULL;
uint8_t we_locked;
we_locked = 0;
while (1) { /* spin */
old_state = descr->pg_cache_descr_state;
old_users = old_state >> PG_CACHE_DESCR_SHIFT;
if (unlikely(we_locked)) {
assert(old_state & PG_CACHE_DESCR_LOCKED);
new_state = (1 << PG_CACHE_DESCR_SHIFT) | PG_CACHE_DESCR_ALLOCATED;
ret_state = ulong_compare_and_swap(&descr->pg_cache_descr_state, old_state, new_state);
if (old_state == ret_state) {
/* success */
break;
}
continue; /* spin */
}
if (old_state & PG_CACHE_DESCR_LOCKED) {
assert(0 == old_users);
continue; /* spin */
}
if (0 == old_state) {
/* no page cache descriptor has been allocated */
if (NULL == pg_cache_descr) {
pg_cache_descr = rrdeng_create_pg_cache_descr(ctx);
}
new_state = PG_CACHE_DESCR_LOCKED;
ret_state = ulong_compare_and_swap(&descr->pg_cache_descr_state, 0, new_state);
if (0 == ret_state) {
we_locked = 1;
descr->pg_cache_descr = pg_cache_descr;
pg_cache_descr->descr = descr;
pg_cache_descr = NULL; /* make sure we don't free pg_cache_descr */
/* retry */
continue;
}
continue; /* spin */
}
/* page cache descriptor is already allocated */
assert(old_state & PG_CACHE_DESCR_ALLOCATED);
new_state = (old_users + 1) << PG_CACHE_DESCR_SHIFT;
new_state |= old_state & PG_CACHE_DESCR_FLAGS_MASK;
ret_state = ulong_compare_and_swap(&descr->pg_cache_descr_state, old_state, new_state);
if (old_state == ret_state) {
/* success */
break;
}
/* spin */
}
if (pg_cache_descr) {
rrdeng_destroy_pg_cache_descr(ctx, pg_cache_descr);
}
pg_cache_descr = descr->pg_cache_descr;
uv_mutex_lock(&pg_cache_descr->mutex);
}
void rrdeng_page_descr_mutex_unlock(struct rrdengine_instance *ctx, struct rrdeng_page_descr *descr)
{
unsigned long old_state, new_state, ret_state, old_users;
struct page_cache_descr *pg_cache_descr;
uint8_t we_locked;
uv_mutex_unlock(&descr->pg_cache_descr->mutex);
we_locked = 0;
while (1) { /* spin */
old_state = descr->pg_cache_descr_state;
old_users = old_state >> PG_CACHE_DESCR_SHIFT;
if (unlikely(we_locked)) {
assert(0 == old_users);
ret_state = ulong_compare_and_swap(&descr->pg_cache_descr_state, old_state, 0);
if (old_state == ret_state) {
/* success */
break;
}
continue; /* spin */
}
if (old_state & PG_CACHE_DESCR_LOCKED) {
assert(0 == old_users);
continue; /* spin */
}
assert(old_state & PG_CACHE_DESCR_ALLOCATED);
pg_cache_descr = descr->pg_cache_descr;
/* caller is the only page cache descriptor user and there are no pending references on the page */
if ((old_state & PG_CACHE_DESCR_DESTROY) && (1 == old_users) &&
!pg_cache_descr->flags && !pg_cache_descr->refcnt) {
new_state = PG_CACHE_DESCR_LOCKED;
ret_state = ulong_compare_and_swap(&descr->pg_cache_descr_state, old_state, new_state);
if (old_state == ret_state) {
we_locked = 1;
rrdeng_destroy_pg_cache_descr(ctx, pg_cache_descr);
/* retry */
continue;
}
continue; /* spin */
}
assert(old_users > 0);
new_state = (old_users - 1) << PG_CACHE_DESCR_SHIFT;
new_state |= old_state & PG_CACHE_DESCR_FLAGS_MASK;
ret_state = ulong_compare_and_swap(&descr->pg_cache_descr_state, old_state, new_state);
if (old_state == ret_state) {
/* success */
break;
}
/* spin */
}
}
/*
* Tries to deallocate page cache descriptor. If it fails, it postpones deallocation by setting the
* PG_CACHE_DESCR_DESTROY flag which will be eventually cleared by a different context after doing
* the deallocation.
*/
void rrdeng_try_deallocate_pg_cache_descr(struct rrdengine_instance *ctx, struct rrdeng_page_descr *descr)
{
unsigned long old_state, new_state, ret_state, old_users;
struct page_cache_descr *pg_cache_descr;
uint8_t just_locked, we_freed, must_unlock;
just_locked = 0;
we_freed = 0;
must_unlock = 0;
while (1) { /* spin */
old_state = descr->pg_cache_descr_state;
old_users = old_state >> PG_CACHE_DESCR_SHIFT;
if (unlikely(just_locked)) {
assert(0 == old_users);
must_unlock = 1;
just_locked = 0;
/* Try deallocate if there are no pending references on the page */
if (!pg_cache_descr->flags && !pg_cache_descr->refcnt) {
rrdeng_destroy_pg_cache_descr(ctx, pg_cache_descr);
we_freed = 1;
/* success */
continue;
}
continue; /* spin */
}
if (unlikely(must_unlock)) {
assert(0 == old_users);
if (we_freed) {
/* success */
new_state = 0;
} else {
new_state = old_state | PG_CACHE_DESCR_DESTROY;
new_state &= ~PG_CACHE_DESCR_LOCKED;
}
ret_state = ulong_compare_and_swap(&descr->pg_cache_descr_state, old_state, new_state);
if (old_state == ret_state) {
/* unlocked */
return;
}
continue; /* spin */
}
if (!(old_state & PG_CACHE_DESCR_ALLOCATED)) {
/* don't do anything */
return;
}
if (old_state & PG_CACHE_DESCR_LOCKED) {
assert(0 == old_users);
continue; /* spin */
}
pg_cache_descr = descr->pg_cache_descr;
/* caller is the only page cache descriptor user */
if (0 == old_users) {
new_state = old_state | PG_CACHE_DESCR_LOCKED;
ret_state = ulong_compare_and_swap(&descr->pg_cache_descr_state, old_state, new_state);
if (old_state == ret_state) {
just_locked = 1;
/* retry */
continue;
}
continue; /* spin */
}
if (old_state & PG_CACHE_DESCR_DESTROY) {
/* don't do anything */
return;
}
/* plant PG_CACHE_DESCR_DESTROY so that other contexts eventually free the page cache descriptor */
new_state = old_state | PG_CACHE_DESCR_DESTROY;
ret_state = ulong_compare_and_swap(&descr->pg_cache_descr_state, old_state, new_state);
if (old_state == ret_state) {
/* success */
return;
}
/* spin */
}
}
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