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-rw-r--r--database/engine/rrdenglocking.c233
1 files changed, 233 insertions, 0 deletions
diff --git a/database/engine/rrdenglocking.c b/database/engine/rrdenglocking.c
new file mode 100644
index 000000000..0eb9019b4
--- /dev/null
+++ b/database/engine/rrdenglocking.c
@@ -0,0 +1,233 @@
+// 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 */
+ }
+} \ No newline at end of file
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