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Convert rtree code to use C11 atomics

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In the process, I changed the implementation of rtree_elm_acquire so that it
won't even try to CAS if its initial read (getting the extent + lock bit)
indicates that the CAS is doomed to fail.  This can significantly improve
performance under contention.
This commit is contained in:
David Goldblatt
2017-03-09 14:49:32 -08:00
committed by David Goldblatt
parent 3a2b183d5f
commit 21a68e2d22
3 changed files with 62 additions and 39 deletions
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50
src/rtree.c
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@@ -7,7 +7,7 @@
*/
bool
rtree_new(rtree_t *rtree) {
rtree->root_pun = NULL;
atomic_store_p(&rtree->root, NULL, ATOMIC_RELAXED);
if (malloc_mutex_init(&rtree->init_lock, "rtree", WITNESS_RANK_RTREE)) {
return true;
}
@@ -54,7 +54,8 @@ rtree_delete_subtree(tsdn_t *tsdn, rtree_t *rtree, rtree_elm_t *node,
nchildren = ZU(1) << rtree_levels[level].bits;
for (i = 0; i < nchildren; i++) {
rtree_elm_t *child = node[i].child;
rtree_elm_t *child = (rtree_elm_t *)atomic_load_p(
&node[i].child_or_extent, ATOMIC_RELAXED);
if (child != NULL) {
rtree_delete_subtree(tsdn, rtree, child, level +
1);
@@ -66,19 +67,25 @@ rtree_delete_subtree(tsdn_t *tsdn, rtree_t *rtree, rtree_elm_t *node,
void
rtree_delete(tsdn_t *tsdn, rtree_t *rtree) {
if (rtree->root_pun != NULL) {
rtree_delete_subtree(tsdn, rtree, rtree->root, 0);
rtree_elm_t *rtree_root = (rtree_elm_t *)atomic_load_p(&rtree->root,
ATOMIC_RELAXED);
if (rtree_root != NULL) {
rtree_delete_subtree(tsdn, rtree, rtree_root, 0);
}
}
#endif
static rtree_elm_t *
rtree_node_init(tsdn_t *tsdn, rtree_t *rtree, unsigned level,
rtree_elm_t **elmp) {
atomic_p_t *elmp) {
rtree_elm_t *node;
malloc_mutex_lock(tsdn, &rtree->init_lock);
node = atomic_read_p((void**)elmp);
/*
* If *elmp is non-null, then it was initialized with the init lock
* held, so we can get by with 'relaxed' here.
*/
node = atomic_load_p(elmp, ATOMIC_RELAXED);
if (node == NULL) {
node = rtree_node_alloc(tsdn, rtree, ZU(1) <<
rtree_levels[level].bits);
@@ -86,7 +93,11 @@ rtree_node_init(tsdn_t *tsdn, rtree_t *rtree, unsigned level,
malloc_mutex_unlock(tsdn, &rtree->init_lock);
return NULL;
}
atomic_write_p((void **)elmp, node);
/*
* Even though we hold the lock, a later reader might not; we
* need release semantics.
*/
atomic_store_p(elmp, node, ATOMIC_RELEASE);
}
malloc_mutex_unlock(tsdn, &rtree->init_lock);
@@ -102,11 +113,14 @@ static rtree_elm_t *
rtree_child_tryread(rtree_elm_t *elm, bool dependent) {
rtree_elm_t *child;
/* Double-checked read (first read may be stale). */
child = elm->child;
if (!dependent && !rtree_node_valid(child)) {
child = (rtree_elm_t *)atomic_read_p(&elm->pun);
if (dependent) {
child = (rtree_elm_t *)atomic_load_p(&elm->child_or_extent,
ATOMIC_RELAXED);
} else {
child = (rtree_elm_t *)atomic_load_p(&elm->child_or_extent,
ATOMIC_ACQUIRE);
}
assert(!dependent || child != NULL);
return child;
}
@@ -118,7 +132,8 @@ rtree_child_read(tsdn_t *tsdn, rtree_t *rtree, rtree_elm_t *elm, unsigned level,
child = rtree_child_tryread(elm, dependent);
if (!dependent && unlikely(!rtree_node_valid(child))) {
child = rtree_node_init(tsdn, rtree, level+1, &elm->child);
child = rtree_node_init(tsdn, rtree, level + 1,
&elm->child_or_extent);
}
assert(!dependent || child != NULL);
return child;
@@ -126,10 +141,13 @@ rtree_child_read(tsdn_t *tsdn, rtree_t *rtree, rtree_elm_t *elm, unsigned level,
static rtree_elm_t *
rtree_subtree_tryread(rtree_t *rtree, bool dependent) {
/* Double-checked read (first read may be stale). */
rtree_elm_t *subtree = rtree->root;
if (!dependent && unlikely(!rtree_node_valid(subtree))) {
subtree = (rtree_elm_t *)atomic_read_p(&rtree->root_pun);
rtree_elm_t *subtree;
if (dependent) {
subtree = (rtree_elm_t *)atomic_load_p(&rtree->root,
ATOMIC_RELAXED);
} else {
subtree = (rtree_elm_t *)atomic_load_p(&rtree->root,
ATOMIC_ACQUIRE);
}
assert(!dependent || subtree != NULL);
return subtree;