* See also Kir Fraser's dissertation "Practical Lock Freedom".
* www.cl.cam.ac.uk/techreports/UCAM-CL-TR-579.pdf
*
- * This code is written for the x86 memory-model. The algorithim depends on certain stores and
- * loads being ordered. Be careful, this code won't work correctly on platforms with weaker memory
- * models if you don't add memory barriers in the right places.
+ * I've generalized the data structure to support update operations like set() and CAS() in addition to
+ * the normal add() and remove() operations.
+ *
+ * Warning: This code is written for the x86 memory-model. The algorithim depends on certain stores
+ * and loads being ordered. This code won't work correctly on platforms with weaker memory models if
+ * you don't add memory barriers in the right places.
*/
#include <stdio.h>
#include <string.h>
-#define ENABLE_TRACE
-
#include "common.h"
#include "runtime.h"
-#include "mlocal.h"
+#include "skiplist.h"
#include "mem.h"
-#include "tls.h"
-// Setting MAX_LEVEL to 0 essentially makes this data structure the Harris-Michael lock-free list
-// (in list.c).
+// Setting MAX_LEVEL to 0 essentially makes this data structure the Harris-Michael lock-free list (in list.c).
#define MAX_LEVEL 31
-typedef struct node {
+typedef struct sl_iter node_t;
+
+struct sl_iter {
void *key;
uint64_t val;
int top_level;
- struct node *next[];
-} node_t;
+ node_t *next[];
+};
struct sl {
node_t *head;
- cmp_fun_t cmp_fun;
- clone_fun_t clone_fun;
+ const datatype_t *key_type;
};
-static const map_impl_t sl_map_impl = {
- (map_alloc_t)sl_alloc, (map_cas_t)sl_cas, (map_get_t)sl_lookup, (map_remove_t)sl_remove,
- (map_count_t)sl_count, (map_print_t)sl_print, (map_free_t)sl_free
-};
-
-const map_impl_t *MAP_TYPE_SKIPLIST = &sl_map_impl;
-
static int random_level (void) {
unsigned r = nbd_rand();
if (r & 1)
return item;
}
-skiplist_t *sl_alloc (cmp_fun_t cmp_fun, hash_fun_t hash_fun, clone_fun_t clone_fun) {
+skiplist_t *sl_alloc (const datatype_t *key_type) {
skiplist_t *sl = (skiplist_t *)nbd_malloc(sizeof(skiplist_t));
- sl->cmp_fun = cmp_fun;
- sl->clone_fun = clone_fun;
+ sl->key_type = key_type;
sl->head = node_alloc(MAX_LEVEL, NULL, 0);
memset(sl->head->next, 0, (MAX_LEVEL+1) * sizeof(skiplist_t *));
return sl;
void sl_free (skiplist_t *sl) {
node_t *item = sl->head->next[0];
while (item) {
- node_t *next = (node_t *)STRIP_TAG(item->next[0]);
+ node_t *next = (node_t *)STRIP_TAG(item->next[0], TAG1);
nbd_free(item);
item = next;
}
uint64_t count = 0;
node_t *item = sl->head->next[0];
while (item) {
- if (!IS_TAGGED(item->next[0])) {
+ if (!IS_TAGGED(item->next[0], TAG1)) {
count++;
}
- item = (node_t *)STRIP_TAG(item->next[0]);
+ item = (node_t *)STRIP_TAG(item->next[0], TAG1);
}
return count;
}
for (int level = start_level; level >= 0; --level) {
TRACE("s3", "find_preds: level %llu", level, 0);
item = pred->next[level];
- if (EXPECT_FALSE(IS_TAGGED(item))) {
+ if (EXPECT_FALSE(IS_TAGGED(item, TAG1))) {
TRACE("s2", "find_preds: pred %p is marked for removal (item %p); retry", pred, item);
return find_preds(preds, succs, n, sl, key, help_remove); // retry
}
node_t *next = item->next[level];
// A tag means an item is logically removed but not physically unlinked yet.
- while (EXPECT_FALSE(IS_TAGGED(next))) {
+ while (EXPECT_FALSE(IS_TAGGED(next, TAG1))) {
// Skip over logically removed items.
if (!help_remove) {
- item = (node_t *)STRIP_TAG(item->next);
+ item = (node_t *)STRIP_TAG(item->next, TAG1);
if (EXPECT_FALSE(item == NULL))
break;
TRACE("s3", "find_preds: skipping marked item %p (next is %p)", item, next);
// Unlink logically removed items.
node_t *other;
TRACE("s3", "find_preds: unlinking marked item %p; next is %p", item, next);
- if ((other = SYNC_CAS(&pred->next[level], item, STRIP_TAG(next))) == item) {
- item = (node_t *)STRIP_TAG(next);
+ if ((other = SYNC_CAS(&pred->next[level], item, STRIP_TAG(next, TAG1))) == item) {
+ item = (node_t *)STRIP_TAG(next, TAG1);
if (EXPECT_FALSE(item == NULL))
break;
next = item->next[level];
// The thread that completes the unlink should free the memory.
if (level == 0) {
- if (sl->clone_fun != NULL) {
+ if (sl->key_type != NULL) {
nbd_defer_free((void*)other->key);
}
nbd_defer_free(other);
} else {
TRACE("s3", "find_preds: lost race to unlink item %p from pred %p", item, pred);
TRACE("s3", "find_preds: pred's link changed to %p", other, 0);
- if (IS_TAGGED(other))
+ if (IS_TAGGED(other, TAG1))
return find_preds(preds, succs, n, sl, key, help_remove); // retry
item = other;
if (EXPECT_FALSE(item == NULL))
break;
TRACE("s4", "find_preds: visiting item %p (next is %p)", item, next);
- TRACE("s4", "find_preds: key %p val %p", STRIP_TAG(item->key), item->val);
+ TRACE("s4", "find_preds: key %p val %p", STRIP_TAG(item->key, TAG1), item->val);
- if (EXPECT_TRUE(sl->cmp_fun == NULL)) {
+ if (EXPECT_TRUE(sl->key_type == NULL)) {
d = (uint64_t)item->key - (uint64_t)key;
} else {
- d = sl->cmp_fun(item->key, key);
+ d = sl->key_type->cmp(item->key, key);
}
if (d >= 0) {
return DOES_NOT_EXIST;
}
+void *sl_min_key (skiplist_t *sl) {
+ node_t *item = sl->head->next[0];
+ while (item != NULL) {
+ node_t *next = item->next[0];
+ if (!IS_TAGGED(next, TAG1))
+ return item->key;
+ item = (node_t *)STRIP_TAG(next, TAG1);
+ }
+ return DOES_NOT_EXIST;
+}
+
uint64_t sl_cas (skiplist_t *sl, void *key, uint64_t expectation, uint64_t new_val) {
TRACE("s1", "sl_cas: key %p skiplist %p", key, sl);
TRACE("s1", "sl_cas: expectation %p new value %p", expectation, new_val);
// First insert <new_item> into the bottom level.
TRACE("s3", "sl_cas: attempting to insert item between %p and %p", preds[0], nexts[0]);
- void *new_key = (sl->clone_fun == NULL) ? key : sl->clone_fun(key);
+ void *new_key = (sl->key_type == NULL) ? key : sl->key_type->clone(key);
new_item = node_alloc(n, new_key, new_val);
node_t *pred = preds[0];
node_t *next = new_item->next[0] = nexts[0];
break; // success
}
TRACE("s3", "sl_cas: failed to change pred's link: expected %p found %p", next, other);
- if (sl->clone_fun != NULL) {
+ if (sl->key_type != NULL) {
nbd_free(new_key);
}
nbd_free(new_item);
do {
// There in no need to continue linking in the item if another thread removed it.
node_t *old_next = ((volatile node_t *)new_item)->next[level];
- if (IS_TAGGED(old_next))
+ if (IS_TAGGED(old_next, TAG1))
return DOES_NOT_EXIST; // success
// Use a CAS so we do not inadvertantly stomp on a mark another thread placed on the item.
node_t *old_next = item->next[level];
do {
next = old_next;
- old_next = SYNC_CAS(&item->next[level], next, TAG_VALUE(next));
- if (IS_TAGGED(old_next)) {
+ old_next = SYNC_CAS(&item->next[level], next, TAG_VALUE(next, TAG1));
+ if (IS_TAGGED(old_next, TAG1)) {
TRACE("s2", "sl_remove: %p is already marked for removal by another thread at level %llu", item, level);
break;
}
} while (next != old_next);
node_t *pred = preds[level];
- TRACE("s2", "sl_remove: linking the item's pred %p to the item's successor %p", pred, STRIP_TAG(next));
+ TRACE("s2", "sl_remove: linking the item's pred %p to the item's successor %p", pred, STRIP_TAG(next, TAG1));
node_t *other = NULL;
- if ((other = SYNC_CAS(&pred->next[level], item, STRIP_TAG(next))) != item) {
+ if ((other = SYNC_CAS(&pred->next[level], item, STRIP_TAG(next, TAG1))) != item) {
TRACE("s1", "sl_remove: unlink failed; pred's link changed from %p to %p", item, other);
// If our former predecessor now points past us we know another thread unlinked us. Otherwise, we need
// to search for a new set of preds.
continue; // <pred> points past <item> to the end of the list; go on to the next level.
int d = -1;
- if (!IS_TAGGED(other)) {
- if (EXPECT_TRUE(sl->cmp_fun == NULL)) {
+ if (!IS_TAGGED(other, TAG1)) {
+ if (EXPECT_TRUE(sl->key_type == NULL)) {
d = (uint64_t)item->key - (uint64_t)other->key;
} else {
- d = sl->cmp_fun(item->key, other->key);
+ d = sl->key_type->cmp(item->key, other->key);
}
}
if (d > 0) {
node_t *old_next = item->next[0];
do {
next = old_next;
- old_next = SYNC_CAS(&item->next[0], next, TAG_VALUE(next));
- if (IS_TAGGED(old_next)) {
+ old_next = SYNC_CAS(&item->next[0], next, TAG_VALUE(next, TAG1));
+ if (IS_TAGGED(old_next, TAG1)) {
TRACE("s2", "sl_remove: %p is already marked for removal by another thread at level 0", item, 0);
return DOES_NOT_EXIST;
}
TRACE("s1", "sl_remove: marked item %p removed at level 0", item, 0);
// Atomically swap out the item's value in case another thread is updating the item while we are
- // removing it. This establishes which one occurs first, the update or the remove.
+ // removing it. This establishes which operation occurs first logically, the update or the remove.
uint64_t val = SYNC_SWAP(&item->val, DOES_NOT_EXIST);
TRACE("s2", "sl_remove: replaced item %p's value with DOES_NOT_EXIT", item, 0);
node_t *pred = preds[0];
- TRACE("s2", "sl_remove: linking the item's pred %p to the item's successor %p", pred, STRIP_TAG(next));
- if (SYNC_CAS(&pred->next[0], item, STRIP_TAG(next))) {
+ TRACE("s2", "sl_remove: linking the item's pred %p to the item's successor %p", pred, STRIP_TAG(next, TAG1));
+ if (SYNC_CAS(&pred->next[0], item, STRIP_TAG(next, TAG1))) {
TRACE("s2", "sl_remove: unlinked item %p from the skiplist at level 0", item, 0);
// The thread that completes the unlink should free the memory.
- if (sl->clone_fun != NULL) {
+ if (sl->key_type != NULL) {
nbd_defer_free(item->key);
}
nbd_defer_free(item);
int i = 0;
while (item) {
node_t *next = item->next[level];
- printf("%s%p ", IS_TAGGED(next) ? "*" : "", item);
- item = (node_t *)STRIP_TAG(next);
+ printf("%s%p ", IS_TAGGED(next, TAG1) ? "*" : "", item);
+ item = (node_t *)STRIP_TAG(next, TAG1);
if (i++ > 30) {
printf("...");
break;
printf("\n");
fflush(stdout);
}
-
node_t *item = sl->head;
int i = 0;
while (item) {
- int is_marked = IS_TAGGED(item->next[0]);
+ int is_marked = IS_TAGGED(item->next[0], TAG1);
printf("%s%p:%p ", is_marked ? "*" : "", item, item->key);
if (item != sl->head) {
printf("[%d]", item->top_level);
printf("[HEAD]");
}
for (int level = 1; level <= item->top_level; ++level) {
- node_t *next = (node_t *)STRIP_TAG(item->next[level]);
- is_marked = IS_TAGGED(item->next[0]);
+ node_t *next = (node_t *)STRIP_TAG(item->next[level], TAG1);
+ is_marked = IS_TAGGED(item->next[0], TAG1);
printf(" %p%s", next, is_marked ? "*" : "");
if (item == sl->head && item->next[level] == NULL)
break;
}
printf("\n");
fflush(stdout);
- item = (node_t *)STRIP_TAG(item->next[0]);
+ item = (node_t *)STRIP_TAG(item->next[0], TAG1);
if (i++ > 30) {
printf("...\n");
break;
}
}
}
+
+sl_iter_t *sl_iter_start (skiplist_t *sl, void *key) {
+ node_t *item;
+ find_preds(NULL, &item, 0, sl, key, FALSE);
+ return item;
+}
+
+sl_iter_t *sl_iter_next (sl_iter_t *iter) {
+ assert(iter);
+ if (EXPECT_FALSE(!iter))
+ return NULL;
+
+ node_t *next = iter->next[0];
+ while (next != NULL && IS_TAGGED(next->next[0], TAG1)) {
+ next = (node_t *)STRIP_TAG(next->next[0], TAG1);
+ }
+
+ return next;
+}
+
+uint64_t sl_iter_val (sl_iter_t *iter) {
+ return iter->val;
+}
+
+void *sl_iter_key (sl_iter_t *iter) {
+ return iter->key;
+}
projects / nbds / blobdiff