* See also Kir Fraser's dissertation "Practical Lock Freedom"
* www.cl.cam.ac.uk/techreports/UCAM-CL-TR-579.pdf
*
+ * This code depends on certain stores and loads being ordered. Be careful on non-x86 platforms
+ * with weaker memory-models. This code probably won't work without adding some memory barriers.
*/
#include <stdio.h>
#include <string.h>
#include "struct.h"
#include "mem.h"
-#define MAX_LEVEL 3
+#define MAX_LEVEL 31
typedef struct node {
uint64_t key;
return item;
}
-skiplist_t *skiplist_alloc (void) {
+skiplist_t *sl_alloc (void) {
skiplist_t *skiplist = (skiplist_t *)nbd_malloc(sizeof(skiplist_t));
skiplist->head = node_alloc(MAX_LEVEL, 0, 0);
skiplist->last = node_alloc(MAX_LEVEL, (uint64_t)-1, 0);
}
// Fast find that does not help unlink partially removed nodes and does not return the node's predecessors.
-uint64_t skiplist_lookup (skiplist_t *skiplist, uint64_t key) {
- TRACE("s3", "skiplist_lookup: searching for key %p in skiplist %p", key, skiplist);
+uint64_t sl_lookup (skiplist_t *skiplist, uint64_t key) {
+ TRACE("s3", "sl_lookup: searching for key %p in skiplist %p", key, skiplist);
node_t *item = find_preds(NULL, skiplist, key, FALSE);
// If we found an <item> matching the <key> return its value.
}
// Insert the <key> if it doesn't already exist in the <skiplist>
-uint64_t skiplist_add_i (int n, skiplist_t *skiplist, uint64_t key, uint64_t value) {
- TRACE("s3", "skiplist_add: inserting key %p value %p", key, value);
+uint64_t sl_add_r (int r, skiplist_t *skiplist, uint64_t key, uint64_t value) {
+ TRACE("s3", "sl_add: inserting key %p value %p", key, value);
node_t *preds[MAX_LEVEL+1];
node_t *item = NULL;
do {
// If a node matching <key> already exists in the skiplist, return its value.
if (next->key == key) {
- TRACE("s3", "skiplist_add: there is already an item %p (value %p) with the same key", next, next->value);
+ TRACE("s3", "sl_add: there is already an item %p (value %p) with the same key", next, next->value);
if (EXPECT_FALSE(item != NULL)) { nbd_free(item); }
return next->value;
}
// First insert <item> into the bottom level.
- if (EXPECT_TRUE(item == NULL)) { item = node_alloc(random_level(n), key, value); }
- TRACE("s3", "skiplist_add: attempting to insert item between %p and %p", preds[0], next);
+ if (EXPECT_TRUE(item == NULL)) { item = node_alloc(random_level(r), key, value); }
+ TRACE("s3", "sl_add: attempting to insert item between %p and %p", preds[0], next);
item->next[0] = next;
for (int level = 1; level <= item->top_level; ++level) {
item->next[level] = preds[level]->next[level];
}
node_t *other = SYNC_CAS(&preds[0]->next[0], next, item);
if (other == next) {
- TRACE("s3", "skiplist_add: successfully inserted item %p at level 0", item, 0);
+ TRACE("s3", "sl_add: successfully inserted item %p at level 0", item, 0);
break; // success
}
- TRACE("s3", "skiplist_add: failed to change pred's link: expected %p found %p", next, other);
+ TRACE("s3", "sl_add: failed to change pred's link: expected %p found %p", next, other);
} while (1);
break;
} while (1);
- TRACE("s3", "skiplist_add: attempting to insert item between %p and %p", pred, next);
+ TRACE("s3", "sl_add: attempting to insert item between %p and %p", pred, next);
node_t *other = SYNC_CAS(&pred->next[level], next, item);
if (other == next) {
- TRACE("s3", "skiplist_add: successfully inserted item %p at level %llu", item, level);
+ TRACE("s3", "sl_add: successfully inserted item %p at level %llu", item, level);
break; // success
}
- TRACE("s3", "skiplist_add: failed to change pred's link: expected %p found %p", next, other);
+ TRACE("s3", "sl_add: failed to change pred's link: expected %p found %p", next, other);
} while (1);
}
return value;
}
-uint64_t skiplist_remove (skiplist_t *skiplist, uint64_t key) {
- TRACE("s3", "skiplist_remove: removing item with key %p from skiplist %p", key, skiplist);
+uint64_t sl_remove (skiplist_t *skiplist, uint64_t key) {
+ TRACE("s3", "sl_remove: removing item with key %p from skiplist %p", key, skiplist);
node_t *preds[MAX_LEVEL+1];
node_t *item = find_preds(preds, skiplist, key, TRUE);
if (item->key != key) {
- TRACE("s3", "skiplist_remove: remove failed, an item with a matching key does not exist in the skiplist", 0, 0);
+ TRACE("s3", "sl_remove: remove failed, an item with a matching key does not exist in the skiplist", 0, 0);
return DOES_NOT_EXIST;
}
// them succeeds.
for (int level = item->top_level; level >= 0; --level) {
if (EXPECT_FALSE(IS_TAGGED(item->next[level]))) {
- TRACE("s3", "skiplist_remove: %p is already marked for removal by another thread", item, 0);
+ TRACE("s3", "sl_remove: %p is already marked for removal by another thread", item, 0);
if (level == 0)
return DOES_NOT_EXIST;
continue;
}
node_t *next = SYNC_FETCH_AND_OR(&item->next[level], TAG);
if (EXPECT_FALSE(IS_TAGGED(next))) {
- TRACE("s3", "skiplist_remove: lost race -- %p is already marked for removal by another thread", item, 0);
+ TRACE("s3", "sl_remove: lost race -- %p is already marked for removal by another thread", item, 0);
if (level == 0)
return DOES_NOT_EXIST;
continue;
while (level >= 0) {
node_t *pred = preds[level];
node_t *next = item->next[level];
- TRACE("s3", "skiplist_remove: link item's pred %p to it's successor %p", pred, STRIP_TAG(next));
+ TRACE("s3", "sl_remove: link item's pred %p to it's successor %p", pred, STRIP_TAG(next));
node_t *other = NULL;
if ((other = SYNC_CAS(&pred->next[level], item, STRIP_TAG(next))) != item) {
- TRACE("s3", "skiplist_remove: unlink failed; pred's link changed from %p to %p", item, other);
+ TRACE("s3", "sl_remove: unlink failed; pred's link changed from %p to %p", item, other);
// By marking the item earlier, we logically removed it. It is safe to leave the item partially
// unlinked. Another thread will finish physically removing it from the skiplist.
return value;
return value;
}
-void skiplist_print (skiplist_t *skiplist) {
+void sl_print (skiplist_t *skiplist) {
for (int level = MAX_LEVEL; level >= 0; --level) {
- printf("(%d) ", level);
node_t *item = skiplist->head;
+ if (item->next[level] == skiplist->last)
+ continue;
+ printf("(%d) ", level);
while (item) {
node_t *next = item->next[level];
printf("%s%p:0x%llx ", IS_TAGGED(next) ? "*" : "", item, item->key);
fflush(stdout);
}
+ printf("\n");
node_t *item = skiplist->head;
while (item) {
assert(item->top_level <= MAX_LEVEL);
int is_marked = IS_TAGGED(item->next[0]);
printf("%s%p:0x%llx (%d", is_marked ? "*" : "", item, item->key, item->top_level);
- for (int i = 1; i <= item->top_level; ++i) {
- node_t *next = (node_t *)STRIP_TAG(item->next[i]);
- printf(" %p:0x%llx", item->next[i], next ? next->key : 0);
+ for (int level = 1; level <= item->top_level; ++level) {
+ node_t *next = (node_t *)STRIP_TAG(item->next[level]);
+ printf(" %p:0x%llx", item->next[level], next ? next->key : 0);
+ if (item == skiplist->head && item->next[level] == skiplist->last)
+ break;
+ if (item == skiplist->last && item->next[level] == NULL)
+ break;
}
printf(")\n");
fflush(stdout);
static volatile int wait_;
static long num_threads_;
-static skiplist_t *skiplist_;
+static skiplist_t *sl_;
void *worker (void *arg) {
int id = (int)(size_t)arg;
int n = rand_r(&rand_seed);
int key = (n & 0xF) + 1;
if (n & (1 << 8)) {
- skiplist_add_i(n, skiplist_, key, 1);
+ sl_add_r(n, sl_, key, 1);
} else {
- skiplist_remove(skiplist_, key);
+ sl_remove(sl_, key);
}
rcu_update();
}
}
- skiplist_ = skiplist_alloc();
+ sl_ = sl_alloc();
struct timeval tv1, tv2;
gettimeofday(&tv1, NULL);
gettimeofday(&tv2, NULL);
int ms = (int)(1000000*(tv2.tv_sec - tv1.tv_sec) + tv2.tv_usec - tv1.tv_usec) / 1000;
printf("Th:%ld Time:%dms\n", num_threads_, ms);
- skiplist_print(skiplist_);
+ sl_print(sl_);
lwt_dump("lwt.out");
return 0;
projects / nbds / blobdiff