return ll;
}
-static node_t *find_pred (node_t **pred_ptr, list_t *ll, const void *key_data, uint32_t key_len, int help_remove) {
+static int find_pred (node_t **pred_ptr, node_t **item_ptr, list_t *ll, const void *key_data, uint32_t key_len, int help_remove) {
node_t *pred = ll->head;
node_t *item = pred->next;
- TRACE("l3", "find_pred: searching for key %p in ll (head is %p)", key_data, pred);
+ TRACE("l2", "find_pred: searching for key %p in ll (head is %p)", key_data, pred);
while (item != NULL) {
node_t *next = item->next;
- TRACE("l3", "find_pred: visiting item %p (next %p)", item, next);
- TRACE("l3", "find_pred: key %p", STRIP_TAG(item->key), item->val);
// A tag means an item is logically removed but not physically unlinked yet.
while (EXPECT_FALSE(IS_TAGGED(next))) {
item = (node_t *)STRIP_TAG(item->next);
if (EXPECT_FALSE(item == NULL))
break;
+ TRACE("l3", "find_pred: skipping marked item %p (next is %p)", item, next);
next = item->next;
continue;
}
// Unlink logically removed items.
node_t *other;
+ TRACE("l3", "find_pred: unlinking marked item %p next is %p", item, next);
if ((other = SYNC_CAS(&pred->next, item, STRIP_TAG(next))) == item) {
+ TRACE("l2", "find_pred: unlinked item %p from pred %p", item, pred);
item = (node_t *)STRIP_TAG(next);
if (EXPECT_FALSE(item == NULL))
break;
next = item->next;
- TRACE("l3", "find_pred: unlinked item %p from pred %p", item, pred);
- TRACE("l3", "find_pred: now item is %p next is %p", item, next);
+ TRACE("l3", "find_pred: now current item is %p next is %p", item, next);
// The thread that completes the unlink should free the memory.
node_defer_free(other);
} else {
- TRACE("l3", "find_pred: lost race to unlink from pred %p; its link changed to %p", pred, other);
+ TRACE("l2", "find_pred: lost a race to unlink item %p from pred %p", item, pred);
+ TRACE("l2", "find_pred: pred's link changed to %p", other, 0);
if (IS_TAGGED(other))
- return find_pred(pred_ptr, ll, key_data, key_len, help_remove); // retry
+ return find_pred(pred_ptr, item_ptr, ll, key_data, key_len, help_remove); // retry
item = other;
if (EXPECT_FALSE(item == NULL))
break;
if (EXPECT_FALSE(item == NULL))
break;
+ TRACE("l3", "find_pred: visiting item %p (next is %p)", item, next);
+ TRACE("l4", "find_pred: key %p val %p", STRIP_TAG(item->key), item->val);
+
+ // A tagged key is an integer, otherwise it is a pointer to a string
+ int d;
+ if (IS_TAGGED(item->key)) {
+ d = (STRIP_TAG(item->key) - (uint64_t)key_data);
+ } else {
+ int item_key_len = item->key->len;
+ int len = (key_len < item_key_len) ? key_len : item_key_len;
+ d = memcmp(item->key->data, key_data, len);
+ if (d == 0) { d = item_key_len - key_len; }
+ }
+
// If we reached the key (or passed where it should be), we found the right predesssor
- int x = (IS_TAGGED(item->key))
- ? (STRIP_TAG(item->key) - (uint64_t)key_data)
- : ns_cmp_raw(item->key, key_data, key_len);
- if (x >= 0) {
- TRACE("l3", "find_pred: found pred %p item %p", pred, item);
+ if (d >= 0) {
if (pred_ptr != NULL) {
*pred_ptr = pred;
}
- return x == 0 ? item : NULL;
+ *item_ptr = item;
+ if (d == 0) {
+ TRACE("l2", "find_pred: found matching item %p in list, pred is %p", item, pred);
+ return TRUE;
+ }
+ TRACE("l2", "find_pred: found proper place for key %p in list, pred is %p. returning null", key_data, pred);
+ return FALSE;
}
pred = item;
item = next;
-
}
// <key> is not in <ll>.
if (pred_ptr != NULL) {
*pred_ptr = pred;
}
- return NULL;
+ *item_ptr = NULL;
+ TRACE("l2", "find_pred: reached end of list. last item is %p", pred, 0);
+ return FALSE;
}
// Fast find. Do not help unlink partially removed nodes and do not return the found item's predecessor.
uint64_t ll_lookup (list_t *ll, const void *key_data, uint32_t key_len) {
- TRACE("l3", "ll_lookup: searching for key %p in list %p", key_data, ll);
- node_t *item = find_pred(NULL, ll, key_data, key_len, FALSE);
+ TRACE("l1", "ll_lookup: searching for key %p in list %p", key_data, ll);
+ node_t *item;
+ int found = find_pred(NULL, &item, ll, key_data, key_len, FALSE);
// If we found an <item> matching the key return its value.
- return item != NULL ? item->val : DOES_NOT_EXIST;
+ if (found) {
+ uint64_t val = item->val;
+ if (val != DOES_NOT_EXIST) {
+ TRACE("l1", "ll_lookup: found item %p. val %p. returning item", item, item->val);
+ return val;
+ }
+ }
+
+ TRACE("l1", "ll_lookup: no item in the list matched the key", 0, 0);
+ return DOES_NOT_EXIST;
}
-// Insert a new item if a matching key doesn't already exist in <ll>
-uint64_t ll_cas (list_t *ll, const void *key_data, uint32_t key_len, uint64_t expected_val, uint64_t new_val) {
- assert(new_val != DOES_NOT_EXIST);
- TRACE("l3", "ll_cas: inserting key %p val %p", key_data, new_val);
+uint64_t ll_cas (list_t *ll, const void *key_data, uint32_t key_len, uint64_t expectation, uint64_t new_val) {
+ TRACE("l1", "ll_cas: key %p list %p", key_data, ll);
+ TRACE("l1", "ll_cas: expectation %p new value %p", expectation, new_val);
+ ASSERT((int64_t)new_val > 0);
+
+ node_t *pred, *old_item;
do {
- node_t *pred;
- node_t *old_item = find_pred(&pred, ll, key_data, key_len, TRUE);
+ if (!find_pred(&pred, &old_item, ll, key_data, key_len, TRUE)) {
- // If a node matching the key already exists in <ll> return its value.
- if (old_item != NULL) {
- TRACE("l3", "ll_cas: there is already an item %p (value %p) with the same key", old_item, old_item->val);
- return old_item->val;
- }
+ // There is no existing item in the list that matches the key.
+ if (EXPECT_FALSE((int64_t)expectation > 0 || expectation == EXPECT_EXISTS)) {
+ TRACE("l1", "ll_cas: the expectation was not met, the list was not changed", 0, 0);
+ return DOES_NOT_EXIST; // failure
+ }
+
+ ASSERT(expectation == EXPECT_DOES_NOT_EXIST || expectation == EXPECT_WHATEVER);
+
+ // Create a new item and insert it into the list.
+ TRACE("l2", "ll_cas: attempting to insert item between %p and %p", pred, pred->next);
+ node_t *new_item = node_alloc(key_data, key_len, new_val);
+ node_t *next = new_item->next = old_item;
+ node_t *other = SYNC_CAS(&pred->next, next, new_item);
+ if (other == next) {
+ TRACE("l1", "ll_cas: successfully inserted new item %p", new_item, 0);
+ return DOES_NOT_EXIST; // success
+ }
- TRACE("l3", "ll_cas: attempting to insert item between %p and %p", pred, pred->next);
- node_t *new_item = node_alloc(key_data, key_len, new_val);
- node_t *next = new_item->next = pred->next;
- node_t *other = SYNC_CAS(&pred->next, next, new_item);
- if (other == next) {
- TRACE("l3", "ll_cas: successfully inserted item %p", new_item, 0);
- return DOES_NOT_EXIST; // success
+ // Lost a race. Failed to insert the new item into the list.
+ TRACE("l1", "ll_cas: lost a race. CAS failed. expected pred's link to be %p but found %p", next, other);
+ node_free(new_item);
+ continue; // retry
}
- TRACE("l3", "ll_cas: failed to change pred's link: expected %p found %p", next, other);
- node_free(new_item);
+ // Found an item in the list that matches the key.
+ uint64_t old_item_val = old_item->val;
+ do {
+ // If the item's value is DOES_NOT_EXIST it means another thread removed the node out from under us.
+ if (EXPECT_FALSE(old_item_val == DOES_NOT_EXIST)) {
+ TRACE("l2", "ll_cas: lost a race, found an item but another thread removed it. retry", 0, 0);
+ break; // retry
+ }
+
+ if (EXPECT_FALSE(expectation == EXPECT_DOES_NOT_EXIST)) {
+ TRACE("l1", "ll_cas: found an item %p in the list that matched the key. the expectation was "
+ "not met, the list was not changed", old_item, old_item_val);
+ return old_item_val; // failure
+ }
+
+ // Use a CAS and not a SWAP. If the node is in the process of being removed and we used a SWAP, we could
+ // replace DOES_NOT_EXIST with our value. Then another thread that is updating the value could think it
+ // succeeded and return our value even though we indicated that the node has been removed. If the CAS
+ // fails it means another thread either removed the node or updated its value.
+ uint64_t ret_val = SYNC_CAS(&old_item->val, old_item_val, new_val);
+ if (ret_val == old_item_val) {
+ TRACE("l1", "ll_cas: the CAS succeeded. updated the value of the item", 0, 0);
+ return ret_val; // success
+ }
+ TRACE("l2", "ll_cas: lost a race. the CAS failed. another thread changed the item's value", 0, 0);
+
+ old_item_val = ret_val;
+ } while (1);
} while (1);
}
uint64_t ll_remove (list_t *ll, const void *key_data, uint32_t key_len) {
- TRACE("l3", "ll_remove: removing item with key %p from list %p", key_data, ll);
+ TRACE("l1", "ll_remove: removing item with key %p from list %p", key_data, ll);
node_t *pred;
- node_t *item = find_pred(&pred, ll, key_data, key_len, TRUE);
- if (item == NULL) {
- TRACE("l3", "ll_remove: remove failed, an item with a matching key does not exist in the list", 0, 0);
+ node_t *item;
+ int found = find_pred(&pred, &item, ll, key_data, key_len, TRUE);
+ if (!found) {
+ TRACE("l1", "ll_remove: remove failed, an item with a matching key does not exist in the list", 0, 0);
return DOES_NOT_EXIST;
}
// Mark <item> removed. This must be atomic. If multiple threads try to remove the same item
// only one of them should succeed.
- if (EXPECT_FALSE(IS_TAGGED(item->next))) {
- TRACE("l3", "ll_remove: %p is already marked for removal by another thread", item, 0);
- return DOES_NOT_EXIST;
- }
- node_t *next = SYNC_FETCH_AND_OR(&item->next, TAG);
- if (EXPECT_FALSE(IS_TAGGED(next))) {
- TRACE("l3", "ll_remove: lost race -- %p is already marked for removal by another thread", item, 0);
- return DOES_NOT_EXIST;
- }
+ node_t *next;
+ node_t *old_next = item->next;
+ do {
+ next = old_next;
+ old_next = SYNC_CAS(&item->next, next, TAG_VALUE(next));
+ if (IS_TAGGED(old_next)) {
+ TRACE("l1", "ll_remove: lost a race -- %p is already marked for removal by another thread", item, 0);
+ return DOES_NOT_EXIST;
+ }
+ } while (next != old_next);
+ TRACE("l2", "ll_remove: logically removed item %p", item, 0);
+ ASSERT(!IS_TAGGED(item->next));
+
+ // This has to be an atomic swap in case another thread is updating the item while we are removing it.
+ uint64_t val = SYNC_SWAP(&item->val, DOES_NOT_EXIST);
- uint64_t val = item->val;
+ TRACE("l2", "ll_remove: replaced item's val %p with DOES_NOT_EXIT", val, 0);
// Unlink <item> from <ll>. If we lose a race to another thread just back off. It is safe to leave the
// item logically removed for a later call (or some other thread) to physically unlink. By marking the
// item earlier, we logically removed it.
- TRACE("l3", "ll_remove: link item's pred %p to it's successor %p", pred, next);
+ TRACE("l2", "ll_remove: unlink the item by linking its pred %p to its successor %p", pred, next);
node_t *other;
if ((other = SYNC_CAS(&pred->next, item, next)) != item) {
- TRACE("l3", "ll_remove: unlink failed; pred's link changed from %p to %p", item, other);
+ TRACE("l1", "ll_remove: unlink failed; pred's link changed from %p to %p", item, other);
return val;
}
// The thread that completes the unlink should free the memory.
- node_defer_free(item);
+ node_defer_free((node_t *)item);
+ TRACE("l1", "ll_remove: successfully unlinked item %p from the list", item, 0);
return val;
}
node_t *item;
item = ll->head->next;
while (item) {
+ node_t *next = item->next;
+ if (IS_TAGGED(item)) {
+ printf("*");
+ }
+ printf("%p:", item);
if (IS_TAGGED(item->key)) {
printf("0x%llx ", STRIP_TAG(item->key));
} else {
- printf("%s ", (char *)ns_data(item->key));
+ printf("%s ", (char *)item->key->data);
}
fflush(stdout);
- item = item->next;
+ item = (node_t *)STRIP_TAG(next);
}
printf("\n");
}
projects / nbds / blobdiff