+++ /dev/null
-/*
- * Written by Josh Dybnis and released to the public domain, as explained at
- * http://creativecommons.org/licenses/publicdomain
- *
- * Harris-Michael lock-free list-based set
- * http://www.research.ibm.com/people/m/michael/spaa-2002.pdf
- */
-#include <stdio.h>
-#include <string.h>
-
-#include "common.h"
-#include "struct.h"
-#include "nstring.h"
-#include "mem.h"
-
-typedef struct node {
- nstring_t *key;
- uint64_t val;
- struct node *next;
-} node_t;
-
-struct ll {
- node_t *head;
-};
-
-static node_t *node_alloc (const void *key_data, uint32_t key_len, uint64_t val) {
- node_t *item = (node_t *)nbd_malloc(sizeof(node_t));
- memset(item, 0, sizeof(node_t));
- // If <key_len> is -1 it indicates <key_data> is an integer and not a pointer
- item->key = (key_len == (unsigned)-1)
- ? (void *)TAG_VALUE(key_data)
- : ns_alloc(key_data, key_len);
- item->val = val;
- return item;
-}
-
-static void node_free (node_t *item) {
- if (!IS_TAGGED(item->key)) {
- nbd_free(item->key);
- }
- nbd_free(item);
-}
-
-static void node_defer_free (node_t *item) {
- if (!IS_TAGGED(item->key)) {
- nbd_defer_free(item->key);
- }
- nbd_defer_free(item);
-}
-
-list_t *ll_alloc (void) {
- list_t *ll = (list_t *)nbd_malloc(sizeof(list_t));
- ll->head = node_alloc(" ", 0, 0);
- ll->head->next = NULL;
- return ll;
-}
-
-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("l2", "find_pred: searching for key %p in ll (head is %p)", key_data, pred);
-
- while (item != NULL) {
- node_t *next = item->next;
-
- // A tag means an item is logically removed but not physically unlinked yet.
- while (EXPECT_FALSE(IS_TAGGED(next))) {
-
- // Skip over logically removed items.
- if (!help_remove) {
- 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: 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("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, item_ptr, ll, key_data, key_len, help_remove); // retry
- item = other;
- if (EXPECT_FALSE(item == NULL))
- break;
- next = item->next;
- }
- }
-
- 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
- if (d >= 0) {
- if (pred_ptr != NULL) {
- *pred_ptr = pred;
- }
- *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", key_data, pred);
- return FALSE;
- }
-
- pred = item;
- item = next;
- }
-
- // <key> is not in <ll>.
- if (pred_ptr != NULL) {
- *pred_ptr = pred;
- }
- *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("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.
- 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;
-}
-
-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);
-
- do {
- node_t *pred, *old_item;
- if (!find_pred(&pred, &old_item, ll, key_data, key_len, TRUE)) {
-
- // There was not an 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
- }
-
- // 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
- }
-
- // 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("l1", "ll_remove: removing item with key %p from list %p", key_data, ll);
- node_t *pred;
- 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.
- 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);
- 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("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("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);
- TRACE("l1", "ll_remove: successfully unlinked item %p from the list", item, 0);
- return val;
-}
-
-void ll_print (list_t *ll) {
- 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 *)item->key->data);
- }
- fflush(stdout);
- item = (node_t *)STRIP_TAG(next);
- }
- printf("\n");
-}
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