X-Git-Url: https://pd.if.org/git/?p=nbds;a=blobdiff_plain;f=struct%2Flist.c;fp=struct%2Flist.c;h=0000000000000000000000000000000000000000;hp=5849247abd9a2a59f188c3e244d97acdd472643f;hb=025017478bb385da88a6b185849c8bcffeb2e2aa;hpb=2d93f3b29622488bde80b6cd18661fd7eb603eee diff --git a/struct/list.c b/struct/list.c deleted file mode 100644 index 5849247..0000000 --- a/struct/list.c +++ /dev/null @@ -1,294 +0,0 @@ -/* - * 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 -#include - -#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 is -1 it indicates 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; - } - - // is not in . - 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 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 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 from . 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"); -}