--- /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 "mlocal.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;
+}
+
+void ll_free (list_t *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 == CAS_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 == CAS_EXPECT_DOES_NOT_EXIST || expectation == CAS_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 == CAS_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");
+}
projects / nbds / blobdiff