typedef struct list {
node_t *head;
- node_t *last;
} list_t;
node_t *node_alloc (uint64_t key, uint64_t value) {
list_t *ll_alloc (void) {
list_t *list = (list_t *)nbd_malloc(sizeof(list_t));
- list->head = node_alloc(0, 0);
- list->last = node_alloc((uint64_t)-1, 0);
- list->head->next = list->last;
+ list->head = node_alloc((uint64_t)-1, 0);
+ list->head->next = NULL;
return list;
}
node_t *pred = list->head;
node_t *item = pred->next;
TRACE("l3", "find_pred: searching for key %p in list (head is %p)", key, pred);
-#ifndef NDEBUG
- int count = 0;
-#endif
- do {
+ 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", item->key, item->value);
// Skip over partially removed items.
if (!help_remove) {
item = (node_t *)STRIP_TAG(item->next);
+ if (EXPECT_FALSE(item == NULL))
+ break;
next = item->next;
continue;
}
node_t *other;
if ((other = SYNC_CAS(&pred->next, item, STRIP_TAG(next))) == item) {
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);
// The thread that completes the unlink should free the memory.
nbd_defer_free(other);
} else {
- TRACE("l3", "find_pred: lost race to unlink item from pred %p; its link changed to %p", pred, other);
+ TRACE("l3", "find_pred: lost race to unlink from pred %p; its link changed to %p", pred, other);
if (IS_TAGGED(other))
return find_pred(pred_ptr, list, key, help_remove); // retry
item = other;
+ if (EXPECT_FALSE(item == NULL))
+ break;
next = item->next;
}
}
+ if (EXPECT_FALSE(item == NULL))
+ break;
+
// If we reached the key (or passed where it should be), we found the right predesssor
if (item->key >= key) {
TRACE("l3", "find_pred: found pred %p item %p", pred, item);
return item;
}
- assert(count++ < 18);
pred = item;
item = next;
- } while (1);
+ }
+
+ // <key> is not in the list.
+ if (pred_ptr != NULL) {
+ *pred_ptr = pred;
+ }
+ return NULL;
}
// Fast find. Do not help unlink partially removed nodes and do not return the found item's predecessor.
node_t *item = find_pred(NULL, list, key, FALSE);
// If we found an <item> matching the <key> return its value.
- return (item->key == key) ? item->value : DOES_NOT_EXIST;
+ return (item && item->key == key) ? item->value : DOES_NOT_EXIST;
}
// Insert the <key>, if it doesn't already exist in the <list>
node_t *next = find_pred(&pred, list, key, TRUE);
// If a node matching <key> already exists in the list, return its value.
- if (next->key == key) {
+ if (next != NULL && next->key == key) {
TRACE("l3", "ll_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;
TRACE("l3", "ll_remove: removing item with key %p from list %p", key, list);
node_t *pred;
node_t *item = find_pred(&pred, list, key, TRUE);
- if (item->key != key) {
+ if (item == NULL || item->key != key) {
TRACE("l3", "ll_remove: remove failed, an item with a matching key does not exist in the list", 0, 0);
return DOES_NOT_EXIST;
}
void ll_print (list_t *list) {
node_t *item;
- item = list->head;
+ item = list->head->next;
while (item) {
printf("0x%llx ", item->key);
fflush(stdout);
static list_t *ll_;
void *worker (void *arg) {
- int id = (int)(size_t)arg;
-
- unsigned int rand_seed = id+1;//rdtsc_l();
// Wait for all the worker threads to be ready.
SYNC_ADD(&wait_, -1);
do {} while (wait_);
for (int i = 0; i < NUM_ITERATIONS/num_threads_; ++i) {
- int n = rand_r(&rand_seed);
- int key = (n & 0xF) + 1;
- if (n & (1 << 8)) {
+ unsigned r = nbd_rand();
+ int key = (r & 0xF);
+ if (r & (1 << 8)) {
ll_add(ll_, key, 1);
} else {
ll_remove(ll_, key);
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);
ll_print(ll_);
- lwt_dump("lwt.out");
+ printf("Th:%ld Time:%dms\n", num_threads_, ms);
return 0;
}
* Written by Josh Dybnis and released to the public domain, as explained at
* http://creativecommons.org/licenses/publicdomain
*
- * C implementation of the lock-free skiplist data-structure created by Maurice Herlihy,
- * Yossi Lev, and Nir Shavit. See "The Art of Multiprocessor Programming"
+ * Implementation of the lock-free skiplist data-structure created by Maurice Herlihy, Yossi Lev,
+ * and Nir Shavit. See Herlihy's and Shivit's book "The Art of Multiprocessor Programming".
* http://www.amazon.com/Art-Multiprocessor-Programming-Maurice-Herlihy/dp/0123705916/
*
- * See also Kir Fraser's dissertation "Practical Lock Freedom"
+ * 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.
+ * This code is written for the x86 memory-model. The algorithim depends on certain stores and
+ * loads being ordered. Be careful, this code probably won't work correctly on platforms with
+ * weaker memory models if you don't add memory barriers in the right places.
*/
#include <stdio.h>
#include <string.h>
#include "common.h"
+#include "runtime.h"
#include "struct.h"
#include "mem.h"
+#include "tls.h"
+// Setting MAX_LEVEL to 0 essentially makes this data structure the Harris-Michael lock-free list
+// in list.c
#define MAX_LEVEL 31
typedef struct node {
typedef struct skiplist {
node_t *head;
- node_t *last;
- int top_level;
} skiplist_t;
-static int random_level (int r) {
+static int random_level (void) {
+ unsigned r = nbd_rand();
if (r&1)
return 0;
- int n = __builtin_ctz(r);
- if (n < MAX_LEVEL)
- return n;
- return MAX_LEVEL;
+ int n = __builtin_ctz(r)-1;
+#if MAX_LEVEL < 31
+ if (n > MAX_LEVEL)
+ return MAX_LEVEL;
+#endif
+ assert(n <= MAX_LEVEL);
+ return n;
}
-node_t *node_alloc (int top_level, uint64_t key, uint64_t value) {
- assert(top_level >= 0 && top_level <= MAX_LEVEL);
- size_t sz = sizeof(node_t) + (top_level + 1) * sizeof(node_t *);
+node_t *node_alloc (int level, uint64_t key, uint64_t value) {
+ assert(level >= 0 && level <= MAX_LEVEL);
+ size_t sz = sizeof(node_t) + (level + 1) * sizeof(node_t *);
node_t *item = (node_t *)nbd_malloc(sz);
memset(item, 0, sz);
item->key = key;
item->value = value;
- item->top_level = top_level;
+ item->top_level = level;
return item;
}
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);
- for (int level = 0; level <= MAX_LEVEL; ++level) {
- skiplist->head->next[level] = skiplist->last;
- }
+ memset(skiplist->head->next, 0, (MAX_LEVEL+1) * sizeof(skiplist_t *));
return skiplist;
}
-static node_t *find_preds (node_t **preds, skiplist_t *skiplist, uint64_t key, int help_remove) {
+static node_t *find_preds (node_t *preds[MAX_LEVEL+1], int n, skiplist_t *skiplist, uint64_t key, int help_remove) {
node_t *pred = skiplist->head;
node_t *item = NULL;
TRACE("s3", "find_preds: searching for key %p in skiplist (head is %p)", key, pred);
-#ifndef NDEBUG
- int count = 0;
-#endif
+
+ // Optimization for small lists. No need to traverse empty higher levels.
+ assert(MAX_LEVEL > 2);
+ int start_level = 2;
+ while (pred->next[start_level+1] != NULL) {
+ start_level += start_level - 1;
+ if (EXPECT_FALSE(start_level >= MAX_LEVEL)) {
+ start_level = MAX_LEVEL;
+ break;
+ }
+ }
+ if (EXPECT_FALSE(start_level < n)) {
+ start_level = n;
+ }
// Traverse the levels of the skiplist from the top level to the bottom
- for (int level = MAX_LEVEL; level >= 0; --level) {
+ for (int level = start_level; level >= 0; --level) {
TRACE("s3", "find_preds: level %llu", level, 0);
item = pred->next[level];
- if (IS_TAGGED(item)) {
+ if (EXPECT_FALSE(IS_TAGGED(item))) {
TRACE("s3", "find_preds: pred %p is marked for removal (item %p); retry", pred, item);
- return find_preds(preds, skiplist, key, help_remove); // retry
+ return find_preds(preds, n, skiplist, key, help_remove); // retry
}
- do {
+ while (item != NULL) {
node_t *next = item->next[level];
TRACE("s3", "find_preds: visiting item %p (next %p)", item, next);
TRACE("s3", "find_preds: key %p", item->key, 0);
// Skip over partially removed items.
if (!help_remove) {
item = (node_t *)STRIP_TAG(item->next);
+ if (EXPECT_FALSE(item == NULL))
+ break;
next = item->next[level];
continue;
}
node_t *other;
if ((other = SYNC_CAS(&pred->next[level], item, STRIP_TAG(next))) == item) {
item = (node_t *)STRIP_TAG(next);
+ if (EXPECT_FALSE(item == NULL))
+ break;
next = item->next[level];
TRACE("s3", "find_preds: unlinked item %p from pred %p", item, pred);
TRACE("s3", "find_preds: now item is %p next is %p", item, next);
// The thread that completes the unlink should free the memory.
if (level == 0) { nbd_defer_free(other); }
} else {
- TRACE("s3", "find_preds: lost race to unlink item from pred %p; its link changed to %p",pred,other);
+ TRACE("s3", "find_preds: lost race to unlink from pred %p; its link changed to %p", pred, other);
if (IS_TAGGED(other))
- return find_preds(preds, skiplist, key, help_remove); // retry
+ return find_preds(preds, n, skiplist, key, help_remove); // retry
item = other;
+ if (EXPECT_FALSE(item == NULL))
+ break;
next = item->next[level];
}
}
+ if (EXPECT_FALSE(item == NULL))
+ break;
+
// If we reached the key (or passed where it should be), we found a pred. Save it and continue down.
if (item->key >= key) {
TRACE("s3", "find_preds: found pred %p item %p", pred, item);
- if (preds != NULL) {
- preds[level] = pred;
- }
break;
}
- assert(count++ < 18);
pred = item;
item = next;
-
- } while (1);
+ }
+ if (preds != NULL) {
+ preds[level] = pred;
+ }
+ }
+ if (n == -1 && item != NULL) {
+ assert(preds != NULL);
+ for (int level = start_level + 1; level <= item->top_level; ++level) {
+ preds[level] = skiplist->head;
+ }
}
return item;
}
// Fast find that does not help unlink partially removed nodes and does not return the node's predecessors.
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);
+ node_t *item = find_preds(NULL, 0, skiplist, key, FALSE);
// If we found an <item> matching the <key> return its value.
- return (item->key == key) ? item->value : DOES_NOT_EXIST;
+ return (item && item->key == key) ? item->value : DOES_NOT_EXIST;
}
// Insert the <key> if it doesn't already exist in the <skiplist>
-uint64_t sl_add_r (int r, skiplist_t *skiplist, uint64_t key, uint64_t value) {
+uint64_t sl_add (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 {
- node_t *next = find_preds(preds, skiplist, key, TRUE);
+ int n = random_level();
+ node_t *next = find_preds(preds, n, skiplist, key, TRUE);
// If a node matching <key> already exists in the skiplist, return its value.
- if (next->key == key) {
+ if (next != NULL && next->key == key) {
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(r), key, value); }
+ if (EXPECT_TRUE(item == NULL)) { item = node_alloc(n, 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 *pred = preds[level];
+ item->next[level] = pred->next[level];
}
- node_t *other = SYNC_CAS(&preds[0]->next[0], next, item);
+ node_t *pred = preds[0];
+ node_t *other = SYNC_CAS(&pred->next[0], next, item);
if (other == next) {
TRACE("s3", "sl_add: successfully inserted item %p at level 0", item, 0);
break; // success
// Insert <item> into the skiplist from the bottom level up.
for (int level = 1; level <= item->top_level; ++level) {
do {
- node_t *pred = preds[level];
- node_t *next = pred->next[level];
- while (EXPECT_FALSE(IS_TAGGED(next) || next->key < key)) {
- find_preds(preds, skiplist, key, TRUE);
+ node_t *pred;
+ node_t *next;
+ do {
pred = preds[level];
next = pred->next[level];
- }
+ if (next == NULL) // item goes at the end of the list
+ break;
+ if (!IS_TAGGED(next) && next->key > key) // pred's link changed
+ break;
+ find_preds(preds, item->top_level, skiplist, key, TRUE);
+ } while (1);
do {
// There in no need to continue linking in the item if another thread removed it.
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) {
+ node_t *item = find_preds(preds, -1, skiplist, key, TRUE);
+ if (item == NULL || item->key != key) {
TRACE("s3", "sl_remove: remove failed, an item with a matching key does not exist in the skiplist", 0, 0);
return DOES_NOT_EXIST;
}
void sl_print (skiplist_t *skiplist) {
for (int level = MAX_LEVEL; level >= 0; --level) {
node_t *item = skiplist->head;
- if (item->next[level] == skiplist->last)
+ if (item->next[level] == NULL)
continue;
printf("(%d) ", level);
while (item) {
node_t *next = item->next[level];
- printf("%s%p:0x%llx ", IS_TAGGED(next) ? "*" : "", item, item->key);
+ printf("%s%p ", IS_TAGGED(next) ? "*" : "", item);
item = (node_t *)STRIP_TAG(next);
}
printf("\n");
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);
+ printf("%s%p:0x%llx [%d]", is_marked ? "*" : "", item, item->key, item->top_level);
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)
+ is_marked = IS_TAGGED(item->next[0]);
+ printf(" %p%s", next, is_marked ? "*" : "");
+ if (item == skiplist->head && item->next[level] == NULL)
break;
}
- printf(")\n");
+ printf("\n");
fflush(stdout);
item = (node_t *)STRIP_TAG(item->next[0]);
}
static skiplist_t *sl_;
void *worker (void *arg) {
- int id = (int)(size_t)arg;
-
- unsigned int rand_seed = id+1;//rdtsc_l();
// Wait for all the worker threads to be ready.
SYNC_ADD(&wait_, -1);
do {} while (wait_);
for (int i = 0; i < NUM_ITERATIONS/num_threads_; ++i) {
- int n = rand_r(&rand_seed);
- int key = (n & 0xF) + 1;
- if (n & (1 << 8)) {
- sl_add_r(n, sl_, key, 1);
+ unsigned r = nbd_rand();
+ int key = (r & 0xF) + 1;
+ if (r & (1 << 8)) {
+ sl_add(sl_, key, 1);
} else {
sl_remove(sl_, key);
}
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);
sl_print(sl_);
- lwt_dump("lwt.out");
+ printf("Th:%ld Time:%dms\n", num_threads_, ms);
return 0;
}
projects / nbds / commitdiff