/trunk/src/nbds/map/unsafe_skiplist.c

  1/* 
  2 * Written by Josh Dybnis and released to the public domain, as explained at
  3 * http://creativecommons.org/licenses/publicdomain
  4 *
  5 * non thread safe skiplist
  6 */
  7
  8#include <stdio.h>
  9#include <string.h>
 10
 11#include "common.h"
 12#include "skiplist.h"
 13#include "runtime.h"
 14#include "mem.h"
 15
 16#define MAX_LEVELS 24
 17
 18typedef struct node {
 19    map_key_t key;
 20    map_val_t val;
 21    int num_levels;
 22    struct node *next[1];
 23} node_t;
 24
 25struct sl_iter {
 26    node_t *next;
 27};
 28
 29struct sl {
 30    node_t *head;
 31    const datatype_t *key_type;
 32    int high_water; // max level of any item in the list
 33};
 34
 35static int random_levels (skiplist_t *sl) {
 36    uint64_t r = nbd_rand();
 37    int z = __builtin_ctz(r);
 38    int levels = (int)(z / 1.5);
 39    if (levels == 0)
 40        return 1;
 41    if (levels > sl->high_water) {
 42        levels = SYNC_ADD(&sl->high_water, 1);
 43        TRACE("s2", "random_levels: increased high water mark to %lld", sl->high_water, 0);
 44    }
 45    if (levels > MAX_LEVELS) { levels = MAX_LEVELS; }
 46    return levels;
 47}
 48
 49static node_t *node_alloc (int num_levels, map_key_t key, map_val_t val) {
 50    assert(num_levels > 0 && num_levels <= MAX_LEVELS);
 51    size_t sz = sizeof(node_t) + (num_levels - 1) * sizeof(node_t *);
 52    node_t *item = (node_t *)nbd_malloc(sz);
 53    memset(item, 0, sz);
 54    item->key = key;
 55    item->val = val;
 56    item->num_levels = num_levels;
 57    TRACE("s2", "node_alloc: new node %p (%llu levels)", item, num_levels);
 58    return item;
 59}
 60
 61skiplist_t *sl_alloc (const datatype_t *key_type) {
 62    skiplist_t *sl = (skiplist_t *)nbd_malloc(sizeof(skiplist_t));
 63    sl->key_type = key_type;
 64    sl->high_water = 1;
 65    sl->head = node_alloc(MAX_LEVELS, 0, 0);
 66    memset(sl->head->next, 0, MAX_LEVELS * sizeof(skiplist_t *));
 67    return sl;
 68}
 69
 70void sl_free (skiplist_t *sl) {
 71    node_t *item = sl->head->next[0];
 72    while (item) {
 73        node_t *next = item->next[0];
 74        if (sl->key_type != NULL) {
 75            nbd_free((void *)item->key);
 76        }
 77        nbd_free(item);
 78        item = next;
 79    }
 80}
 81
 82size_t sl_count (skiplist_t *sl) {
 83    size_t count = 0;
 84    node_t *item = sl->head->next[0];
 85    while (item) {
 86        count++;
 87        item = item->next[0];
 88    }
 89    return count;
 90}
 91
 92static node_t *find_preds (node_t **preds, node_t **succs, int n, skiplist_t *sl, map_key_t key, int unlink) {
 93    node_t *pred = sl->head;
 94    node_t *item = NULL;
 95    TRACE("s2", "find_preds: searching for key %p in skiplist (head is %p)", key, pred);
 96    int d = 0;
 97
 98    // Traverse the levels of <sl> from the top level to the bottom
 99    for (int level = sl->high_water - 1; level >= 0; --level) {
100        node_t *next = pred->next[level];
101        if (next == DOES_NOT_EXIST && level >= n)
102            continue;
103        TRACE("s3", "find_preds: traversing level %p starting at %p", level, pred);
104        item = next;
105        while (item != NULL) {
106            next = item->next[level];
107
108            if (EXPECT_TRUE(sl->key_type == NULL)) {
109                d = item->key - key;
110            } else {
111                d = sl->key_type->cmp((void *)item->key, (void *)key);
112            }
113
114            if (d >= 0) {
115                if (d == 0 && unlink) {
116                    pred->next[level] = next;
117                    TRACE("s3", "find_preds: unlinked item from pred %p", pred, 0);
118                    item = next;
119                    next = (item != NULL) ? item->next[level] : DOES_NOT_EXIST;
120                }
121                break;
122            }
123
124            pred = item;
125            item = next;
126        }
127
128        TRACE("s3", "find_preds: found pred %p next %p", pred, item);
129
130        if (level < n) { 
131            if (preds != NULL) {
132                preds[level] = pred;
133            }
134            if (succs != NULL) {
135                succs[level] = item;
136            }
137        }
138    }
139
140    if (d == 0) {
141        TRACE("s2", "find_preds: found matching item %p in skiplist, pred is %p", item, pred);
142        return item;
143    }
144    TRACE("s2", "find_preds: found proper place for key %p in skiplist, pred is %p. returning null", key, pred);
145    return NULL;
146}
147
148// Fast find that does not return the node's predecessors.
149map_val_t sl_lookup (skiplist_t *sl, map_key_t key) {
150    TRACE("s1", "sl_lookup: searching for key %p in skiplist %p", key, sl);
151    node_t *item = find_preds(NULL, NULL, 0, sl, key, FALSE);
152
153    // If we found an <item> matching the <key> return its value.
154    if (item != NULL) {
155        map_val_t val = item->val;
156        return val;
157    }
158
159    TRACE("s1", "sl_lookup: no item in the skiplist matched the key", 0, 0);
160    return DOES_NOT_EXIST;
161}
162
163map_key_t sl_min_key (skiplist_t *sl) {
164    node_t *item = sl->head->next[0];
165    while (item != NULL)
166        return item->key;
167    return DOES_NOT_EXIST;
168}
169
170map_val_t sl_cas (skiplist_t *sl, map_key_t key, map_val_t expectation, map_val_t new_val) {
171    TRACE("s1", "sl_cas: key %p skiplist %p", key, sl);
172    TRACE("s1", "sl_cas: expectation %p new value %p", expectation, new_val);
173    ASSERT((int64_t)new_val > 0);
174
175    node_t *preds[MAX_LEVELS];
176    node_t *nexts[MAX_LEVELS];
177    node_t *new_item = NULL;
178    int n = random_levels(sl);
179    node_t *old_item = find_preds(preds, nexts, n, sl, key, FALSE);
180
181    // If there is already an item in the skiplist that matches the key just update its value.
182    if (old_item != NULL) {
183        map_val_t old_val = old_item->val;
184        if (expectation == CAS_EXPECT_DOES_NOT_EXIST || 
185           (expectation != CAS_EXPECT_WHATEVER && expectation != CAS_EXPECT_EXISTS && expectation != old_val)) {
186            TRACE("s1", "sl_cas: the expectation was not met; the skiplist was not changed", 0, 0);
187            return old_val;
188        } 
189        old_item->val = new_val;
190        return old_val;
191    }
192
193    if (EXPECT_FALSE(expectation != CAS_EXPECT_DOES_NOT_EXIST && expectation != CAS_EXPECT_WHATEVER)) {
194        TRACE("s1", "sl_cas: the expectation was not met, the skiplist was not changed", 0, 0);
195        return DOES_NOT_EXIST; // failure, the caller expected an item for the <key> to already exist 
196    }
197
198    TRACE("s3", "sl_cas: inserting a new item between %p and %p", preds[0], nexts[0]);
199
200    // Create a new node and insert it into the skiplist.
201    map_key_t new_key = sl->key_type == NULL ? key : (map_key_t)sl->key_type->clone((void *)key);
202    new_item = node_alloc(n, new_key, new_val);
203
204    // Set <new_item>'s next pointers to their proper values
205    for (int level = 0; level < new_item->num_levels; ++level) {
206        new_item->next[level] = nexts[level];
207    }
208
209    // Link <new_item> into <sl> 
210    for (int level = 0; level < new_item->num_levels; ++level) {
211        preds[level]->next[level] = new_item;
212    }
213
214    return DOES_NOT_EXIST; // success, inserted a new item
215}
216
217map_val_t sl_remove (skiplist_t *sl, map_key_t key) {
218    TRACE("s1", "sl_remove: removing item with key %p from skiplist %p", key, sl);
219    node_t *preds[MAX_LEVELS];
220    node_t *item = find_preds(preds, NULL, sl->high_water, sl, key, FALSE);
221    if (item == NULL) {
222        TRACE("s3", "sl_remove: remove failed, an item with a matching key does not exist in the skiplist", 0, 0);
223        return DOES_NOT_EXIST;
224    }
225    map_val_t val = item->val; 
226
227    // unlink the item
228    find_preds(NULL, NULL, 0, sl, key, TRUE);
229
230    // free the node
231    if (sl->key_type != NULL) {
232        nbd_free((void *)item->key);
233    }
234    nbd_free(item);
235
236    return val;
237}
238
239void sl_print (skiplist_t *sl) {
240
241    printf("high water: %d levels\n", sl->high_water);
242    for (int level = MAX_LEVELS - 1; level >= 0; --level) {
243        node_t *item = sl->head;
244        if (item->next[level] == DOES_NOT_EXIST)
245            continue;
246        printf("(%d) ", level);
247        int i = 0;
248        while (item) {
249            node_t *next = item->next[level];
250            printf("%p ", item);
251            item = next;
252            if (i++ > 30) {
253                printf("...");
254                break;
255            }
256        }
257        printf("\n");
258        fflush(stdout);
259    }
260    node_t *item = sl->head;
261    int i = 0;
262    while (item) {
263        printf("%p:0x%llx ", item, (uint64_t)item->key);
264        if (item != sl->head) {
265            printf("[%d]", item->num_levels);
266        } else {
267            printf("[HEAD]");
268        }
269        for (int level = 1; level < item->num_levels; ++level) {
270            node_t *next = item->next[level];
271            printf(" %p", next);
272            if (item == sl->head && item->next[level] == DOES_NOT_EXIST)
273                break;
274        }
275        printf("\n");
276        fflush(stdout);
277        item = item->next[0];
278        if (i++ > 30) {
279            printf("...\n");
280            break;
281        }
282    }
283}
284
285sl_iter_t *sl_iter_begin (skiplist_t *sl, map_key_t key) {
286    sl_iter_t *iter = (sl_iter_t *)nbd_malloc(sizeof(sl_iter_t));
287    if (key != DOES_NOT_EXIST) {
288        find_preds(NULL, &iter->next, 1, sl, key, FALSE);
289    } else {
290        iter->next = sl->head->next[0];
291    }
292    return iter;
293}
294
295map_val_t sl_iter_next (sl_iter_t *iter, map_key_t *key_ptr) {
296    assert(iter);
297    node_t *item = iter->next;
298    if (item == NULL) {
299        iter->next = NULL;
300        return DOES_NOT_EXIST;
301    }
302    iter->next = item->next[0];
303    if (key_ptr != NULL) {
304        *key_ptr = item->key;
305    }
306    return item->val;
307}
308
309void sl_iter_free (sl_iter_t *iter) {
310    nbd_free(iter);
311}