X-Git-Url: https://pd.if.org/git/?p=nbds;a=blobdiff_plain;f=map%2Funsafe_skiplist.c;fp=map%2Funsafe_skiplist.c;h=f54e10d53d7b55edf175641b093a161696a3b9ba;hp=0000000000000000000000000000000000000000;hb=778b8c8ca708b082a1192acfb114a6751b2ad7c9;hpb=5aa9223647fbb52fa8941d92c8896ebaf148b41c

diff --git a/map/unsafe_skiplist.c b/map/unsafe_skiplist.c
new file mode 100644
index 0000000..f54e10d
--- /dev/null
+++ b/map/unsafe_skiplist.c
@@ -0,0 +1,355 @@
+/* 
+ * Written by Josh Dybnis and released to the public domain, as explained at
+ * http://creativecommons.org/licenses/publicdomain
+ *
+ * non thread safe skiplist
+ */
+
+#include <stdio.h>
+#include <string.h>
+
+#include "common.h"
+#include "skiplist.h"
+#include "runtime.h"
+#include "mem.h"
+
+#define MAX_LEVEL 31
+
+typedef struct node {
+    map_key_t key;
+    map_val_t val;
+    int top_level;
+    struct node *next[1];
+} node_t;
+
+struct sl_iter {
+    node_t *next;
+};
+
+struct sl {
+    node_t *head;
+    const datatype_t *key_type;
+    int high_water; // max level of any item in the list
+};
+
+static int random_level (void) {
+    unsigned r = nbd_rand();
+    int n = __builtin_ctz(r) / 2;
+    if (n > MAX_LEVEL) { n = MAX_LEVEL; }
+    return n;
+}
+
+static node_t *node_alloc (int level, map_key_t key, map_val_t val) {
+    assert(level >= 0 && level <= MAX_LEVEL);
+    size_t sz = sizeof(node_t) + level * sizeof(node_t *);
+    node_t *item = (node_t *)nbd_malloc(sz);
+    memset(item, 0, sz);
+    item->key = key;
+    item->val = val;
+    item->top_level = level;
+    TRACE("s2", "node_alloc: new node %p (%llu levels)", item, level);
+    return item;
+}
+
+skiplist_t *sl_alloc (const datatype_t *key_type) {
+    skiplist_t *sl = (skiplist_t *)nbd_malloc(sizeof(skiplist_t));
+    sl->key_type = key_type;
+    sl->high_water = 0;
+    sl->head = node_alloc(MAX_LEVEL, 0, 0);
+    memset(sl->head->next, 0, (MAX_LEVEL+1) * sizeof(skiplist_t *));
+    return sl;
+}
+
+void sl_free (skiplist_t *sl) {
+    node_t *item = sl->head->next[0];
+    while (item) {
+        node_t *next = item->next[0];
+        if (sl->key_type != NULL) {
+            nbd_free((void *)item->key);
+        }
+        nbd_free(item);
+        item = next;
+    }
+}
+
+size_t sl_count (skiplist_t *sl) {
+    size_t count = 0;
+    node_t *item = sl->head->next[0];
+    while (item) {
+        count++;
+        item = item->next[0];
+    }
+    return count;
+}
+
+static node_t *find_preds (node_t **preds, node_t **succs, int n, skiplist_t *sl, map_key_t key, int help_remove) {
+    node_t *pred = sl->head;
+    node_t *item = NULL;
+    TRACE("s2", "find_preds: searching for key %p in skiplist (head is %p)", key, pred);
+    int d = 0;
+    int start_level = sl->high_water;
+    if (EXPECT_FALSE(start_level < n)) {
+        start_level = n;
+    }
+
+    // Traverse the levels of <sl> from the top level to the bottom
+    for (int level = start_level; level >= 0; --level) {
+        node_t *next = pred->next[level];
+        if (next == DOES_NOT_EXIST && level > n)
+            continue;
+        TRACE("s3", "find_preds: traversing level %p starting at %p", level, pred);
+        item = next;
+        while (item != NULL) {
+            next = item->next[level];
+
+            if (EXPECT_TRUE(sl->key_type == NULL)) {
+                d = item->key - key;
+            } else {
+                d = sl->key_type->cmp((void *)item->key, (void *)key);
+            }
+
+            if (d >= 0)
+                break;
+
+            pred = item;
+            item = next;
+        }
+
+        TRACE("s3", "find_preds: found pred %p next %p", pred, item);
+
+        // The cast to unsigned is for the case when n is -1.
+        if ((unsigned)level <= (unsigned)n) { 
+            if (preds != NULL) {
+                preds[level] = pred;
+            }
+            if (succs != NULL) {
+                succs[level] = item;
+            }
+        }
+    }
+
+    // fill in empty levels
+    if (n == -1 && item != NULL && preds != NULL) {
+        assert(item->top_level <= MAX_LEVEL);
+        for (int level = start_level + 1; level <= item->top_level; ++level) {
+            preds[level] = sl->head;
+        }
+    }
+
+    if (d == 0) {
+        TRACE("s2", "find_preds: found matching item %p in skiplist, pred is %p", item, pred);
+        return item;
+    }
+    TRACE("s2", "find_preds: found proper place for key %p in skiplist, pred is %p. returning null", key, pred);
+    return NULL;
+}
+
+static void sl_unlink (skiplist_t *sl, map_key_t key) {
+    node_t *pred = sl->head;
+    node_t *item = NULL;
+    TRACE("s2", "sl_unlink: unlinking marked item with key %p", key, 0);
+    int d = 0;
+
+    // Traverse the levels of <sl>
+    for (int level = sl->high_water; level >= 0; --level) {
+        node_t *next = pred->next[level];
+        if (next == DOES_NOT_EXIST)
+            continue;
+        TRACE("s3", "sl_unlink: traversing level %p starting at %p", level, pred);
+        item = next;
+        while (item != NULL) {
+            next = item->next[level];
+
+            if (EXPECT_TRUE(sl->key_type == NULL)) {
+                d = item->key - key;
+            } else {
+                d = sl->key_type->cmp((void *)item->key, (void *)key);
+            }
+
+            if (d == 0) {
+                pred->next[level] = next;
+                TRACE("s3", "sl_unlink: unlinked item from pred %p", pred, 0);
+                item = next;
+                next = (item != NULL) ? item->next[level] : DOES_NOT_EXIST;
+                break;
+            }
+            if (d > 0) 
+                break;
+
+            pred = item;
+            item = next;
+        }
+
+        TRACE("s3", "sl_unlink: at pred %p next %p", pred, item);
+    }
+}
+
+// Fast find that does not return the node's predecessors.
+map_val_t sl_lookup (skiplist_t *sl, map_key_t key) {
+    TRACE("s1", "sl_lookup: searching for key %p in skiplist %p", key, sl);
+    node_t *item = find_preds(NULL, NULL, 0, sl, key, FALSE);
+
+    // If we found an <item> matching the <key> return its value.
+    if (item != NULL) {
+        map_val_t val = item->val;
+        return val;
+    }
+
+    TRACE("l1", "sl_lookup: no item in the skiplist matched the key", 0, 0);
+    return DOES_NOT_EXIST;
+}
+
+map_key_t sl_min_key (skiplist_t *sl) {
+    node_t *item = sl->head->next[0];
+    while (item != NULL)
+        return item->key;
+    return DOES_NOT_EXIST;
+}
+
+map_val_t sl_cas (skiplist_t *sl, map_key_t key, map_val_t expectation, map_val_t new_val) {
+    TRACE("s1", "sl_cas: key %p skiplist %p", key, sl);
+    TRACE("s1", "sl_cas: expectation %p new value %p", expectation, new_val);
+    ASSERT((int64_t)new_val > 0);
+
+    node_t *preds[MAX_LEVEL+1];
+    node_t *nexts[MAX_LEVEL+1];
+    node_t *new_item = NULL;
+    int n = random_level();
+    node_t *old_item = find_preds(preds, nexts, n, sl, key, TRUE);
+
+    // If there is already an item in the skiplist that matches the key just update its value.
+    if (old_item != NULL) {
+        map_val_t old_val = old_item->val;
+        if (expectation == CAS_EXPECT_DOES_NOT_EXIST || 
+           (expectation != CAS_EXPECT_WHATEVER && expectation != CAS_EXPECT_EXISTS && expectation != old_val)) {
+            TRACE("s1", "update_item: found an item %p in the skiplist that matched the key. the expectation was "
+                    "not met, the skiplist was not changed", item, old_val);
+            return old_val;
+        } 
+        old_item->val = new_val;
+        return old_val;
+    }
+
+    if (EXPECT_FALSE(expectation != CAS_EXPECT_DOES_NOT_EXIST && expectation != CAS_EXPECT_WHATEVER)) {
+        TRACE("l1", "sl_cas: the expectation was not met, the skiplist was not changed", 0, 0);
+        return DOES_NOT_EXIST; // failure, the caller expected an item for the <key> to already exist 
+    }
+
+    TRACE("s3", "sl_cas: inserting a new item between %p and %p", preds[0], nexts[0]);
+
+    // Create a new node and insert it into the skiplist.
+    map_key_t new_key = sl->key_type == NULL ? key : (map_key_t)sl->key_type->clone((void *)key);
+    if (n > sl->high_water) {
+        n = ++sl->high_water;
+        TRACE("s2", "sl_cas: incremented high water mark to %p", sl->high_water, 0);
+    }
+    new_item = node_alloc(n, new_key, new_val);
+
+    // Set <new_item>'s next pointers to their proper values
+    for (int level = 0; level <= new_item->top_level; ++level) {
+        new_item->next[level] = nexts[level];
+    }
+
+    // Link <new_item> into <sl> 
+    for (int level = 0; level <= new_item->top_level; ++level) {
+        preds[level]->next[level] = new_item;
+    }
+
+    return DOES_NOT_EXIST; // success, inserted a new item
+}
+
+map_val_t sl_remove (skiplist_t *sl, map_key_t key) {
+    TRACE("s1", "sl_remove: removing item with key %p from skiplist %p", key, sl);
+    node_t *preds[MAX_LEVEL+1];
+    node_t *item = find_preds(preds, NULL, -1, sl, key, TRUE);
+    if (item == NULL) {
+        TRACE("s3", "sl_remove: remove failed, an item with a matching key does not exist in the skiplist", 0, 0);
+        return DOES_NOT_EXIST;
+    }
+    map_val_t val = item->val; 
+
+    // unlink the item
+    sl_unlink(sl, key);
+
+    // free the node
+    if (sl->key_type != NULL) {
+        nbd_free((void *)item->key);
+    }
+    nbd_free(item);
+
+    return val;
+}
+
+void sl_print (skiplist_t *sl) {
+
+    printf("high water: %d levels\n", sl->high_water);
+    for (int level = MAX_LEVEL; level >= 0; --level) {
+        node_t *item = sl->head;
+        if (item->next[level] == DOES_NOT_EXIST)
+            continue;
+        printf("(%d) ", level);
+        int i = 0;
+        while (item) {
+            node_t *next = item->next[level];
+            printf("%p ", item);
+            item = next;
+            if (i++ > 30) {
+                printf("...");
+                break;
+            }
+        }
+        printf("\n");
+        fflush(stdout);
+    }
+    node_t *item = sl->head;
+    int i = 0;
+    while (item) {
+        printf("%p:0x%llx ", item, (uint64_t)item->key);
+        if (item != sl->head) {
+            printf("[%d]", item->top_level);
+        } else {
+            printf("[HEAD]");
+        }
+        for (int level = 1; level <= item->top_level; ++level) {
+            node_t *next = item->next[level];
+            printf(" %p", next);
+            if (item == sl->head && item->next[level] == DOES_NOT_EXIST)
+                break;
+        }
+        printf("\n");
+        fflush(stdout);
+        item = item->next[0];
+        if (i++ > 30) {
+            printf("...\n");
+            break;
+        }
+    }
+}
+
+sl_iter_t *sl_iter_begin (skiplist_t *sl, map_key_t key) {
+    sl_iter_t *iter = (sl_iter_t *)nbd_malloc(sizeof(sl_iter_t));
+    if (key != DOES_NOT_EXIST) {
+        find_preds(NULL, &iter->next, 0, sl, key, FALSE);
+    } else {
+        iter->next = sl->head->next[0];
+    }
+    return iter;
+}
+
+map_val_t sl_iter_next (sl_iter_t *iter, map_key_t *key_ptr) {
+    assert(iter);
+    node_t *item = iter->next;
+    if (item == NULL) {
+        iter->next = NULL;
+        return DOES_NOT_EXIST;
+    }
+    iter->next = item->next[0];
+    if (key_ptr != NULL) {
+        *key_ptr = item->key;
+    }
+    return item->val;
+}
+
+void sl_iter_free (sl_iter_t *iter) {
+    nbd_free(iter);
+}