Bug fix in ht_iter_next() from Rui Ueyama

[nbds] / map / hashtable.c

diff --git a/map/hashtable.c b/map/hashtable.c
index 88bf6311efcea09aeca0bae1cff82fa62595d7a0..bff782f84afdf46867dcbc27275402f1e3ac18dd 100644 (file)
--- a/map/hashtable.c
+++ b/map/hashtable.c
@@ -10,6 +10,8 @@
  * Every atomic operation is also an implicit full memory barrier. The upshot is that it simplifies
  * the code a bit, but it won't be as fast as it could be on platforms that provide weaker 
  * operations like and unfenced CAS which would still do the job.
+ *
+ * 11FebO9 - Bug fix in ht_iter_next() from Rui Ueyama
  */
 
 #include <stdio.h>
@@ -34,6 +36,9 @@ typedef struct hti {
     volatile entry_t *table;
     hashtable_t *ht; // parent ht;
     struct hti *next;
+#ifdef USE_SYSTEM_MALLOC
+    void *unaligned_table_ptr; // system malloc doesn't guarentee cache-line alignment
+#endif
     unsigned scale;
     int max_probe;
     int ref_count;
@@ -136,13 +141,16 @@ static volatile entry_t *hti_lookup (hti_t *hti, map_key_t key, uint32_t key_has
 static hti_t *hti_alloc (hashtable_t *parent, int scale) {
     hti_t *hti = (hti_t *)nbd_malloc(sizeof(hti_t));
     memset(hti, 0, sizeof(hti_t));
+    hti->scale = scale;
 
     size_t sz = sizeof(entry_t) * (1 << scale);
-    entry_t *table = nbd_malloc(sz);
-    memset(table, 0, sz);
-    hti->table = table;
-
-    hti->scale = scale;
+#ifdef USE_SYSTEM_MALLOC
+    hti->unaligned_table_ptr = nbd_malloc(sz + CACHE_LINE_SIZE - 1);
+    hti->table = (void *)(((size_t)hti->unaligned_table_ptr + CACHE_LINE_SIZE - 1) & ~(CACHE_LINE_SIZE - 1));
+#else
+    hti->table = nbd_malloc(sz);
+#endif
+    memset((void *)hti->table, 0, sz);
 
     // When searching for a key probe a maximum of 1/4 of the buckets up to 1000 buckets.
     hti->max_probe = ((1 << (hti->scale - 2)) / ENTRIES_PER_BUCKET) + 4;
@@ -178,7 +186,11 @@ static void hti_start_copy (hti_t *hti) {
     if (old_next != NULL) {
         // Another thread beat us to it.
         TRACE("h0", "hti_start_copy: lost race to install new hti; found %p", old_next, 0);
-        nbd_free(next);
+#ifdef USE_SYSTEM_MALLOC
+        nbd_free(next->unaligned_table_ptr);
+#else
+        nbd_free((void *)next->table);
+#endif
         return;
     }
     TRACE("h0", "hti_start_copy: new hti %p scale %llu", next, next->scale);
@@ -278,8 +290,8 @@ static int hti_copy_entry (hti_t *ht1, volatile entry_t *ht1_ent, uint32_t key_h
     // Update the count if we were the one that completed the copy.
     if (old_ht2_ent_val == DOES_NOT_EXIST) {
         TRACE("h0", "hti_copy_entry: key %p value %p copied to new entry", key, ht1_ent_val);
-        SYNC_ADD(&ht1->count, -1);
-        SYNC_ADD(&ht2->count, 1);
+        (void)SYNC_ADD(&ht1->count, -1);
+        (void)SYNC_ADD(&ht2->count, 1);
         return TRUE;
     }
 
@@ -364,9 +376,9 @@ static map_val_t hti_cas (hti_t *hti, map_key_t key, uint32_t key_hash, map_val_
     map_val_t ent_val = ent->val;
     if (EXPECT_FALSE(IS_TAGGED(ent_val, TAG1))) {
         if (ent_val != COPIED_VALUE && ent_val != TAG_VALUE(TOMBSTONE, TAG1)) {
-            int did_copy = hti_copy_entry(hti, ent, key_hash, ((volatile hti_t *)hti)->next);
+            int did_copy = hti_copy_entry(hti, ent, key_hash, VOLATILE_DEREF(hti).next);
             if (did_copy) {
-                SYNC_ADD(&hti->num_entries_copied, 1);
+                (void)SYNC_ADD(&hti->num_entries_copied, 1);
             }
             TRACE("h0", "hti_cas: value in the middle of a copy, copy completed by %s", 
                         (did_copy ? "self" : "other"), 0);
@@ -400,9 +412,9 @@ static map_val_t hti_cas (hti_t *hti, map_key_t key, uint32_t key_hash, map_val_
 
     // The set succeeded. Adjust the value count.
     if (old_existed && new == DOES_NOT_EXIST) {
-        SYNC_ADD(&hti->count, -1);
+        (void)SYNC_ADD(&hti->count, -1);
     } else if (!old_existed && new != DOES_NOT_EXIST) {
-        SYNC_ADD(&hti->count, 1);
+        (void)SYNC_ADD(&hti->count, 1);
     }
 
     // Return the previous value.
@@ -419,7 +431,7 @@ static map_val_t hti_get (hti_t *hti, map_key_t key, uint32_t key_hash) {
     // searching the table. In that case, if a copy is in progress the key 
     // might exist in the copy.
     if (EXPECT_FALSE(ent == NULL)) {
-        if (((volatile hti_t *)hti)->next != NULL)
+        if (VOLATILE_DEREF(hti).next != NULL)
             return hti_get(hti->next, key, key_hash); // recursive tail-call
         return DOES_NOT_EXIST;
     }
@@ -431,12 +443,12 @@ static map_val_t hti_get (hti_t *hti, map_key_t key, uint32_t key_hash) {
     map_val_t ent_val = ent->val;
     if (EXPECT_FALSE(IS_TAGGED(ent_val, TAG1))) {
         if (EXPECT_FALSE(ent_val != COPIED_VALUE && ent_val != TAG_VALUE(TOMBSTONE, TAG1))) {
-            int did_copy = hti_copy_entry(hti, ent, key_hash, ((volatile hti_t *)hti)->next);
+            int did_copy = hti_copy_entry(hti, ent, key_hash, VOLATILE_DEREF(hti).next);
             if (did_copy) {
-                SYNC_ADD(&hti->num_entries_copied, 1);
+                (void)SYNC_ADD(&hti->num_entries_copied, 1);
             }
         }
-        return hti_get(((volatile hti_t *)hti)->next, key, key_hash); // tail-call
+        return hti_get(VOLATILE_DEREF(hti).next, key, key_hash); // tail-call
     }
 
     return (ent_val == TOMBSTONE) ? DOES_NOT_EXIST : ent_val;
@@ -508,7 +520,11 @@ static void hti_defer_free (hti_t *hti) {
             rcu_defer_free(GET_PTR(key));
         }
     }
+#ifdef USE_SYSTEM_MALLOC
+    rcu_defer_free(hti->unaligned_table_ptr);
+#else
     rcu_defer_free((void *)hti->table);
+#endif
     rcu_defer_free(hti);
 }
 
@@ -663,9 +679,6 @@ map_val_t ht_iter_next (ht_iter_t *iter, map_key_t *key_ptr) {
 
     } while (key == DOES_NOT_EXIST || val == DOES_NOT_EXIST || val == TOMBSTONE);
 
-    if (key_ptr) {
-        *key_ptr = key;
-    }
     if (val == COPIED_VALUE) {
         const datatype_t *key_type = iter->hti->ht->key_type;
 #ifdef NBD32
@@ -674,8 +687,15 @@ map_val_t ht_iter_next (ht_iter_t *iter, map_key_t *key_ptr) {
         uint32_t hash = (key_type == NULL) ? murmur32_8b((uint64_t)key) : key_type->hash((void *)key);
 #endif
         val = hti_get(iter->hti->next, (map_key_t)ent->key, hash);
+
+        // Go to the next entry if key is already deleted.
+        if (val == DOES_NOT_EXIST)
+            return ht_iter_next(iter, key_ptr); // recursive tail-call
     } 
 
+    if (key_ptr) {
+        *key_ptr = key;
+    }
     return val;
 }