optimize: large /etc/hosts files reading

profiling found some hot paths that could be optimized to reduce
insert times into the cache.

Fix By: Brad House (@bradh352)

src/lib/ares__hosts_file.c

@@ -313,81 +313,51 @@ fail:
   return NULL;
 }
 
-static ares_bool_t ares__hosts_entry_ipaddr_exists(ares_hosts_entry_t *entry,
-                                                   const char         *ipaddr)
-{
-  ares__llist_node_t *node;
-
-  for (node = ares__llist_node_first(entry->ips); node != NULL;
-       node = ares__llist_node_next(node)) {
-    const char *myaddr = ares__llist_node_val(node);
-    if (strcmp(myaddr, ipaddr) == 0) {
-      return ARES_TRUE;
-    }
-  }
-
-  return ARES_FALSE;
-}
-
-static ares_bool_t ares__hosts_entry_host_exists(ares_hosts_entry_t *entry,
-                                                 const char         *host)
-{
-  ares__llist_node_t *node;
-
-  for (node = ares__llist_node_first(entry->ips); node != NULL;
-       node = ares__llist_node_next(node)) {
-    const char *myhost = ares__llist_node_val(node);
-    if (strcasecmp(myhost, host) == 0) {
-      return ARES_TRUE;
-    }
-  }
-
-  return ARES_FALSE;
-}
+typedef enum {
+  ARES_MATCH_NONE   = 0,
+  ARES_MATCH_IPADDR = 1,
+  ARES_MATCH_HOST   = 2
+} ares_hosts_file_match_t;
 
-static ares_status_t ares__hosts_file_merge_entry(ares_hosts_entry_t *existing,
-                                                  ares_hosts_entry_t *entry)
+static ares_status_t ares__hosts_file_merge_entry(ares_hosts_file_t  *hf,
+                                                  ares_hosts_entry_t *existing,
+                                                  ares_hosts_entry_t *entry,
+                                                  ares_hosts_file_match_t matchtype)
 {
   ares__llist_node_t *node;
 
-  while ((node = ares__llist_node_first(entry->ips)) != NULL) {
-    char *ipaddr = ares__llist_node_claim(node);
+  /* If we matched on IP address, we know there can only be 1, so there's no
+   * reason to do anything */
+  if (matchtype != ARES_MATCH_IPADDR) {
+    while ((node = ares__llist_node_first(entry->ips)) != NULL) {
+      const char *ipaddr = ares__llist_node_val(node);
 
-    if (ares__hosts_entry_ipaddr_exists(existing, ipaddr)) {
-      ares_free(ipaddr);
-      continue;
-    }
+      if (ares__htable_strvp_get_direct(hf->iphash, ipaddr) != NULL) {
+        ares__llist_node_destroy(node);
+        continue;
+      }
 
-    if (ares__llist_insert_last(existing->ips, ipaddr) == NULL) {
-      ares_free(ipaddr);
-      return ARES_ENOMEM;
+      ares__llist_node_move_parent_last(node, existing->ips);
     }
   }
 
 
   while ((node = ares__llist_node_first(entry->hosts)) != NULL) {
-    char *hostname = ares__llist_node_claim(node);
+    const char *hostname = ares__llist_node_val(node);
 
-    if (ares__hosts_entry_host_exists(existing, hostname)) {
-      ares_free(hostname);
+    if (ares__htable_strvp_get_direct(hf->hosthash, hostname) != NULL) {
+      ares__llist_node_destroy(node);
       continue;
     }
 
-    if (ares__llist_insert_last(existing->hosts, hostname) == NULL) {
-      ares_free(hostname);
-      return ARES_ENOMEM;
-    }
+    ares__llist_node_move_parent_last(node, existing->hosts);
   }
 
   ares__hosts_entry_destroy(entry);
   return ARES_SUCCESS;
 }
 
-typedef enum {
-  ARES_MATCH_NONE   = 0,
-  ARES_MATCH_IPADDR = 1,
-  ARES_MATCH_HOST   = 2
-} ares_hosts_file_match_t;
+
 
 static ares_hosts_file_match_t
   ares__hosts_file_match(const ares_hosts_file_t *hf, ares_hosts_entry_t *entry,
@@ -435,7 +405,7 @@ static ares_status_t ares__hosts_file_add(ares_hosts_file_t  *hosts,
   matchtype = ares__hosts_file_match(hosts, entry, &match);
 
   if (matchtype != ARES_MATCH_NONE) {
-    status = ares__hosts_file_merge_entry(match, entry);
+    status = ares__hosts_file_merge_entry(hosts, match, entry, matchtype);
     if (status != ARES_SUCCESS) {
       ares__hosts_entry_destroy(entry);
       return status;
@@ -481,6 +451,22 @@ static ares_status_t ares__hosts_file_add(ares_hosts_file_t  *hosts,
   return ARES_SUCCESS;
 }
 
+static ares_bool_t ares__hosts_entry_isdup(ares_hosts_entry_t *entry,
+                                           const char         *host)
+{
+  ares__llist_node_t *node;
+
+  for (node = ares__llist_node_first(entry->ips); node != NULL;
+       node = ares__llist_node_next(node)) {
+    const char *myhost = ares__llist_node_val(node);
+    if (strcasecmp(myhost, host) == 0) {
+      return ARES_TRUE;
+    }
+  }
+
+  return ARES_FALSE;
+}
+
 static ares_status_t ares__parse_hosts_hostnames(ares__buf_t        *buf,
                                                  ares_hosts_entry_t *entry)
 {
@@ -531,7 +517,7 @@ static ares_status_t ares__parse_hosts_hostnames(ares__buf_t        *buf,
     }
 
     /* Don't add a duplicate to the same entry */
-    if (ares__hosts_entry_host_exists(entry, hostname)) {
+    if (ares__hosts_entry_isdup(entry, hostname)) {
       continue;
     }
 

src/lib/ares__htable.c

@@ -66,7 +66,7 @@ static unsigned int ares__htable_generate_seed(ares__htable_t *htable)
 
 static void ares__htable_buckets_destroy(ares__llist_t **buckets,
                                          unsigned int    size,
-                                         unsigned char   destroy_vals)
+                                         ares_bool_t     destroy_vals)
 {
   unsigned int i;
 
@@ -94,7 +94,7 @@ void ares__htable_destroy(ares__htable_t *htable)
   if (htable == NULL) {
     return;
   }
-  ares__htable_buckets_destroy(htable->buckets, htable->size, 1);
+  ares__htable_buckets_destroy(htable->buckets, htable->size, ARES_TRUE);
   ares_free(htable);
 }
 
@@ -180,11 +180,40 @@ static ares_bool_t ares__htable_expand(ares__htable_t *htable)
 
   for (i = 0; i < old_size; i++) {
     ares__llist_node_t *node;
-    for (node = ares__llist_node_first(htable->buckets[i]); node != NULL;
-         node = ares__llist_node_next(node)) {
+
+    /* Nothing in this bucket */
+    if (htable->buckets[i] == NULL)
+      continue;
+
+    /* Fast past optimization (most likely case), there is likely only a single
+     * entry in both the source and destination, check for this to confirm and
+     * if so, just move the bucket over */
+    if (ares__llist_len(htable->buckets[i]) == 1) {
+      void  *val = ares__llist_first_val(htable->buckets[i]);
+      size_t idx = HASH_IDX(htable, htable->bucket_key(val));
+
+      if (buckets[idx] == NULL) {
+        /* Swap! */
+        buckets[idx]       = htable->buckets[i];
+        htable->buckets[i] = NULL;
+        continue;
+      }
+    }
+
+    /* Slow path, collisions */
+    while ((node = ares__llist_node_first(htable->buckets[i])) != NULL) {
       void  *val = ares__llist_node_val(node);
       size_t idx = HASH_IDX(htable, htable->bucket_key(val));
 
+      /* Try fast path again as maybe we popped one collision off and the
+       * next we can reuse the llist parent */
+      if (buckets[idx] == NULL && ares__llist_len(htable->buckets[i]) == 1) {
+        /* Swap! */
+        buckets[idx]       = htable->buckets[i];
+        htable->buckets[i] = NULL;
+        break;
+      }
+
       if (buckets[idx] == NULL) {
         buckets[idx] = ares__llist_create(htable->bucket_free);
       }
@@ -192,19 +221,17 @@ static ares_bool_t ares__htable_expand(ares__htable_t *htable)
         goto fail;
       }
 
-      if (ares__llist_insert_first(buckets[idx], val) == NULL) {
-        goto fail;
-      }
+      ares__llist_node_move_parent_first(node, buckets[idx]);
     }
   }
 
   /* Swap out buckets */
-  ares__htable_buckets_destroy(htable->buckets, old_size, 0);
+  ares__htable_buckets_destroy(htable->buckets, old_size, ARES_FALSE);
   htable->buckets = buckets;
   return ARES_TRUE;
 
 fail:
-  ares__htable_buckets_destroy(buckets, htable->size, 0);
+  ares__htable_buckets_destroy(buckets, htable->size, ARES_FALSE);
   htable->size = old_size;
 
   return ARES_FALSE;

src/lib/ares__llist.c

@@ -71,24 +71,14 @@ typedef enum {
   ARES__LLIST_INSERT_BEFORE
 } ares__llist_insert_type_t;
 
-static ares__llist_node_t *ares__llist_insert_at(ares__llist_t            *list,
-                                                 ares__llist_insert_type_t type,
-                                                 ares__llist_node_t       *at,
-                                                 void                     *val)
+static void ares__llist_attach_at(ares__llist_t            *list,
+                                  ares__llist_insert_type_t type,
+                                  ares__llist_node_t       *at,
+                                  ares__llist_node_t       *node)
 {
-  ares__llist_node_t *node = NULL;
-
-  if (list == NULL || val == NULL) {
-    return NULL;
-  }
-
-  node = ares_malloc_zero(sizeof(*node));
-
-  if (node == NULL) {
-    return NULL;
-  }
+  if (list == NULL || node == NULL)
+    return;
 
-  node->data   = val;
   node->parent = list;
 
   if (type == ARES__LLIST_INSERT_BEFORE && (at == list->head || at == NULL)) {
@@ -126,6 +116,27 @@ static ares__llist_node_t *ares__llist_insert_at(ares__llist_t            *list,
   }
 
   list->cnt++;
+}
+
+static ares__llist_node_t *ares__llist_insert_at(ares__llist_t            *list,
+                                                 ares__llist_insert_type_t type,
+                                                 ares__llist_node_t       *at,
+                                                 void                     *val)
+{
+  ares__llist_node_t *node = NULL;
+
+  if (list == NULL || val == NULL) {
+    return NULL;
+  }
+
+  node = ares_malloc_zero(sizeof(*node));
+
+  if (node == NULL) {
+    return NULL;
+  }
+
+  node->data = val;
+  ares__llist_attach_at(list, type, at, node);
 
   return node;
 }
@@ -233,17 +244,14 @@ void *ares__llist_last_val(ares__llist_t *list)
   return ares__llist_node_val(ares__llist_node_last(list));
 }
 
-void *ares__llist_node_claim(ares__llist_node_t *node)
+static void ares__llist_node_detach(ares__llist_node_t *node)
 {
-  void          *val;
   ares__llist_t *list;
 
-  if (node == NULL) {
-    return NULL;
-  }
+  if (node == NULL)
+    return;
 
   list = node->parent;
-  val  = node->data;
 
   if (node->prev) {
     node->prev->next = node->next;
@@ -260,9 +268,22 @@ void *ares__llist_node_claim(ares__llist_node_t *node)
   if (node == list->tail) {
     list->tail = node->prev;
   }
-  ares_free(node);
 
+  node->parent = NULL;
   list->cnt--;
+}
+
+void *ares__llist_node_claim(ares__llist_node_t *node)
+{
+  void          *val;
+
+  if (node == NULL) {
+    return NULL;
+  }
+
+  val  = node->data;
+  ares__llist_node_detach(node);
+  ares_free(node);
 
   return val;
 }
@@ -313,3 +334,23 @@ void ares__llist_destroy(ares__llist_t *list)
   }
   ares_free(list);
 }
+
+void ares__llist_node_move_parent_last(ares__llist_node_t *node,
+                                       ares__llist_t *new_parent)
+{
+  if (node == NULL || new_parent == NULL)
+    return;
+
+  ares__llist_node_detach(node);
+  ares__llist_attach_at(new_parent, ARES__LLIST_INSERT_TAIL, NULL, node);
+}
+
+void ares__llist_node_move_parent_first(ares__llist_node_t *node,
+                                        ares__llist_t *new_parent)
+{
+  if (node == NULL || new_parent == NULL)
+    return;
+
+  ares__llist_node_detach(node);
+  ares__llist_attach_at(new_parent, ARES__LLIST_INSERT_HEAD, NULL, node);
+}

src/lib/ares__llist.h

@@ -198,6 +198,23 @@ void ares__llist_node_destroy(ares__llist_node_t *node);
  */
 void ares__llist_destroy(ares__llist_t *list);
 
+/*! Detach node from the current list and re-attach it to the new list as the
+ *  last entry.
+ *
+ * \param[in] node   node to move
+ * \param[in] parent new list
+ */
+void ares__llist_node_move_parent_last(ares__llist_node_t *node,
+                                       ares__llist_t *new_parent);
+
+/*! Detach node from the current list and re-attach it to the new list as the
+ *  first entry.
+ *
+ * \param[in] node   node to move
+ * \param[in] parent new list
+ */
+void ares__llist_node_move_parent_first(ares__llist_node_t *node,
+                                        ares__llist_t *new_parent);
 /*! @} */
 
 #endif /* __ARES__LLIST_H */