Merge "Avoid multiple dns lookups for the same query"
diff --git a/libc/netbsd/resolv/res_cache.c b/libc/netbsd/resolv/res_cache.c
index 284ca2f..2dcb164 100644
--- a/libc/netbsd/resolv/res_cache.c
+++ b/libc/netbsd/resolv/res_cache.c
@@ -1159,6 +1159,15 @@
* inlined in the Entry structure.
*/
+/* Maximum time for a thread to wait for an pending request */
+#define PENDING_REQUEST_TIMEOUT 20;
+
+typedef struct pending_req_info {
+ unsigned int hash;
+ pthread_cond_t cond;
+ struct pending_req_info* next;
+} PendingReqInfo;
+
typedef struct resolv_cache {
int max_entries;
int num_entries;
@@ -1167,6 +1176,7 @@
unsigned generation;
int last_id;
Entry* entries;
+ PendingReqInfo pending_requests;
} Cache;
typedef struct resolv_cache_info {
@@ -1181,6 +1191,107 @@
#define HTABLE_VALID(x) ((x) != NULL && (x) != HTABLE_DELETED)
static void
+_cache_flush_pending_requests_locked( struct resolv_cache* cache )
+{
+ struct pending_req_info *ri, *tmp;
+ if (cache) {
+ ri = cache->pending_requests.next;
+
+ while (ri) {
+ tmp = ri;
+ ri = ri->next;
+ pthread_cond_broadcast(&tmp->cond);
+
+ pthread_cond_destroy(&tmp->cond);
+ free(tmp);
+ }
+
+ cache->pending_requests.next = NULL;
+ }
+}
+
+/* return 0 if no pending request is found matching the key
+ * if a matching request is found the calling thread will wait
+ * and return 1 when released */
+static int
+_cache_check_pending_request_locked( struct resolv_cache* cache, Entry* key )
+{
+ struct pending_req_info *ri, *prev;
+ int exist = 0;
+
+ if (cache && key) {
+ ri = cache->pending_requests.next;
+ prev = &cache->pending_requests;
+ while (ri) {
+ if (ri->hash == key->hash) {
+ exist = 1;
+ break;
+ }
+ prev = ri;
+ ri = ri->next;
+ }
+
+ if (!exist) {
+ ri = calloc(1, sizeof(struct pending_req_info));
+ if (ri) {
+ ri->hash = key->hash;
+ pthread_cond_init(&ri->cond, NULL);
+ prev->next = ri;
+ }
+ } else {
+ struct timespec ts = {0,0};
+ ts.tv_sec = _time_now() + PENDING_REQUEST_TIMEOUT;
+ int rv = pthread_cond_timedwait(&ri->cond, &cache->lock, &ts);
+ }
+ }
+
+ return exist;
+}
+
+/* notify any waiting thread that waiting on a request
+ * matching the key has been added to the cache */
+static void
+_cache_notify_waiting_tid_locked( struct resolv_cache* cache, Entry* key )
+{
+ struct pending_req_info *ri, *prev;
+
+ if (cache && key) {
+ ri = cache->pending_requests.next;
+ prev = &cache->pending_requests;
+ while (ri) {
+ if (ri->hash == key->hash) {
+ pthread_cond_broadcast(&ri->cond);
+ break;
+ }
+ prev = ri;
+ ri = ri->next;
+ }
+
+ // remove item from list and destroy
+ if (ri) {
+ prev->next = ri->next;
+ pthread_cond_destroy(&ri->cond);
+ free(ri);
+ }
+ }
+}
+
+/* notify the cache that the query failed */
+void
+_resolv_cache_query_failed( struct resolv_cache* cache,
+ const void* query,
+ int querylen)
+{
+ Entry key[1];
+
+ if (cache && entry_init_key(key, query, querylen)) {
+ pthread_mutex_lock(&cache->lock);
+ _cache_notify_waiting_tid_locked(cache, key);
+ pthread_mutex_unlock(&cache->lock);
+ }
+}
+
+static void
_cache_flush_locked( Cache* cache )
{
int nn;
@@ -1197,6 +1308,9 @@
}
}
+ // flush pending request
+ _cache_flush_pending_requests_locked(cache);
+
cache->mru_list.mru_next = cache->mru_list.mru_prev = &cache->mru_list;
cache->num_entries = 0;
cache->last_id = 0;
@@ -1470,7 +1584,17 @@
if (e == NULL) {
XLOG( "NOT IN CACHE");
- goto Exit;
+ // calling thread will wait if an outstanding request is found
+ // that matching this query
+ if (!_cache_check_pending_request_locked(cache, key)) {
+ goto Exit;
+ } else {
+ lookup = _cache_lookup_p(cache, key);
+ e = *lookup;
+ if (e == NULL) {
+ goto Exit;
+ }
+ }
}
now = _time_now();
@@ -1573,6 +1697,7 @@
_cache_dump_mru(cache);
#endif
Exit:
+ _cache_notify_waiting_tid_locked(cache, key);
pthread_mutex_unlock( &cache->lock );
}
diff --git a/libc/netbsd/resolv/res_send.c b/libc/netbsd/resolv/res_send.c
index dbad6dd..2f131f1 100644
--- a/libc/netbsd/resolv/res_send.c
+++ b/libc/netbsd/resolv/res_send.c
@@ -646,6 +646,9 @@
errno = terrno;
return (-1);
fail:
+#if USE_RESOLV_CACHE
+ _resolv_cache_query_failed(cache, buf, buflen);
+#endif
res_nclose(statp);
return (-1);
}
diff --git a/libc/private/resolv_cache.h b/libc/private/resolv_cache.h
index 2a54453..1dcc53f 100644
--- a/libc/private/resolv_cache.h
+++ b/libc/private/resolv_cache.h
@@ -95,4 +95,10 @@
const void* answer,
int answerlen );
+/* Notify the cache a request failed */
+extern void
+_resolv_cache_query_failed( struct resolv_cache* cache,
+ const void* query,
+ int querylen);
+
#endif /* _RESOLV_CACHE_H_ */
