resolve: cache lookup for async resolvers

While waiting for a host resolve, check if the host cache may have
gotten the name already (by someone else), for when the same name is
resolved by several simultanoues requests.

The resolver thread occasionally gets stuck in getaddrinfo() when the
DNS or anything else is crappy or slow, so when a host is found in the
DNS cache, leave the thread alone and let itself cleanup the mess.

1 files changed, 53 insertions, 15 deletions

diff --git a/lib/asyn-thread.c b/lib/asyn-thread.c
index 31a313281..6cdc9adff 100644
--- a/lib/asyn-thread.c
+++ b/lib/asyn-thread.c
@@ -166,6 +166,7 @@ struct thread_sync_data {
 #ifdef HAVE_GETADDRINFO
   struct addrinfo hints;
 #endif
+  struct thread_data *td; /* for thread-self cleanup */
 };
 
 struct thread_data {
@@ -202,13 +203,16 @@ void destroy_thread_sync_data(struct thread_sync_data * tsd)
 
 /* Initialize resolver thread synchronization data */
 static
-int init_thread_sync_data(struct thread_sync_data * tsd,
+int init_thread_sync_data(struct thread_data * td,
                            const char * hostname,
                            int port,
                            const struct addrinfo *hints)
 {
+  struct thread_sync_data *tsd = &td->tsd;
+
   memset(tsd, 0, sizeof(*tsd));
 
+  tsd->td = td;
   tsd->port = port;
 #ifdef HAVE_GETADDRINFO
   DEBUGASSERT(hints);
@@ -266,6 +270,7 @@ static int getaddrinfo_complete(struct connectdata *conn)
 static unsigned int CURL_STDCALL getaddrinfo_thread (void *arg)
 {
   struct thread_sync_data *tsd = (struct thread_sync_data*)arg;
+  struct thread_data *td = tsd->td;
   char service[12];
   int rc;
 
@@ -280,8 +285,16 @@ static unsigned int CURL_STDCALL getaddrinfo_thread (void *arg)
   }
 
   Curl_mutex_acquire(tsd->mtx);
-  tsd->done = 1;
-  Curl_mutex_release(tsd->mtx);
+  if(tsd->done) {
+    /* too late, gotta clean up the mess */
+    Curl_mutex_release(tsd->mtx);
+    destroy_thread_sync_data(tsd);
+    free(td);
+  }
+  else {
+    tsd->done = 1;
+    Curl_mutex_release(tsd->mtx);
+  }
 
   return 0;
 }
@@ -294,6 +307,7 @@ static unsigned int CURL_STDCALL getaddrinfo_thread (void *arg)
 static unsigned int CURL_STDCALL gethostbyname_thread (void *arg)
 {
   struct thread_sync_data *tsd = (struct thread_sync_data *)arg;
+  struct thread_data *td = tsd->td;
 
   tsd->res = Curl_ipv4_resolve_r(tsd->hostname, tsd->port);
 
@@ -304,8 +318,16 @@ static unsigned int CURL_STDCALL gethostbyname_thread (void *arg)
   }
 
   Curl_mutex_acquire(tsd->mtx);
-  tsd->done = 1;
-  Curl_mutex_release(tsd->mtx);
+  if(tsd->done) {
+    /* too late, gotta clean up the mess */
+    Curl_mutex_release(tsd->mtx);
+    destroy_thread_sync_data(tsd);
+    free(td);
+  }
+  else {
+    tsd->done = 1;
+    Curl_mutex_release(tsd->mtx);
+  }
 
   return 0;
 }
@@ -317,21 +339,37 @@ static unsigned int CURL_STDCALL gethostbyname_thread (void *arg)
  */
 static void destroy_async_data (struct Curl_async *async)
 {
-  if(async->hostname)
-    free(async->hostname);
-
   if(async->os_specific) {
     struct thread_data *td = (struct thread_data*) async->os_specific;
+    int done;
+
+    /*
+     * if the thread is still blocking in the resolve syscall, detach it and
+     * let the thread do the cleanup...
+     */
+    Curl_mutex_acquire(td->tsd.mtx);
+    done = td->tsd.done;
+    td->tsd.done = 1;
+    Curl_mutex_release(td->tsd.mtx);
+
+    if(!done) {
+      Curl_thread_destroy(td->thread_hnd);
+    }
+    else {
+      if(td->thread_hnd != curl_thread_t_null)
+        Curl_thread_join(&td->thread_hnd);
 
-    if(td->thread_hnd != curl_thread_t_null)
-      Curl_thread_join(&td->thread_hnd);
-
-    destroy_thread_sync_data(&td->tsd);
+      destroy_thread_sync_data(&td->tsd);
 
-    free(async->os_specific);
+      free(async->os_specific);
+    }
   }
-  async->hostname = NULL;
   async->os_specific = NULL;
+
+  if(async->hostname)
+    free(async->hostname);
+
+  async->hostname = NULL;
 }
 
 /*
@@ -357,7 +395,7 @@ static bool init_resolve_thread (struct connectdata *conn,
   conn->async.dns = NULL;
   td->thread_hnd = curl_thread_t_null;
 
-  if(!init_thread_sync_data(&td->tsd, hostname, port, hints))
+  if(!init_thread_sync_data(td, hostname, port, hints))
     goto err_exit;
 
   Curl_safefree(conn->async.hostname);