Merge branch 'resolver-thread-pool' into 'main'

gthreadedresolver: Switch to using a separate thread pool and support timeouts

See merge request GNOME/glib!3397

6 files changed, 626 insertions, 134 deletions

diff --git a/docs/reference/gio/gio-sections-common.txt b/docs/reference/gio/gio-sections-common.txt
index 63d167678..f5737ef42 100644
--- a/docs/reference/gio/gio-sections-common.txt
+++ b/docs/reference/gio/gio-sections-common.txt
@@ -1934,6 +1934,8 @@ g_resolver_lookup_service
 g_resolver_lookup_service_async
 g_resolver_lookup_service_finish
 g_resolver_free_targets
+g_resolver_get_timeout
+g_resolver_set_timeout
 <SUBSECTION>
 GResolverRecordType
 g_resolver_lookup_records
diff --git a/gio/gresolver.c b/gio/gresolver.c
index 6a735e8d9..676f1e271 100644
--- a/gio/gresolver.c
+++ b/gio/gresolver.c
@@ -55,8 +55,18 @@
  * #GNetworkAddress and #GNetworkService provide wrappers around
  * #GResolver functionality that also implement #GSocketConnectable,
  * making it easy to connect to a remote host/service.
+ *
+ * The default resolver (see g_resolver_get_default()) has a timeout of 30s set
+ * on it since GLib 2.78. Earlier versions of GLib did not support resolver
+ * timeouts.
  */
 
+typedef enum {
+  PROP_TIMEOUT = 1,
+} GResolverProperty;
+
+static GParamSpec *props[PROP_TIMEOUT + 1] = { NULL, };
+
 enum {
   RELOAD,
   LAST_SIGNAL
@@ -65,11 +75,11 @@ enum {
 static guint signals[LAST_SIGNAL] = { 0 };
 
 struct _GResolverPrivate {
+  unsigned timeout_ms;
+
 #ifdef G_OS_UNIX
   GMutex mutex;
   time_t resolv_conf_timestamp;  /* protected by @mutex */
-#else
-  int dummy;
 #endif
 };
 
@@ -152,6 +162,42 @@ g_resolver_real_lookup_service_finish (GResolver            *resolver,
 }
 
 static void
+g_resolver_get_property (GObject    *object,
+                         guint       prop_id,
+                         GValue     *value,
+                         GParamSpec *pspec)
+{
+  GResolver *self = G_RESOLVER (object);
+
+  switch ((GResolverProperty) prop_id)
+    {
+    case PROP_TIMEOUT:
+      g_value_set_uint (value, g_resolver_get_timeout (self));
+      break;
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
+    }
+}
+
+static void
+g_resolver_set_property (GObject      *object,
+                         guint         prop_id,
+                         const GValue *value,
+                         GParamSpec   *pspec)
+{
+  GResolver *self = G_RESOLVER (object);
+
+  switch ((GResolverProperty) prop_id)
+    {
+    case PROP_TIMEOUT:
+      g_resolver_set_timeout (self, g_value_get_uint (value));
+      break;
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
+    }
+}
+
+static void
 g_resolver_finalize (GObject *object)
 {
 #ifdef G_OS_UNIX
@@ -168,6 +214,8 @@ g_resolver_class_init (GResolverClass *resolver_class)
 {
   GObjectClass *object_class = G_OBJECT_CLASS (resolver_class);
 
+  object_class->get_property = g_resolver_get_property;
+  object_class->set_property = g_resolver_set_property;
   object_class->finalize = g_resolver_finalize;
 
   /* Automatically pass these over to the lookup_records methods */
@@ -176,6 +224,31 @@ g_resolver_class_init (GResolverClass *resolver_class)
   resolver_class->lookup_service_finish = g_resolver_real_lookup_service_finish;
 
   /**
+   * GResolver:timeout:
+   *
+   * The timeout applied to all resolver lookups, in milliseconds.
+   *
+   * This may be changed through the lifetime of the #GResolver. The new value
+   * will apply to any lookups started after the change, but not to any
+   * already-ongoing lookups.
+   *
+   * If this is `0`, no timeout is applied to lookups.
+   *
+   * No timeout was applied to lookups before this property was added in
+   * GLib 2.78.
+   *
+   * Since: 2.78
+   */
+  props[PROP_TIMEOUT] =
+    g_param_spec_uint ("timeout",
+                       P_("Timeout"),
+                       P_("Timeout (ms) applied to all resolver lookups"),
+                       0, G_MAXUINT, 0,
+                       G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS | G_PARAM_EXPLICIT_NOTIFY);
+
+  g_object_class_install_properties (object_class, G_N_ELEMENTS (props), props);
+
+  /**
    * GResolver::reload:
    * @resolver: a #GResolver
    *
@@ -230,7 +303,9 @@ g_resolver_get_default (void)
 
   G_LOCK (default_resolver);
   if (!default_resolver)
-    default_resolver = g_object_new (G_TYPE_THREADED_RESOLVER, NULL);
+    default_resolver = g_object_new (G_TYPE_THREADED_RESOLVER,
+                                     "timeout", 30000,
+                                     NULL);
   ret = g_object_ref (default_resolver);
   G_UNLOCK (default_resolver);
 
@@ -1245,6 +1320,49 @@ g_resolver_get_serial (GResolver *resolver)
 }
 
 /**
+ * g_resolver_get_timeout:
+ * @resolver: a #GResolver
+ *
+ * Get the timeout applied to all resolver lookups. See #GResolver:timeout.
+ *
+ * Returns: the resolver timeout, in milliseconds, or `0` for no timeout
+ * Since: 2.78
+ */
+unsigned
+g_resolver_get_timeout (GResolver *resolver)
+{
+  GResolverPrivate *priv = g_resolver_get_instance_private (resolver);
+
+  g_return_val_if_fail (G_IS_RESOLVER (resolver), 0);
+
+  return priv->timeout_ms;
+}
+
+/**
+ * g_resolver_set_timeout:
+ * @resolver: a #GResolver
+ * @timeout_ms: timeout in milliseconds, or `0` for no timeouts
+ *
+ * Set the timeout applied to all resolver lookups. See #GResolver:timeout.
+ *
+ * Since: 2.78
+ */
+void
+g_resolver_set_timeout (GResolver *resolver,
+                        unsigned   timeout_ms)
+{
+  GResolverPrivate *priv = g_resolver_get_instance_private (resolver);
+
+  g_return_if_fail (G_IS_RESOLVER (resolver));
+
+  if (priv->timeout_ms == timeout_ms)
+    return;
+
+  priv->timeout_ms = timeout_ms;
+  g_object_notify_by_pspec (G_OBJECT (resolver), props[PROP_TIMEOUT]);
+}
+
+/**
  * g_resolver_error_quark:
  *
  * Gets the #GResolver Error Quark.
diff --git a/gio/gresolver.h b/gio/gresolver.h
index 2dffeadbf..9b9a8a81a 100644
--- a/gio/gresolver.h
+++ b/gio/gresolver.h
@@ -277,6 +277,11 @@ GList     *g_resolver_lookup_records_finish            (GResolver
 GIO_AVAILABLE_IN_ALL
 void       g_resolver_free_targets                     (GList                     *targets);
 
+GIO_AVAILABLE_IN_2_78
+unsigned   g_resolver_get_timeout                      (GResolver                 *resolver);
+GIO_AVAILABLE_IN_2_78
+void       g_resolver_set_timeout                      (GResolver                 *resolver,
+                                                        unsigned                   timeout_ms);
 
 /**
  * G_RESOLVER_ERROR:
diff --git a/gio/gthreadedresolver.c b/gio/gthreadedresolver.c
index 68b5c20d7..b452d1e1b 100644
--- a/gio/gthreadedresolver.c
+++ b/gio/gthreadedresolver.c
@@ -28,6 +28,7 @@
 #include <stdio.h>
 #include <string.h>
 
+#include "glib/glib-private.h"
 #include "gthreadedresolver.h"
 #include "gnetworkingprivate.h"
 
@@ -38,12 +39,83 @@
 #include "gsocketaddress.h"
 #include "gsrvtarget.h"
 
+/*
+ * GThreadedResolver is a threaded wrapper around the system libc’s
+ * `getaddrinfo()`.
+ *
+ * It has to be threaded, as `getaddrinfo()` is synchronous. libc does provide
+ * `getaddrinfo_a()` as an asynchronous version of `getaddrinfo()`, but it does
+ * not integrate with a poll loop. It requires use of sigevent to notify of
+ * completion of an asynchronous operation. That either emits a signal, or calls
+ * a callback function in a newly spawned thread.
+ *
+ * A signal (`SIGEV_SIGNAL`) can’t be used for completion as (aside from being
+ * another expensive round trip into the kernel) GLib cannot pick a `SIG*`
+ * number which is guaranteed to not be in use elsewhere in the process. Various
+ * other things could be interfering with signal dispositions, such as gdb or
+ * other libraries in the process. Using a `signalfd()`
+ * [cannot improve this situation](https://ldpreload.com/blog/signalfd-is-useless).
+ *
+ * A callback function in a newly spawned thread (`SIGEV_THREAD`) could be used,
+ * but that is very expensive. Internally, glibc currently also just implements
+ * `getaddrinfo_a()`
+ * [using its own thread pool](https://github.com/bminor/glibc/blob/master/resolv/gai_misc.c),
+ * and then
+ * [spawns an additional thread for each completion callback](https://github.com/bminor/glibc/blob/master/resolv/gai_notify.c).
+ * That is very expensive.
+ *
+ * No other appropriate sigevent callback types
+ * [currently exist](https://sourceware.org/bugzilla/show_bug.cgi?id=30287), and
+ * [others agree that sigevent is not great](http://davmac.org/davpage/linux/async-io.html#posixaio).
+ *
+ * Hence, #GThreadedResolver calls the normal synchronous `getaddrinfo()` in its
+ * own thread pool. Previously, #GThreadedResolver used the thread pool which is
+ * internal to #GTask by calling g_task_run_in_thread(). That lead to exhaustion
+ * of the #GTask thread pool in some situations, though, as DNS lookups are
+ * quite frequent leaf operations in some use cases. Now, #GThreadedResolver
+ * uses its own private thread pool.
+ *
+ * This is similar to what
+ * [libasyncns](http://git.0pointer.net/libasyncns.git/tree/libasyncns/asyncns.h)
+ * and other multi-threaded users of `getaddrinfo()` do.
+ */
+
+struct _GThreadedResolver
+{
+  GResolver parent_instance;
+
+  GThreadPool *thread_pool;  /* (owned) */
+};
 
 G_DEFINE_TYPE (GThreadedResolver, g_threaded_resolver, G_TYPE_RESOLVER)
 
+static void run_task_in_thread_pool_async (GThreadedResolver *self,
+                                           GTask             *task);
+static void run_task_in_thread_pool_sync (GThreadedResolver *self,
+                                          GTask             *task);
+static void threaded_resolver_worker_cb (gpointer task_data,
+                                         gpointer user_data);
+
 static void
-g_threaded_resolver_init (GThreadedResolver *gtr)
+g_threaded_resolver_init (GThreadedResolver *self)
 {
+  self->thread_pool = g_thread_pool_new_full (threaded_resolver_worker_cb,
+                                              self,
+                                              (GDestroyNotify) g_object_unref,
+                                              20,
+                                              FALSE,
+                                              NULL);
+}
+
+static void
+g_threaded_resolver_finalize (GObject *object)
+{
+  GThreadedResolver *self = G_THREADED_RESOLVER (object);
+
+  g_thread_pool_free (self->thread_pool, TRUE, FALSE);
+  self->thread_pool = NULL;
+
+  G_OBJECT_CLASS (g_threaded_resolver_parent_class)->finalize (object);
 }
 
 static GResolverError
@@ -67,35 +139,127 @@ g_resolver_error_from_addrinfo_error (gint err)
 }
 
 typedef struct {
-  char *hostname;
-  int address_family;
+  enum {
+    LOOKUP_BY_NAME,
+    LOOKUP_BY_ADDRESS,
+    LOOKUP_RECORDS,
+  } lookup_type;
+
+  union {
+    struct {
+      char *hostname;
+      int address_family;
+    } lookup_by_name;
+    struct {
+      GInetAddress *address;  /* (owned) */
+    } lookup_by_address;
+    struct {
+      char *rrname;
+      GResolverRecordType record_type;
+    } lookup_records;
+  };
+
+  GCond cond;  /* used for signalling completion of the task when running it sync */
+  GMutex lock;
+
+  GSource *timeout_source;  /* (nullable) (owned) */
+  GSource *cancellable_source;  /* (nullable) (owned) */
+
+  /* This enum indicates that a particular code path has claimed the
+   * task and is shortly about to call g_task_return_*() on it.
+   * This must be accessed with GThreadedResolver.lock held. */
+  enum
+    {
+      NOT_YET,
+      COMPLETED,  /* libc lookup call has completed successfully or errored */
+      TIMED_OUT,
+      CANCELLED,
+    } will_return;
+
+  /* Whether the thread pool thread executing this lookup has finished executing
+   * it and g_task_return_*() has been called on it already.
+   * This must be accessed with GThreadedResolver.lock held. */
+  gboolean has_returned;
 } LookupData;
 
 static LookupData *
-lookup_data_new (const char *hostname,
-                 int         address_family)
+lookup_data_new_by_name (const char *hostname,
+                         int         address_family)
 {
-  LookupData *data = g_new (LookupData, 1);
-  data->hostname = g_strdup (hostname);
-  data->address_family = address_family;
-  return data;
+  LookupData *data = g_new0 (LookupData, 1);
+  data->lookup_type = LOOKUP_BY_NAME;
+  g_cond_init (&data->cond);
+  g_mutex_init (&data->lock);
+  data->lookup_by_name.hostname = g_strdup (hostname);
+  data->lookup_by_name.address_family = address_family;
+  return g_steal_pointer (&data);
+}
+
+static LookupData *
+lookup_data_new_by_address (GInetAddress *address)
+{
+  LookupData *data = g_new0 (LookupData, 1);
+  data->lookup_type = LOOKUP_BY_ADDRESS;
+  g_cond_init (&data->cond);
+  g_mutex_init (&data->lock);
+  data->lookup_by_address.address = g_object_ref (address);
+  return g_steal_pointer (&data);
+}
+
+static LookupData *
+lookup_data_new_records (const gchar         *rrname,
+                         GResolverRecordType  record_type)
+{
+  LookupData *data = g_new0 (LookupData, 1);
+  data->lookup_type = LOOKUP_RECORDS;
+  g_cond_init (&data->cond);
+  g_mutex_init (&data->lock);
+  data->lookup_records.rrname = g_strdup (rrname);
+  data->lookup_records.record_type = record_type;
+  return g_steal_pointer (&data);
 }
 
 static void
 lookup_data_free (LookupData *data)
 {
-  g_free (data->hostname);
+  switch (data->lookup_type) {
+  case LOOKUP_BY_NAME:
+    g_free (data->lookup_by_name.hostname);
+    break;
+  case LOOKUP_BY_ADDRESS:
+    g_clear_object (&data->lookup_by_address.address);
+    break;
+  case LOOKUP_RECORDS:
+    g_free (data->lookup_records.rrname);
+    break;
+  default:
+    g_assert_not_reached ();
+  }
+
+  if (data->timeout_source != NULL)
+    {
+      g_source_destroy (data->timeout_source);
+      g_clear_pointer (&data->timeout_source, g_source_unref);
+    }
+
+  if (data->cancellable_source != NULL)
+    {
+      g_source_destroy (data->cancellable_source);
+      g_clear_pointer (&data->cancellable_source, g_source_unref);
+    }
+
+  g_mutex_clear (&data->lock);
+  g_cond_clear (&data->cond);
+
   g_free (data);
 }
 
-static void
-do_lookup_by_name (GTask         *task,
-                   gpointer       source_object,
-                   gpointer       task_data,
-                   GCancellable  *cancellable)
+static GList *
+do_lookup_by_name (const gchar   *hostname,
+                   int            address_family,
+                   GCancellable  *cancellable,
+                   GError       **error)
 {
-  LookupData *lookup_data = task_data;
-  const char *hostname = lookup_data->hostname;
   struct addrinfo *res = NULL;
   GList *addresses;
   gint retval;
@@ -111,7 +275,7 @@ do_lookup_by_name (GTask         *task,
   addrinfo_hints.ai_socktype = SOCK_STREAM;
   addrinfo_hints.ai_protocol = IPPROTO_TCP;
 
-  addrinfo_hints.ai_family = lookup_data->address_family;
+  addrinfo_hints.ai_family = address_family;
   retval = getaddrinfo (hostname, NULL, &addrinfo_hints, &res);
 
   if (retval == 0)
@@ -137,21 +301,23 @@ do_lookup_by_name (GTask         *task,
           g_object_unref (sockaddr);
         }
 
+      g_clear_pointer (&res, freeaddrinfo);
+
       if (addresses != NULL)
         {
           addresses = g_list_reverse (addresses);
-          g_task_return_pointer (task, addresses,
-                                 (GDestroyNotify)g_resolver_free_addresses);
+          return g_steal_pointer (&addresses);
         }
       else
         {
           /* All addresses failed to be converted to GSocketAddresses. */
-          g_task_return_new_error (task,
-                                   G_RESOLVER_ERROR,
-                                   G_RESOLVER_ERROR_NOT_FOUND,
-                                   _("Error resolving “%s”: %s"),
-                                   hostname,
-                                   _("No valid addresses were found"));
+          g_set_error (error,
+                       G_RESOLVER_ERROR,
+                       G_RESOLVER_ERROR_NOT_FOUND,
+                       _("Error resolving “%s”: %s"),
+                       hostname,
+                       _("No valid addresses were found"));
+          return NULL;
         }
     }
   else
@@ -164,16 +330,17 @@ do_lookup_by_name (GTask         *task,
         error_message = g_strdup ("[Invalid UTF-8]");
 #endif
 
-      g_task_return_new_error (task,
-                               G_RESOLVER_ERROR,
-                               g_resolver_error_from_addrinfo_error (retval),
-                               _("Error resolving “%s”: %s"),
-                               hostname, error_message);
+      g_clear_pointer (&res, freeaddrinfo);
+
+      g_set_error (error,
+                   G_RESOLVER_ERROR,
+                   g_resolver_error_from_addrinfo_error (retval),
+                   _("Error resolving “%s”: %s"),
+                   hostname, error_message);
       g_free (error_message);
-    }
 
-  if (res)
-    freeaddrinfo (res);
+      return NULL;
+    }
 }
 
 static GList *
@@ -182,17 +349,19 @@ lookup_by_name (GResolver     *resolver,
                 GCancellable  *cancellable,
                 GError       **error)
 {
+  GThreadedResolver *self = G_THREADED_RESOLVER (resolver);
   GTask *task;
   GList *addresses;
   LookupData *data;
 
-  data = lookup_data_new (hostname, AF_UNSPEC);
+  data = lookup_data_new_by_name (hostname, AF_UNSPEC);
   task = g_task_new (resolver, cancellable, NULL, NULL);
   g_task_set_source_tag (task, lookup_by_name);
   g_task_set_name (task, "[gio] resolver lookup");
-  g_task_set_task_data (task, data, (GDestroyNotify)lookup_data_free);
-  g_task_set_return_on_cancel (task, TRUE);
-  g_task_run_in_thread_sync (task, do_lookup_by_name);
+  g_task_set_task_data (task, g_steal_pointer (&data), (GDestroyNotify) lookup_data_free);
+
+  run_task_in_thread_pool_sync (self, task);
+
   addresses = g_task_propagate_pointer (task, error);
   g_object_unref (task);
 
@@ -224,17 +393,19 @@ lookup_by_name_with_flags (GResolver                 *resolver,
                            GCancellable              *cancellable,
                            GError                   **error)
 {
+  GThreadedResolver *self = G_THREADED_RESOLVER (resolver);
   GTask *task;
   GList *addresses;
   LookupData *data;
 
-  data = lookup_data_new (hostname, flags_to_family (flags));
+  data = lookup_data_new_by_name (hostname, flags_to_family (flags));
   task = g_task_new (resolver, cancellable, NULL, NULL);
   g_task_set_source_tag (task, lookup_by_name_with_flags);
   g_task_set_name (task, "[gio] resolver lookup");
-  g_task_set_task_data (task, data, (GDestroyNotify)lookup_data_free);
-  g_task_set_return_on_cancel (task, TRUE);
-  g_task_run_in_thread_sync (task, do_lookup_by_name);
+  g_task_set_task_data (task, g_steal_pointer (&data), (GDestroyNotify) lookup_data_free);
+
+  run_task_in_thread_pool_sync (self, task);
+
   addresses = g_task_propagate_pointer (task, error);
   g_object_unref (task);
 
@@ -249,16 +420,22 @@ lookup_by_name_with_flags_async (GResolver                *resolver,
                                  GAsyncReadyCallback       callback,
                                  gpointer                  user_data)
 {
+  GThreadedResolver *self = G_THREADED_RESOLVER (resolver);
   GTask *task;
   LookupData *data;
 
-  data = lookup_data_new (hostname, flags_to_family (flags));
+  data = lookup_data_new_by_name (hostname, flags_to_family (flags));
   task = g_task_new (resolver, cancellable, callback, user_data);
+
+  g_debug ("%s: starting new lookup for %s with GTask %p, LookupData %p",
+           G_STRFUNC, hostname, task, data);
+
   g_task_set_source_tag (task, lookup_by_name_with_flags_async);
   g_task_set_name (task, "[gio] resolver lookup");
-  g_task_set_task_data (task, data, (GDestroyNotify)lookup_data_free);
-  g_task_set_return_on_cancel (task, TRUE);
-  g_task_run_in_thread (task, do_lookup_by_name);
+  g_task_set_task_data (task, g_steal_pointer (&data), (GDestroyNotify) lookup_data_free);
+
+  run_task_in_thread_pool_async (self, task);
+
   g_object_unref (task);
 }
 
@@ -297,13 +474,11 @@ lookup_by_name_with_flags_finish (GResolver     *resolver,
   return g_task_propagate_pointer (G_TASK (result), error);
 }
 
-static void
-do_lookup_by_address (GTask         *task,
-                      gpointer       source_object,
-                      gpointer       task_data,
-                      GCancellable  *cancellable)
+static gchar *
+do_lookup_by_address (GInetAddress  *address,
+                      GCancellable  *cancellable,
+                      GError       **error)
 {
-  GInetAddress *address = task_data;
   struct sockaddr_storage sockaddr_address;
   gsize sockaddr_address_size;
   GSocketAddress *gsockaddr;
@@ -319,7 +494,7 @@ do_lookup_by_address (GTask         *task,
   retval = getnameinfo ((struct sockaddr *) &sockaddr_address, sockaddr_address_size,
                         name, sizeof (name), NULL, 0, NI_NAMEREQD);
   if (retval == 0)
-    g_task_return_pointer (task, g_strdup (name), g_free);
+    return g_strdup (name);
   else
     {
       gchar *phys;
@@ -333,14 +508,16 @@ do_lookup_by_address (GTask         *task,
 #endif
 
       phys = g_inet_address_to_string (address);
-      g_task_return_new_error (task,
-                               G_RESOLVER_ERROR,
-                               g_resolver_error_from_addrinfo_error (retval),
-                               _("Error reverse-resolving “%s”: %s"),
-                               phys ? phys : "(unknown)",
-                               error_message);
+      g_set_error (error,
+                   G_RESOLVER_ERROR,
+                   g_resolver_error_from_addrinfo_error (retval),
+                   _("Error reverse-resolving “%s”: %s"),
+                   phys ? phys : "(unknown)",
+                   error_message);
       g_free (phys);
       g_free (error_message);
+
+      return NULL;
     }
 }
 
@@ -350,15 +527,19 @@ lookup_by_address (GResolver        *resolver,
                    GCancellable     *cancellable,
                    GError          **error)
 {
+  GThreadedResolver *self = G_THREADED_RESOLVER (resolver);
+  LookupData *data = NULL;
   GTask *task;
   gchar *name;
 
+  data = lookup_data_new_by_address (address);
   task = g_task_new (resolver, cancellable, NULL, NULL);
   g_task_set_source_tag (task, lookup_by_address);
   g_task_set_name (task, "[gio] resolver lookup");
-  g_task_set_task_data (task, g_object_ref (address), g_object_unref);
-  g_task_set_return_on_cancel (task, TRUE);
-  g_task_run_in_thread_sync (task, do_lookup_by_address);
+  g_task_set_task_data (task, g_steal_pointer (&data), (GDestroyNotify) lookup_data_free);
+
+  run_task_in_thread_pool_sync (self, task);
+
   name = g_task_propagate_pointer (task, error);
   g_object_unref (task);
 
@@ -372,14 +553,18 @@ lookup_by_address_async (GResolver           *resolver,
                          GAsyncReadyCallback  callback,
                          gpointer             user_data)
 {
+  GThreadedResolver *self = G_THREADED_RESOLVER (resolver);
+  LookupData *data = NULL;
   GTask *task;
 
+  data = lookup_data_new_by_address (address);
   task = g_task_new (resolver, cancellable, callback, user_data);
   g_task_set_source_tag (task, lookup_by_address_async);
   g_task_set_name (task, "[gio] resolver lookup");
-  g_task_set_task_data (task, g_object_ref (address), g_object_unref);
-  g_task_set_return_on_cancel (task, TRUE);
-  g_task_run_in_thread (task, do_lookup_by_address);
+  g_task_set_task_data (task, g_steal_pointer (&data), (GDestroyNotify) lookup_data_free);
+
+  run_task_in_thread_pool_async (self, task);
+
   g_object_unref (task);
 }
 
@@ -1066,18 +1251,6 @@ g_resolver_records_from_DnsQuery (const gchar  *rrname,
 
 #endif
 
-typedef struct {
-  char *rrname;
-  GResolverRecordType record_type;
-} LookupRecordsData;
-
-static void
-free_lookup_records_data (LookupRecordsData *lrd)
-{
-  g_free (lrd->rrname);
-  g_slice_free (LookupRecordsData, lrd);
-}
-
 static void
 free_records (GList *records)
 {
@@ -1093,15 +1266,13 @@ int res_query(const char *, int, int, u_char *, int);
 #endif
 #endif
 
-static void
-do_lookup_records (GTask         *task,
-                   gpointer       source_object,
-                   gpointer       task_data,
-                   GCancellable  *cancellable)
+static GList *
+do_lookup_records (const gchar          *rrname,
+                   GResolverRecordType   record_type,
+                   GCancellable         *cancellable,
+                   GError              **error)
 {
-  LookupRecordsData *lrd = task_data;
   GList *records;
-  GError *error = NULL;
 
 #if defined(G_OS_UNIX)
   gint len = 512;
@@ -1125,21 +1296,21 @@ do_lookup_records (GTask         *task,
   struct __res_state res = { 0, };
   if (res_ninit (&res) != 0)
     {
-      g_task_return_new_error (task, G_RESOLVER_ERROR, G_RESOLVER_ERROR_INTERNAL,
-                               _("Error resolving “%s”"), lrd->rrname);
-      return;
+      g_set_error (error, G_RESOLVER_ERROR, G_RESOLVER_ERROR_INTERNAL,
+                   _("Error resolving “%s”"), rrname);
+      return NULL;
     }
 #endif
 
-  rrtype = g_resolver_record_type_to_rrtype (lrd->record_type);
+  rrtype = g_resolver_record_type_to_rrtype (record_type);
   answer = g_byte_array_new ();
   for (;;)
     {
       g_byte_array_set_size (answer, len * 2);
 #if defined(HAVE_RES_NQUERY)
-      len = res_nquery (&res, lrd->rrname, C_IN, rrtype, answer->data, answer->len);
+      len = res_nquery (&res, rrname, C_IN, rrtype, answer->data, answer->len);
 #else
-      len = res_query (lrd->rrname, C_IN, rrtype, answer->data, answer->len);
+      len = res_query (rrname, C_IN, rrtype, answer->data, answer->len);
 #endif
 
       /* If answer fit in the buffer then we're done */
@@ -1153,7 +1324,7 @@ do_lookup_records (GTask         *task,
     }
 
   herr = h_errno;
-  records = g_resolver_records_from_res_query (lrd->rrname, rrtype, answer->data, len, herr, &error);
+  records = g_resolver_records_from_res_query (rrname, rrtype, answer->data, len, herr, error);
   g_byte_array_free (answer, TRUE);
 
 #ifdef HAVE_RES_NQUERY
@@ -1174,18 +1345,15 @@ do_lookup_records (GTask         *task,
   DNS_RECORD *results = NULL;
   WORD dnstype;
 
-  dnstype = g_resolver_record_type_to_dnstype (lrd->record_type);
-  status = DnsQuery_A (lrd->rrname, dnstype, DNS_QUERY_STANDARD, NULL, &results, NULL);
-  records = g_resolver_records_from_DnsQuery (lrd->rrname, dnstype, status, results, &error);
+  dnstype = g_resolver_record_type_to_dnstype (record_type);
+  status = DnsQuery_A (rrname, dnstype, DNS_QUERY_STANDARD, NULL, &results, NULL);
+  records = g_resolver_records_from_DnsQuery (rrname, dnstype, status, results, error);
   if (results != NULL)
     DnsRecordListFree (results, DnsFreeRecordList);
 
 #endif
 
-  if (records)
-    g_task_return_pointer (task, records, (GDestroyNotify) free_records);
-  else
-    g_task_return_error (task, error);
+  return g_steal_pointer (&records);
 }
 
 static GList *
@@ -1195,21 +1363,20 @@ lookup_records (GResolver              *resolver,
                 GCancellable           *cancellable,
                 GError                **error)
 {
+  GThreadedResolver *self = G_THREADED_RESOLVER (resolver);
   GTask *task;
   GList *records;
-  LookupRecordsData *lrd;
+  LookupData *data = NULL;
 
   task = g_task_new (resolver, cancellable, NULL, NULL);
   g_task_set_source_tag (task, lookup_records);
   g_task_set_name (task, "[gio] resolver lookup records");
 
-  lrd = g_slice_new (LookupRecordsData);
-  lrd->rrname = g_strdup (rrname);
-  lrd->record_type = record_type;
-  g_task_set_task_data (task, lrd, (GDestroyNotify) free_lookup_records_data);
+  data = lookup_data_new_records (rrname, record_type);
+  g_task_set_task_data (task, g_steal_pointer (&data), (GDestroyNotify) lookup_data_free);
+
+  run_task_in_thread_pool_sync (self, task);
 
-  g_task_set_return_on_cancel (task, TRUE);
-  g_task_run_in_thread_sync (task, do_lookup_records);
   records = g_task_propagate_pointer (task, error);
   g_object_unref (task);
 
@@ -1224,20 +1391,19 @@ lookup_records_async (GResolver           *resolver,
                       GAsyncReadyCallback  callback,
                       gpointer             user_data)
 {
+  GThreadedResolver *self = G_THREADED_RESOLVER (resolver);
   GTask *task;
-  LookupRecordsData *lrd;
+  LookupData *data = NULL;
 
   task = g_task_new (resolver, cancellable, callback, user_data);
   g_task_set_source_tag (task, lookup_records_async);
   g_task_set_name (task, "[gio] resolver lookup records");
 
-  lrd = g_slice_new (LookupRecordsData);
-  lrd->rrname = g_strdup (rrname);
-  lrd->record_type = record_type;
-  g_task_set_task_data (task, lrd, (GDestroyNotify) free_lookup_records_data);
+  data = lookup_data_new_records (rrname, record_type);
+  g_task_set_task_data (task, g_steal_pointer (&data), (GDestroyNotify) lookup_data_free);
+
+  run_task_in_thread_pool_async (self, task);
 
-  g_task_set_return_on_cancel (task, TRUE);
-  g_task_run_in_thread (task, do_lookup_records);
   g_object_unref (task);
 }
 
@@ -1251,12 +1417,210 @@ lookup_records_finish (GResolver     *resolver,
   return g_task_propagate_pointer (G_TASK (result), error);
 }
 
+/* Will be called in the GLib worker thread, so must lock all accesses to shared
+ * data. */
+static gboolean
+timeout_cb (gpointer user_data)
+{
+  GTask *task = G_TASK (user_data);
+  LookupData *data = g_task_get_task_data (task);
+  gboolean should_return;
+
+  g_mutex_lock (&data->lock);
+
+  should_return = g_atomic_int_compare_and_exchange (&data->will_return, NOT_YET, TIMED_OUT);
+  g_clear_pointer (&data->timeout_source, g_source_unref);
+
+  g_mutex_unlock (&data->lock);
+
+  if (should_return)
+    g_task_return_new_error (task, G_IO_ERROR, G_IO_ERROR_TIMED_OUT,
+                             _("Socket I/O timed out"));
+
+  /* Signal completion of the task. */
+  g_mutex_lock (&data->lock);
+  g_assert (!data->has_returned);
+  data->has_returned = TRUE;
+  g_cond_broadcast (&data->cond);
+  g_mutex_unlock (&data->lock);
+
+  return G_SOURCE_REMOVE;
+}
+
+/* Will be called in the GLib worker thread, so must lock all accesses to shared
+ * data. */
+static gboolean
+cancelled_cb (GCancellable *cancellable,
+              gpointer      user_data)
+{
+  GTask *task = G_TASK (user_data);
+  LookupData *data = g_task_get_task_data (task);
+  gboolean should_return;
+
+  g_mutex_lock (&data->lock);
+
+  g_assert (g_cancellable_is_cancelled (cancellable));
+  should_return = g_atomic_int_compare_and_exchange (&data->will_return, NOT_YET, CANCELLED);
+  g_clear_pointer (&data->cancellable_source, g_source_unref);
+
+  g_mutex_unlock (&data->lock);
+
+  if (should_return)
+    g_task_return_error_if_cancelled (task);
+
+  /* Signal completion of the task. */
+  g_mutex_lock (&data->lock);
+  g_assert (!data->has_returned);
+  data->has_returned = TRUE;
+  g_cond_broadcast (&data->cond);
+  g_mutex_unlock (&data->lock);
+
+  return G_SOURCE_REMOVE;
+}
+
+static void
+run_task_in_thread_pool_async (GThreadedResolver *self,
+                               GTask             *task)
+{
+  LookupData *data = g_task_get_task_data (task);
+  guint timeout_ms = g_resolver_get_timeout (G_RESOLVER (self));
+  GCancellable *cancellable = g_task_get_cancellable (task);
+
+  g_mutex_lock (&data->lock);
+
+  g_thread_pool_push (self->thread_pool, g_object_ref (task), NULL);
+
+  if (timeout_ms != 0)
+    {
+      data->timeout_source = g_timeout_source_new (timeout_ms);
+      g_source_set_static_name (data->timeout_source, "[gio] threaded resolver timeout");
+      g_source_set_callback (data->timeout_source, G_SOURCE_FUNC (timeout_cb), task, NULL);
+      g_source_attach (data->timeout_source, GLIB_PRIVATE_CALL (g_get_worker_context) ());
+    }
+
+  if (cancellable != NULL)
+    {
+      data->cancellable_source = g_cancellable_source_new (cancellable);
+      g_source_set_static_name (data->cancellable_source, "[gio] threaded resolver cancellable");
+      g_source_set_callback (data->cancellable_source, G_SOURCE_FUNC (cancelled_cb), task, NULL);
+      g_source_attach (data->cancellable_source, GLIB_PRIVATE_CALL (g_get_worker_context) ());
+    }
+
+  g_mutex_unlock (&data->lock);
+}
+
+static void
+run_task_in_thread_pool_sync (GThreadedResolver *self,
+                              GTask             *task)
+{
+  LookupData *data = g_task_get_task_data (task);
+
+  run_task_in_thread_pool_async (self, task);
+
+  g_mutex_lock (&data->lock);
+  while (!data->has_returned)
+    g_cond_wait (&data->cond, &data->lock);
+  g_mutex_unlock (&data->lock);
+}
+
+static void
+threaded_resolver_worker_cb (gpointer task_data,
+                             gpointer user_data)
+{
+  GTask *task = G_TASK (g_steal_pointer (&task_data));
+  LookupData *data = g_task_get_task_data (task);
+  GCancellable *cancellable = g_task_get_cancellable (task);
+  GError *local_error = NULL;
+  gboolean should_return;
+
+  switch (data->lookup_type) {
+  case LOOKUP_BY_NAME:
+    {
+      GList *addresses = do_lookup_by_name (data->lookup_by_name.hostname,
+                                            data->lookup_by_name.address_family,
+                                            cancellable,
+                                            &local_error);
+
+      g_mutex_lock (&data->lock);
+      should_return = g_atomic_int_compare_and_exchange (&data->will_return, NOT_YET, COMPLETED);
+      g_mutex_unlock (&data->lock);
+
+      if (should_return)
+        {
+          if (addresses != NULL)
+            g_task_return_pointer (task, g_steal_pointer (&addresses), (GDestroyNotify) g_resolver_free_addresses);
+          else
+            g_task_return_error (task, g_steal_pointer (&local_error));
+        }
+
+      g_clear_pointer (&addresses, g_resolver_free_addresses);
+    }
+    break;
+  case LOOKUP_BY_ADDRESS:
+    {
+      gchar *name = do_lookup_by_address (data->lookup_by_address.address,
+                                          cancellable,
+                                          &local_error);
+
+      g_mutex_lock (&data->lock);
+      should_return = g_atomic_int_compare_and_exchange (&data->will_return, NOT_YET, COMPLETED);
+      g_mutex_unlock (&data->lock);
+
+      if (should_return)
+        {
+          if (name != NULL)
+            g_task_return_pointer (task, g_steal_pointer (&name), g_free);
+          else
+            g_task_return_error (task, g_steal_pointer (&local_error));
+        }
+
+      g_clear_pointer (&name, g_free);
+    }
+    break;
+  case LOOKUP_RECORDS:
+    {
+      GList *records = do_lookup_records (data->lookup_records.rrname,
+                                          data->lookup_records.record_type,
+                                          cancellable,
+                                          &local_error);
+
+      g_mutex_lock (&data->lock);
+      should_return = g_atomic_int_compare_and_exchange (&data->will_return, NOT_YET, COMPLETED);
+      g_mutex_unlock (&data->lock);
+
+      if (should_return)
+        {
+          if (records != NULL)
+            g_task_return_pointer (task, g_steal_pointer (&records), (GDestroyNotify) free_records);
+          else
+            g_task_return_error (task, g_steal_pointer (&local_error));
+        }
+
+      g_clear_pointer (&records, free_records);
+    }
+    break;
+  default:
+    g_assert_not_reached ();
+  }
+
+  /* Signal completion of a task. */
+  g_mutex_lock (&data->lock);
+  g_assert (!data->has_returned);
+  data->has_returned = TRUE;
+  g_cond_broadcast (&data->cond);
+  g_mutex_unlock (&data->lock);
+
+  g_object_unref (task);
+}
 
 static void
 g_threaded_resolver_class_init (GThreadedResolverClass *threaded_class)
 {
+  GObjectClass *object_class = G_OBJECT_CLASS (threaded_class);
   GResolverClass *resolver_class = G_RESOLVER_CLASS (threaded_class);
 
+  object_class->finalize = g_threaded_resolver_finalize;
+
   resolver_class->lookup_by_name                   = lookup_by_name;
   resolver_class->lookup_by_name_async             = lookup_by_name_async;
   resolver_class->lookup_by_name_finish            = lookup_by_name_finish;
diff --git a/gio/gthreadedresolver.h b/gio/gthreadedresolver.h
index ea76e4bfd..099df5b84 100644
--- a/gio/gthreadedresolver.h
+++ b/gio/gthreadedresolver.h
@@ -21,28 +21,23 @@
 #ifndef __G_THREADED_RESOLVER_H__
 #define __G_THREADED_RESOLVER_H__
 
+#include <gio/gio.h>
 #include <gio/gresolver.h>
 
 G_BEGIN_DECLS
 
+/**
+ * GThreadedResolver:
+ *
+ * #GThreadedResolver is an implementation of #GResolver which calls the libc
+ * lookup functions in threads to allow them to run asynchronously.
+ *
+ * Since: 2.20
+ */
 #define G_TYPE_THREADED_RESOLVER         (g_threaded_resolver_get_type ())
-#define G_THREADED_RESOLVER(o)           (G_TYPE_CHECK_INSTANCE_CAST ((o), G_TYPE_THREADED_RESOLVER, GThreadedResolver))
-#define G_THREADED_RESOLVER_CLASS(k)     (G_TYPE_CHECK_CLASS_CAST((k), G_TYPE_THREADED_RESOLVER, GThreadedResolverClass))
-#define G_IS_THREADED_RESOLVER(o)        (G_TYPE_CHECK_INSTANCE_TYPE ((o), G_TYPE_THREADED_RESOLVER))
-#define G_IS_THREADED_RESOLVER_CLASS(k)  (G_TYPE_CHECK_CLASS_TYPE ((k), G_TYPE_THREADED_RESOLVER))
-#define G_THREADED_RESOLVER_GET_CLASS(o) (G_TYPE_INSTANCE_GET_CLASS ((o), G_TYPE_THREADED_RESOLVER, GThreadedResolverClass))
-
-typedef struct {
-  GResolver parent_instance;
-} GThreadedResolver;
-
-typedef struct {
-  GResolverClass parent_class;
-
-} GThreadedResolverClass;
 
 GIO_AVAILABLE_IN_ALL
-GType g_threaded_resolver_get_type (void) G_GNUC_CONST;
+G_DECLARE_FINAL_TYPE (GThreadedResolver, g_threaded_resolver, G, THREADED_RESOLVER, GResolver)
 
 /* Used for a private test API */
 #ifdef G_OS_UNIX
diff --git a/gio/tests/resolver.c b/gio/tests/resolver.c
index ec9b9e9de..b8adb4a36 100644
--- a/gio/tests/resolver.c
+++ b/gio/tests/resolver.c
@@ -41,6 +41,7 @@ static int nlookups = 0;
 static gboolean synchronous = FALSE;
 static guint connectable_count = 0;
 static GResolverRecordType record_type = 0;
+static gint timeout_ms = 0;
 
 static G_NORETURN void
 usage (void)
@@ -688,7 +689,7 @@ static gboolean
 async_cancel (GIOChannel *source, GIOCondition cond, gpointer cancel)
 {
   g_cancellable_cancel (cancel);
-  return FALSE;
+  return G_SOURCE_REMOVE;
 }
 #endif
 
@@ -722,6 +723,7 @@ static const GOptionEntry option_entries[] = {
   { "synchronous", 's', 0, G_OPTION_ARG_NONE, &synchronous, "Synchronous connections", NULL },
   { "connectable", 'c', 0, G_OPTION_ARG_INT, &connectable_count, "Connectable count", "C" },
   { "special-type", 't', 0, G_OPTION_ARG_CALLBACK, record_type_arg, "Record type like MX, TXT, NS or SOA", "RR" },
+  { "timeout", 0, 0, G_OPTION_ARG_INT, &timeout_ms, "Timeout (ms)", "ms" },
   G_OPTION_ENTRY_NULL,
 };
 
@@ -732,7 +734,7 @@ main (int argc, char **argv)
   GError *error = NULL;
 #ifdef G_OS_UNIX
   GIOChannel *chan;
-  guint watch;
+  GSource *watch_source = NULL;
 #endif
 
   context = g_option_context_new ("lookups ...");
@@ -749,6 +751,9 @@ main (int argc, char **argv)
 
   resolver = g_resolver_get_default ();
 
+  if (timeout_ms != 0)
+    g_resolver_set_timeout (resolver, timeout_ms);
+
   cancellable = g_cancellable_new ();
 
 #ifdef G_OS_UNIX
@@ -763,7 +768,9 @@ main (int argc, char **argv)
       exit (1);
     }
   chan = g_io_channel_unix_new (cancel_fds[0]);
-  watch = g_io_add_watch (chan, G_IO_IN, async_cancel, cancellable);
+  watch_source = g_io_create_watch (chan, G_IO_IN);
+  g_source_set_callback (watch_source, (GSourceFunc) async_cancel, cancellable, NULL);
+  g_source_attach (watch_source, NULL);
   g_io_channel_unref (chan);
 #endif
 
@@ -787,7 +794,8 @@ main (int argc, char **argv)
   g_main_loop_unref (loop);
 
 #ifdef G_OS_UNIX
-  g_source_remove (watch);
+  g_source_destroy (watch_source);
+  g_clear_pointer (&watch_source, g_source_unref);
 #endif
   g_object_unref (cancellable);
   g_option_context_free (context);