sd-resolve: rework sd-resolve to be callback based, similar in style to sd-bus and...

[elogind.git] / src / libsystemd / sd-bus / sd-bus.c

diff --git a/src/libsystemd/sd-bus/sd-bus.c b/src/libsystemd/sd-bus/sd-bus.c
index 15c767723c13cebb9b5c2fe8442ac45d410f4ff9..dc54e211a490b3918a400bc7c8eebfa5a0da780f 100644 (file)
--- a/src/libsystemd/sd-bus/sd-bus.c
+++ b/src/libsystemd/sd-bus/sd-bus.c
@@ -111,6 +111,12 @@ static void bus_node_destroy(sd_bus *b, struct node *n) {
 static void bus_reset_queues(sd_bus *b) {
         assert(b);
 
+        /* NOTE: We _must_ decrement b->Xqueue_size before calling
+         * sd_bus_message_unref() for _each_ message. Otherwise the
+         * self-reference checks in sd_bus_unref() will fire for each message.
+         * We would thus recurse into sd_bus_message_unref() and trigger the
+         * assert(m->n_ref > 0) */
+
         while (b->rqueue_size > 0)
                 sd_bus_message_unref(b->rqueue[--b->rqueue_size]);
 
@@ -1388,6 +1394,24 @@ _public_ sd_bus *sd_bus_unref(sd_bus *bus) {
         if (!bus)
                 return NULL;
 
+        /* TODO/FIXME: It's naive to think REFCNT_GET() is thread-safe in any
+         * way but exclusive REFCNT_DEC(). The current logic _must_ lock around
+         * REFCNT_GET() until REFCNT_DEC() or two threads might end up in
+         * parallel in bus_reset_queues(). But locking would totally break the
+         * recursion we introduce by bus_reset_queues()...
+         * (Imagine one thread in sd_bus_message_unref() setting n_ref to 0 and
+         * thus calling into sd_bus_unref(). If at the same time the real
+         * thread calls sd_bus_unref(), both end up with "q == true" and will
+         * call into bus_reset_queues().
+         * If we require the main bus to be alive until all dispatch threads
+         * are done, there is no need to do ref-counts at all. So in both ways,
+         * the REFCNT thing is humbug.)
+         *
+         * On a second note: messages are *not* required to have ->bus set nor
+         * does it have to be _this_ bus that they're assigned to. This whole
+         * ref-cnt checking breaks apart if a message is not assigned to us.
+         * (which is _very_ easy to trigger with the current API). */
+
         if (REFCNT_GET(bus->n_ref) == bus->rqueue_size + bus->wqueue_size + 1) {
                 bool q = true;
 
@@ -1408,7 +1432,10 @@ _public_ sd_bus *sd_bus_unref(sd_bus *bus) {
                 /* We are the only holders on the messages, and the
                  * messages are the only holders on us, so let's drop
                  * the messages and thus implicitly also kill our own
-                 * last references */
+                 * last references.
+                 * bus_reset_queues() decrements the queue-size before
+                 * calling into sd_bus_message_unref(). Thus, it
+                 * protects us from recursion. */
 
                 if (q)
                         bus_reset_queues(bus);
@@ -3038,7 +3065,7 @@ _public_ int sd_bus_attach_event(sd_bus *bus, sd_event *event, int priority) {
 
         bus->event_priority = priority;
 
-        r = sd_event_add_monotonic(bus->event, &bus->time_event_source, 0, 0, time_callback, bus);
+        r = sd_event_add_time(bus->event, &bus->time_event_source, CLOCK_MONOTONIC, 0, 0, time_callback, bus);
         if (r < 0)
                 goto fail;
 
@@ -3079,9 +3106,7 @@ _public_ int sd_bus_detach_event(sd_bus *bus) {
                 bus->quit_event_source = sd_event_source_unref(bus->quit_event_source);
         }
 
-        if (bus->event)
-                bus->event = sd_event_unref(bus->event);
-
+        bus->event = sd_event_unref(bus->event);
         return 1;
 }
 
@@ -3241,7 +3266,7 @@ _public_ int sd_bus_get_peer_creds(sd_bus *bus, uint64_t mask, sd_bus_creds **re
         assert_return(ret, -EINVAL);
         assert_return(!bus_pid_changed(bus), -ECHILD);
 
-        if (!bus->is_kernel)
+        if (bus->is_kernel)
                 return -ENOTSUP;
 
         if (!BUS_IS_OPEN(bus->state))