resolved: fix notification iteration logic when transactions are completed

When a transaction is complete, and we notify its owners, make sure we deal
correctly with the requesters removing themselves from the list of owners while
we continue iterating.

This was previously already dealt with with transactions that require other
transactions for DNSSEC purposes, fix this for other possibly transaction
owners too now.

Since iterating through "Set" objects is not safe regarding removal of entries
from it, rework the logic to use two Sets, and move each entry we notified from
one set to the other set before we dispatch the notification. This move operation
requires no additional memory, and enables us to ensure that we don't notify
any object twice.

Fixes: #2676

2 files changed, 9 insertions, 0 deletions

diff --git a/src/basic/macro.h b/src/basic/macro.h
index 2695d0edb7..ab5cc97e17 100644
--- a/src/basic/macro.h
+++ b/src/basic/macro.h
@@ -361,6 +361,12 @@ static inline unsigned long ALIGN_POWER2(unsigned long u) {
                 _found;                         \
         })
 
+#define SWAP_TWO(x, y) do {                        \
+                typeof(x) _t = (x);                \
+                (x) = (y);                         \
+                (y) = (_t);                        \
+        } while (false)
+
 /* Define C11 thread_local attribute even on older gcc compiler
  * version */
 #ifndef thread_local
diff --git a/src/basic/set.h b/src/basic/set.h
index 2bff5062da..e0d9dd001c 100644
--- a/src/basic/set.h
+++ b/src/basic/set.h
@@ -126,6 +126,9 @@ int set_put_strdupv(Set *s, char **l);
 #define SET_FOREACH(e, s, i) \
         for ((i) = ITERATOR_FIRST; set_iterate((s), &(i), (void**)&(e)); )
 
+#define SET_FOREACH_MOVE(e, d, s)                                       \
+        for (; ({ e = set_first(s); assert_se(!e || set_move_one(d, s, e) >= 0); e; }); )
+
 DEFINE_TRIVIAL_CLEANUP_FUNC(Set*, set_free);
 DEFINE_TRIVIAL_CLEANUP_FUNC(Set*, set_free_free);