Fix: sessiond: assertion hit in ltt_sessions_ht_empty

[lttng-tools.git] / src / bin / lttng-sessiond / session.cpp

diff --git a/src/bin/lttng-sessiond/session.cpp b/src/bin/lttng-sessiond/session.cpp
index fc43684e9b2b2a4035b4837ccae9fcd73f0c0344..304589068aaaf6a4d45c4431103b262a6665ff25 100644 (file)
--- a/src/bin/lttng-sessiond/session.cpp
+++ b/src/bin/lttng-sessiond/session.cpp
@@ -377,24 +377,45 @@ end:
 
 /*
  * Test if ltt_sessions_ht_by_id/name are empty.
- * Return 1 if empty, 0 if not empty.
+ * Return `false` if hash table objects are null.
  * The session list lock must be held.
  */
-static int ltt_sessions_ht_empty(void)
+static bool ltt_sessions_ht_empty(void)
 {
-       unsigned long count;
+       bool empty = false;
 
        if (!ltt_sessions_ht_by_id) {
-               count = 0;
+               /* The hash tables do not exist yet. */
                goto end;
        }
 
        LTTNG_ASSERT(ltt_sessions_ht_by_name);
 
-       count = lttng_ht_get_count(ltt_sessions_ht_by_id);
-       LTTNG_ASSERT(count == lttng_ht_get_count(ltt_sessions_ht_by_name));
+       if (lttng_ht_get_count(ltt_sessions_ht_by_id) == 0) {
+               /* Not empty.*/
+               goto end;
+       }
+
+       /*
+        * At this point it is expected that the `ltt_sessions_ht_by_name` ht is
+        * empty.
+        *
+        * The removal from both hash tables is done in two different
+        * places:
+        *   - removal from `ltt_sessions_ht_by_name` is done during
+        *     `session_destroy()`
+        *   - removal from `ltt_sessions_ht_by_id` is done later
+        *     in `session_release()` on the last reference put.
+        *
+        * This means that it is possible for `ltt_sessions_ht_by_name` to be
+        * empty but for `ltt_sessions_ht_by_id` to still contain objects when
+        * multiple sessions exists. The reverse is false, hence this sanity
+        * check.
+        */
+       LTTNG_ASSERT(lttng_ht_get_count(ltt_sessions_ht_by_name) == 0);
+       empty = true;
 end:
-       return count ? 0 : 1;
+       return empty;
 }
 
 /*