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-rw-r--r--src/lib/thread/threads.h12
1 files changed, 11 insertions, 1 deletions
diff --git a/src/lib/thread/threads.h b/src/lib/thread/threads.h
index ecf60641b5..de3da6a585 100644
--- a/src/lib/thread/threads.h
+++ b/src/lib/thread/threads.h
@@ -131,7 +131,17 @@ atomic_counter_init(atomic_counter_t *counter)
{
atomic_init(&counter->val, 0);
}
-/** Clean up all resources held by an atomic counter. */
+/** Clean up all resources held by an atomic counter.
+ *
+ * This usage note applies to the compat_threads implementation of
+ * atomic_counter_destroy():
+ * Destroying a locked mutex is undefined behaviour. Global mutexes may be
+ * locked when they are passed to this function, because multiple threads can
+ * still access them. So we can either:
+ * - destroy on shutdown, and re-initialise when tor re-initialises, or
+ * - skip destroying and re-initialisation, using a sentinel variable.
+ * See #31735 for details.
+ */
static inline void
atomic_counter_destroy(atomic_counter_t *counter)
{