After, synchronize_rcu() must be called. When it returns, the old
values are not in usage anymore.
+Usage of liburcu-defer
+
+ * #include <urcu-defer.h>
+ * Link with "-lurcu-defer"
+ * Provides call_rcu() primitive to enqueue delayed callbacks. Queued
+ callbacks are executed in batch periodically after a grace period.
+ Do _not_ use call_rcu() within a read-side critical section, because
+ it may call synchronize_rcu() if the thread queue is full.
+
Being careful with signals
The liburcu library uses signals internally. The signal handler is