- After, synchronize_rcu() must be called. When it returns, the old values
- are not in usage anymore.
-
-
-Usage of DEBUG_FULL_MB
-
- DEBUG_FULL_MB uses full SMP barriers for readers. This eliminates the
- need for signals but results in slower reads.
-
+ 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
+ registered with the SA_RESTART flag. However, these signals may cause
+ some non-restartable system calls to fail with errno = EINTR. Care
+ should be taken to restart system calls manually if they fail with this
+ error. A list of non-restartable system calls may be found in
+ signal(7). The liburcu-mb and liburcu-qsbr versions of the Userspace RCU
+ library do not require any signal.
+
+ Read-side critical sections are allowed in a signal handler with
+ liburcu and liburcu-mb. Be careful, however, to disable these signals
+ between thread creation and calls to rcu_register_thread(), because a
+ signal handler nesting on an unregistered thread would not be allowed to
+ call rcu_read_lock().
+
+ Read-side critical sections are _not_ allowed in a signal handler with
+ liburcu-qsbr, unless signals are disabled explicitly around each
+ rcu_quiescent_state() calls, when threads are put offline and around
+ calls to synchronize_rcu(). Even then, we do not recommend it.
+
+Usage of DEBUG_RCU
+
+ DEBUG_RCU is used to add internal debugging self-checks to the
+ RCU library. This define adds a performance penalty when enabled.
+ Can be enabled by uncommenting the corresponding line in
+ Makefile.build.inc.