+ After, synchronize_rcu() must be called. When it returns, the old
+ values are not in usage anymore.
+
+Usage of liburcu-defer
+
+ * Follow instructions for either liburcu, liburcu-qsbr,
+ liburcu-mb, liburcu-signal, or liburcu-bp above.
+ The liburcu-defer functionality is pulled into each of
+ those library modules.
+ * Provides defer_rcu() primitive to enqueue delayed callbacks. Queued
+ callbacks are executed in batch periodically after a grace period.
+ Do _not_ use defer_rcu() within a read-side critical section, because
+ it may call synchronize_rcu() if the thread queue is full.
+ This can lead to deadlock or worse.
+ * Requires that rcu_defer_barrier() must be called in library destructor
+ if a library queues callbacks and is expected to be unloaded with
+ dlclose().
+ * Its API is currently experimental. It may change in future library
+ releases.
+
+Usage of urcu-call-rcu
+
+ * Follow instructions for either liburcu, liburcu-qsbr,
+ liburcu-mb, liburcu-signal, or liburcu-bp above.
+ The urcu-call-rcu functionality is provided for each of
+ these library modules.
+ * Provides the call_rcu() primitive to enqueue delayed callbacks
+ in a manner similar to defer_rcu(), but without ever delaying
+ for a grace period. On the other hand, call_rcu()'s best-case
+ overhead is not quite as good as that of defer_rcu().
+ * Provides call_rcu() to allow asynchronous handling of RCU
+ grace periods. A number of additional functions are provided
+ to manage the helper threads used by call_rcu(), but reasonable
+ defaults are used if these additional functions are not invoked.
+ See API.txt for more details.
+
+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.
+
+Interaction with mutexes
+
+ One must be careful to do not cause deadlocks due to interaction of
+ synchronize_rcu() and RCU read-side with mutexes. If synchronize_rcu()
+ is called with a mutex held, this mutex (or any mutex which has this
+ mutex in its dependency chain) should not be acquired from within a RCU
+ read-side critical section.
+
+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.