-Userspace RCU Implementatation
+Userspace RCU Implementation
by Mathieu Desnoyers and Paul E. McKenney
BUILDING
Writing
rcu_assign_pointer() and rcu_xchg_pointer() may be called anywhere.
- After, synchronize_rcu() must be called. When it returns, the old values
- are not in usage anymore.
+ After, synchronize_rcu() must be called. When it returns, the old
+ values are not in usage anymore.
+Being careful with signals
-Usage of DEBUG_FULL_MB
+ The urcu 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). To ensure the Userspace RCU library does not use signals,
+ see "Usage of liburcu-mb" below.
- DEBUG_FULL_MB uses full SMP barriers for readers. This eliminates the
- need for signals but results in slower reads.
+ Read-side critical sections can 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().
+Usage of liburcu
+
+ This is the preferred version of the library, both in terms of speed and
+ flexibility. Define _LGPL_SOURCE if your code is LGPL or GPL (otherwise
+ function calls will be generated instead of inlines). Use the urcu.h
+ header. Link the application with "-lurcu".
+
+Usage of liburcu-mb
+
+ Compile code with "-DCONFIG_URCU_AVOID_SIGNALS" and link with
+ "-lurcu-mb" to use a version of the urcu library which does not need to
+ reserve a signal number. CONFIG_URCU_AVOID_SIGNALS uses full SMP
+ barriers for readers. This eliminates the need for signals but results
+ in slower reads.
+
+Usage of liburcu-qsbr
+
+ The QSBR flavor of RCU needs to have each reader thread executing
+ rcu_quiescent_state() periodically to progress. rcu_thread_online() and
+ rcu_thread_offline() can be used to mark long periods for which the
+ threads are not active. Link with "-lurcu-qsbr" and use urcu-qsbr.h.
+
+Usage of DEBUG_RCU
+
+ DEBUG_RCU is used to add internal debugging self-checks to the
+ RCU library. This define adds a performance penality when enabled.
+ Can be enabled by uncommenting the corresponding line in
+ Makefile.build.inc.
Usage of DEBUG_YIELD
DEBUG_YIELD is used to add random delays in the code for testing
purposes.
+