-Userspace RCU Implementatation
+Userspace RCU Implementation
by Mathieu Desnoyers and Paul E. McKenney
BUILDING
--------
make
+ #force 32-bit build with: make -f Makefile32
+ #force 64-bit build with: make -f Makefile64
make install
QUICK START GUIDE
-----------------
+Usage of all urcu libraries
+
+ * Define _LGPL_SOURCE (only) if your code is LGPL or GPL compatible
+ before including the urcu.h or urcu-qsbr.h header. If your application
+ is distributed under another license, function calls will be generated
+ instead of inlines, so your application can link with the library.
+ * Linking with one of the libraries below is always necessary even for
+ LGPL and GPL applications.
+
+Usage of liburcu
+
+ * #include <urcu.h>
+ * Link the application with "-lurcu".
+ * This is the preferred version of the library, both in terms of speed
+ and flexibility. Requires a signal, typically SIGUSR1. Can be
+ overridden with -DSIGURCU by modifying Makefile.build.inc.
+
+Usage of liburcu-mb
+
+ * #include <urcu.h>
+ * Compile any _LGPL_SOURCE code using this library with "-DURCU_MB".
+ * Link with "-lurcu-mb".
+ * This version of the urcu library does not need to
+ reserve a signal number. URCU_MB uses full memory barriers for
+ readers. This eliminates the need for signals but results in slower
+ reads.
+
+Usage of liburcu-qsbr
+
+ * #include <urcu-qsbr.h>
+ * Link with "-lurcu-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. It provides the fastest read-side at the
+ expense of more intrusiveness in the application code.
+
Initialization
Each thread that has reader critical sections (that uses
rcu_read_lock()/rcu_read_unlock() must first register to the URCU
- library. This is done by calling rcu_register_thread().
+ library. This is done by calling rcu_register_thread(). Unregistration
+ must be performed before exiting the thread by using
+ rcu_unregister_thread().
Reading
Being careful with signals
- The library uses signals internally. The signal handler is
+ 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). To ensure the Userspace RCU library does not use signals,
- define CONFIG_URCU_AVOID_SIGNALS at compile-time.
-
-Usage of CONFIG_URCU_AVOID_SIGNALS
-
- CONFIG_URCU_AVOID_SIGNALS uses full SMP barriers for readers. This
- eliminates the need for signals but results in slower reads.
-
+ 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.
Usage of DEBUG_YIELD
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