Userspace RCU Implementatation by Mathieu Desnoyers and Paul E. McKenney BUILDING -------- make make install QUICK START GUIDE ----------------- 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(). Reading Reader critical sections must be protected by locating them between calls to rcu_read_lock() and rcu_read_unlock(). Inside that lock, rcu_dereference() may be called to read an RCU protected pointer. 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. Being careful with signals The 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. Read-side critical sections can sit in a signal handler. 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 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. 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.