1 Userspace RCU Implementation
2 by Mathieu Desnoyers and Paul E. McKenney
16 Each thread that has reader critical sections (that uses
17 rcu_read_lock()/rcu_read_unlock() must first register to the URCU
18 library. This is done by calling rcu_register_thread().
22 Reader critical sections must be protected by locating them between
23 calls to rcu_read_lock() and rcu_read_unlock(). Inside that lock,
24 rcu_dereference() may be called to read an RCU protected pointer.
28 rcu_assign_pointer() and rcu_xchg_pointer() may be called anywhere.
29 After, synchronize_rcu() must be called. When it returns, the old
30 values are not in usage anymore.
32 Being careful with signals
34 The urcu library uses signals internally. The signal handler is
35 registered with the SA_RESTART flag. However, these signals may cause
36 some non-restartable system calls to fail with errno = EINTR. Care
37 should be taken to restart system calls manually if they fail with this
38 error. A list of non-restartable system calls may be found in
39 signal(7). To ensure the Userspace RCU library does not use signals,
40 see "Usage of liburcu-mb" below.
42 Read-side critical sections can are allowed in a signal handler with
43 liburcu and liburcu-mb. Be careful, however, to disable these signals
44 between thread creation and calls to rcu_register_thread(), because a
45 signal handler nesting on an unregistered thread would not be allowed to
50 This is the preferred version of the library, both in terms of speed and
51 flexibility. Define _LGPL_SOURCE if your code is LGPL or GPL (otherwise
52 function calls will be generated instead of inlines). Use the urcu.h
53 header. Link the application with "-lurcu".
57 Compile code with "-DCONFIG_URCU_AVOID_SIGNALS" and link with
58 "-lurcu-mb" to use a version of the urcu library which does not need to
59 reserve a signal number. CONFIG_URCU_AVOID_SIGNALS uses full SMP
60 barriers for readers. This eliminates the need for signals but results
65 The QSBR flavor of RCU needs to have each reader thread executing
66 rcu_quiescent_state() periodically to progress. rcu_thread_online() and
67 rcu_thread_offline() can be used to mark long periods for which the
68 threads are not active. Link with "-lurcu-qsbr" and use urcu-qsbr.h.
72 DEBUG_RCU is used to add internal debugging self-checks to the
73 RCU library. This define adds a performance penality when enabled.
74 Can be enabled by uncommenting the corresponding line in
79 DEBUG_YIELD is used to add random delays in the code for testing