1 Userspace RCU Implementation
2 by Mathieu Desnoyers and Paul E. McKenney
8 #force 32-bit build with: make -f Makefile32
9 #force 64-bit build with: make -f Makefile64
16 Usage of all urcu libraries
18 * Define _LGPL_SOURCE (only) if your code is LGPL or GPL compatible
19 before including the urcu.h or urcu-qsbr.h header. If your application
20 is distributed under another license, function calls will be generated
21 instead of inlines, so your application can link with the library.
22 * Linking with one of the libraries below is always necessary even for
23 LGPL and GPL applications.
28 * Link the application with "-lurcu".
29 * This is the preferred version of the library, both in terms of speed
30 and flexibility. Requires a signal, typically SIGUSR1. Can be
31 overridden with -DSIGURCU by modifying Makefile.build.inc.
36 * Compile any _LGPL_SOURCE code using this library with "-DURCU_MB".
37 * Link with "-lurcu-mb".
38 * This version of the urcu library does not need to
39 reserve a signal number. URCU_MB uses full memory barriers for
40 readers. This eliminates the need for signals but results in slower
45 * #include <urcu-qsbr.h>
46 * Link with "-lurcu-qsbr".
47 * The QSBR flavor of RCU needs to have each reader thread executing
48 rcu_quiescent_state() periodically to progress. rcu_thread_online()
49 and rcu_thread_offline() can be used to mark long periods for which
50 the threads are not active. It provides the fastest read-side at the
51 expense of more intrusiveness in the application code.
55 Each thread that has reader critical sections (that uses
56 rcu_read_lock()/rcu_read_unlock() must first register to the URCU
57 library. This is done by calling rcu_register_thread(). Unregistration
58 must be performed before exiting the thread by using
59 rcu_unregister_thread().
63 Reader critical sections must be protected by locating them between
64 calls to rcu_read_lock() and rcu_read_unlock(). Inside that lock,
65 rcu_dereference() may be called to read an RCU protected pointer.
69 rcu_assign_pointer() and rcu_xchg_pointer() may be called anywhere.
70 After, synchronize_rcu() must be called. When it returns, the old
71 values are not in usage anymore.
73 Being careful with signals
75 The liburcu library uses signals internally. The signal handler is
76 registered with the SA_RESTART flag. However, these signals may cause
77 some non-restartable system calls to fail with errno = EINTR. Care
78 should be taken to restart system calls manually if they fail with this
79 error. A list of non-restartable system calls may be found in
80 signal(7). The liburcu-mb and liburcu-qsbr versions of the Userspace RCU
81 library do not require any signal.
83 Read-side critical sections are allowed in a signal handler with
84 liburcu and liburcu-mb. Be careful, however, to disable these signals
85 between thread creation and calls to rcu_register_thread(), because a
86 signal handler nesting on an unregistered thread would not be allowed to
89 Read-side critical sections are _not_ allowed in a signal handler with
90 liburcu-qsbr, unless signals are disabled explicitly around each
91 rcu_quiescent_state() calls, when threads are put offline and around
92 calls to synchronize_rcu(). Even then, we do not recommend it.
96 DEBUG_RCU is used to add internal debugging self-checks to the
97 RCU library. This define adds a performance penalty when enabled.
98 Can be enabled by uncommenting the corresponding line in
103 DEBUG_YIELD is used to add random delays in the code for testing