Add missing rcu_cmpxchg_pointer define
[urcu.git] / README
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7ac06cef 1Userspace RCU Implementation
c97ae6eb 2by Mathieu Desnoyers and Paul E. McKenney
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4BUILDING
5--------
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c97ae6eb 7 make
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8 #force 32-bit build with: make -f Makefile32
9 #force 64-bit build with: make -f Makefile64
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10 make install
11
aa8c36e0 12
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13QUICK START GUIDE
14-----------------
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16Usage of all urcu libraries
17
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.
24
25Usage of liburcu
26
27 * #include <urcu.h>
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.
32
33Usage of liburcu-mb
34
35 * #include <urcu.h>
256dd999 36 * Compile any _LGPL_SOURCE code using this library with "-DURCU_MB".
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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
41 reads.
42
43Usage of liburcu-qsbr
44
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.
52
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53Initialization
54
55 Each thread that has reader critical sections (that uses
56 rcu_read_lock()/rcu_read_unlock() must first register to the URCU
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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().
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60
61Reading
62
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.
66
67Writing
68
69 rcu_assign_pointer() and rcu_xchg_pointer() may be called anywhere.
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70 After, synchronize_rcu() must be called. When it returns, the old
71 values are not in usage anymore.
c97ae6eb 72
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73Being careful with signals
74
0a1d290b 75 The liburcu library uses signals internally. The signal handler is
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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
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80 signal(7). The liburcu-mb and liburcu-qsbr versions of the Userspace RCU
81 library do not require any signal.
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0a1d290b 83 Read-side critical sections are allowed in a signal handler with
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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
87 call rcu_read_lock().
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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.
c97ae6eb 93
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94Usage of DEBUG_RCU
95
96 DEBUG_RCU is used to add internal debugging self-checks to the
0a1d290b 97 RCU library. This define adds a performance penalty when enabled.
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98 Can be enabled by uncommenting the corresponding line in
99 Makefile.build.inc.
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100
101Usage of DEBUG_YIELD
102
103 DEBUG_YIELD is used to add random delays in the code for testing
104 purposes.
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