Commit | Line | Data |
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7ac06cef | 1 | Userspace RCU Implementation |
c97ae6eb | 2 | by Mathieu Desnoyers and Paul E. McKenney |
6991f61a | 3 | |
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4 | BUILDING |
5 | -------- | |
6991f61a | 6 | |
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7 | make |
8 | make install | |
9 | ||
aa8c36e0 | 10 | |
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11 | QUICK START GUIDE |
12 | ----------------- | |
aa8c36e0 | 13 | |
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14 | Usage of all urcu libraries |
15 | ||
16 | * Define _LGPL_SOURCE (only) if your code is LGPL or GPL compatible | |
17 | before including the urcu.h or urcu-qsbr.h header. If your application | |
18 | is distributed under another license, function calls will be generated | |
19 | instead of inlines, so your application can link with the library. | |
20 | * Linking with one of the libraries below is always necessary even for | |
21 | LGPL and GPL applications. | |
22 | ||
23 | Usage of liburcu | |
24 | ||
25 | * #include <urcu.h> | |
26 | * Link the application with "-lurcu". | |
27 | * This is the preferred version of the library, both in terms of speed | |
28 | and flexibility. Requires a signal, typically SIGUSR1. Can be | |
29 | overridden with -DSIGURCU by modifying Makefile.build.inc. | |
30 | ||
31 | Usage of liburcu-mb | |
32 | ||
33 | * #include <urcu.h> | |
34 | * Compile code with "-DURCU_MB" | |
35 | * Link with "-lurcu-mb". | |
36 | * This version of the urcu library does not need to | |
37 | reserve a signal number. URCU_MB uses full memory barriers for | |
38 | readers. This eliminates the need for signals but results in slower | |
39 | reads. | |
40 | ||
41 | Usage of liburcu-qsbr | |
42 | ||
43 | * #include <urcu-qsbr.h> | |
44 | * Link with "-lurcu-qsbr". | |
45 | * The QSBR flavor of RCU needs to have each reader thread executing | |
46 | rcu_quiescent_state() periodically to progress. rcu_thread_online() | |
47 | and rcu_thread_offline() can be used to mark long periods for which | |
48 | the threads are not active. It provides the fastest read-side at the | |
49 | expense of more intrusiveness in the application code. | |
50 | ||
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51 | Initialization |
52 | ||
53 | Each thread that has reader critical sections (that uses | |
54 | rcu_read_lock()/rcu_read_unlock() must first register to the URCU | |
4c1471de MD |
55 | library. This is done by calling rcu_register_thread(). Unregistration |
56 | must be performed before exiting the thread by using | |
57 | rcu_unregister_thread(). | |
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58 | |
59 | Reading | |
60 | ||
61 | Reader critical sections must be protected by locating them between | |
62 | calls to rcu_read_lock() and rcu_read_unlock(). Inside that lock, | |
63 | rcu_dereference() may be called to read an RCU protected pointer. | |
64 | ||
65 | Writing | |
66 | ||
67 | rcu_assign_pointer() and rcu_xchg_pointer() may be called anywhere. | |
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68 | After, synchronize_rcu() must be called. When it returns, the old |
69 | values are not in usage anymore. | |
c97ae6eb | 70 | |
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71 | Being careful with signals |
72 | ||
0a1d290b | 73 | The liburcu library uses signals internally. The signal handler is |
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74 | registered with the SA_RESTART flag. However, these signals may cause |
75 | some non-restartable system calls to fail with errno = EINTR. Care | |
76 | should be taken to restart system calls manually if they fail with this | |
77 | error. A list of non-restartable system calls may be found in | |
0a1d290b MD |
78 | signal(7). The liburcu-mb and liburcu-qsbr versions of the Userspace RCU |
79 | library do not require any signal. | |
c97ae6eb | 80 | |
0a1d290b | 81 | Read-side critical sections are allowed in a signal handler with |
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82 | liburcu and liburcu-mb. Be careful, however, to disable these signals |
83 | between thread creation and calls to rcu_register_thread(), because a | |
84 | signal handler nesting on an unregistered thread would not be allowed to | |
85 | call rcu_read_lock(). | |
cee02f0a | 86 | |
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87 | Read-side critical sections are _not_ allowed in a signal handler with |
88 | liburcu-qsbr, unless signals are disabled explicitly around each | |
89 | rcu_quiescent_state() calls, when threads are put offline and around | |
90 | calls to synchronize_rcu(). Even then, we do not recommend it. | |
c97ae6eb | 91 | |
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92 | Usage of DEBUG_RCU |
93 | ||
94 | DEBUG_RCU is used to add internal debugging self-checks to the | |
0a1d290b | 95 | RCU library. This define adds a performance penalty when enabled. |
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96 | Can be enabled by uncommenting the corresponding line in |
97 | Makefile.build.inc. | |
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98 | |
99 | Usage of DEBUG_YIELD | |
100 | ||
101 | DEBUG_YIELD is used to add random delays in the code for testing | |
102 | purposes. |