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 | |
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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13 | QUICK START GUIDE |
14 | ----------------- | |
aa8c36e0 | 15 | |
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16 | Usage 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 | ||
25 | Usage 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 | ||
33 | Usage 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 | ||
43 | Usage 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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53 | Initialization |
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 | |
61 | Reading | |
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 | ||
67 | Writing | |
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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73 | Being 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. | |
c97ae6eb | 82 | |
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(). | |
cee02f0a | 88 | |
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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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94 | Usage 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 | |
101 | Usage of DEBUG_YIELD | |
102 | ||
103 | DEBUG_YIELD is used to add random delays in the code for testing | |
104 | purposes. |