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 | ./bootstrap (skip if using tarball) |
8 | ./configure | |
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9 | make |
10 | make install | |
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11 | |
12 | Note: Forcing 32-bit build: | |
13 | * CFLAGS=-m32 ./configure | |
14 | ||
15 | Forcing 64-bit build: | |
16 | * CFLAGS=-m64 ./configure | |
aa8c36e0 | 17 | |
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18 | ARCHITECTURES SUPPORTED |
19 | ----------------------- | |
20 | ||
21 | Currently, x86 (only Pentium and +), x86 64, PowerPC 32/64 and S390 are | |
22 | supported. The current use of sys_futex() makes it Linux-dependent, although | |
23 | this portability limitation might go away in a near future by using the pthread | |
24 | cond vars. Also, the restriction against i386 and i486 might go away if we | |
25 | integrate some of glibc runtime CPU-detection tests. | |
26 | ||
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27 | QUICK START GUIDE |
28 | ----------------- | |
aa8c36e0 | 29 | |
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30 | Usage of all urcu libraries |
31 | ||
32 | * Define _LGPL_SOURCE (only) if your code is LGPL or GPL compatible | |
33 | before including the urcu.h or urcu-qsbr.h header. If your application | |
34 | is distributed under another license, function calls will be generated | |
35 | instead of inlines, so your application can link with the library. | |
36 | * Linking with one of the libraries below is always necessary even for | |
37 | LGPL and GPL applications. | |
38 | ||
39 | Usage of liburcu | |
40 | ||
41 | * #include <urcu.h> | |
42 | * Link the application with "-lurcu". | |
43 | * This is the preferred version of the library, both in terms of speed | |
44 | and flexibility. Requires a signal, typically SIGUSR1. Can be | |
45 | overridden with -DSIGURCU by modifying Makefile.build.inc. | |
46 | ||
47 | Usage of liburcu-mb | |
48 | ||
49 | * #include <urcu.h> | |
256dd999 | 50 | * Compile any _LGPL_SOURCE code using this library with "-DURCU_MB". |
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51 | * Link with "-lurcu-mb". |
52 | * This version of the urcu library does not need to | |
53 | reserve a signal number. URCU_MB uses full memory barriers for | |
54 | readers. This eliminates the need for signals but results in slower | |
55 | reads. | |
56 | ||
57 | Usage of liburcu-qsbr | |
58 | ||
59 | * #include <urcu-qsbr.h> | |
60 | * Link with "-lurcu-qsbr". | |
61 | * The QSBR flavor of RCU needs to have each reader thread executing | |
62 | rcu_quiescent_state() periodically to progress. rcu_thread_online() | |
63 | and rcu_thread_offline() can be used to mark long periods for which | |
64 | the threads are not active. It provides the fastest read-side at the | |
65 | expense of more intrusiveness in the application code. | |
66 | ||
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67 | Usage of liburcu-bp |
68 | ||
69 | * #include <urcu-bp.h> | |
70 | * Link with "-lurcu-bp". | |
71 | * The BP library flavor stands for "bulletproof". It is specifically | |
72 | designed to help tracing library to hook on applications without | |
73 | requiring to modify these applications. urcu_init(), | |
74 | rcu_register_thread() and rcu_unregister_thread() all become nops. | |
75 | The state is dealt with by the library internally at the expense of | |
76 | read-side and write-side performance. | |
77 | ||
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78 | Initialization |
79 | ||
80 | Each thread that has reader critical sections (that uses | |
81 | rcu_read_lock()/rcu_read_unlock() must first register to the URCU | |
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82 | library. This is done by calling rcu_register_thread(). Unregistration |
83 | must be performed before exiting the thread by using | |
84 | rcu_unregister_thread(). | |
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85 | |
86 | Reading | |
87 | ||
88 | Reader critical sections must be protected by locating them between | |
89 | calls to rcu_read_lock() and rcu_read_unlock(). Inside that lock, | |
90 | rcu_dereference() may be called to read an RCU protected pointer. | |
91 | ||
92 | Writing | |
93 | ||
94 | rcu_assign_pointer() and rcu_xchg_pointer() may be called anywhere. | |
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95 | After, synchronize_rcu() must be called. When it returns, the old |
96 | values are not in usage anymore. | |
c97ae6eb | 97 | |
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98 | Usage of liburcu-defer |
99 | ||
100 | * #include <urcu-defer.h> | |
101 | * Link with "-lurcu-defer" | |
102 | * Provides call_rcu() primitive to enqueue delayed callbacks. Queued | |
103 | callbacks are executed in batch periodically after a grace period. | |
104 | Do _not_ use call_rcu() within a read-side critical section, because | |
105 | it may call synchronize_rcu() if the thread queue is full. | |
106 | ||
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107 | Being careful with signals |
108 | ||
0a1d290b | 109 | The liburcu library uses signals internally. The signal handler is |
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110 | registered with the SA_RESTART flag. However, these signals may cause |
111 | some non-restartable system calls to fail with errno = EINTR. Care | |
112 | should be taken to restart system calls manually if they fail with this | |
113 | error. A list of non-restartable system calls may be found in | |
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114 | signal(7). The liburcu-mb and liburcu-qsbr versions of the Userspace RCU |
115 | library do not require any signal. | |
c97ae6eb | 116 | |
0a1d290b | 117 | Read-side critical sections are allowed in a signal handler with |
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118 | liburcu and liburcu-mb. Be careful, however, to disable these signals |
119 | between thread creation and calls to rcu_register_thread(), because a | |
120 | signal handler nesting on an unregistered thread would not be allowed to | |
121 | call rcu_read_lock(). | |
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123 | Read-side critical sections are _not_ allowed in a signal handler with |
124 | liburcu-qsbr, unless signals are disabled explicitly around each | |
125 | rcu_quiescent_state() calls, when threads are put offline and around | |
126 | calls to synchronize_rcu(). Even then, we do not recommend it. | |
c97ae6eb | 127 | |
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128 | Usage of DEBUG_RCU |
129 | ||
130 | DEBUG_RCU is used to add internal debugging self-checks to the | |
0a1d290b | 131 | RCU library. This define adds a performance penalty when enabled. |
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132 | Can be enabled by uncommenting the corresponding line in |
133 | Makefile.build.inc. | |
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134 | |
135 | Usage of DEBUG_YIELD | |
136 | ||
137 | DEBUG_YIELD is used to add random delays in the code for testing | |
138 | purposes. |