Fix powerpc uatomic 4-byte cmpxchg (cmpd -> cmpw)
[urcu.git] / README
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7ac06cef 1Userspace RCU Implementation
c97ae6eb 2by Mathieu Desnoyers and Paul E. McKenney
6991f61a 3
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4BUILDING
5--------
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7 ./bootstrap (skip if using tarball)
8 ./configure
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9 make
10 make install
9ca52251 11
7d413817 12 Hints: Forcing 32-bit build:
c4c18179 13 * CFLAGS="-m32 -g -O2" ./configure
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14
15 Forcing 64-bit build:
c4c18179 16 * CFLAGS="-m64 -g -O2" ./configure
aa8c36e0 17
f39cd442 18 Forcing a 32-bit build with 386 backward compatibility:
c5b9f8ff 19 * CFLAGS="-m32 -g -O2" ./configure --host=i386-pc-linux-gnu
7d413817 20
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21 Forcing a 32-bit build for Sparcv9 (typical for Sparc v9)
22 * CFLAGS="-m32 -Wa,-Av9a -g -O2" ./configure
23
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24ARCHITECTURES SUPPORTED
25-----------------------
26
c0a68bfa 27Currently, x86 (i386, i486, i586, i686), x86 64-bit, PowerPC 32/64, S390, S390x
795d506a 28and Sparcv9 32/64 are supported. Only tested on Linux so far, but should
c0a68bfa 29theoretically work on other operating systems.
c51e75e6 30
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31Alpha and ia64 architectures are supported, but depend on 4.x gcc with atomic
32builtins support.
33
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34The gcc compiler versions 3.3, 3.4, 4.0, 4.1, 4.2, 4.3, 4.4 and 4.5 are
35supported, with the following exceptions:
36
37- gcc 3.3 and 3.4 have a bug that prevents them from generating volatile
38 accesses to offsets in a TLS structure on 32-bit x86. These versions are
39 therefore not compatible with liburcu on x86 32-bit (i386, i486, i586, i686).
40 The problem has been reported to the gcc community:
41 http://www.mail-archive.com/gcc-bugs@gcc.gnu.org/msg281255.html
42
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43QUICK START GUIDE
44-----------------
aa8c36e0 45
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46Usage of all urcu libraries
47
48 * Define _LGPL_SOURCE (only) if your code is LGPL or GPL compatible
49 before including the urcu.h or urcu-qsbr.h header. If your application
50 is distributed under another license, function calls will be generated
51 instead of inlines, so your application can link with the library.
52 * Linking with one of the libraries below is always necessary even for
53 LGPL and GPL applications.
54
55Usage of liburcu
56
57 * #include <urcu.h>
58 * Link the application with "-lurcu".
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59 * This is the preferred version of the library, in terms of
60 grace-period detection speed, read-side speed and flexibility.
61 Dynamically detects kernel support for sys_membarrier(). Falls back
62 on urcu-mb scheme if support is not present, which has slower
63 read-side.
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64
65Usage of liburcu-qsbr
66
67 * #include <urcu-qsbr.h>
68 * Link with "-lurcu-qsbr".
69 * The QSBR flavor of RCU needs to have each reader thread executing
70 rcu_quiescent_state() periodically to progress. rcu_thread_online()
71 and rcu_thread_offline() can be used to mark long periods for which
72 the threads are not active. It provides the fastest read-side at the
73 expense of more intrusiveness in the application code.
74
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75Usage of liburcu-mb
76
77 * #include <urcu.h>
78 * Compile any _LGPL_SOURCE code using this library with "-DRCU_MB".
79 * Link with "-lurcu-mb".
80 * This version of the urcu library uses memory barriers on the writer
81 and reader sides. This results in faster grace-period detection, but
82 results in slower reads.
83
84Usage of liburcu-signal
85
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86 * #include <urcu.h>
87 * Compile any _LGPL_SOURCE code using this library with "-DRCU_SIGNAL".
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88 * Link the application with "-lurcu-signal".
89 * Version of the library that requires a signal, typically SIGUSR1. Can
90 be overridden with -DSIGRCU by modifying Makefile.build.inc.
91
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92Usage of liburcu-bp
93
94 * #include <urcu-bp.h>
95 * Link with "-lurcu-bp".
96 * The BP library flavor stands for "bulletproof". It is specifically
97 designed to help tracing library to hook on applications without
02be5561 98 requiring to modify these applications. rcu_init(),
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99 rcu_register_thread() and rcu_unregister_thread() all become nops.
100 The state is dealt with by the library internally at the expense of
101 read-side and write-side performance.
102
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103Initialization
104
105 Each thread that has reader critical sections (that uses
106 rcu_read_lock()/rcu_read_unlock() must first register to the URCU
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107 library. This is done by calling rcu_register_thread(). Unregistration
108 must be performed before exiting the thread by using
109 rcu_unregister_thread().
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110
111Reading
112
113 Reader critical sections must be protected by locating them between
114 calls to rcu_read_lock() and rcu_read_unlock(). Inside that lock,
115 rcu_dereference() may be called to read an RCU protected pointer.
116
117Writing
118
119 rcu_assign_pointer() and rcu_xchg_pointer() may be called anywhere.
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120 After, synchronize_rcu() must be called. When it returns, the old
121 values are not in usage anymore.
c97ae6eb 122
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123Usage of liburcu-defer
124
125 * #include <urcu-defer.h>
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126 * Link with "-lurcu-defer", and also with one of the urcu library
127 (either urcu, urcu-bp, urcu-mb or urcu-qsbr).
632dd6ba 128 * Provides defer_rcu() primitive to enqueue delayed callbacks. Queued
ec4e58a3 129 callbacks are executed in batch periodically after a grace period.
632dd6ba 130 Do _not_ use defer_rcu() within a read-side critical section, because
ec4e58a3 131 it may call synchronize_rcu() if the thread queue is full.
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132 * Provides defer_rcu_ratelimit() primitive, which acts just like
133 defer_rcu(), but takes an additional rate limiter callback forcing
134 synchronized callback execution of the limiter returns non-zero.
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135 * Requires that rcu_defer_barrier() must be called in library destructor
136 if a library queues callbacks and is expected to be unloaded with
137 dlclose().
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138 * Its API is currently experimental. It may change in future library
139 releases.
ec4e58a3 140
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141Being careful with signals
142
0a1d290b 143 The liburcu library uses signals internally. The signal handler is
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144 registered with the SA_RESTART flag. However, these signals may cause
145 some non-restartable system calls to fail with errno = EINTR. Care
146 should be taken to restart system calls manually if they fail with this
147 error. A list of non-restartable system calls may be found in
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148 signal(7). The liburcu-mb and liburcu-qsbr versions of the Userspace RCU
149 library do not require any signal.
c97ae6eb 150
0a1d290b 151 Read-side critical sections are allowed in a signal handler with
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152 liburcu and liburcu-mb. Be careful, however, to disable these signals
153 between thread creation and calls to rcu_register_thread(), because a
154 signal handler nesting on an unregistered thread would not be allowed to
155 call rcu_read_lock().
cee02f0a 156
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157 Read-side critical sections are _not_ allowed in a signal handler with
158 liburcu-qsbr, unless signals are disabled explicitly around each
159 rcu_quiescent_state() calls, when threads are put offline and around
160 calls to synchronize_rcu(). Even then, we do not recommend it.
c97ae6eb 161
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162Interaction with mutexes
163
164 One must be careful to do not cause deadlocks due to interaction of
165 synchronize_rcu() and RCU read-side with mutexes. If synchronize_rcu()
166 is called with a mutex held, this mutex (or any mutex which has this
167 mutex in its dependency chain) should not be acquired from within a RCU
168 read-side critical section.
169
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170Usage of DEBUG_RCU
171
172 DEBUG_RCU is used to add internal debugging self-checks to the
0a1d290b 173 RCU library. This define adds a performance penalty when enabled.
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174 Can be enabled by uncommenting the corresponding line in
175 Makefile.build.inc.
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176
177Usage of DEBUG_YIELD
178
179 DEBUG_YIELD is used to add random delays in the code for testing
180 purposes.
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181
182SMP support
183
184 By default the library is configured to use synchronization primitives
185 adequate for SMP systems. On uniprocessor systems, support for SMP
186 systems can be disabled with:
187
188 ./configure --disable-smp-support
189
190 theoretically yielding slightly better performance.
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