1 #ifndef _URCU_QSBR_STATIC_H
2 #define _URCU_QSBR_STATIC_H
7 * Userspace RCU QSBR header.
9 * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu-qsbr.h for linking
10 * dynamically with the userspace rcu QSBR library.
12 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
13 * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
15 * This library is free software; you can redistribute it and/or
16 * modify it under the terms of the GNU Lesser General Public
17 * License as published by the Free Software Foundation; either
18 * version 2.1 of the License, or (at your option) any later version.
20 * This library is distributed in the hope that it will be useful,
21 * but WITHOUT ANY WARRANTY; without even the implied warranty of
22 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
23 * Lesser General Public License for more details.
25 * You should have received a copy of the GNU Lesser General Public
26 * License along with this library; if not, write to the Free Software
27 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
29 * IBM's contributions to this file may be relicensed under LGPLv2 or later.
39 #include <urcu/compiler.h>
40 #include <urcu/arch.h>
41 #include <urcu/arch_uatomic.h>
42 #include <urcu/list.h>
45 * Identify a shared load. A smp_rmc() or smp_mc() should come before the load.
47 #define _LOAD_SHARED(p) ACCESS_ONCE(p)
50 * Load a data from shared memory, doing a cache flush if required.
52 #define LOAD_SHARED(p) \
59 * Identify a shared store. A smp_wmc() or smp_mc() should follow the store.
61 #define _STORE_SHARED(x, v) ({ ACCESS_ONCE(x) = (v); })
64 * Store v into x, where x is located in shared memory. Performs the required
65 * cache flush after writing. Returns v.
67 #define STORE_SHARED(x, v) \
69 _STORE_SHARED(x, v); \
75 * _rcu_dereference - reads (copy) a RCU-protected pointer to a local variable
76 * into a RCU read-side critical section. The pointer can later be safely
77 * dereferenced within the critical section.
79 * This ensures that the pointer copy is invariant thorough the whole critical
82 * Inserts memory barriers on architectures that require them (currently only
83 * Alpha) and documents which pointers are protected by RCU.
85 * Should match rcu_assign_pointer() or rcu_xchg_pointer().
88 #define _rcu_dereference(p) ({ \
89 typeof(p) _________p1 = LOAD_SHARED(p); \
90 smp_read_barrier_depends(); \
94 #define futex(...) syscall(__NR_futex, __VA_ARGS__)
99 * This code section can only be included in LGPL 2.1 compatible source code.
100 * See below for the function call wrappers which can be used in code meant to
101 * be only linked with the Userspace RCU library. This comes with a small
102 * performance degradation on the read-side due to the added function calls.
103 * This is required to permit relinking with newer versions of the library.
107 * If a reader is really non-cooperative and refuses to commit its
108 * urcu_reader.ctr count to memory (there is no barrier in the reader
109 * per-se), kick it after a few loops waiting for it.
111 #define KICK_READER_LOOPS 10000
114 * Active attempts to check for reader Q.S. before calling futex().
116 #define RCU_QS_ACTIVE_ATTEMPTS 100
119 #define rcu_assert(args...) assert(args)
121 #define rcu_assert(args...)
130 #define YIELD_READ (1 << 0)
131 #define YIELD_WRITE (1 << 1)
133 /* maximum sleep delay, in us */
136 extern unsigned int yield_active
;
137 extern unsigned int __thread rand_yield
;
139 static inline void debug_yield_read(void)
141 if (yield_active
& YIELD_READ
)
142 if (rand_r(&rand_yield
) & 0x1)
143 usleep(rand_r(&rand_yield
) % MAX_SLEEP
);
146 static inline void debug_yield_write(void)
148 if (yield_active
& YIELD_WRITE
)
149 if (rand_r(&rand_yield
) & 0x1)
150 usleep(rand_r(&rand_yield
) % MAX_SLEEP
);
153 static inline void debug_yield_init(void)
155 rand_yield
= time(NULL
) ^ pthread_self();
158 static inline void debug_yield_read(void)
162 static inline void debug_yield_write(void)
166 static inline void debug_yield_init(void)
172 static inline void reader_barrier()
177 #define RCU_GP_ONLINE (1UL << 0)
178 #define RCU_GP_CTR (1UL << 1)
181 * Global quiescent period counter with low-order bits unused.
182 * Using a int rather than a char to eliminate false register dependencies
183 * causing stalls on some architectures.
185 extern unsigned long urcu_gp_ctr
;
188 /* Data used by both reader and synchronize_rcu() */
190 /* Data used for registry */
191 struct list_head head
__attribute__((aligned(CACHE_LINE_SIZE
)));
195 extern struct urcu_reader __thread urcu_reader
;
200 * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
202 static inline void wake_up_gp(void)
204 if (unlikely(uatomic_read(&gp_futex
) == -1)) {
205 uatomic_set(&gp_futex
, 0);
206 futex(&gp_futex
, FUTEX_WAKE
, 1,
211 #if (BITS_PER_LONG < 64)
212 static inline int rcu_gp_ongoing(unsigned long *value
)
214 unsigned long reader_gp
;
218 reader_gp
= LOAD_SHARED(*value
);
219 return reader_gp
&& ((reader_gp
^ urcu_gp_ctr
) & RCU_GP_CTR
);
221 #else /* !(BITS_PER_LONG < 64) */
222 static inline int rcu_gp_ongoing(unsigned long *value
)
224 unsigned long reader_gp
;
228 reader_gp
= LOAD_SHARED(*value
);
229 return reader_gp
&& (reader_gp
- urcu_gp_ctr
> ULONG_MAX
/ 2);
231 #endif /* !(BITS_PER_LONG < 64) */
233 static inline void _rcu_read_lock(void)
235 rcu_assert(urcu_reader
.ctr
);
238 static inline void _rcu_read_unlock(void)
242 static inline void _rcu_quiescent_state(void)
245 _STORE_SHARED(urcu_reader
.ctr
, _LOAD_SHARED(urcu_gp_ctr
));
246 smp_mb(); /* write urcu_reader.ctr before read futex */
251 static inline void _rcu_thread_offline(void)
254 STORE_SHARED(urcu_reader
.ctr
, 0);
255 smp_mb(); /* write urcu_reader.ctr before read futex */
259 static inline void _rcu_thread_online(void)
261 _STORE_SHARED(urcu_reader
.ctr
, LOAD_SHARED(urcu_gp_ctr
));
266 * _rcu_assign_pointer - assign (publicize) a pointer to a new data structure
267 * meant to be read by RCU read-side critical sections. Returns the assigned
270 * Documents which pointers will be dereferenced by RCU read-side critical
271 * sections and adds the required memory barriers on architectures requiring
272 * them. It also makes sure the compiler does not reorder code initializing the
273 * data structure before its publication.
275 * Should match rcu_dereference_pointer().
278 #define _rcu_assign_pointer(p, v) \
280 if (!__builtin_constant_p(v) || \
283 STORE_SHARED(p, v); \
287 * _rcu_cmpxchg_pointer - same as rcu_assign_pointer, but tests if the pointer
288 * is as expected by "old". If succeeds, returns the previous pointer to the
289 * data structure, which can be safely freed after waiting for a quiescent state
290 * using synchronize_rcu(). If fails (unexpected value), returns old (which
291 * should not be freed !).
294 #define _rcu_cmpxchg_pointer(p, old, _new) \
296 if (!__builtin_constant_p(_new) || \
299 uatomic_cmpxchg(p, old, _new); \
303 * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous
304 * pointer to the data structure, which can be safely freed after waiting for a
305 * quiescent state using synchronize_rcu().
308 #define _rcu_xchg_pointer(p, v) \
310 if (!__builtin_constant_p(v) || \
313 uatomic_xchg(p, v); \
317 * Exchanges the pointer and waits for quiescent state.
318 * The pointer returned can be freed.
320 #define _rcu_publish_content(p, v) \
323 oldptr = _rcu_xchg_pointer(p, v); \
328 #endif /* _URCU_QSBR_STATIC_H */