urcu-qsbr.h

   1 #ifndef _URCU_QSBR_H
   2 #define _URCU_QSBR_H
   3
   4 /*
   5  * urcu-static.h
   6  *
   7  * Userspace RCU header.
   8  *
   9  * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu.h for linking
  10  * dynamically with the userspace rcu library.
  11  *
  12  * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
  13  * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
  14  *
  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.
  19  *
  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.
  24  *
  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
  28  *
  29  * IBM's contributions to this file may be relicensed under LGPLv2 or later.
  30  */
  31
  32 #include <stdlib.h>
  33 #include <pthread.h>
  34 #include <assert.h>
  35
  36 #include <compiler.h>
  37 #include <arch.h>
  38
  39 /*
  40  * Identify a shared load. A smp_rmc() or smp_mc() should come before the load.
  41  */
  42 #define _LOAD_SHARED(p)        ACCESS_ONCE(p)
  43
  44 /*
  45  * Load a data from shared memory, doing a cache flush if required.
  46  */
  47 #define LOAD_SHARED(p)                  \
  48         ({                              \
  49                 smp_rmc();              \
  50                 _LOAD_SHARED(p);        \
  51         })
  52
  53 /*
  54  * Identify a shared store. A smp_wmc() or smp_mc() should follow the store.
  55  */
  56 #define _STORE_SHARED(x, v)     ({ ACCESS_ONCE(x) = (v); })
  57
  58 /*
  59  * Store v into x, where x is located in shared memory. Performs the required
  60  * cache flush after writing. Returns v.
  61  */
  62 #define STORE_SHARED(x, v)              \
  63         ({                              \
  64                 _STORE_SHARED(x, v);    \
  65                 smp_wmc();              \
  66                 (v);                    \
  67         })
  68
  69 /**
  70  * _rcu_dereference - reads (copy) a RCU-protected pointer to a local variable
  71  * into a RCU read-side critical section. The pointer can later be safely
  72  * dereferenced within the critical section.
  73  *
  74  * This ensures that the pointer copy is invariant thorough the whole critical
  75  * section.
  76  *
  77  * Inserts memory barriers on architectures that require them (currently only
  78  * Alpha) and documents which pointers are protected by RCU.
  79  *
  80  * Should match rcu_assign_pointer() or rcu_xchg_pointer().
  81  */
  82
  83 #define _rcu_dereference(p)     ({                                      \
  84                                 typeof(p) _________p1 = LOAD_SHARED(p); \
  85                                 smp_read_barrier_depends();             \
  86                                 (_________p1);                          \
  87                                 })
  88
  89 /*
  90  * This code section can only be included in LGPL 2.1 compatible source code.
  91  * See below for the function call wrappers which can be used in code meant to
  92  * be only linked with the Userspace RCU library. This comes with a small
  93  * performance degradation on the read-side due to the added function calls.
  94  * This is required to permit relinking with newer versions of the library.
  95  */
  96
  97 /*
  98  * The signal number used by the RCU library can be overridden with
  99  * -DSIGURCU= when compiling the library.
 100  */
 101 #ifndef SIGURCU
 102 #define SIGURCU SIGUSR1
 103 #endif
 104
 105 /*
 106  * If a reader is really non-cooperative and refuses to commit its
 107  * rcu_reader_qs_gp count to memory (there is no barrier in the reader
 108  * per-se), kick it after a few loops waiting for it.
 109  */
 110 #define KICK_READER_LOOPS 10000
 111
 112 #ifdef DEBUG_RCU
 113 #define rcu_assert(args...)     assert(args)
 114 #else
 115 #define rcu_assert(args...)
 116 #endif
 117
 118 #ifdef DEBUG_YIELD
 119 #include <sched.h>
 120 #include <time.h>
 121 #include <pthread.h>
 122 #include <unistd.h>
 123
 124 #define YIELD_READ      (1 << 0)
 125 #define YIELD_WRITE     (1 << 1)
 126
 127 /* maximum sleep delay, in us */
 128 #define MAX_SLEEP 50
 129
 130 extern unsigned int yield_active;
 131 extern unsigned int __thread rand_yield;
 132
 133 static inline void debug_yield_read(void)
 134 {
 135         if (yield_active & YIELD_READ)
 136                 if (rand_r(&rand_yield) & 0x1)
 137                         usleep(rand_r(&rand_yield) % MAX_SLEEP);
 138 }
 139
 140 static inline void debug_yield_write(void)
 141 {
 142         if (yield_active & YIELD_WRITE)
 143                 if (rand_r(&rand_yield) & 0x1)
 144                         usleep(rand_r(&rand_yield) % MAX_SLEEP);
 145 }
 146
 147 static inline void debug_yield_init(void)
 148 {
 149         rand_yield = time(NULL) ^ pthread_self();
 150 }
 151 #else
 152 static inline void debug_yield_read(void)
 153 {
 154 }
 155
 156 static inline void debug_yield_write(void)
 157 {
 158 }
 159
 160 static inline void debug_yield_init(void)
 161 {
 162
 163 }
 164 #endif
 165
 166 static inline void reader_barrier()
 167 {
 168         smp_mb();
 169 }
 170
 171 /*
 172  * Global quiescent period counter with low-order bits unused.
 173  * Using a int rather than a char to eliminate false register dependencies
 174  * causing stalls on some architectures.
 175  */
 176 extern long urcu_gp_ctr;
 177
 178 extern long __thread rcu_reader_qs_gp;
 179
 180 static inline int rcu_gp_ongoing(long *value)
 181 {
 182         if (value == NULL)
 183                 return 0;
 184
 185         return LOAD_SHARED(*value) & 1;
 186 }
 187
 188 static inline void _rcu_read_lock(void)
 189 {
 190         rcu_assert(rcu_reader_qs_gp & 1);
 191 }
 192
 193 static inline void _rcu_read_unlock(void)
 194 {
 195 }
 196
 197 static inline void _rcu_quiescent_state(void)
 198 {
 199         smp_mb();
 200         rcu_reader_qs_gp = ACCESS_ONCE(urcu_gp_ctr) + 1;
 201         smp_mb();
 202 }
 203
 204 static inline void _rcu_thread_offline(void)
 205 {
 206         smp_mb();
 207         rcu_reader_qs_gp = ACCESS_ONCE(urcu_gp_ctr);
 208 }
 209
 210 static inline void _rcu_thread_online(void)
 211 {
 212         rcu_reader_qs_gp = ACCESS_ONCE(urcu_gp_ctr) + 1;
 213         smp_mb();
 214 }
 215
 216 /**
 217  * _rcu_assign_pointer - assign (publicize) a pointer to a new data structure
 218  * meant to be read by RCU read-side critical sections. Returns the assigned
 219  * value.
 220  *
 221  * Documents which pointers will be dereferenced by RCU read-side critical
 222  * sections and adds the required memory barriers on architectures requiring
 223  * them. It also makes sure the compiler does not reorder code initializing the
 224  * data structure before its publication.
 225  *
 226  * Should match rcu_dereference_pointer().
 227  */
 228
 229 #define _rcu_assign_pointer(p, v)                       \
 230         ({                                              \
 231                 if (!__builtin_constant_p(v) ||         \
 232                     ((v) != NULL))                      \
 233                         wmb();                          \
 234                 STORE_SHARED(p, v);                     \
 235         })
 236
 237 /**
 238  * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous
 239  * pointer to the data structure, which can be safely freed after waiting for a
 240  * quiescent state using synchronize_rcu().
 241  */
 242
 243 #define _rcu_xchg_pointer(p, v)                         \
 244         ({                                              \
 245                 if (!__builtin_constant_p(v) ||         \
 246                     ((v) != NULL))                      \
 247                         wmb();                          \
 248                 xchg(p, v);                             \
 249         })
 250
 251 /*
 252  * Exchanges the pointer and waits for quiescent state.
 253  * The pointer returned can be freed.
 254  */
 255 #define _rcu_publish_content(p, v)                      \
 256         ({                                              \
 257                 void *oldptr;                           \
 258                 oldptr = _rcu_xchg_pointer(p, v);       \
 259                 synchronize_rcu();                      \
 260                 oldptr;                                 \
 261         })
 262
 263 extern void synchronize_rcu(void);
 264
 265 /*
 266  * Reader thread registration.
 267  */
 268 extern void rcu_register_thread(void);
 269 extern void rcu_unregister_thread(void);
 270
 271 #endif /* _URCU_QSBR_H */