urcu-static.h

   1 #ifndef _URCU_STATIC_H
   2 #define _URCU_STATIC_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 <syscall.h>
  35 #include <unistd.h>
  36
  37 #include <urcu/compiler.h>
  38 #include <urcu/arch.h>
  39 #include <urcu/system.h>
  40 #include <urcu/uatomic_arch.h>
  41 #include <urcu/list.h>
  42 #include <urcu/urcu-futex.h>
  43
  44 #ifdef __cplusplus
  45 extern "C" {
  46 #endif
  47
  48 /* Default is RCU_MEMBARRIER */
  49 #if !defined(RCU_MEMBARRIER) && !defined(RCU_MB) && !defined(RCU_SIGNAL)
  50 #define RCU_MEMBARRIER
  51 #endif
  52
  53 #ifdef RCU_MEMBARRIER
  54 #include <unistd.h>
  55 #include <sys/syscall.h>
  56
  57 /* If the headers do not support SYS_membarrier, statically use RCU_MB */
  58 #ifdef SYS_membarrier
  59 # define MEMBARRIER_EXPEDITED           (1 << 0)
  60 # define MEMBARRIER_DELAYED             (1 << 1)
  61 # define MEMBARRIER_QUERY               (1 << 16)
  62 # define membarrier(...)                syscall(__NR_membarrier, __VA_ARGS__)
  63 #else
  64 # undef RCU_MEMBARRIER
  65 # define RCU_MB
  66 #endif
  67 #endif
  68
  69 /*
  70  * This code section can only be included in LGPL 2.1 compatible source code.
  71  * See below for the function call wrappers which can be used in code meant to
  72  * be only linked with the Userspace RCU library. This comes with a small
  73  * performance degradation on the read-side due to the added function calls.
  74  * This is required to permit relinking with newer versions of the library.
  75  */
  76
  77 /*
  78  * The signal number used by the RCU library can be overridden with
  79  * -DSIGRCU= when compiling the library.
  80  * Provide backward compatibility for liburcu 0.3.x SIGURCU.
  81  */
  82 #ifdef SIGURCU
  83 #define SIGRCU SIGURCU
  84 #endif
  85
  86 #ifndef SIGRCU
  87 #define SIGRCU SIGUSR1
  88 #endif
  89
  90 /*
  91  * If a reader is really non-cooperative and refuses to commit its
  92  * rcu_active_readers count to memory (there is no barrier in the reader
  93  * per-se), kick it after a few loops waiting for it.
  94  */
  95 #define KICK_READER_LOOPS 10000
  96
  97 /*
  98  * Active attempts to check for reader Q.S. before calling futex().
  99  */
 100 #define RCU_QS_ACTIVE_ATTEMPTS 100
 101
 102 #ifdef DEBUG_RCU
 103 #define rcu_assert(args...)     assert(args)
 104 #else
 105 #define rcu_assert(args...)
 106 #endif
 107
 108 #ifdef DEBUG_YIELD
 109 #include <sched.h>
 110 #include <time.h>
 111 #include <pthread.h>
 112 #include <unistd.h>
 113
 114 #define YIELD_READ      (1 << 0)
 115 #define YIELD_WRITE     (1 << 1)
 116
 117 /*
 118  * Updates with RCU_SIGNAL are much slower. Account this in the delay.
 119  */
 120 #ifdef RCU_SIGNAL
 121 /* maximum sleep delay, in us */
 122 #define MAX_SLEEP 30000
 123 #else
 124 #define MAX_SLEEP 50
 125 #endif
 126
 127 extern unsigned int yield_active;
 128 extern unsigned int __thread rand_yield;
 129
 130 static inline void debug_yield_read(void)
 131 {
 132         if (yield_active & YIELD_READ)
 133                 if (rand_r(&rand_yield) & 0x1)
 134                         usleep(rand_r(&rand_yield) % MAX_SLEEP);
 135 }
 136
 137 static inline void debug_yield_write(void)
 138 {
 139         if (yield_active & YIELD_WRITE)
 140                 if (rand_r(&rand_yield) & 0x1)
 141                         usleep(rand_r(&rand_yield) % MAX_SLEEP);
 142 }
 143
 144 static inline void debug_yield_init(void)
 145 {
 146         rand_yield = time(NULL) ^ pthread_self();
 147 }
 148 #else
 149 static inline void debug_yield_read(void)
 150 {
 151 }
 152
 153 static inline void debug_yield_write(void)
 154 {
 155 }
 156
 157 static inline void debug_yield_init(void)
 158 {
 159
 160 }
 161 #endif
 162
 163 #ifdef RCU_MEMBARRIER
 164 extern int has_sys_membarrier;
 165
 166 static inline void smp_mb_light()
 167 {
 168         if (likely(has_sys_membarrier))
 169                 barrier();
 170         else
 171                 smp_mb();
 172 }
 173 #endif
 174
 175 #ifdef RCU_MB
 176 static inline void smp_mb_light()
 177 {
 178         smp_mb();
 179 }
 180 #endif
 181
 182 #ifdef RCU_SIGNAL
 183 static inline void smp_mb_light()
 184 {
 185         barrier();
 186 }
 187 #endif
 188
 189 /*
 190  * The trick here is that RCU_GP_CTR_PHASE must be a multiple of 8 so we can use
 191  * a full 8-bits, 16-bits or 32-bits bitmask for the lower order bits.
 192  */
 193 #define RCU_GP_COUNT            (1UL << 0)
 194 /* Use the amount of bits equal to half of the architecture long size */
 195 #define RCU_GP_CTR_PHASE        (1UL << (sizeof(long) << 2))
 196 #define RCU_GP_CTR_NEST_MASK    (RCU_GP_CTR_PHASE - 1)
 197
 198 /*
 199  * Global quiescent period counter with low-order bits unused.
 200  * Using a int rather than a char to eliminate false register dependencies
 201  * causing stalls on some architectures.
 202  */
 203 extern long rcu_gp_ctr;
 204
 205 struct rcu_reader {
 206         /* Data used by both reader and synchronize_rcu() */
 207         long ctr;
 208         char need_mb;
 209         /* Data used for registry */
 210         struct list_head head __attribute__((aligned(CACHE_LINE_SIZE)));
 211         pthread_t tid;
 212 };
 213
 214 extern struct rcu_reader __thread rcu_reader;
 215
 216 extern int gp_futex;
 217
 218 /*
 219  * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
 220  */
 221 static inline void wake_up_gp(void)
 222 {
 223         if (unlikely(uatomic_read(&gp_futex) == -1)) {
 224                 uatomic_set(&gp_futex, 0);
 225                 futex_async(&gp_futex, FUTEX_WAKE, 1,
 226                       NULL, NULL, 0);
 227         }
 228 }
 229
 230 static inline int rcu_old_gp_ongoing(long *value)
 231 {
 232         long v;
 233
 234         if (value == NULL)
 235                 return 0;
 236         /*
 237          * Make sure both tests below are done on the same version of *value
 238          * to insure consistency.
 239          */
 240         v = LOAD_SHARED(*value);
 241         return (v & RCU_GP_CTR_NEST_MASK) &&
 242                  ((v ^ rcu_gp_ctr) & RCU_GP_CTR_PHASE);
 243 }
 244
 245 static inline void _rcu_read_lock(void)
 246 {
 247         long tmp;
 248
 249         tmp = rcu_reader.ctr;
 250         /*
 251          * rcu_gp_ctr is
 252          *   RCU_GP_COUNT | (~RCU_GP_CTR_PHASE or RCU_GP_CTR_PHASE)
 253          */
 254         if (likely(!(tmp & RCU_GP_CTR_NEST_MASK))) {
 255                 _STORE_SHARED(rcu_reader.ctr, _LOAD_SHARED(rcu_gp_ctr));
 256                 /*
 257                  * Set active readers count for outermost nesting level before
 258                  * accessing the pointer. See smp_mb_heavy().
 259                  */
 260                 smp_mb_light();
 261         } else {
 262                 _STORE_SHARED(rcu_reader.ctr, tmp + RCU_GP_COUNT);
 263         }
 264 }
 265
 266 static inline void _rcu_read_unlock(void)
 267 {
 268         long tmp;
 269
 270         tmp = rcu_reader.ctr;
 271         /*
 272          * Finish using rcu before decrementing the pointer.
 273          * See smp_mb_heavy().
 274          */
 275         if (likely((tmp & RCU_GP_CTR_NEST_MASK) == RCU_GP_COUNT)) {
 276                 smp_mb_light();
 277                 _STORE_SHARED(rcu_reader.ctr, rcu_reader.ctr - RCU_GP_COUNT);
 278                 /* write rcu_reader.ctr before read futex */
 279                 smp_mb_light();
 280                 wake_up_gp();
 281         } else {
 282                 _STORE_SHARED(rcu_reader.ctr, rcu_reader.ctr - RCU_GP_COUNT);
 283         }
 284 }
 285
 286 #ifdef __cplusplus
 287 }
 288 #endif
 289
 290 #endif /* _URCU_STATIC_H */