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(...)                syscall(__NR_membarrier, __VA_ARGS__)
  62 #else
  63 # undef RCU_MEMBARRIER
  64 # define RCU_MB
  65 #endif
  66 #endif
  67
  68 /*
  69  * This code section can only be included in LGPL 2.1 compatible source code.
  70  * See below for the function call wrappers which can be used in code meant to
  71  * be only linked with the Userspace RCU library. This comes with a small
  72  * performance degradation on the read-side due to the added function calls.
  73  * This is required to permit relinking with newer versions of the library.
  74  */
  75
  76 /*
  77  * The signal number used by the RCU library can be overridden with
  78  * -DSIGRCU= when compiling the library.
  79  */
  80 #ifndef SIGRCU
  81 #define SIGRCU SIGUSR1
  82 #endif
  83
  84 /*
  85  * If a reader is really non-cooperative and refuses to commit its
  86  * rcu_active_readers count to memory (there is no barrier in the reader
  87  * per-se), kick it after a few loops waiting for it.
  88  */
  89 #define KICK_READER_LOOPS 10000
  90
  91 /*
  92  * Active attempts to check for reader Q.S. before calling futex().
  93  */
  94 #define RCU_QS_ACTIVE_ATTEMPTS 100
  95
  96 #ifdef DEBUG_RCU
  97 #define rcu_assert(args...)     assert(args)
  98 #else
  99 #define rcu_assert(args...)
 100 #endif
 101
 102 #ifdef DEBUG_YIELD
 103 #include <sched.h>
 104 #include <time.h>
 105 #include <pthread.h>
 106 #include <unistd.h>
 107
 108 #define YIELD_READ      (1 << 0)
 109 #define YIELD_WRITE     (1 << 1)
 110
 111 /*
 112  * Updates with RCU_SIGNAL are much slower. Account this in the delay.
 113  */
 114 #ifdef RCU_SIGNAL
 115 /* maximum sleep delay, in us */
 116 #define MAX_SLEEP 30000
 117 #else
 118 #define MAX_SLEEP 50
 119 #endif
 120
 121 extern unsigned int yield_active;
 122 extern unsigned int __thread rand_yield;
 123
 124 static inline void debug_yield_read(void)
 125 {
 126         if (yield_active & YIELD_READ)
 127                 if (rand_r(&rand_yield) & 0x1)
 128                         usleep(rand_r(&rand_yield) % MAX_SLEEP);
 129 }
 130
 131 static inline void debug_yield_write(void)
 132 {
 133         if (yield_active & YIELD_WRITE)
 134                 if (rand_r(&rand_yield) & 0x1)
 135                         usleep(rand_r(&rand_yield) % MAX_SLEEP);
 136 }
 137
 138 static inline void debug_yield_init(void)
 139 {
 140         rand_yield = time(NULL) ^ pthread_self();
 141 }
 142 #else
 143 static inline void debug_yield_read(void)
 144 {
 145 }
 146
 147 static inline void debug_yield_write(void)
 148 {
 149 }
 150
 151 static inline void debug_yield_init(void)
 152 {
 153
 154 }
 155 #endif
 156
 157 #ifdef RCU_MEMBARRIER
 158 extern int has_sys_membarrier;
 159
 160 static inline void smp_mb_light()
 161 {
 162         if (likely(has_sys_membarrier))
 163                 barrier();
 164         else
 165                 smp_mb();
 166 }
 167 #endif
 168
 169 #ifdef RCU_MB
 170 static inline void smp_mb_light()
 171 {
 172         smp_mb();
 173 }
 174 #endif
 175
 176 #ifdef RCU_SIGNAL
 177 static inline void smp_mb_light()
 178 {
 179         barrier();
 180 }
 181 #endif
 182
 183 /*
 184  * The trick here is that RCU_GP_CTR_PHASE must be a multiple of 8 so we can use
 185  * a full 8-bits, 16-bits or 32-bits bitmask for the lower order bits.
 186  */
 187 #define RCU_GP_COUNT            (1UL << 0)
 188 /* Use the amount of bits equal to half of the architecture long size */
 189 #define RCU_GP_CTR_PHASE        (1UL << (sizeof(long) << 2))
 190 #define RCU_GP_CTR_NEST_MASK    (RCU_GP_CTR_PHASE - 1)
 191
 192 /*
 193  * Global quiescent period counter with low-order bits unused.
 194  * Using a int rather than a char to eliminate false register dependencies
 195  * causing stalls on some architectures.
 196  */
 197 extern long rcu_gp_ctr;
 198
 199 struct rcu_reader {
 200         /* Data used by both reader and synchronize_rcu() */
 201         long ctr;
 202         char need_mb;
 203         /* Data used for registry */
 204         struct list_head head __attribute__((aligned(CACHE_LINE_SIZE)));
 205         pthread_t tid;
 206 };
 207
 208 extern struct rcu_reader __thread rcu_reader;
 209
 210 extern int gp_futex;
 211
 212 /*
 213  * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
 214  */
 215 static inline void wake_up_gp(void)
 216 {
 217         if (unlikely(uatomic_read(&gp_futex) == -1)) {
 218                 uatomic_set(&gp_futex, 0);
 219                 futex_async(&gp_futex, FUTEX_WAKE, 1,
 220                       NULL, NULL, 0);
 221         }
 222 }
 223
 224 static inline int rcu_old_gp_ongoing(long *value)
 225 {
 226         long v;
 227
 228         if (value == NULL)
 229                 return 0;
 230         /*
 231          * Make sure both tests below are done on the same version of *value
 232          * to insure consistency.
 233          */
 234         v = LOAD_SHARED(*value);
 235         return (v & RCU_GP_CTR_NEST_MASK) &&
 236                  ((v ^ rcu_gp_ctr) & RCU_GP_CTR_PHASE);
 237 }
 238
 239 static inline void _rcu_read_lock(void)
 240 {
 241         long tmp;
 242
 243         tmp = rcu_reader.ctr;
 244         /*
 245          * rcu_gp_ctr is
 246          *   RCU_GP_COUNT | (~RCU_GP_CTR_PHASE or RCU_GP_CTR_PHASE)
 247          */
 248         if (likely(!(tmp & RCU_GP_CTR_NEST_MASK))) {
 249                 _STORE_SHARED(rcu_reader.ctr, _LOAD_SHARED(rcu_gp_ctr));
 250                 /*
 251                  * Set active readers count for outermost nesting level before
 252                  * accessing the pointer. See smp_mb_heavy().
 253                  */
 254                 smp_mb_light();
 255         } else {
 256                 _STORE_SHARED(rcu_reader.ctr, tmp + RCU_GP_COUNT);
 257         }
 258 }
 259
 260 static inline void _rcu_read_unlock(void)
 261 {
 262         long tmp;
 263
 264         tmp = rcu_reader.ctr;
 265         /*
 266          * Finish using rcu before decrementing the pointer.
 267          * See smp_mb_heavy().
 268          */
 269         if (likely((tmp & RCU_GP_CTR_NEST_MASK) == RCU_GP_COUNT)) {
 270                 smp_mb_light();
 271                 _STORE_SHARED(rcu_reader.ctr, rcu_reader.ctr - RCU_GP_COUNT);
 272                 /* write rcu_reader.ctr before read futex */
 273                 smp_mb_light();
 274                 wake_up_gp();
 275         } else {
 276                 _STORE_SHARED(rcu_reader.ctr, rcu_reader.ctr - RCU_GP_COUNT);
 277         }
 278 }
 279
 280 #ifdef __cplusplus
 281 }
 282 #endif
 283
 284 #endif /* _URCU_STATIC_H */