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/arch_uatomic.h>
  41 #include <urcu/list.h>
  42
  43 #define futex(...)              syscall(__NR_futex, __VA_ARGS__)
  44 #define FUTEX_WAIT              0
  45 #define FUTEX_WAKE              1
  46
  47 /*
  48  * This code section can only be included in LGPL 2.1 compatible source code.
  49  * See below for the function call wrappers which can be used in code meant to
  50  * be only linked with the Userspace RCU library. This comes with a small
  51  * performance degradation on the read-side due to the added function calls.
  52  * This is required to permit relinking with newer versions of the library.
  53  */
  54
  55 /*
  56  * The signal number used by the RCU library can be overridden with
  57  * -DSIGURCU= when compiling the library.
  58  */
  59 #ifndef SIGURCU
  60 #define SIGURCU SIGUSR1
  61 #endif
  62
  63 /*
  64  * If a reader is really non-cooperative and refuses to commit its
  65  * urcu_active_readers count to memory (there is no barrier in the reader
  66  * per-se), kick it after a few loops waiting for it.
  67  */
  68 #define KICK_READER_LOOPS 10000
  69
  70 /*
  71  * Active attempts to check for reader Q.S. before calling futex().
  72  */
  73 #define RCU_QS_ACTIVE_ATTEMPTS 100
  74
  75 #ifdef DEBUG_RCU
  76 #define rcu_assert(args...)     assert(args)
  77 #else
  78 #define rcu_assert(args...)
  79 #endif
  80
  81 #ifdef DEBUG_YIELD
  82 #include <sched.h>
  83 #include <time.h>
  84 #include <pthread.h>
  85 #include <unistd.h>
  86
  87 #define YIELD_READ      (1 << 0)
  88 #define YIELD_WRITE     (1 << 1)
  89
  90 /*
  91  * Updates without URCU_MB are much slower. Account this in
  92  * the delay.
  93  */
  94 #ifdef URCU_MB
  95 /* maximum sleep delay, in us */
  96 #define MAX_SLEEP 50
  97 #else
  98 #define MAX_SLEEP 30000
  99 #endif
 100
 101 extern unsigned int yield_active;
 102 extern unsigned int __thread rand_yield;
 103
 104 static inline void debug_yield_read(void)
 105 {
 106         if (yield_active & YIELD_READ)
 107                 if (rand_r(&rand_yield) & 0x1)
 108                         usleep(rand_r(&rand_yield) % MAX_SLEEP);
 109 }
 110
 111 static inline void debug_yield_write(void)
 112 {
 113         if (yield_active & YIELD_WRITE)
 114                 if (rand_r(&rand_yield) & 0x1)
 115                         usleep(rand_r(&rand_yield) % MAX_SLEEP);
 116 }
 117
 118 static inline void debug_yield_init(void)
 119 {
 120         rand_yield = time(NULL) ^ pthread_self();
 121 }
 122 #else
 123 static inline void debug_yield_read(void)
 124 {
 125 }
 126
 127 static inline void debug_yield_write(void)
 128 {
 129 }
 130
 131 static inline void debug_yield_init(void)
 132 {
 133
 134 }
 135 #endif
 136
 137 #ifdef URCU_MB
 138 static inline void reader_barrier()
 139 {
 140         smp_mb();
 141 }
 142 #else
 143 static inline void reader_barrier()
 144 {
 145         barrier();
 146 }
 147 #endif
 148
 149 /*
 150  * The trick here is that RCU_GP_CTR_BIT must be a multiple of 8 so we can use a
 151  * full 8-bits, 16-bits or 32-bits bitmask for the lower order bits.
 152  */
 153 #define RCU_GP_COUNT            (1UL << 0)
 154 /* Use the amount of bits equal to half of the architecture long size */
 155 #define RCU_GP_CTR_BIT          (1UL << (sizeof(long) << 2))
 156 #define RCU_GP_CTR_NEST_MASK    (RCU_GP_CTR_BIT - 1)
 157
 158 /*
 159  * Global quiescent period counter with low-order bits unused.
 160  * Using a int rather than a char to eliminate false register dependencies
 161  * causing stalls on some architectures.
 162  */
 163 extern long urcu_gp_ctr;
 164
 165 struct urcu_reader {
 166         /* Data used by both reader and synchronize_rcu() */
 167         long ctr;
 168         char need_mb;
 169         /* Data used for registry */
 170         struct list_head head __attribute__((aligned(CACHE_LINE_SIZE)));
 171         pthread_t tid;
 172 };
 173
 174 extern struct urcu_reader __thread urcu_reader;
 175
 176 extern int gp_futex;
 177
 178 /*
 179  * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
 180  */
 181 static inline void wake_up_gp(void)
 182 {
 183         if (unlikely(uatomic_read(&gp_futex) == -1)) {
 184                 uatomic_set(&gp_futex, 0);
 185                 futex(&gp_futex, FUTEX_WAKE, 1,
 186                       NULL, NULL, 0);
 187         }
 188 }
 189
 190 static inline int rcu_old_gp_ongoing(long *value)
 191 {
 192         long v;
 193
 194         if (value == NULL)
 195                 return 0;
 196         /*
 197          * Make sure both tests below are done on the same version of *value
 198          * to insure consistency.
 199          */
 200         v = LOAD_SHARED(*value);
 201         return (v & RCU_GP_CTR_NEST_MASK) &&
 202                  ((v ^ urcu_gp_ctr) & RCU_GP_CTR_BIT);
 203 }
 204
 205 static inline void _rcu_read_lock(void)
 206 {
 207         long tmp;
 208
 209         tmp = urcu_reader.ctr;
 210         /* urcu_gp_ctr = RCU_GP_COUNT | (~RCU_GP_CTR_BIT or RCU_GP_CTR_BIT) */
 211         if (likely(!(tmp & RCU_GP_CTR_NEST_MASK))) {
 212                 _STORE_SHARED(urcu_reader.ctr, _LOAD_SHARED(urcu_gp_ctr));
 213                 /*
 214                  * Set active readers count for outermost nesting level before
 215                  * accessing the pointer. See force_mb_all_threads().
 216                  */
 217                 reader_barrier();
 218         } else {
 219                 _STORE_SHARED(urcu_reader.ctr, tmp + RCU_GP_COUNT);
 220         }
 221 }
 222
 223 static inline void _rcu_read_unlock(void)
 224 {
 225         long tmp;
 226
 227         tmp = urcu_reader.ctr;
 228         /*
 229          * Finish using rcu before decrementing the pointer.
 230          * See force_mb_all_threads().
 231          */
 232         if (likely((tmp & RCU_GP_CTR_NEST_MASK) == RCU_GP_COUNT)) {
 233                 reader_barrier();
 234                 _STORE_SHARED(urcu_reader.ctr, urcu_reader.ctr - RCU_GP_COUNT);
 235                 /* write urcu_reader.ctr before read futex */
 236                 reader_barrier();
 237                 wake_up_gp();
 238         } else {
 239                 _STORE_SHARED(urcu_reader.ctr, urcu_reader.ctr - RCU_GP_COUNT);
 240         }
 241 }
 242
 243 #endif /* _URCU_STATIC_H */