urcu-qsbr-static.h

   1 #ifndef _URCU_QSBR_STATIC_H
   2 #define _URCU_QSBR_STATIC_H
   3
   4 /*
   5  * urcu-qsbr-static.h
   6  *
   7  * Userspace RCU QSBR header.
   8  *
   9  * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu-qsbr.h for linking
  10  * dynamically with the userspace rcu QSBR 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 #include <limits.h>
  36 #include <syscall.h>
  37 #include <unistd.h>
  38
  39 #include <urcu/compiler.h>
  40 #include <urcu/arch.h>
  41 #include <urcu/system.h>
  42 #include <urcu/uatomic_arch.h>
  43 #include <urcu/list.h>
  44 #include <urcu/urcu-futex.h>
  45
  46 #ifdef __cplusplus
  47 extern "C" {
  48 #endif
  49
  50 /*
  51  * This code section can only be included in LGPL 2.1 compatible source code.
  52  * See below for the function call wrappers which can be used in code meant to
  53  * be only linked with the Userspace RCU library. This comes with a small
  54  * performance degradation on the read-side due to the added function calls.
  55  * This is required to permit relinking with newer versions of the library.
  56  */
  57
  58 /*
  59  * If a reader is really non-cooperative and refuses to commit its
  60  * urcu_reader.ctr count to memory (there is no barrier in the reader
  61  * per-se), kick it after a few loops waiting for it.
  62  */
  63 #define KICK_READER_LOOPS 10000
  64
  65 /*
  66  * Active attempts to check for reader Q.S. before calling futex().
  67  */
  68 #define RCU_QS_ACTIVE_ATTEMPTS 100
  69
  70 #ifdef DEBUG_RCU
  71 #define rcu_assert(args...)     assert(args)
  72 #else
  73 #define rcu_assert(args...)
  74 #endif
  75
  76 #ifdef DEBUG_YIELD
  77 #include <sched.h>
  78 #include <time.h>
  79 #include <pthread.h>
  80 #include <unistd.h>
  81
  82 #define YIELD_READ      (1 << 0)
  83 #define YIELD_WRITE     (1 << 1)
  84
  85 /* maximum sleep delay, in us */
  86 #define MAX_SLEEP 50
  87
  88 extern unsigned int yield_active;
  89 extern unsigned int __thread rand_yield;
  90
  91 static inline void debug_yield_read(void)
  92 {
  93         if (yield_active & YIELD_READ)
  94                 if (rand_r(&rand_yield) & 0x1)
  95                         usleep(rand_r(&rand_yield) % MAX_SLEEP);
  96 }
  97
  98 static inline void debug_yield_write(void)
  99 {
 100         if (yield_active & YIELD_WRITE)
 101                 if (rand_r(&rand_yield) & 0x1)
 102                         usleep(rand_r(&rand_yield) % MAX_SLEEP);
 103 }
 104
 105 static inline void debug_yield_init(void)
 106 {
 107         rand_yield = time(NULL) ^ pthread_self();
 108 }
 109 #else
 110 static inline void debug_yield_read(void)
 111 {
 112 }
 113
 114 static inline void debug_yield_write(void)
 115 {
 116 }
 117
 118 static inline void debug_yield_init(void)
 119 {
 120
 121 }
 122 #endif
 123
 124 static inline void reader_barrier()
 125 {
 126         smp_mb();
 127 }
 128
 129 #define RCU_GP_ONLINE           (1UL << 0)
 130 #define RCU_GP_CTR              (1UL << 1)
 131
 132 /*
 133  * Global quiescent period counter with low-order bits unused.
 134  * Using a int rather than a char to eliminate false register dependencies
 135  * causing stalls on some architectures.
 136  */
 137 extern unsigned long urcu_gp_ctr;
 138
 139 struct urcu_reader {
 140         /* Data used by both reader and synchronize_rcu() */
 141         unsigned long ctr;
 142         /* Data used for registry */
 143         struct list_head head __attribute__((aligned(CACHE_LINE_SIZE)));
 144         pthread_t tid;
 145 };
 146
 147 extern struct urcu_reader __thread urcu_reader;
 148
 149 extern int gp_futex;
 150
 151 /*
 152  * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
 153  */
 154 static inline void wake_up_gp(void)
 155 {
 156         if (unlikely(uatomic_read(&gp_futex) == -1)) {
 157                 uatomic_set(&gp_futex, 0);
 158                 futex_noasync(&gp_futex, FUTEX_WAKE, 1,
 159                       NULL, NULL, 0);
 160         }
 161 }
 162
 163 #if (BITS_PER_LONG < 64)
 164 static inline int rcu_gp_ongoing(unsigned long *value)
 165 {
 166         unsigned long reader_gp;
 167
 168         if (value == NULL)
 169                 return 0;
 170         reader_gp = LOAD_SHARED(*value);
 171         return reader_gp && ((reader_gp ^ urcu_gp_ctr) & RCU_GP_CTR);
 172 }
 173 #else /* !(BITS_PER_LONG < 64) */
 174 static inline int rcu_gp_ongoing(unsigned long *value)
 175 {
 176         unsigned long reader_gp;
 177
 178         if (value == NULL)
 179                 return 0;
 180         reader_gp = LOAD_SHARED(*value);
 181         return reader_gp && (reader_gp - urcu_gp_ctr > ULONG_MAX / 2);
 182 }
 183 #endif  /* !(BITS_PER_LONG < 64) */
 184
 185 static inline void _rcu_read_lock(void)
 186 {
 187         rcu_assert(urcu_reader.ctr);
 188 }
 189
 190 static inline void _rcu_read_unlock(void)
 191 {
 192 }
 193
 194 static inline void _rcu_quiescent_state(void)
 195 {
 196         smp_mb();
 197         _STORE_SHARED(urcu_reader.ctr, _LOAD_SHARED(urcu_gp_ctr));
 198         smp_mb();       /* write urcu_reader.ctr before read futex */
 199         wake_up_gp();
 200         smp_mb();
 201 }
 202
 203 static inline void _rcu_thread_offline(void)
 204 {
 205         smp_mb();
 206         STORE_SHARED(urcu_reader.ctr, 0);
 207         smp_mb();       /* write urcu_reader.ctr before read futex */
 208         wake_up_gp();
 209 }
 210
 211 static inline void _rcu_thread_online(void)
 212 {
 213         _STORE_SHARED(urcu_reader.ctr, LOAD_SHARED(urcu_gp_ctr));
 214         smp_mb();
 215 }
 216
 217 #ifdef __cplusplus
 218 }
 219 #endif
 220
 221 #endif /* _URCU_QSBR_STATIC_H */