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