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