urcu/static/urcu-bp.h

   1 #ifndef _URCU_BP_STATIC_H
   2 #define _URCU_BP_STATIC_H
   3
   4 /*
   5  * urcu-bp-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@efficios.com>
  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.h>
  41 #include <urcu/list.h>
  42
  43 /*
  44  * This code section can only be included in LGPL 2.1 compatible source code.
  45  * See below for the function call wrappers which can be used in code meant to
  46  * be only linked with the Userspace RCU library. This comes with a small
  47  * performance degradation on the read-side due to the added function calls.
  48  * This is required to permit relinking with newer versions of the library.
  49  */
  50
  51 #ifdef __cplusplus
  52 extern "C" {
  53 #endif
  54
  55 /*
  56  * Active attempts to check for reader Q.S. before calling sleep().
  57  */
  58 #define RCU_QS_ACTIVE_ATTEMPTS 100
  59
  60 #ifdef DEBUG_RCU
  61 #define rcu_assert(args...)     assert(args)
  62 #else
  63 #define rcu_assert(args...)
  64 #endif
  65
  66 #ifdef DEBUG_YIELD
  67 #include <sched.h>
  68 #include <time.h>
  69 #include <pthread.h>
  70 #include <unistd.h>
  71
  72 #define YIELD_READ      (1 << 0)
  73 #define YIELD_WRITE     (1 << 1)
  74
  75 /*
  76  * Updates without RCU_MB are much slower. Account this in
  77  * the delay.
  78  */
  79 /* maximum sleep delay, in us */
  80 #define MAX_SLEEP 50
  81
  82 extern unsigned int yield_active;
  83 extern unsigned int __thread rand_yield;
  84
  85 static inline void debug_yield_read(void)
  86 {
  87         if (yield_active & YIELD_READ)
  88                 if (rand_r(&rand_yield) & 0x1)
  89                         usleep(rand_r(&rand_yield) % MAX_SLEEP);
  90 }
  91
  92 static inline void debug_yield_write(void)
  93 {
  94         if (yield_active & YIELD_WRITE)
  95                 if (rand_r(&rand_yield) & 0x1)
  96                         usleep(rand_r(&rand_yield) % MAX_SLEEP);
  97 }
  98
  99 static inline void debug_yield_init(void)
 100 {
 101         rand_yield = time(NULL) ^ pthread_self();
 102 }
 103 #else
 104 static inline void debug_yield_read(void)
 105 {
 106 }
 107
 108 static inline void debug_yield_write(void)
 109 {
 110 }
 111
 112 static inline void debug_yield_init(void)
 113 {
 114
 115 }
 116 #endif
 117
 118 /*
 119  * The trick here is that RCU_GP_CTR_PHASE must be a multiple of 8 so we can use a
 120  * full 8-bits, 16-bits or 32-bits bitmask for the lower order bits.
 121  */
 122 #define RCU_GP_COUNT            (1UL << 0)
 123 /* Use the amount of bits equal to half of the architecture long size */
 124 #define RCU_GP_CTR_PHASE                (1UL << (sizeof(long) << 2))
 125 #define RCU_GP_CTR_NEST_MASK    (RCU_GP_CTR_PHASE - 1)
 126
 127 /*
 128  * Used internally by _rcu_read_lock.
 129  */
 130 extern void rcu_bp_register(void);
 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 long rcu_gp_ctr;
 138
 139 struct rcu_reader {
 140         /* Data used by both reader and synchronize_rcu() */
 141         long ctr;
 142         /* Data used for registry */
 143         struct cds_list_head node __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
 144         pthread_t tid;
 145         int alloc;      /* registry entry allocated */
 146 };
 147
 148 /*
 149  * Bulletproof version keeps a pointer to a registry not part of the TLS.
 150  * Adds a pointer dereference on the read-side, but won't require to unregister
 151  * the reader thread.
 152  */
 153 extern struct rcu_reader __thread *rcu_reader;
 154
 155 static inline int rcu_old_gp_ongoing(long *value)
 156 {
 157         long v;
 158
 159         if (value == NULL)
 160                 return 0;
 161         /*
 162          * Make sure both tests below are done on the same version of *value
 163          * to insure consistency.
 164          */
 165         v = CMM_LOAD_SHARED(*value);
 166         return (v & RCU_GP_CTR_NEST_MASK) &&
 167                  ((v ^ rcu_gp_ctr) & RCU_GP_CTR_PHASE);
 168 }
 169
 170 static inline void _rcu_read_lock(void)
 171 {
 172         long tmp;
 173
 174         /* Check if registered */
 175         if (unlikely(!rcu_reader))
 176                 rcu_bp_register();
 177
 178         cmm_barrier();  /* Ensure the compiler does not reorder us with mutex */
 179         tmp = rcu_reader->ctr;
 180         /*
 181          * rcu_gp_ctr is
 182          *   RCU_GP_COUNT | (~RCU_GP_CTR_PHASE or RCU_GP_CTR_PHASE)
 183          */
 184         if (likely(!(tmp & RCU_GP_CTR_NEST_MASK))) {
 185                 _CMM_STORE_SHARED(rcu_reader->ctr, _CMM_LOAD_SHARED(rcu_gp_ctr));
 186                 /*
 187                  * Set active readers count for outermost nesting level before
 188                  * accessing the pointer.
 189                  */
 190                 cmm_smp_mb();
 191         } else {
 192                 _CMM_STORE_SHARED(rcu_reader->ctr, tmp + RCU_GP_COUNT);
 193         }
 194 }
 195
 196 static inline void _rcu_read_unlock(void)
 197 {
 198         /*
 199          * Finish using rcu before decrementing the pointer.
 200          */
 201         cmm_smp_mb();
 202         _CMM_STORE_SHARED(rcu_reader->ctr, rcu_reader->ctr - RCU_GP_COUNT);
 203         cmm_barrier();  /* Ensure the compiler does not reorder us with mutex */
 204 }
 205
 206 #ifdef __cplusplus
 207 }
 208 #endif
 209
 210 #endif /* _URCU_BP_STATIC_H */