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 CODE THAT IS TO BE RECOMPILED ON EACH LIBURCU
  10  * RELEASE. See urcu.h for linking 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 <unistd.h>
  35
  36 #include <urcu/compiler.h>
  37 #include <urcu/arch.h>
  38 #include <urcu/system.h>
  39 #include <urcu/uatomic.h>
  40 #include <urcu/list.h>
  41 #include <urcu/tls-compat.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 #ifdef DEBUG_RCU
  56 #define rcu_assert(args...)     assert(args)
  57 #else
  58 #define rcu_assert(args...)
  59 #endif
  60
  61 enum rcu_state {
  62         RCU_READER_ACTIVE_CURRENT,
  63         RCU_READER_ACTIVE_OLD,
  64         RCU_READER_INACTIVE,
  65 };
  66
  67 #ifdef DEBUG_YIELD
  68 #include <sched.h>
  69 #include <time.h>
  70 #include <pthread.h>
  71 #include <unistd.h>
  72
  73 #define RCU_YIELD_READ  (1 << 0)
  74 #define RCU_YIELD_WRITE (1 << 1)
  75
  76 /*
  77  * Updates without RCU_MB are much slower. Account this in
  78  * the delay.
  79  */
  80 /* maximum sleep delay, in us */
  81 #define MAX_SLEEP 50
  82
  83 extern unsigned int rcu_yield_active;
  84 extern DECLARE_URCU_TLS(unsigned int, rcu_rand_yield);
  85
  86 static inline void rcu_debug_yield_read(void)
  87 {
  88         if (rcu_yield_active & RCU_YIELD_READ)
  89                 if (rand_r(&URCU_TLS(rcu_rand_yield)) & 0x1)
  90                         usleep(rand_r(&URCU_TLS(rcu_rand_yield)) % MAX_SLEEP);
  91 }
  92
  93 static inline void rcu_debug_yield_write(void)
  94 {
  95         if (rcu_yield_active & RCU_YIELD_WRITE)
  96                 if (rand_r(&URCU_TLS(rcu_rand_yield)) & 0x1)
  97                         usleep(rand_r(&URCU_TLS(rcu_rand_yield)) % MAX_SLEEP);
  98 }
  99
 100 static inline void rcu_debug_yield_init(void)
 101 {
 102         URCU_TLS(rcu_rand_yield) = time(NULL) ^ (unsigned long) pthread_self();
 103 }
 104 #else
 105 static inline void rcu_debug_yield_read(void)
 106 {
 107 }
 108
 109 static inline void rcu_debug_yield_write(void)
 110 {
 111 }
 112
 113 static inline void rcu_debug_yield_init(void)
 114 {
 115
 116 }
 117 #endif
 118
 119 /*
 120  * The trick here is that RCU_GP_CTR_PHASE must be a multiple of 8 so we can use a
 121  * full 8-bits, 16-bits or 32-bits bitmask for the lower order bits.
 122  */
 123 #define RCU_GP_COUNT            (1UL << 0)
 124 /* Use the amount of bits equal to half of the architecture long size */
 125 #define RCU_GP_CTR_PHASE                (1UL << (sizeof(long) << 2))
 126 #define RCU_GP_CTR_NEST_MASK    (RCU_GP_CTR_PHASE - 1)
 127
 128 /*
 129  * Used internally by _rcu_read_lock.
 130  */
 131 extern void rcu_bp_register(void);
 132
 133 /*
 134  * Global quiescent period counter with low-order bits unused.
 135  * Using a int rather than a char to eliminate false register dependencies
 136  * causing stalls on some architectures.
 137  */
 138 extern unsigned long rcu_gp_ctr;
 139
 140 struct rcu_reader {
 141         /* Data used by both reader and synchronize_rcu() */
 142         unsigned long ctr;
 143         /* Data used for registry */
 144         struct cds_list_head node __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
 145         pthread_t tid;
 146         int alloc;      /* registry entry allocated */
 147 };
 148
 149 /*
 150  * Bulletproof version keeps a pointer to a registry not part of the TLS.
 151  * Adds a pointer dereference on the read-side, but won't require to unregister
 152  * the reader thread.
 153  */
 154 extern DECLARE_URCU_TLS(struct rcu_reader *, rcu_reader);
 155
 156 static inline enum rcu_state rcu_reader_state(unsigned long *ctr)
 157 {
 158         unsigned long v;
 159
 160         if (ctr == NULL)
 161                 return RCU_READER_INACTIVE;
 162         /*
 163          * Make sure both tests below are done on the same version of *value
 164          * to insure consistency.
 165          */
 166         v = CMM_LOAD_SHARED(*ctr);
 167         if (!(v & RCU_GP_CTR_NEST_MASK))
 168                 return RCU_READER_INACTIVE;
 169         if (!((v ^ rcu_gp_ctr) & RCU_GP_CTR_PHASE))
 170                 return RCU_READER_ACTIVE_CURRENT;
 171         return RCU_READER_ACTIVE_OLD;
 172 }
 173
 174 /*
 175  * Helper for _rcu_read_lock().  The format of rcu_gp_ctr (as well as
 176  * the per-thread rcu_reader.ctr) has the upper bits containing a count of
 177  * _rcu_read_lock() nesting, and a lower-order bit that contains either zero
 178  * or RCU_GP_CTR_PHASE.  The smp_mb_slave() ensures that the accesses in
 179  * _rcu_read_lock() happen before the subsequent read-side critical section.
 180  */
 181 static inline void _rcu_read_lock_update(unsigned long tmp)
 182 {
 183         if (caa_likely(!(tmp & RCU_GP_CTR_NEST_MASK))) {
 184                 _CMM_STORE_SHARED(URCU_TLS(rcu_reader)->ctr, _CMM_LOAD_SHARED(rcu_gp_ctr));
 185                 cmm_smp_mb();
 186         } else
 187                 _CMM_STORE_SHARED(URCU_TLS(rcu_reader)->ctr, tmp + RCU_GP_COUNT);
 188 }
 189
 190 /*
 191  * Enter an RCU read-side critical section.
 192  *
 193  * The first cmm_barrier() call ensures that the compiler does not reorder
 194  * the body of _rcu_read_lock() with a mutex.
 195  *
 196  * This function and its helper are both less than 10 lines long.  The
 197  * intent is that this function meets the 10-line criterion in LGPL,
 198  * allowing this function to be invoked directly from non-LGPL code.
 199  */
 200 static inline void _rcu_read_lock(void)
 201 {
 202         unsigned long tmp;
 203
 204         if (caa_unlikely(!URCU_TLS(rcu_reader)))
 205                 rcu_bp_register(); /* If not yet registered. */
 206         cmm_barrier();  /* Ensure the compiler does not reorder us with mutex */
 207         tmp = URCU_TLS(rcu_reader)->ctr;
 208         _rcu_read_lock_update(tmp);
 209 }
 210
 211 /*
 212  * Exit an RCU read-side critical section.  This function is less than
 213  * 10 lines of code, and is intended to be usable by non-LGPL code, as
 214  * called out in LGPL.
 215  */
 216 static inline void _rcu_read_unlock(void)
 217 {
 218         /*
 219          * Finish using rcu before decrementing the pointer.
 220          */
 221         cmm_smp_mb();
 222         _CMM_STORE_SHARED(URCU_TLS(rcu_reader)->ctr, URCU_TLS(rcu_reader)->ctr - RCU_GP_COUNT);
 223         cmm_barrier();  /* Ensure the compiler does not reorder us with mutex */
 224 }
 225
 226 /*
 227  * Returns whether within a RCU read-side critical section.
 228  *
 229  * This function is less than 10 lines long.  The intent is that this
 230  * function meets the 10-line criterion for LGPL, allowing this function
 231  * to be invoked directly from non-LGPL code.
 232  */
 233 static inline int _rcu_read_ongoing(void)
 234 {
 235         if (caa_unlikely(!URCU_TLS(rcu_reader)))
 236                 rcu_bp_register(); /* If not yet registered. */
 237         return URCU_TLS(rcu_reader)->ctr & RCU_GP_CTR_NEST_MASK;
 238 }
 239
 240 #ifdef __cplusplus
 241 }
 242 #endif
 243
 244 #endif /* _URCU_BP_STATIC_H */