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 struct rcu_gp {
 134         /*
 135          * Global grace period counter.
 136          * Contains the current RCU_GP_CTR_PHASE.
 137          * Also has a RCU_GP_COUNT of 1, to accelerate the reader fast path.
 138          * Written to only by writer with mutex taken.
 139          * Read by both writer and readers.
 140          */
 141         unsigned long ctr;
 142 } __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
 143
 144 extern struct rcu_gp rcu_gp;
 145
 146 struct rcu_reader {
 147         /* Data used by both reader and synchronize_rcu() */
 148         unsigned long ctr;
 149         /* Data used for registry */
 150         struct cds_list_head node __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
 151         pthread_t tid;
 152         int alloc;      /* registry entry allocated */
 153 };
 154
 155 /*
 156  * Bulletproof version keeps a pointer to a registry not part of the TLS.
 157  * Adds a pointer dereference on the read-side, but won't require to unregister
 158  * the reader thread.
 159  */
 160 extern DECLARE_URCU_TLS(struct rcu_reader *, rcu_reader);
 161
 162 static inline enum rcu_state rcu_reader_state(unsigned long *ctr)
 163 {
 164         unsigned long v;
 165
 166         if (ctr == NULL)
 167                 return RCU_READER_INACTIVE;
 168         /*
 169          * Make sure both tests below are done on the same version of *value
 170          * to insure consistency.
 171          */
 172         v = CMM_LOAD_SHARED(*ctr);
 173         if (!(v & RCU_GP_CTR_NEST_MASK))
 174                 return RCU_READER_INACTIVE;
 175         if (!((v ^ rcu_gp.ctr) & RCU_GP_CTR_PHASE))
 176                 return RCU_READER_ACTIVE_CURRENT;
 177         return RCU_READER_ACTIVE_OLD;
 178 }
 179
 180 /*
 181  * Helper for _rcu_read_lock().  The format of rcu_gp.ctr (as well as
 182  * the per-thread rcu_reader.ctr) has the upper bits containing a count of
 183  * _rcu_read_lock() nesting, and a lower-order bit that contains either zero
 184  * or RCU_GP_CTR_PHASE.  The smp_mb_slave() ensures that the accesses in
 185  * _rcu_read_lock() happen before the subsequent read-side critical section.
 186  */
 187 static inline void _rcu_read_lock_update(unsigned long tmp)
 188 {
 189         if (caa_likely(!(tmp & RCU_GP_CTR_NEST_MASK))) {
 190                 _CMM_STORE_SHARED(URCU_TLS(rcu_reader)->ctr, _CMM_LOAD_SHARED(rcu_gp.ctr));
 191                 cmm_smp_mb();
 192         } else
 193                 _CMM_STORE_SHARED(URCU_TLS(rcu_reader)->ctr, tmp + RCU_GP_COUNT);
 194 }
 195
 196 /*
 197  * Enter an RCU read-side critical section.
 198  *
 199  * The first cmm_barrier() call ensures that the compiler does not reorder
 200  * the body of _rcu_read_lock() with a mutex.
 201  *
 202  * This function and its helper are both less than 10 lines long.  The
 203  * intent is that this function meets the 10-line criterion in LGPL,
 204  * allowing this function to be invoked directly from non-LGPL code.
 205  */
 206 static inline void _rcu_read_lock(void)
 207 {
 208         unsigned long tmp;
 209
 210         if (caa_unlikely(!URCU_TLS(rcu_reader)))
 211                 rcu_bp_register(); /* If not yet registered. */
 212         cmm_barrier();  /* Ensure the compiler does not reorder us with mutex */
 213         tmp = URCU_TLS(rcu_reader)->ctr;
 214         _rcu_read_lock_update(tmp);
 215 }
 216
 217 /*
 218  * Exit an RCU read-side critical section.  This function is less than
 219  * 10 lines of code, and is intended to be usable by non-LGPL code, as
 220  * called out in LGPL.
 221  */
 222 static inline void _rcu_read_unlock(void)
 223 {
 224         /*
 225          * Finish using rcu before decrementing the pointer.
 226          */
 227         cmm_smp_mb();
 228         _CMM_STORE_SHARED(URCU_TLS(rcu_reader)->ctr, URCU_TLS(rcu_reader)->ctr - RCU_GP_COUNT);
 229         cmm_barrier();  /* Ensure the compiler does not reorder us with mutex */
 230 }
 231
 232 /*
 233  * Returns whether within a RCU read-side critical section.
 234  *
 235  * This function is less than 10 lines long.  The intent is that this
 236  * function meets the 10-line criterion for LGPL, allowing this function
 237  * to be invoked directly from non-LGPL code.
 238  */
 239 static inline int _rcu_read_ongoing(void)
 240 {
 241         if (caa_unlikely(!URCU_TLS(rcu_reader)))
 242                 rcu_bp_register(); /* If not yet registered. */
 243         return URCU_TLS(rcu_reader)->ctr & RCU_GP_CTR_NEST_MASK;
 244 }
 245
 246 #ifdef __cplusplus
 247 }
 248 #endif
 249
 250 #endif /* _URCU_BP_STATIC_H */