urcu/static/urcu.h

   1 #ifndef _URCU_STATIC_H
   2 #define _URCU_STATIC_H
   3
   4 /*
   5  * urcu-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 #include <stdint.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 #include <urcu/futex.h>
  43 #include <urcu/tls-compat.h>
  44
  45 #ifdef __cplusplus
  46 extern "C" {
  47 #endif
  48
  49 /* Default is RCU_MEMBARRIER */
  50 #if !defined(RCU_MEMBARRIER) && !defined(RCU_MB) && !defined(RCU_SIGNAL)
  51 #define RCU_MEMBARRIER
  52 #endif
  53
  54 /*
  55  * RCU_MEMBARRIER is only possibly available on Linux. Fallback to RCU_MB
  56  * otherwise.
  57  */
  58 #if !defined(__linux__) && defined(RCU_MEMBARRIER)
  59 #undef RCU_MEMBARRIER
  60 #define RCU_MB
  61 #endif
  62
  63 /*
  64  * The ABI of sys_membarrier changed after its original implementation.
  65  * Disable it for now. Use RCU_MB flavor instead.
  66  */
  67 #ifdef RCU_MEMBARRIER
  68 #undef RCU_MEMBARRIER
  69 #define RCU_MB
  70 #endif
  71
  72 /*
  73  * This code section can only be included in LGPL 2.1 compatible source code.
  74  * See below for the function call wrappers which can be used in code meant to
  75  * be only linked with the Userspace RCU library. This comes with a small
  76  * performance degradation on the read-side due to the added function calls.
  77  * This is required to permit relinking with newer versions of the library.
  78  */
  79
  80 /*
  81  * The signal number used by the RCU library can be overridden with
  82  * -DSIGRCU= when compiling the library.
  83  * Provide backward compatibility for liburcu 0.3.x SIGURCU.
  84  */
  85 #ifdef SIGURCU
  86 #define SIGRCU SIGURCU
  87 #endif
  88
  89 #ifndef SIGRCU
  90 #define SIGRCU SIGUSR1
  91 #endif
  92
  93 #ifdef DEBUG_RCU
  94 #define rcu_assert(args...)     assert(args)
  95 #else
  96 #define rcu_assert(args...)
  97 #endif
  98
  99 #ifdef DEBUG_YIELD
 100 #include <sched.h>
 101 #include <time.h>
 102 #include <pthread.h>
 103 #include <unistd.h>
 104
 105 #define YIELD_READ      (1 << 0)
 106 #define YIELD_WRITE     (1 << 1)
 107
 108 /*
 109  * Updates with RCU_SIGNAL are much slower. Account this in the delay.
 110  */
 111 #ifdef RCU_SIGNAL
 112 /* maximum sleep delay, in us */
 113 #define MAX_SLEEP 30000
 114 #else
 115 #define MAX_SLEEP 50
 116 #endif
 117
 118 extern unsigned int yield_active;
 119 extern DECLARE_URCU_TLS(unsigned int, rand_yield);
 120
 121 static inline void debug_yield_read(void)
 122 {
 123         if (yield_active & YIELD_READ)
 124                 if (rand_r(&URCU_TLS(rand_yield)) & 0x1)
 125                         usleep(rand_r(&URCU_TLS(rand_yield)) % MAX_SLEEP);
 126 }
 127
 128 static inline void debug_yield_write(void)
 129 {
 130         if (yield_active & YIELD_WRITE)
 131                 if (rand_r(&URCU_TLS(rand_yield)) & 0x1)
 132                         usleep(rand_r(&URCU_TLS(rand_yield)) % MAX_SLEEP);
 133 }
 134
 135 static inline void debug_yield_init(void)
 136 {
 137         URCU_TLS(rand_yield) = time(NULL) ^ (unsigned long) pthread_self();
 138 }
 139 #else
 140 static inline void debug_yield_read(void)
 141 {
 142 }
 143
 144 static inline void debug_yield_write(void)
 145 {
 146 }
 147
 148 static inline void debug_yield_init(void)
 149 {
 150
 151 }
 152 #endif
 153
 154 /*
 155  * RCU memory barrier broadcast group. Currently, only broadcast to all process
 156  * threads is supported (group 0).
 157  *
 158  * Slave barriers are only guaranteed to be ordered wrt master barriers.
 159  *
 160  * The pair ordering is detailed as (O: ordered, X: not ordered) :
 161  *               slave  master
 162  *        slave    X      O
 163  *        master   O      O
 164  */
 165
 166 #define MB_GROUP_ALL            0
 167 #define RCU_MB_GROUP            MB_GROUP_ALL
 168
 169 #ifdef RCU_MEMBARRIER
 170 extern int has_sys_membarrier;
 171
 172 static inline void smp_mb_slave(int group)
 173 {
 174         if (caa_likely(has_sys_membarrier))
 175                 cmm_barrier();
 176         else
 177                 cmm_smp_mb();
 178 }
 179 #endif
 180
 181 #ifdef RCU_MB
 182 static inline void smp_mb_slave(int group)
 183 {
 184         cmm_smp_mb();
 185 }
 186 #endif
 187
 188 #ifdef RCU_SIGNAL
 189 static inline void smp_mb_slave(int group)
 190 {
 191         cmm_barrier();
 192 }
 193 #endif
 194
 195 /*
 196  * The trick here is that RCU_GP_CTR_PHASE must be a multiple of 8 so we can use
 197  * a full 8-bits, 16-bits or 32-bits bitmask for the lower order bits.
 198  */
 199 #define RCU_GP_COUNT            (1UL << 0)
 200 /* Use the amount of bits equal to half of the architecture long size */
 201 #define RCU_GP_CTR_PHASE        (1UL << (sizeof(unsigned long) << 2))
 202 #define RCU_GP_CTR_NEST_MASK    (RCU_GP_CTR_PHASE - 1)
 203
 204 /*
 205  * Global quiescent period counter with low-order bits unused.
 206  * Using a int rather than a char to eliminate false register dependencies
 207  * causing stalls on some architectures.
 208  */
 209 extern unsigned long rcu_gp_ctr;
 210
 211 struct rcu_reader {
 212         /* Data used by both reader and synchronize_rcu() */
 213         unsigned long ctr;
 214         char need_mb;
 215         /* Data used for registry */
 216         struct cds_list_head node __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
 217         pthread_t tid;
 218 };
 219
 220 extern DECLARE_URCU_TLS(struct rcu_reader, rcu_reader);
 221
 222 extern int32_t gp_futex;
 223
 224 /*
 225  * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
 226  */
 227 static inline void wake_up_gp(void)
 228 {
 229         if (caa_unlikely(uatomic_read(&gp_futex) == -1)) {
 230                 uatomic_set(&gp_futex, 0);
 231                 /*
 232                  * Ignoring return value until we can make this function
 233                  * return something (because urcu_die() is not publicly
 234                  * exposed).
 235                  */
 236                 (void) futex_async(&gp_futex, FUTEX_WAKE, 1,
 237                                 NULL, NULL, 0);
 238         }
 239 }
 240
 241 static inline int rcu_gp_ongoing(unsigned long *ctr)
 242 {
 243         unsigned long v;
 244
 245         /*
 246          * Make sure both tests below are done on the same version of *value
 247          * to insure consistency.
 248          */
 249         v = CMM_LOAD_SHARED(*ctr);
 250         return (v & RCU_GP_CTR_NEST_MASK) &&
 251                  ((v ^ rcu_gp_ctr) & RCU_GP_CTR_PHASE);
 252 }
 253
 254 /*
 255  * Helper for _rcu_read_lock().  The format of rcu_gp_ctr (as well as
 256  * the per-thread rcu_reader.ctr) has the upper bits containing a count of
 257  * _rcu_read_lock() nesting, and a lower-order bit that contains either zero
 258  * or RCU_GP_CTR_PHASE.  The smp_mb_slave() ensures that the accesses in
 259  * _rcu_read_lock() happen before the subsequent read-side critical section.
 260  */
 261 static inline void _rcu_read_lock_update(unsigned long tmp)
 262 {
 263         if (caa_likely(!(tmp & RCU_GP_CTR_NEST_MASK))) {
 264                 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, _CMM_LOAD_SHARED(rcu_gp_ctr));
 265                 smp_mb_slave(RCU_MB_GROUP);
 266         } else
 267                 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, tmp + RCU_GP_COUNT);
 268 }
 269
 270 /*
 271  * Enter an RCU read-side critical section.
 272  *
 273  * The first cmm_barrier() call ensures that the compiler does not reorder
 274  * the body of _rcu_read_lock() with a mutex.
 275  *
 276  * This function and its helper are both less than 10 lines long.  The
 277  * intent is that this function meets the 10-line criterion in LGPL,
 278  * allowing this function to be invoked directly from non-LGPL code.
 279  */
 280 static inline void _rcu_read_lock(void)
 281 {
 282         unsigned long tmp;
 283
 284         cmm_barrier();
 285         tmp = URCU_TLS(rcu_reader).ctr;
 286         _rcu_read_lock_update(tmp);
 287 }
 288
 289 /*
 290  * This is a helper function for _rcu_read_unlock().
 291  *
 292  * The first smp_mb_slave() call ensures that the critical section is
 293  * seen to precede the store to rcu_reader.ctr.
 294  * The second smp_mb_slave() call ensures that we write to rcu_reader.ctr
 295  * before reading the update-side futex.
 296  */
 297 static inline void _rcu_read_unlock_update_and_wakeup(unsigned long tmp)
 298 {
 299         if (caa_likely((tmp & RCU_GP_CTR_NEST_MASK) == RCU_GP_COUNT)) {
 300                 smp_mb_slave(RCU_MB_GROUP);
 301                 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, URCU_TLS(rcu_reader).ctr - RCU_GP_COUNT);
 302                 smp_mb_slave(RCU_MB_GROUP);
 303                 wake_up_gp();
 304         } else
 305                 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, URCU_TLS(rcu_reader).ctr - RCU_GP_COUNT);
 306 }
 307
 308 /*
 309  * Exit an RCU read-side crtical section.  Both this function and its
 310  * helper are smaller than 10 lines of code, and are intended to be
 311  * usable by non-LGPL code, as called out in LGPL.
 312  */
 313 static inline void _rcu_read_unlock(void)
 314 {
 315         unsigned long tmp;
 316
 317         tmp = URCU_TLS(rcu_reader).ctr;
 318         _rcu_read_unlock_update_and_wakeup(tmp);
 319         cmm_barrier();  /* Ensure the compiler does not reorder us with mutex */
 320 }
 321
 322 #ifdef __cplusplus
 323 }
 324 #endif
 325
 326 #endif /* _URCU_STATIC_H */