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 #include <urcu/rand-compat.h>
  45
  46 #ifdef __cplusplus
  47 extern "C" {
  48 #endif
  49
  50 /* Default is RCU_MEMBARRIER */
  51 #if !defined(RCU_MEMBARRIER) && !defined(RCU_MB) && !defined(RCU_SIGNAL)
  52 #define RCU_MEMBARRIER
  53 #endif
  54
  55 /*
  56  * This code section can only be included in LGPL 2.1 compatible source code.
  57  * See below for the function call wrappers which can be used in code meant to
  58  * be only linked with the Userspace RCU library. This comes with a small
  59  * performance degradation on the read-side due to the added function calls.
  60  * This is required to permit relinking with newer versions of the library.
  61  */
  62
  63 /*
  64  * The signal number used by the RCU library can be overridden with
  65  * -DSIGRCU= when compiling the library.
  66  * Provide backward compatibility for liburcu 0.3.x SIGURCU.
  67  */
  68 #ifdef SIGURCU
  69 #define SIGRCU SIGURCU
  70 #endif
  71
  72 #ifndef SIGRCU
  73 #define SIGRCU SIGUSR1
  74 #endif
  75
  76 enum rcu_state {
  77         RCU_READER_ACTIVE_CURRENT,
  78         RCU_READER_ACTIVE_OLD,
  79         RCU_READER_INACTIVE,
  80 };
  81
  82 #ifdef DEBUG_RCU
  83 #define rcu_assert(args...)     assert(args)
  84 #else
  85 #define rcu_assert(args...)
  86 #endif
  87
  88 #ifdef DEBUG_YIELD
  89 #include <sched.h>
  90 #include <time.h>
  91 #include <pthread.h>
  92 #include <unistd.h>
  93
  94 #define RCU_YIELD_READ  (1 << 0)
  95 #define RCU_YIELD_WRITE (1 << 1)
  96
  97 /*
  98  * Updates with RCU_SIGNAL are much slower. Account this in the delay.
  99  */
 100 #ifdef RCU_SIGNAL
 101 /* maximum sleep delay, in us */
 102 #define MAX_SLEEP 30000
 103 #else
 104 #define MAX_SLEEP 50
 105 #endif
 106
 107 extern unsigned int rcu_yield_active;
 108 extern DECLARE_URCU_TLS(unsigned int, rcu_rand_yield);
 109
 110 static inline void rcu_debug_yield_read(void)
 111 {
 112         if (rcu_yield_active & RCU_YIELD_READ)
 113                 if (rand_r(&URCU_TLS(rcu_rand_yield)) & 0x1)
 114                         usleep(rand_r(&URCU_TLS(rcu_rand_yield)) % MAX_SLEEP);
 115 }
 116
 117 static inline void rcu_debug_yield_write(void)
 118 {
 119         if (rcu_yield_active & RCU_YIELD_WRITE)
 120                 if (rand_r(&URCU_TLS(rcu_rand_yield)) & 0x1)
 121                         usleep(rand_r(&URCU_TLS(rcu_rand_yield)) % MAX_SLEEP);
 122 }
 123
 124 static inline void rcu_debug_yield_init(void)
 125 {
 126         URCU_TLS(rcu_rand_yield) = time(NULL) ^ (unsigned long) pthread_self();
 127 }
 128 #else
 129 static inline void rcu_debug_yield_read(void)
 130 {
 131 }
 132
 133 static inline void rcu_debug_yield_write(void)
 134 {
 135 }
 136
 137 static inline void rcu_debug_yield_init(void)
 138 {
 139
 140 }
 141 #endif
 142
 143 /*
 144  * RCU memory barrier broadcast group. Currently, only broadcast to all process
 145  * threads is supported (group 0).
 146  *
 147  * Slave barriers are only guaranteed to be ordered wrt master barriers.
 148  *
 149  * The pair ordering is detailed as (O: ordered, X: not ordered) :
 150  *               slave  master
 151  *        slave    X      O
 152  *        master   O      O
 153  */
 154
 155 #define MB_GROUP_ALL            0
 156 #define RCU_MB_GROUP            MB_GROUP_ALL
 157
 158 #ifdef RCU_MEMBARRIER
 159 extern int rcu_has_sys_membarrier;
 160
 161 static inline void smp_mb_slave(int group)
 162 {
 163         if (caa_likely(rcu_has_sys_membarrier))
 164                 cmm_barrier();
 165         else
 166                 cmm_smp_mb();
 167 }
 168 #endif
 169
 170 #ifdef RCU_MB
 171 static inline void smp_mb_slave(int group)
 172 {
 173         cmm_smp_mb();
 174 }
 175 #endif
 176
 177 #ifdef RCU_SIGNAL
 178 static inline void smp_mb_slave(int group)
 179 {
 180         cmm_barrier();
 181 }
 182 #endif
 183
 184 /*
 185  * The trick here is that RCU_GP_CTR_PHASE must be a multiple of 8 so we can use
 186  * a full 8-bits, 16-bits or 32-bits bitmask for the lower order bits.
 187  */
 188 #define RCU_GP_COUNT            (1UL << 0)
 189 /* Use the amount of bits equal to half of the architecture long size */
 190 #define RCU_GP_CTR_PHASE        (1UL << (sizeof(unsigned long) << 2))
 191 #define RCU_GP_CTR_NEST_MASK    (RCU_GP_CTR_PHASE - 1)
 192
 193 struct rcu_gp {
 194         /*
 195          * Global grace period counter.
 196          * Contains the current RCU_GP_CTR_PHASE.
 197          * Also has a RCU_GP_COUNT of 1, to accelerate the reader fast path.
 198          * Written to only by writer with mutex taken.
 199          * Read by both writer and readers.
 200          */
 201         unsigned long ctr;
 202
 203         int32_t futex;
 204 } __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
 205
 206 extern struct rcu_gp rcu_gp;
 207
 208 struct rcu_reader {
 209         /* Data used by both reader and synchronize_rcu() */
 210         unsigned long ctr;
 211         char need_mb;
 212         /* Data used for registry */
 213         struct cds_list_head node __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
 214         pthread_t tid;
 215 };
 216
 217 extern DECLARE_URCU_TLS(struct rcu_reader, rcu_reader);
 218
 219 /*
 220  * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
 221  */
 222 static inline void wake_up_gp(void)
 223 {
 224         if (caa_unlikely(uatomic_read(&rcu_gp.futex) == -1)) {
 225                 uatomic_set(&rcu_gp.futex, 0);
 226                 futex_async(&rcu_gp.futex, FUTEX_WAKE, 1,
 227                       NULL, NULL, 0);
 228         }
 229 }
 230
 231 static inline enum rcu_state rcu_reader_state(unsigned long *ctr)
 232 {
 233         unsigned long v;
 234
 235         /*
 236          * Make sure both tests below are done on the same version of *value
 237          * to insure consistency.
 238          */
 239         v = CMM_LOAD_SHARED(*ctr);
 240         if (!(v & RCU_GP_CTR_NEST_MASK))
 241                 return RCU_READER_INACTIVE;
 242         if (!((v ^ rcu_gp.ctr) & RCU_GP_CTR_PHASE))
 243                 return RCU_READER_ACTIVE_CURRENT;
 244         return RCU_READER_ACTIVE_OLD;
 245 }
 246
 247 /*
 248  * Helper for _rcu_read_lock().  The format of rcu_gp.ctr (as well as
 249  * the per-thread rcu_reader.ctr) has the upper bits containing a count of
 250  * _rcu_read_lock() nesting, and a lower-order bit that contains either zero
 251  * or RCU_GP_CTR_PHASE.  The smp_mb_slave() ensures that the accesses in
 252  * _rcu_read_lock() happen before the subsequent read-side critical section.
 253  */
 254 static inline void _rcu_read_lock_update(unsigned long tmp)
 255 {
 256         if (caa_likely(!(tmp & RCU_GP_CTR_NEST_MASK))) {
 257                 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, _CMM_LOAD_SHARED(rcu_gp.ctr));
 258                 smp_mb_slave(RCU_MB_GROUP);
 259         } else
 260                 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, tmp + RCU_GP_COUNT);
 261 }
 262
 263 /*
 264  * Enter an RCU read-side critical section.
 265  *
 266  * The first cmm_barrier() call ensures that the compiler does not reorder
 267  * the body of _rcu_read_lock() with a mutex.
 268  *
 269  * This function and its helper are both less than 10 lines long.  The
 270  * intent is that this function meets the 10-line criterion in LGPL,
 271  * allowing this function to be invoked directly from non-LGPL code.
 272  */
 273 static inline void _rcu_read_lock(void)
 274 {
 275         unsigned long tmp;
 276
 277         cmm_barrier();
 278         tmp = URCU_TLS(rcu_reader).ctr;
 279         _rcu_read_lock_update(tmp);
 280 }
 281
 282 /*
 283  * This is a helper function for _rcu_read_unlock().
 284  *
 285  * The first smp_mb_slave() call ensures that the critical section is
 286  * seen to precede the store to rcu_reader.ctr.
 287  * The second smp_mb_slave() call ensures that we write to rcu_reader.ctr
 288  * before reading the update-side futex.
 289  */
 290 static inline void _rcu_read_unlock_update_and_wakeup(unsigned long tmp)
 291 {
 292         if (caa_likely((tmp & RCU_GP_CTR_NEST_MASK) == RCU_GP_COUNT)) {
 293                 smp_mb_slave(RCU_MB_GROUP);
 294                 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, URCU_TLS(rcu_reader).ctr - RCU_GP_COUNT);
 295                 smp_mb_slave(RCU_MB_GROUP);
 296                 wake_up_gp();
 297         } else
 298                 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, URCU_TLS(rcu_reader).ctr - RCU_GP_COUNT);
 299 }
 300
 301 /*
 302  * Exit an RCU read-side crtical section.  Both this function and its
 303  * helper are smaller than 10 lines of code, and are intended to be
 304  * usable by non-LGPL code, as called out in LGPL.
 305  */
 306 static inline void _rcu_read_unlock(void)
 307 {
 308         unsigned long tmp;
 309
 310         tmp = URCU_TLS(rcu_reader).ctr;
 311         _rcu_read_unlock_update_and_wakeup(tmp);
 312         cmm_barrier();  /* Ensure the compiler does not reorder us with mutex */
 313 }
 314
 315 /*
 316  * Returns whether within a RCU read-side critical section.
 317  *
 318  * This function is less than 10 lines long.  The intent is that this
 319  * function meets the 10-line criterion for LGPL, allowing this function
 320  * to be invoked directly from non-LGPL code.
 321  */
 322 static inline int _rcu_read_ongoing(void)
 323 {
 324         return URCU_TLS(rcu_reader).ctr & RCU_GP_CTR_NEST_MASK;
 325 }
 326
 327 #ifdef __cplusplus
 328 }
 329 #endif
 330
 331 #endif /* _URCU_STATIC_H */