urcu/static/urcu-qsbr.h

   1 #ifndef _URCU_QSBR_STATIC_H
   2 #define _URCU_QSBR_STATIC_H
   3
   4 /*
   5  * urcu-qsbr-static.h
   6  *
   7  * Userspace RCU QSBR 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 <assert.h>
  35 #include <limits.h>
  36 #include <unistd.h>
  37 #include <stdint.h>
  38
  39 #include <urcu/compiler.h>
  40 #include <urcu/arch.h>
  41 #include <urcu/system.h>
  42 #include <urcu/uatomic.h>
  43 #include <urcu/list.h>
  44 #include <urcu/futex.h>
  45 #include <urcu/tls-compat.h>
  46
  47 #ifdef __cplusplus
  48 extern "C" {
  49 #endif
  50
  51 /*
  52  * This code section can only be included in LGPL 2.1 compatible source code.
  53  * See below for the function call wrappers which can be used in code meant to
  54  * be only linked with the Userspace RCU library. This comes with a small
  55  * performance degradation on the read-side due to the added function calls.
  56  * This is required to permit relinking with newer versions of the library.
  57  */
  58
  59 #ifdef DEBUG_RCU
  60 #define rcu_assert(args...)     assert(args)
  61 #else
  62 #define rcu_assert(args...)
  63 #endif
  64
  65 #ifdef DEBUG_YIELD
  66 #include <sched.h>
  67 #include <time.h>
  68 #include <pthread.h>
  69 #include <unistd.h>
  70
  71 #define RCU_YIELD_READ  (1 << 0)
  72 #define RCU_YIELD_WRITE (1 << 1)
  73
  74 /* maximum sleep delay, in us */
  75 #define MAX_SLEEP 50
  76
  77 extern unsigned int rcu_yield_active;
  78 extern DECLARE_URCU_TLS(unsigned int, rcu_rand_yield);
  79
  80 static inline void rcu_debug_yield_read(void)
  81 {
  82         if (rcu_yield_active & RCU_YIELD_READ)
  83                 if (rand_r(&URCU_TLS(rcu_rand_yield)) & 0x1)
  84                         usleep(rand_r(&URCU_TLS(rcu_rand_yield)) % MAX_SLEEP);
  85 }
  86
  87 static inline void rcu_debug_yield_write(void)
  88 {
  89         if (rcu_yield_active & RCU_YIELD_WRITE)
  90                 if (rand_r(&URCU_TLS(rcu_rand_yield)) & 0x1)
  91                         usleep(rand_r(&URCU_TLS(rcu_rand_yield)) % MAX_SLEEP);
  92 }
  93
  94 static inline void rcu_debug_yield_init(void)
  95 {
  96         URCU_TLS(rcu_rand_yield) = time(NULL) ^ (unsigned long) pthread_self();
  97 }
  98 #else
  99 static inline void rcu_debug_yield_read(void)
 100 {
 101 }
 102
 103 static inline void rcu_debug_yield_write(void)
 104 {
 105 }
 106
 107 static inline void rcu_debug_yield_init(void)
 108 {
 109
 110 }
 111 #endif
 112
 113 #define RCU_GP_ONLINE           (1UL << 0)
 114 #define RCU_GP_CTR              (1UL << 1)
 115
 116 /*
 117  * Global quiescent period counter with low-order bits unused.
 118  * Using a int rather than a char to eliminate false register dependencies
 119  * causing stalls on some architectures.
 120  */
 121 extern unsigned long rcu_gp_ctr;
 122
 123 struct rcu_reader {
 124         /* Data used by both reader and synchronize_rcu() */
 125         unsigned long ctr;
 126         /* Data used for registry */
 127         struct cds_list_head node __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
 128         int waiting;
 129         pthread_t tid;
 130 };
 131
 132 extern DECLARE_URCU_TLS(struct rcu_reader, rcu_reader);
 133
 134 extern int32_t rcu_gp_futex;
 135
 136 /*
 137  * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
 138  */
 139 static inline void wake_up_gp(void)
 140 {
 141         if (caa_unlikely(_CMM_LOAD_SHARED(URCU_TLS(rcu_reader).waiting))) {
 142                 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).waiting, 0);
 143                 cmm_smp_mb();
 144                 if (uatomic_read(&rcu_gp_futex) != -1)
 145                         return;
 146                 uatomic_set(&rcu_gp_futex, 0);
 147                 futex_noasync(&rcu_gp_futex, FUTEX_WAKE, 1,
 148                       NULL, NULL, 0);
 149         }
 150 }
 151
 152 static inline int rcu_gp_ongoing(unsigned long *ctr)
 153 {
 154         unsigned long v;
 155
 156         v = CMM_LOAD_SHARED(*ctr);
 157         return v && (v != rcu_gp_ctr);
 158 }
 159
 160 /*
 161  * Enter an RCU read-side critical section.
 162  *
 163  * This function is less than 10 lines long.  The intent is that this
 164  * function meets the 10-line criterion for LGPL, allowing this function
 165  * to be invoked directly from non-LGPL code.
 166  */
 167 static inline void _rcu_read_lock(void)
 168 {
 169         rcu_assert(URCU_TLS(rcu_reader).ctr);
 170 }
 171
 172 /*
 173  * Exit an RCU read-side critical section.
 174  *
 175  * This function is less than 10 lines long.  The intent is that this
 176  * function meets the 10-line criterion for LGPL, allowing this function
 177  * to be invoked directly from non-LGPL code.
 178  */
 179 static inline void _rcu_read_unlock(void)
 180 {
 181 }
 182
 183 /*
 184  * This is a helper function for _rcu_quiescent_state().
 185  * The first cmm_smp_mb() ensures memory accesses in the prior read-side
 186  * critical sections are not reordered with store to
 187  * URCU_TLS(rcu_reader).ctr, and ensures that mutexes held within an
 188  * offline section that would happen to end with this
 189  * rcu_quiescent_state() call are not reordered with
 190  * store to URCU_TLS(rcu_reader).ctr.
 191  */
 192 static inline void _rcu_quiescent_state_update_and_wakeup(unsigned long gp_ctr)
 193 {
 194         cmm_smp_mb();
 195         _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, gp_ctr);
 196         cmm_smp_mb();   /* write URCU_TLS(rcu_reader).ctr before read futex */
 197         wake_up_gp();
 198         cmm_smp_mb();
 199 }
 200
 201 /*
 202  * Inform RCU of a quiescent state.
 203  *
 204  * This function is less than 10 lines long.  The intent is that this
 205  * function meets the 10-line criterion for LGPL, allowing this function
 206  * to be invoked directly from non-LGPL code.
 207  *
 208  * We skip the memory barriers and gp store if our local ctr already
 209  * matches the global rcu_gp_ctr value: this is OK because a prior
 210  * _rcu_quiescent_state() or _rcu_thread_online() already updated it
 211  * within our thread, so we have no quiescent state to report.
 212  */
 213 static inline void _rcu_quiescent_state(void)
 214 {
 215         unsigned long gp_ctr;
 216
 217         if ((gp_ctr = CMM_LOAD_SHARED(rcu_gp_ctr)) == URCU_TLS(rcu_reader).ctr)
 218                 return;
 219         _rcu_quiescent_state_update_and_wakeup(gp_ctr);
 220 }
 221
 222 /*
 223  * Take a thread offline, prohibiting it from entering further RCU
 224  * read-side critical sections.
 225  *
 226  * This function is less than 10 lines long.  The intent is that this
 227  * function meets the 10-line criterion for LGPL, allowing this function
 228  * to be invoked directly from non-LGPL code.
 229  */
 230 static inline void _rcu_thread_offline(void)
 231 {
 232         cmm_smp_mb();
 233         CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, 0);
 234         cmm_smp_mb();   /* write URCU_TLS(rcu_reader).ctr before read futex */
 235         wake_up_gp();
 236         cmm_barrier();  /* Ensure the compiler does not reorder us with mutex */
 237 }
 238
 239 /*
 240  * Bring a thread online, allowing it to once again enter RCU
 241  * read-side critical sections.
 242  *
 243  * This function is less than 10 lines long.  The intent is that this
 244  * function meets the 10-line criterion for LGPL, allowing this function
 245  * to be invoked directly from non-LGPL code.
 246  */
 247 static inline void _rcu_thread_online(void)
 248 {
 249         cmm_barrier();  /* Ensure the compiler does not reorder us with mutex */
 250         _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, CMM_LOAD_SHARED(rcu_gp_ctr));
 251         cmm_smp_mb();
 252 }
 253
 254 #ifdef __cplusplus
 255 }
 256 #endif
 257
 258 #endif /* _URCU_QSBR_STATIC_H */