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 <limits.h>
  35 #include <unistd.h>
  36 #include <stdint.h>
  37
  38 #include <urcu/compiler.h>
  39 #include <urcu/arch.h>
  40 #include <urcu/system.h>
  41 #include <urcu/uatomic.h>
  42 #include <urcu/list.h>
  43 #include <urcu/futex.h>
  44 #include <urcu/tls-compat.h>
  45 #include <urcu/debug.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 enum rcu_state {
  60         RCU_READER_ACTIVE_CURRENT,
  61         RCU_READER_ACTIVE_OLD,
  62         RCU_READER_INACTIVE,
  63 };
  64
  65 #define RCU_GP_ONLINE           (1UL << 0)
  66 #define RCU_GP_CTR              (1UL << 1)
  67
  68 struct rcu_gp {
  69         /*
  70          * Global quiescent period counter with low-order bits unused.
  71          * Using a int rather than a char to eliminate false register
  72          * dependencies causing stalls on some architectures.
  73          */
  74         unsigned long ctr;
  75
  76         int32_t futex;
  77 } __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
  78
  79 extern struct rcu_gp rcu_gp;
  80
  81 struct rcu_reader {
  82         /* Data used by both reader and synchronize_rcu() */
  83         unsigned long ctr;
  84         /* Data used for registry */
  85         struct cds_list_head node __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
  86         int waiting;
  87         pthread_t tid;
  88         /* Reader registered flag, for internal checks. */
  89         unsigned int registered:1;
  90 };
  91
  92 extern DECLARE_URCU_TLS(struct rcu_reader, rcu_reader);
  93
  94 /*
  95  * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
  96  */
  97 static inline void wake_up_gp(void)
  98 {
  99         if (caa_unlikely(_CMM_LOAD_SHARED(URCU_TLS(rcu_reader).waiting))) {
 100                 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).waiting, 0);
 101                 cmm_smp_mb();
 102                 if (uatomic_read(&rcu_gp.futex) != -1)
 103                         return;
 104                 uatomic_set(&rcu_gp.futex, 0);
 105                 /*
 106                  * Ignoring return value until we can make this function
 107                  * return something (because urcu_die() is not publicly
 108                  * exposed).
 109                  */
 110                 (void) futex_noasync(&rcu_gp.futex, FUTEX_WAKE, 1,
 111                                 NULL, NULL, 0);
 112         }
 113 }
 114
 115 static inline enum rcu_state rcu_reader_state(unsigned long *ctr)
 116 {
 117         unsigned long v;
 118
 119         v = CMM_LOAD_SHARED(*ctr);
 120         if (!v)
 121                 return RCU_READER_INACTIVE;
 122         if (v == rcu_gp.ctr)
 123                 return RCU_READER_ACTIVE_CURRENT;
 124         return RCU_READER_ACTIVE_OLD;
 125 }
 126
 127 /*
 128  * Enter an RCU read-side critical section.
 129  *
 130  * This function is less than 10 lines long.  The intent is that this
 131  * function meets the 10-line criterion for LGPL, allowing this function
 132  * to be invoked directly from non-LGPL code.
 133  */
 134 static inline void _rcu_read_lock(void)
 135 {
 136         urcu_assert(URCU_TLS(rcu_reader).ctr);
 137 }
 138
 139 /*
 140  * Exit an RCU read-side critical section.
 141  *
 142  * This function is less than 10 lines long.  The intent is that this
 143  * function meets the 10-line criterion for LGPL, allowing this function
 144  * to be invoked directly from non-LGPL code.
 145  */
 146 static inline void _rcu_read_unlock(void)
 147 {
 148         urcu_assert(URCU_TLS(rcu_reader).ctr);
 149 }
 150
 151 /*
 152  * Returns whether within a RCU read-side critical section.
 153  *
 154  * This function is less than 10 lines long.  The intent is that this
 155  * function meets the 10-line criterion for LGPL, allowing this function
 156  * to be invoked directly from non-LGPL code.
 157  */
 158 static inline int _rcu_read_ongoing(void)
 159 {
 160         return URCU_TLS(rcu_reader).ctr;
 161 }
 162
 163 /*
 164  * This is a helper function for _rcu_quiescent_state().
 165  * The first cmm_smp_mb() ensures memory accesses in the prior read-side
 166  * critical sections are not reordered with store to
 167  * URCU_TLS(rcu_reader).ctr, and ensures that mutexes held within an
 168  * offline section that would happen to end with this
 169  * rcu_quiescent_state() call are not reordered with
 170  * store to URCU_TLS(rcu_reader).ctr.
 171  */
 172 static inline void _rcu_quiescent_state_update_and_wakeup(unsigned long gp_ctr)
 173 {
 174         cmm_smp_mb();
 175         _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, gp_ctr);
 176         cmm_smp_mb();   /* write URCU_TLS(rcu_reader).ctr before read futex */
 177         wake_up_gp();
 178         cmm_smp_mb();
 179 }
 180
 181 /*
 182  * Inform RCU of a quiescent state.
 183  *
 184  * This function is less than 10 lines long.  The intent is that this
 185  * function meets the 10-line criterion for LGPL, allowing this function
 186  * to be invoked directly from non-LGPL code.
 187  *
 188  * We skip the memory barriers and gp store if our local ctr already
 189  * matches the global rcu_gp.ctr value: this is OK because a prior
 190  * _rcu_quiescent_state() or _rcu_thread_online() already updated it
 191  * within our thread, so we have no quiescent state to report.
 192  */
 193 static inline void _rcu_quiescent_state(void)
 194 {
 195         unsigned long gp_ctr;
 196
 197         urcu_assert(URCU_TLS(rcu_reader).registered);
 198         if ((gp_ctr = CMM_LOAD_SHARED(rcu_gp.ctr)) == URCU_TLS(rcu_reader).ctr)
 199                 return;
 200         _rcu_quiescent_state_update_and_wakeup(gp_ctr);
 201 }
 202
 203 /*
 204  * Take a thread offline, prohibiting it from entering further RCU
 205  * read-side critical sections.
 206  *
 207  * This function is less than 10 lines long.  The intent is that this
 208  * function meets the 10-line criterion for LGPL, allowing this function
 209  * to be invoked directly from non-LGPL code.
 210  */
 211 static inline void _rcu_thread_offline(void)
 212 {
 213         urcu_assert(URCU_TLS(rcu_reader).registered);
 214         cmm_smp_mb();
 215         CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, 0);
 216         cmm_smp_mb();   /* write URCU_TLS(rcu_reader).ctr before read futex */
 217         wake_up_gp();
 218         cmm_barrier();  /* Ensure the compiler does not reorder us with mutex */
 219 }
 220
 221 /*
 222  * Bring a thread online, allowing it to once again enter RCU
 223  * read-side critical sections.
 224  *
 225  * This function is less than 10 lines long.  The intent is that this
 226  * function meets the 10-line criterion for LGPL, allowing this function
 227  * to be invoked directly from non-LGPL code.
 228  */
 229 static inline void _rcu_thread_online(void)
 230 {
 231         urcu_assert(URCU_TLS(rcu_reader).registered);
 232         cmm_barrier();  /* Ensure the compiler does not reorder us with mutex */
 233         _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, CMM_LOAD_SHARED(rcu_gp.ctr));
 234         cmm_smp_mb();
 235 }
 236
 237 #ifdef __cplusplus
 238 }
 239 #endif
 240
 241 #endif /* _URCU_QSBR_STATIC_H */