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