include/urcu/static/urcu-bp.h

   1 #ifndef _URCU_BP_STATIC_H
   2 #define _URCU_BP_STATIC_H
   3
   4 /*
   5  * urcu-bp-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
  36 #include <urcu/debug.h>
  37 #include <urcu/config.h>
  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/tls-compat.h>
  44
  45 /*
  46  * This code section can only be included in LGPL 2.1 compatible source code.
  47  * See below for the function call wrappers which can be used in code meant to
  48  * be only linked with the Userspace RCU library. This comes with a small
  49  * performance degradation on the read-side due to the added function calls.
  50  * This is required to permit relinking with newer versions of the library.
  51  */
  52
  53 #ifdef __cplusplus
  54 extern "C" {
  55 #endif
  56
  57 enum urcu_bp_state {
  58         URCU_BP_READER_ACTIVE_CURRENT,
  59         URCU_BP_READER_ACTIVE_OLD,
  60         URCU_BP_READER_INACTIVE,
  61 };
  62
  63 /*
  64  * The trick here is that URCU_BP_GP_CTR_PHASE must be a multiple of 8 so we can use a
  65  * full 8-bits, 16-bits or 32-bits bitmask for the lower order bits.
  66  */
  67 #define URCU_BP_GP_COUNT                (1UL << 0)
  68 /* Use the amount of bits equal to half of the architecture long size */
  69 #define URCU_BP_GP_CTR_PHASE            (1UL << (sizeof(long) << 2))
  70 #define URCU_BP_GP_CTR_NEST_MASK        (URCU_BP_GP_CTR_PHASE - 1)
  71
  72 /*
  73  * Used internally by _urcu_bp_read_lock.
  74  */
  75 extern void urcu_bp_register(void);
  76
  77 struct urcu_bp_gp {
  78         /*
  79          * Global grace period counter.
  80          * Contains the current URCU_BP_GP_CTR_PHASE.
  81          * Also has a URCU_BP_GP_COUNT of 1, to accelerate the reader fast path.
  82          * Written to only by writer with mutex taken.
  83          * Read by both writer and readers.
  84          */
  85         unsigned long ctr;
  86 } __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
  87
  88 extern struct urcu_bp_gp urcu_bp_gp;
  89
  90 struct urcu_bp_reader {
  91         /* Data used by both reader and urcu_bp_synchronize_rcu() */
  92         unsigned long ctr;
  93         /* Data used for registry */
  94         struct cds_list_head node __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
  95         pthread_t tid;
  96         int alloc;      /* registry entry allocated */
  97 };
  98
  99 /*
 100  * Bulletproof version keeps a pointer to a registry not part of the TLS.
 101  * Adds a pointer dereference on the read-side, but won't require to unregister
 102  * the reader thread.
 103  */
 104 extern DECLARE_URCU_TLS(struct urcu_bp_reader *, urcu_bp_reader);
 105
 106 #ifdef CONFIG_RCU_FORCE_SYS_MEMBARRIER
 107 #define urcu_bp_has_sys_membarrier      1
 108 #else
 109 extern int urcu_bp_has_sys_membarrier;
 110 #endif
 111
 112 static inline void urcu_bp_smp_mb_slave(void)
 113 {
 114         if (caa_likely(urcu_bp_has_sys_membarrier))
 115                 cmm_barrier();
 116         else
 117                 cmm_smp_mb();
 118 }
 119
 120 static inline enum urcu_bp_state urcu_bp_reader_state(unsigned long *ctr)
 121 {
 122         unsigned long v;
 123
 124         if (ctr == NULL)
 125                 return URCU_BP_READER_INACTIVE;
 126         /*
 127          * Make sure both tests below are done on the same version of *value
 128          * to insure consistency.
 129          */
 130         v = CMM_LOAD_SHARED(*ctr);
 131         if (!(v & URCU_BP_GP_CTR_NEST_MASK))
 132                 return URCU_BP_READER_INACTIVE;
 133         if (!((v ^ urcu_bp_gp.ctr) & URCU_BP_GP_CTR_PHASE))
 134                 return URCU_BP_READER_ACTIVE_CURRENT;
 135         return URCU_BP_READER_ACTIVE_OLD;
 136 }
 137
 138 /*
 139  * Helper for _urcu_bp_read_lock().  The format of urcu_bp_gp.ctr (as well as
 140  * the per-thread rcu_reader.ctr) has the upper bits containing a count of
 141  * _urcu_bp_read_lock() nesting, and a lower-order bit that contains either zero
 142  * or URCU_BP_GP_CTR_PHASE.  The smp_mb_slave() ensures that the accesses in
 143  * _urcu_bp_read_lock() happen before the subsequent read-side critical section.
 144  */
 145 static inline void _urcu_bp_read_lock_update(unsigned long tmp)
 146 {
 147         if (caa_likely(!(tmp & URCU_BP_GP_CTR_NEST_MASK))) {
 148                 _CMM_STORE_SHARED(URCU_TLS(urcu_bp_reader)->ctr, _CMM_LOAD_SHARED(urcu_bp_gp.ctr));
 149                 urcu_bp_smp_mb_slave();
 150         } else
 151                 _CMM_STORE_SHARED(URCU_TLS(urcu_bp_reader)->ctr, tmp + URCU_BP_GP_COUNT);
 152 }
 153
 154 /*
 155  * Enter an RCU read-side critical section.
 156  *
 157  * The first cmm_barrier() call ensures that the compiler does not reorder
 158  * the body of _urcu_bp_read_lock() with a mutex.
 159  *
 160  * This function and its helper are both less than 10 lines long.  The
 161  * intent is that this function meets the 10-line criterion in LGPL,
 162  * allowing this function to be invoked directly from non-LGPL code.
 163  */
 164 static inline void _urcu_bp_read_lock(void)
 165 {
 166         unsigned long tmp;
 167
 168         if (caa_unlikely(!URCU_TLS(urcu_bp_reader)))
 169                 urcu_bp_register(); /* If not yet registered. */
 170         cmm_barrier();  /* Ensure the compiler does not reorder us with mutex */
 171         tmp = URCU_TLS(urcu_bp_reader)->ctr;
 172         urcu_assert_debug((tmp & URCU_BP_GP_CTR_NEST_MASK) != URCU_BP_GP_CTR_NEST_MASK);
 173         _urcu_bp_read_lock_update(tmp);
 174 }
 175
 176 /*
 177  * Exit an RCU read-side critical section.  This function is less than
 178  * 10 lines of code, and is intended to be usable by non-LGPL code, as
 179  * called out in LGPL.
 180  */
 181 static inline void _urcu_bp_read_unlock(void)
 182 {
 183         unsigned long tmp;
 184
 185         tmp = URCU_TLS(urcu_bp_reader)->ctr;
 186         urcu_assert_debug(tmp & URCU_BP_GP_CTR_NEST_MASK);
 187         /* Finish using rcu before decrementing the pointer. */
 188         urcu_bp_smp_mb_slave();
 189         _CMM_STORE_SHARED(URCU_TLS(urcu_bp_reader)->ctr, tmp - URCU_BP_GP_COUNT);
 190         cmm_barrier();  /* Ensure the compiler does not reorder us with mutex */
 191 }
 192
 193 /*
 194  * Returns whether within a RCU read-side critical section.
 195  *
 196  * This function is less than 10 lines long.  The intent is that this
 197  * function meets the 10-line criterion for LGPL, allowing this function
 198  * to be invoked directly from non-LGPL code.
 199  */
 200 static inline int _urcu_bp_read_ongoing(void)
 201 {
 202         if (caa_unlikely(!URCU_TLS(urcu_bp_reader)))
 203                 urcu_bp_register(); /* If not yet registered. */
 204         return URCU_TLS(urcu_bp_reader)->ctr & URCU_BP_GP_CTR_NEST_MASK;
 205 }
 206
 207 #ifdef __cplusplus
 208 }
 209 #endif
 210
 211 #endif /* _URCU_BP_STATIC_H */