urcu-bp-static.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 LGPL-COMPATIBLE CODE. See urcu.h for linking
  10  * dynamically with the userspace rcu library.
  11  *
  12  * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
  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 <syscall.h>
  35 #include <unistd.h>
  36
  37 #include <urcu/compiler.h>
  38 #include <urcu/arch.h>
  39 #include <urcu/system.h>
  40 #include <urcu/uatomic_arch.h>
  41 #include <urcu/list.h>
  42
  43 /*
  44  * This code section can only be included in LGPL 2.1 compatible source code.
  45  * See below for the function call wrappers which can be used in code meant to
  46  * be only linked with the Userspace RCU library. This comes with a small
  47  * performance degradation on the read-side due to the added function calls.
  48  * This is required to permit relinking with newer versions of the library.
  49  */
  50
  51 /*
  52  * Active attempts to check for reader Q.S. before calling sleep().
  53  */
  54 #define RCU_QS_ACTIVE_ATTEMPTS 100
  55
  56 #ifdef DEBUG_RCU
  57 #define rcu_assert(args...)     assert(args)
  58 #else
  59 #define rcu_assert(args...)
  60 #endif
  61
  62 #ifdef DEBUG_YIELD
  63 #include <sched.h>
  64 #include <time.h>
  65 #include <pthread.h>
  66 #include <unistd.h>
  67
  68 #define YIELD_READ      (1 << 0)
  69 #define YIELD_WRITE     (1 << 1)
  70
  71 /*
  72  * Updates without URCU_MB are much slower. Account this in
  73  * the delay.
  74  */
  75 /* maximum sleep delay, in us */
  76 #define MAX_SLEEP 50
  77
  78 extern unsigned int yield_active;
  79 extern unsigned int __thread rand_yield;
  80
  81 static inline void debug_yield_read(void)
  82 {
  83         if (yield_active & YIELD_READ)
  84                 if (rand_r(&rand_yield) & 0x1)
  85                         usleep(rand_r(&rand_yield) % MAX_SLEEP);
  86 }
  87
  88 static inline void debug_yield_write(void)
  89 {
  90         if (yield_active & YIELD_WRITE)
  91                 if (rand_r(&rand_yield) & 0x1)
  92                         usleep(rand_r(&rand_yield) % MAX_SLEEP);
  93 }
  94
  95 static inline void debug_yield_init(void)
  96 {
  97         rand_yield = time(NULL) ^ pthread_self();
  98 }
  99 #else
 100 static inline void debug_yield_read(void)
 101 {
 102 }
 103
 104 static inline void debug_yield_write(void)
 105 {
 106 }
 107
 108 static inline void debug_yield_init(void)
 109 {
 110
 111 }
 112 #endif
 113
 114 /*
 115  * The trick here is that RCU_GP_CTR_BIT must be a multiple of 8 so we can use a
 116  * full 8-bits, 16-bits or 32-bits bitmask for the lower order bits.
 117  */
 118 #define RCU_GP_COUNT            (1UL << 0)
 119 /* Use the amount of bits equal to half of the architecture long size */
 120 #define RCU_GP_CTR_BIT          (1UL << (sizeof(long) << 2))
 121 #define RCU_GP_CTR_NEST_MASK    (RCU_GP_CTR_BIT - 1)
 122
 123 /*
 124  * Used internally by _rcu_read_lock.
 125  */
 126 extern void rcu_bp_register(void);
 127
 128 /*
 129  * Global quiescent period counter with low-order bits unused.
 130  * Using a int rather than a char to eliminate false register dependencies
 131  * causing stalls on some architectures.
 132  */
 133 extern long urcu_gp_ctr;
 134
 135 struct urcu_reader {
 136         /* Data used by both reader and synchronize_rcu() */
 137         long ctr;
 138         /* Data used for registry */
 139         struct list_head head __attribute__((aligned(CACHE_LINE_SIZE)));
 140         pthread_t tid;
 141         int alloc;      /* registry entry allocated */
 142 };
 143
 144 /*
 145  * Bulletproof version keeps a pointer to a registry not part of the TLS.
 146  * Adds a pointer dereference on the read-side, but won't require to unregister
 147  * the reader thread.
 148  */
 149 extern struct urcu_reader __thread *urcu_reader;
 150
 151 static inline int rcu_old_gp_ongoing(long *value)
 152 {
 153         long v;
 154
 155         if (value == NULL)
 156                 return 0;
 157         /*
 158          * Make sure both tests below are done on the same version of *value
 159          * to insure consistency.
 160          */
 161         v = LOAD_SHARED(*value);
 162         return (v & RCU_GP_CTR_NEST_MASK) &&
 163                  ((v ^ urcu_gp_ctr) & RCU_GP_CTR_BIT);
 164 }
 165
 166 static inline void _rcu_read_lock(void)
 167 {
 168         long tmp;
 169
 170         /* Check if registered */
 171         if (unlikely(!urcu_reader))
 172                 rcu_bp_register();
 173
 174         tmp = urcu_reader->ctr;
 175         /* urcu_gp_ctr = RCU_GP_COUNT | (~RCU_GP_CTR_BIT or RCU_GP_CTR_BIT) */
 176         if (likely(!(tmp & RCU_GP_CTR_NEST_MASK))) {
 177                 _STORE_SHARED(urcu_reader->ctr, _LOAD_SHARED(urcu_gp_ctr));
 178                 /*
 179                  * Set active readers count for outermost nesting level before
 180                  * accessing the pointer.
 181                  */
 182                 smp_mb();
 183         } else {
 184                 _STORE_SHARED(urcu_reader->ctr, tmp + RCU_GP_COUNT);
 185         }
 186 }
 187
 188 static inline void _rcu_read_unlock(void)
 189 {
 190         /*
 191          * Finish using rcu before decrementing the pointer.
 192          */
 193         smp_mb();
 194         _STORE_SHARED(urcu_reader->ctr, urcu_reader->ctr - RCU_GP_COUNT);
 195 }
 196
 197 #endif /* _URCU_BP_STATIC_H */