include/urcu/static/urcu-mb.h

   1 #ifndef _URCU_MB_STATIC_H
   2 #define _URCU_MB_STATIC_H
   3
   4 /*
   5  * urcu-mb-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 #include <stdint.h>
  36
  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/futex.h>
  44 #include <urcu/tls-compat.h>
  45 #include <urcu/debug.h>
  46 #include <urcu/static/urcu-common.h>
  47
  48 #ifdef __cplusplus
  49 extern "C" {
  50 #endif
  51
  52 /*
  53  * This code section can only be included in LGPL 2.1 compatible source code.
  54  * See below for the function call wrappers which can be used in code meant to
  55  * be only linked with the Userspace RCU library. This comes with a small
  56  * performance degradation on the read-side due to the added function calls.
  57  * This is required to permit relinking with newer versions of the library.
  58  */
  59
  60 extern struct urcu_gp urcu_mb_gp;
  61
  62 extern DECLARE_URCU_TLS(struct urcu_reader, urcu_mb_reader);
  63
  64 /*
  65  * Helper for _urcu_mb_read_lock().  The format of urcu_mb_gp.ctr (as well as
  66  * the per-thread rcu_reader.ctr) has the upper bits containing a count of
  67  * _urcu_mb_read_lock() nesting, and a lower-order bit that contains either zero
  68  * or URCU_GP_CTR_PHASE.  The cmm_smp_mb() ensures that the accesses in
  69  * _urcu_mb_read_lock() happen before the subsequent read-side critical section.
  70  */
  71 static inline void _urcu_mb_read_lock_update(unsigned long tmp)
  72 {
  73         if (caa_likely(!(tmp & URCU_GP_CTR_NEST_MASK))) {
  74                 _CMM_STORE_SHARED(URCU_TLS(urcu_mb_reader).ctr, _CMM_LOAD_SHARED(urcu_mb_gp.ctr));
  75                 cmm_smp_mb();
  76         } else
  77                 _CMM_STORE_SHARED(URCU_TLS(urcu_mb_reader).ctr, tmp + URCU_GP_COUNT);
  78 }
  79
  80 /*
  81  * Enter an RCU read-side critical section.
  82  *
  83  * The first cmm_barrier() call ensures that the compiler does not reorder
  84  * the body of _urcu_mb_read_lock() with a mutex.
  85  *
  86  * This function and its helper are both less than 10 lines long.  The
  87  * intent is that this function meets the 10-line criterion in LGPL,
  88  * allowing this function to be invoked directly from non-LGPL code.
  89  */
  90 static inline void _urcu_mb_read_lock(void)
  91 {
  92         unsigned long tmp;
  93
  94         urcu_assert(URCU_TLS(urcu_mb_reader).registered);
  95         cmm_barrier();
  96         tmp = URCU_TLS(urcu_mb_reader).ctr;
  97         urcu_assert((tmp & URCU_GP_CTR_NEST_MASK) != URCU_GP_CTR_NEST_MASK);
  98         _urcu_mb_read_lock_update(tmp);
  99 }
 100
 101 /*
 102  * This is a helper function for _urcu_mb_read_unlock().
 103  *
 104  * The first cmm_smp_mb() call ensures that the critical section is
 105  * seen to precede the store to rcu_reader.ctr.
 106  * The second cmm_smp_mb() call ensures that we write to rcu_reader.ctr
 107  * before reading the update-side futex.
 108  */
 109 static inline void _urcu_mb_read_unlock_update_and_wakeup(unsigned long tmp)
 110 {
 111         if (caa_likely((tmp & URCU_GP_CTR_NEST_MASK) == URCU_GP_COUNT)) {
 112                 cmm_smp_mb();
 113                 _CMM_STORE_SHARED(URCU_TLS(urcu_mb_reader).ctr, tmp - URCU_GP_COUNT);
 114                 cmm_smp_mb();
 115                 urcu_common_wake_up_gp(&urcu_mb_gp);
 116         } else
 117                 _CMM_STORE_SHARED(URCU_TLS(urcu_mb_reader).ctr, tmp - URCU_GP_COUNT);
 118 }
 119
 120 /*
 121  * Exit an RCU read-side crtical section.  Both this function and its
 122  * helper are smaller than 10 lines of code, and are intended to be
 123  * usable by non-LGPL code, as called out in LGPL.
 124  */
 125 static inline void _urcu_mb_read_unlock(void)
 126 {
 127         unsigned long tmp;
 128
 129         urcu_assert(URCU_TLS(urcu_mb_reader).registered);
 130         tmp = URCU_TLS(urcu_mb_reader).ctr;
 131         urcu_assert(tmp & URCU_GP_CTR_NEST_MASK);
 132         _urcu_mb_read_unlock_update_and_wakeup(tmp);
 133         cmm_barrier();  /* Ensure the compiler does not reorder us with mutex */
 134 }
 135
 136 /*
 137  * Returns whether within a RCU read-side critical section.
 138  *
 139  * This function is less than 10 lines long.  The intent is that this
 140  * function meets the 10-line criterion for LGPL, allowing this function
 141  * to be invoked directly from non-LGPL code.
 142  */
 143 static inline int _urcu_mb_read_ongoing(void)
 144 {
 145         return URCU_TLS(urcu_mb_reader).ctr & URCU_GP_CTR_NEST_MASK;
 146 }
 147
 148 #ifdef __cplusplus
 149 }
 150 #endif
 151
 152 #endif /* _URCU_MB_STATIC_H */