include/urcu/static/urcu-signal.h

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