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
  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 /*
  61  * The signal number used by the RCU library can be overridden with
  62  * -DSIGRCU= when compiling the library.
  63  * Provide backward compatibility for liburcu 0.3.x SIGURCU.
  64  */
  65 #ifdef SIGURCU
  66 #define SIGRCU SIGURCU
  67 #endif
  68
  69 #ifndef SIGRCU
  70 #define SIGRCU SIGUSR1
  71 #endif
  72
  73 extern struct urcu_gp urcu_signal_gp;
  74
  75 extern DECLARE_URCU_TLS(struct urcu_reader, urcu_signal_reader);
  76
  77 /*
  78  * Helper for _rcu_read_lock().  The format of urcu_signal_gp.ctr (as well as
  79  * the per-thread rcu_reader.ctr) has the upper bits containing a count of
  80  * _rcu_read_lock() nesting, and a lower-order bit that contains either zero
  81  * or URCU_GP_CTR_PHASE.  The cmm_barrier() ensures that the accesses in
  82  * _rcu_read_lock() happen before the subsequent read-side critical section.
  83  */
  84 static inline void _urcu_signal_read_lock_update(unsigned long tmp)
  85 {
  86         if (caa_likely(!(tmp & URCU_GP_CTR_NEST_MASK))) {
  87                 _CMM_STORE_SHARED(URCU_TLS(urcu_signal_reader).ctr, _CMM_LOAD_SHARED(urcu_signal_gp.ctr));
  88                 cmm_barrier();
  89         } else
  90                 _CMM_STORE_SHARED(URCU_TLS(urcu_signal_reader).ctr, tmp + URCU_GP_COUNT);
  91 }
  92
  93 /*
  94  * Enter an RCU read-side critical section.
  95  *
  96  * The first cmm_barrier() call ensures that the compiler does not reorder
  97  * the body of _rcu_read_lock() with a mutex.
  98  *
  99  * This function and its helper are both less than 10 lines long.  The
 100  * intent is that this function meets the 10-line criterion in LGPL,
 101  * allowing this function to be invoked directly from non-LGPL code.
 102  */
 103 static inline void _urcu_signal_read_lock(void)
 104 {
 105         unsigned long tmp;
 106
 107         urcu_assert(URCU_TLS(urcu_signal_reader).registered);
 108         cmm_barrier();
 109         tmp = URCU_TLS(urcu_signal_reader).ctr;
 110         urcu_assert((tmp & URCU_GP_CTR_NEST_MASK) != URCU_GP_CTR_NEST_MASK);
 111         _urcu_signal_read_lock_update(tmp);
 112 }
 113
 114 /*
 115  * This is a helper function for _rcu_read_unlock().
 116  *
 117  * The first cmm_barrier() call ensures that the critical section is
 118  * seen to precede the store to rcu_reader.ctr.
 119  * The second cmm_barrier() call ensures that we write to rcu_reader.ctr
 120  * before reading the update-side futex.
 121  */
 122 static inline void _urcu_signal_read_unlock_update_and_wakeup(unsigned long tmp)
 123 {
 124         if (caa_likely((tmp & URCU_GP_CTR_NEST_MASK) == URCU_GP_COUNT)) {
 125                 cmm_barrier();
 126                 _CMM_STORE_SHARED(URCU_TLS(urcu_signal_reader).ctr, tmp - URCU_GP_COUNT);
 127                 cmm_barrier();
 128                 urcu_common_wake_up_gp(&urcu_signal_gp);
 129         } else
 130                 _CMM_STORE_SHARED(URCU_TLS(urcu_signal_reader).ctr, tmp - URCU_GP_COUNT);
 131 }
 132
 133 /*
 134  * Exit an RCU read-side crtical section.  Both this function and its
 135  * helper are smaller than 10 lines of code, and are intended to be
 136  * usable by non-LGPL code, as called out in LGPL.
 137  */
 138 static inline void _urcu_signal_read_unlock(void)
 139 {
 140         unsigned long tmp;
 141
 142         urcu_assert(URCU_TLS(urcu_signal_reader).registered);
 143         tmp = URCU_TLS(urcu_signal_reader).ctr;
 144         urcu_assert(tmp & URCU_GP_CTR_NEST_MASK);
 145         _urcu_signal_read_unlock_update_and_wakeup(tmp);
 146         cmm_barrier();  /* Ensure the compiler does not reorder us with mutex */
 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 _urcu_signal_read_ongoing(void)
 157 {
 158         return URCU_TLS(urcu_signal_reader).ctr & URCU_GP_CTR_NEST_MASK;
 159 }
 160
 161 #ifdef __cplusplus
 162 }
 163 #endif
 164
 165 #endif /* _URCU_SIGNAL_STATIC_H */