include/urcu/static/urcu-signal.h

   1 // SPDX-FileCopyrightText: 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   2 // SPDX-FileCopyrightText: 2009 Paul E. McKenney, IBM Corporation.
   3 //
   4 // SPDX-License-Identifier: LGPL-2.1-or-later
   5
   6 #ifndef _URCU_SIGNAL_STATIC_H
   7 #define _URCU_SIGNAL_STATIC_H
   8
   9 /*
  10  * Userspace RCU header.
  11  *
  12  * TO BE INCLUDED ONLY IN CODE THAT IS TO BE RECOMPILED ON EACH LIBURCU
  13  * RELEASE. See urcu.h for linking dynamically with the userspace rcu library.
  14  *
  15  * IBM's contributions to this file may be relicensed under LGPLv2 or later.
  16  */
  17
  18 #include <stdlib.h>
  19 #include <pthread.h>
  20 #include <unistd.h>
  21 #include <stdint.h>
  22
  23 #include <urcu/debug.h>
  24 #include <urcu/config.h>
  25 #include <urcu/compiler.h>
  26 #include <urcu/arch.h>
  27 #include <urcu/system.h>
  28 #include <urcu/uatomic.h>
  29 #include <urcu/list.h>
  30 #include <urcu/futex.h>
  31 #include <urcu/tls-compat.h>
  32 #include <urcu/static/urcu-common.h>
  33 #include <urcu/static/urcu-signal-nr.h>
  34
  35 #ifdef __cplusplus
  36 extern "C" {
  37 #endif
  38
  39 /*
  40  * This code section can only be included in LGPL 2.1 compatible source code.
  41  * See below for the function call wrappers which can be used in code meant to
  42  * be only linked with the Userspace RCU library. This comes with a small
  43  * performance degradation on the read-side due to the added function calls.
  44  * This is required to permit relinking with newer versions of the library.
  45  */
  46
  47 extern struct urcu_gp urcu_signal_gp;
  48
  49 extern DECLARE_URCU_TLS(struct urcu_reader, urcu_signal_reader);
  50
  51 /*
  52  * Helper for _rcu_read_lock().  The format of urcu_signal_gp.ctr (as well as
  53  * the per-thread rcu_reader.ctr) has the lower-order bits containing a count of
  54  * _rcu_read_lock() nesting, and a single high-order URCU_BP_GP_CTR_PHASE bit
  55  * that contains either zero or one.  The cmm_barrier() ensures that the accesses in
  56  * _rcu_read_lock() happen before the subsequent read-side critical section.
  57  */
  58 static inline void _urcu_signal_read_lock_update(unsigned long tmp)
  59 {
  60         if (caa_likely(!(tmp & URCU_GP_CTR_NEST_MASK))) {
  61                 _CMM_STORE_SHARED(URCU_TLS(urcu_signal_reader).ctr, _CMM_LOAD_SHARED(urcu_signal_gp.ctr));
  62                 cmm_smp_mb();
  63         } else
  64                 _CMM_STORE_SHARED(URCU_TLS(urcu_signal_reader).ctr, tmp + URCU_GP_COUNT);
  65 }
  66
  67 /*
  68  * Enter an RCU read-side critical section.
  69  *
  70  * The first cmm_barrier() call ensures that the compiler does not reorder
  71  * the body of _rcu_read_lock() with a mutex.
  72  *
  73  * This function and its helper are both less than 10 lines long.  The
  74  * intent is that this function meets the 10-line criterion in LGPL,
  75  * allowing this function to be invoked directly from non-LGPL code.
  76  */
  77 static inline void _urcu_signal_read_lock(void)
  78 {
  79         unsigned long tmp;
  80
  81         urcu_assert_debug(URCU_TLS(urcu_signal_reader).registered);
  82         cmm_barrier();
  83         tmp = URCU_TLS(urcu_signal_reader).ctr;
  84         urcu_assert_debug((tmp & URCU_GP_CTR_NEST_MASK) != URCU_GP_CTR_NEST_MASK);
  85         _urcu_signal_read_lock_update(tmp);
  86 }
  87
  88 /*
  89  * This is a helper function for _rcu_read_unlock().
  90  *
  91  * The first cmm_barrier() call ensures that the critical section is
  92  * seen to precede the store to rcu_reader.ctr.
  93  * The second cmm_barrier() call ensures that we write to rcu_reader.ctr
  94  * before reading the update-side futex.
  95  */
  96 static inline void _urcu_signal_read_unlock_update_and_wakeup(unsigned long tmp)
  97 {
  98         unsigned long *ctr = &URCU_TLS(urcu_signal_reader).ctr;
  99
 100         if (caa_likely((tmp & URCU_GP_CTR_NEST_MASK) == URCU_GP_COUNT)) {
 101                 uatomic_store(ctr, tmp - URCU_GP_COUNT, CMM_SEQ_CST);
 102                 urcu_common_wake_up_gp(&urcu_signal_gp);
 103         } else {
 104                 uatomic_store(ctr, tmp - URCU_GP_COUNT, CMM_RELAXED);
 105         }
 106 }
 107
 108 /*
 109  * Exit an RCU read-side critical section.  Both this function and its
 110  * helper are smaller than 10 lines of code, and are intended to be
 111  * usable by non-LGPL code, as called out in LGPL.
 112  */
 113 static inline void _urcu_signal_read_unlock(void)
 114 {
 115         unsigned long tmp;
 116
 117         urcu_assert_debug(URCU_TLS(urcu_signal_reader).registered);
 118         tmp = URCU_TLS(urcu_signal_reader).ctr;
 119         urcu_assert_debug(tmp & URCU_GP_CTR_NEST_MASK);
 120         _urcu_signal_read_unlock_update_and_wakeup(tmp);
 121         cmm_barrier();  /* Ensure the compiler does not reorder us with mutex */
 122 }
 123
 124 /*
 125  * Returns whether within a RCU read-side critical section.
 126  *
 127  * This function is less than 10 lines long.  The intent is that this
 128  * function meets the 10-line criterion for LGPL, allowing this function
 129  * to be invoked directly from non-LGPL code.
 130  */
 131 static inline int _urcu_signal_read_ongoing(void)
 132 {
 133         return URCU_TLS(urcu_signal_reader).ctr & URCU_GP_CTR_NEST_MASK;
 134 }
 135
 136 #ifdef __cplusplus
 137 }
 138 #endif
 139
 140 #endif /* _URCU_SIGNAL_STATIC_H */