include/urcu/static/urcu-common.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_COMMON_STATIC_H
   7 #define _URCU_COMMON_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/config.h>
  24 #include <urcu/compiler.h>
  25 #include <urcu/arch.h>
  26 #include <urcu/system.h>
  27 #include <urcu/uatomic.h>
  28 #include <urcu/list.h>
  29 #include <urcu/futex.h>
  30 #include <urcu/tls-compat.h>
  31
  32 #ifdef __cplusplus
  33 extern "C" {
  34 #endif
  35
  36 enum urcu_state {
  37         URCU_READER_ACTIVE_CURRENT,
  38         URCU_READER_ACTIVE_OLD,
  39         URCU_READER_INACTIVE,
  40 };
  41
  42 /*
  43  * The trick here is that URCU_GP_CTR_PHASE must be a multiple of 8 so
  44  * we can use a full 8-bits, 16-bits or 32-bits bitmask for the lower
  45  * order bits.
  46  */
  47 #define URCU_GP_COUNT           (1UL << 0)
  48 /* Use the amount of bits equal to half of the architecture long size */
  49 #define URCU_GP_CTR_PHASE       (1UL << (sizeof(unsigned long) << 2))
  50 #define URCU_GP_CTR_NEST_MASK   (URCU_GP_CTR_PHASE - 1)
  51
  52 struct urcu_gp {
  53         /*
  54          * Global grace period counter.
  55          * Contains the current URCU_GP_CTR_PHASE.
  56          * Also has a URCU_GP_COUNT of 1, to accelerate the reader fast path.
  57          * Written to only by writer with mutex taken.
  58          * Read by both writer and readers.
  59          */
  60         unsigned long ctr;
  61
  62         int32_t futex;
  63 } __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
  64
  65 struct urcu_reader {
  66         /* Data used by both reader and synchronize_rcu() */
  67         unsigned long ctr;
  68         char need_mb;
  69         /* Data used for registry */
  70         struct cds_list_head node __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
  71         pthread_t tid;
  72         /* Reader registered flag, for internal checks. */
  73         unsigned int registered:1;
  74 };
  75
  76 /*
  77  * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
  78  */
  79 static inline void urcu_common_wake_up_gp(struct urcu_gp *gp)
  80 {
  81         if (caa_unlikely(uatomic_read(&gp->futex) == -1)) {
  82                 uatomic_set(&gp->futex, 0);
  83                 /*
  84                  * Ignoring return value until we can make this function
  85                  * return something (because urcu_die() is not publicly
  86                  * exposed).
  87                  */
  88                 (void) futex_async(&gp->futex, FUTEX_WAKE, 1,
  89                                 NULL, NULL, 0);
  90         }
  91 }
  92
  93 static inline enum urcu_state urcu_common_reader_state(struct urcu_gp *gp,
  94                 unsigned long *ctr)
  95 {
  96         unsigned long v;
  97
  98         /*
  99          * Make sure both tests below are done on the same version of *value
 100          * to insure consistency.
 101          */
 102         v = CMM_LOAD_SHARED(*ctr);
 103         if (!(v & URCU_GP_CTR_NEST_MASK))
 104                 return URCU_READER_INACTIVE;
 105         if (!((v ^ gp->ctr) & URCU_GP_CTR_PHASE))
 106                 return URCU_READER_ACTIVE_CURRENT;
 107         return URCU_READER_ACTIVE_OLD;
 108 }
 109
 110 #ifdef __cplusplus
 111 }
 112 #endif
 113
 114 #endif /* _URCU_COMMON_STATIC_H */