src/common/waiter.hpp

   1 /*
   2  * Copyright (C) 2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   3  * Copyright (C) 2017 Jérémie Galarneau <jeremie.galarneau@efficios.com>
   4  *
   5  * SPDX-License-Identifier: LGPL-2.1-only
   6  *
   7  * This code is originally adapted from userspace-rcu's urcu-wait.h
   8  */
   9
  10 #ifndef LTTNG_WAITER_H
  11 #define LTTNG_WAITER_H
  12
  13 #define _LGPL_SOURCE
  14
  15 #include "macros.hpp"
  16
  17 #include <stdbool.h>
  18 #include <stdint.h>
  19 #include <urcu/wfstack.h>
  20
  21 namespace lttng {
  22 namespace synchro {
  23 class waiter;
  24 class wait_queue;
  25
  26 class waker {
  27         friend waiter;
  28
  29 public:
  30         waker(const waker&) = default;
  31         waker(waker&&) = default;
  32         waker& operator=(const waker& other)
  33         {
  34                 _state = other._state;
  35                 return *this;
  36         }
  37         waker& operator=(waker&& other)
  38         {
  39                 _state = other._state;
  40                 return *this;
  41         }
  42
  43         void wake();
  44
  45         ~waker() = default;
  46
  47 private:
  48         waker(int32_t& state) : _state{ state }
  49         {
  50         }
  51
  52         int32_t& _state;
  53 };
  54
  55 class waiter final {
  56         friend wait_queue;
  57
  58 public:
  59         waiter();
  60
  61         /* Deactivate copy and assignment. */
  62         waiter(const waiter&) = delete;
  63         waiter(waiter&&) = delete;
  64         waiter& operator=(const waiter&) = delete;
  65         waiter& operator=(waiter&&) = delete;
  66         ~waiter() = default;
  67
  68         void arm() noexcept;
  69         void wait();
  70
  71         waker get_waker();
  72
  73 private:
  74         cds_wfs_node _wait_queue_node;
  75         int32_t _state;
  76 };
  77
  78 class wait_queue final {
  79 public:
  80         wait_queue();
  81
  82         /* Deactivate copy and assignment. */
  83         wait_queue(const wait_queue&) = delete;
  84         wait_queue(wait_queue&&) = delete;
  85         wait_queue& operator=(const wait_queue&) = delete;
  86         wait_queue& operator=(wait_queue&&) = delete;
  87         ~wait_queue() = default;
  88
  89         /*
  90          * Atomically add a waiter to a wait queue.
  91          * A full memory barrier is issued before being added to the wait queue.
  92          */
  93         void add(waiter& waiter) noexcept;
  94         /*
  95          * Wake every waiter present in the wait queue and remove them from
  96          * the queue.
  97          */
  98         void wake_all();
  99
 100 private:
 101         cds_wfs_stack _stack;
 102 };
 103 } /* namespace synchro */
 104 } /* namespace lttng */
 105
 106 #endif /* LTTNG_WAITER_H */