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 <functional>
  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 final {
  27         friend waiter;
  28
  29 public:
  30         waker(const waker&) noexcept = default;
  31         waker(waker&&) noexcept = default;
  32         waker& operator=(const waker& other) noexcept = default;
  33         waker& operator=(waker&& other) noexcept = default;
  34
  35         void wake();
  36
  37         ~waker() = default;
  38
  39 private:
  40         explicit waker(int32_t& state) noexcept : _state{ state }
  41         {
  42         }
  43
  44         std::reference_wrapper<int32_t> _state;
  45 };
  46
  47 class waiter final {
  48         friend wait_queue;
  49
  50 public:
  51         waiter();
  52
  53         /* Deactivate copy and assignment. */
  54         waiter(const waiter&) = delete;
  55         waiter(waiter&&) = delete;
  56         waiter& operator=(const waiter&) = delete;
  57         waiter& operator=(waiter&&) = delete;
  58         ~waiter() = default;
  59
  60         void arm() noexcept;
  61         void wait();
  62
  63         waker get_waker();
  64
  65 private:
  66         cds_wfs_node _wait_queue_node;
  67         int32_t _state;
  68 };
  69
  70 class wait_queue final {
  71 public:
  72         wait_queue();
  73
  74         /* Deactivate copy and assignment. */
  75         wait_queue(const wait_queue&) = delete;
  76         wait_queue(wait_queue&&) = delete;
  77         wait_queue& operator=(const wait_queue&) = delete;
  78         wait_queue& operator=(wait_queue&&) = delete;
  79         ~wait_queue() = default;
  80
  81         /*
  82          * Atomically add a waiter to a wait queue.
  83          * A full memory barrier is issued before being added to the wait queue.
  84          */
  85         void add(waiter& waiter) noexcept;
  86         /*
  87          * Wake every waiter present in the wait queue and remove them from
  88          * the queue.
  89          */
  90         void wake_all();
  91
  92 private:
  93         cds_wfs_stack _stack;
  94 };
  95 } /* namespace synchro */
  96 } /* namespace lttng */
  97
  98 #endif /* LTTNG_WAITER_H */