Timer.hpp

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// The Reactive C++ Toolbox.
// Copyright (C) 2013-2019 Swirly Cloud Limited
// Copyright (C) 2022 Reactive Markets Limited
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
 
#ifndef TOOLBOX_IO_TIMER_HPP
#define TOOLBOX_IO_TIMER_HPP
 
#include <limits>
#include <toolbox/sys/Time.hpp>
#include <toolbox/util/Slot.hpp>
 
#include <toolbox/Config.h>
 
#include <boost/intrusive_ptr.hpp>
 
#include <memory>
 
namespace toolbox {
inline namespace io {
 
class Timer;
class TimerQueue;
using TimerSlot = BasicSlot<void(CyclTime, Timer&)>;
 
class TOOLBOX_API Timer {
    friend class TimerQueue;
 
  public:
    struct Impl {
        union {
            Impl* next;
            TimerQueue* tq;
        };
        int ref_count;
        long id;
        MonoTime expiry;
        Duration interval;
        TimerSlot slot;
    };
 
    explicit Timer(Impl* impl)
    : impl_{impl, false}
    {
    }
    Timer(std::nullptr_t = nullptr) noexcept {} // NOLINT(hicpp-explicit-conversions)
    ~Timer() = default;
 
    // Copy.
    Timer(const Timer&) = default;
    Timer& operator=(const Timer&) = default;
 
    // Move.
    Timer(Timer&&) noexcept = default;
    Timer& operator=(Timer&&) noexcept = default;
 
    bool empty() const noexcept { return !impl_; }
    explicit operator bool() const noexcept { return impl_ != nullptr; }
    long id() const noexcept { return impl_ ? impl_->id : 0; }
    bool pending() const noexcept { return impl_ != nullptr && bool{impl_->slot}; }
 
    MonoTime expiry() const noexcept { return impl_->expiry; }
    Duration interval() const noexcept { return impl_->interval; }
    template <typename RepT, typename PeriodT>
    void set_interval(std::chrono::duration<RepT, PeriodT> interval) noexcept
    {
        using namespace std::chrono;
        impl_->interval = duration_cast<Duration>(interval);
    }
    void reset(std::nullptr_t = nullptr) noexcept { impl_.reset(); }
    void swap(Timer& rhs) noexcept { impl_.swap(rhs.impl_); }
    void cancel() noexcept;
 
    std::partial_ordering operator<=>(const Timer& rhs) const noexcept
    {
        if (!*this || !rhs) {
            return std::partial_ordering::unordered;
        }
        return id() <=> rhs.id();
    }
 
  private:
    void set_expiry(MonoTime expiry) noexcept { impl_->expiry = expiry; }
    TimerSlot& slot() noexcept { return impl_->slot; }
 
    boost::intrusive_ptr<Timer::Impl> impl_;
};
 
class TOOLBOX_API TimerPool {
    using SlabPtr = std::unique_ptr<Timer::Impl[]>;
 
  public:
    TimerPool() = default;
    ~TimerPool() noexcept = default;
 
    // Copy.
    TimerPool(const TimerPool&) = delete;
    TimerPool& operator=(const TimerPool&) = delete;
 
    // Move.
    TimerPool(TimerPool&&) = delete;
    TimerPool& operator=(TimerPool&&) = delete;
 
    Timer::Impl* allocate();
    void deallocate(Timer::Impl* impl) noexcept
    {
        assert(impl);
        impl->next = free_;
        free_ = impl;
    }
 
  private:
    std::vector<SlabPtr> slabs_;
    Timer::Impl* free_{nullptr};
};
 
class TOOLBOX_API TimerQueue {
    friend class Timer;
    friend void intrusive_ptr_add_ref(Timer::Impl*) noexcept;
    friend void intrusive_ptr_release(Timer::Impl*) noexcept;
 
    using SlabPtr = std::unique_ptr<Timer::Impl[]>;
 
  public:
    TimerQueue(TimerPool& pool) // NOLINT(hicpp-explicit-conversions)
    : pool_{pool}
    {
    }
    ~TimerQueue() noexcept = default;
 
    // Copy.
    TimerQueue(const TimerQueue&) = delete;
    TimerQueue& operator=(const TimerQueue&) = delete;
 
    // Move.
    TimerQueue(TimerQueue&&) = delete;
    TimerQueue& operator=(TimerQueue&&) = delete;
 
    std::size_t size() const noexcept { return heap_.size() - cancelled_; }
    bool empty() const noexcept { return size() == 0; }
    const Timer& front() const { return heap_.front(); }
 
    // clang-format off
    [[nodiscard]] Timer insert(MonoTime expiry, Duration interval, TimerSlot slot);
    [[nodiscard]] Timer insert(MonoTime expiry, TimerSlot slot)
    {
        return insert(expiry, Duration::zero(), slot);
    }
    // clang-format on
 
    int dispatch(CyclTime now, int max_work = std::numeric_limits<int>::max());
 
  private:
    Timer allocate(MonoTime expiry, Duration interval, TimerSlot slot);
    void cancel() noexcept;
    void expire(CyclTime now);
    void gc() noexcept;
    Timer pop() noexcept;
 
    TimerPool& pool_;
    long max_id_{};
    int cancelled_{};
    std::vector<Timer> heap_;
};
 
inline void intrusive_ptr_add_ref(Timer::Impl* impl) noexcept
{
    ++impl->ref_count;
}
 
TOOLBOX_API void intrusive_ptr_release(Timer::Impl* impl) noexcept;
 
inline void Timer::cancel() noexcept
{
    // If pending, then reset the slot and inform the queue that the timer has been cancelled.
    if (impl_ && impl_->slot) {
        impl_->slot.reset();
        impl_->tq->cancel();
    }
}
} // namespace io
} // namespace toolbox
 
#endif // TOOLBOX_IO_TIMER_HPP