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112 lines
3.5 KiB
C++
112 lines
3.5 KiB
C++
/**
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* Copyright (c) 2020, Timothy Stack
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*
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* * Redistributions of source code must retain the above copyright notice, this
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* list of conditions and the following disclaimer.
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* * Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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* * Neither the name of Timothy Stack nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ''AS IS'' AND ANY
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* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE FOR ANY
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* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#ifndef lnav_future_util_hh
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#define lnav_future_util_hh
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#include <deque>
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#include <future>
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namespace lnav {
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namespace futures {
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/**
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* Create a future that is ready to immediately return a result.
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*
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* @tparam T The result type of the future.
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* @param t The value the future should return.
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* @return The new future.
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*/
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template<class T>
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std::future<std::decay_t<T>>
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make_ready_future(T&& t)
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{
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std::promise<std::decay_t<T>> pr;
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auto r = pr.get_future();
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pr.set_value(std::forward<T>(t));
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return r;
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}
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/**
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* A queue used to limit the number of futures that are running concurrently.
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*
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* @tparam T The result of the futures.
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* @tparam MAX_QUEUE_SIZE The maximum number of futures that can be in flight.
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*/
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template<typename T, int MAX_QUEUE_SIZE = 8>
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class future_queue {
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public:
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/**
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* @param processor The function to execute with the result of a future.
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*/
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explicit future_queue(std::function<void(T&)> processor)
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: fq_processor(processor){};
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~future_queue()
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{
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this->pop_to();
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}
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/**
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* Add a future to the queue. If the size of the queue is greater than the
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* MAX_QUEUE_SIZE, this call will block waiting for the first queued
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* future to return a result.
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*
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* @param f The future to add to the queue.
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*/
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void push_back(std::future<T>&& f)
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{
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this->fq_deque.emplace_back(std::move(f));
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this->pop_to(MAX_QUEUE_SIZE);
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}
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/**
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* Removes the next future from the queue, waits for the result, and then
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* repeats until the queue reaches the given size.
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*
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* @param size The new desired size of the queue.
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*/
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void pop_to(size_t size = 0)
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{
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while (this->fq_deque.size() > size) {
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auto v = this->fq_deque.front().get();
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this->fq_processor(v);
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this->fq_deque.pop_front();
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}
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}
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std::function<void(T&)> fq_processor;
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std::deque<std::future<T>> fq_deque;
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};
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} // namespace futures
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} // namespace lnav
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#endif
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