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