// Copyright (c) 2014-2016, The Monero Project
//
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without modification, are
// permitted provided that the following conditions are met:
//
// 1. Redistributions of source code must retain the above copyright notice, this list of
// conditions and the following disclaimer.
//
// 2. 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.
//
// 3. Neither the name of the copyright holder 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 COPYRIGHT HOLDERS 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 COPYRIGHT HOLDER 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,
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// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#include <boost/optional/optional.hpp>
#include <condition_variable>
#include <cstddef>
#include <functional>
#include <thread>
#include <utility>
#include <vector>
namespace tools
{
//! Manages zero or more threads for work dispatching
class thread_group
{
public:
//! Create `min(count, get_max_concurrency()) - 1` threads
explicit thread_group(std::size_t count);
thread_group(thread_group const&) = delete;
thread_group(thread_group&&) = delete;
//! Joins threads, but does not necessarily run all dispatched functions.
~thread_group() = default;
thread_group& operator=(thread_group const&) = delete;
thread_group& operator=(thread_group&&) = delete;
/*! Blocks until all functions provided to `dispatch` complete. Does not
destroy threads. If a dispatched function calls `this->dispatch(...)`,
`this->sync()` will continue to block until that new function completes. */
void sync() noexcept {
if (internal) {
internal->sync();
}
}
/*! Example usage:
std::unique_ptr<thread_group, thread_group::lazy_sync> sync(std::addressof(group));
which guarantees synchronization before the unique_ptr destructor returns. */
struct lazy_sync {
void operator()(thread_group* group) const noexcept {
if (group != nullptr) {
group->sync();
}
}
};
/*! `f` is invoked immediately if the thread_group is empty, otherwise
execution of `f` is queued for next available thread. If `f` is queued, any
exception leaving that function will result in process termination. Use
std::packaged_task if exceptions need to be handled. */
template<typename F>
void dispatch(F&& f) {
if (internal) {
internal->dispatch(std::forward<F>(f));
}
else {
f();
}
}
private:
class data {
public:
data(std::size_t count);
~data() noexcept;
void sync() noexcept;
void dispatch(std::function<void()> f);
private:
struct work;
struct node {
node() = delete;
std::unique_ptr<work> ptr;
};
struct work {
work() = delete;
std::function<void()> f;
node next;
};
//! Requires lock on `mutex`.
std::unique_ptr<work> get_next() noexcept;
//! Blocks until destructor is invoked, only call from thread.
void run() noexcept;
private:
std::vector<std::thread> threads;
node head;
node* last;
std::size_t pending;
std::condition_variable has_work;
std::condition_variable finished_work;
std::mutex mutex;
bool stop;
};
private:
// optionally construct elements, without separate heap allocation
boost::optional<data> internal;
};
}
