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134 lines
4.1 KiB
C++
134 lines
4.1 KiB
C++
// Copyright (c) 2014-2016, The Monero Project
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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 modification, are
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// permitted provided that the following conditions are met:
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//
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// 1. Redistributions of source code must retain the above copyright notice, this list of
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// conditions and the following disclaimer.
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//
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// 2. Redistributions in binary form must reproduce the above copyright notice, this list
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// of conditions and the following disclaimer in the documentation and/or other
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// materials provided with the distribution.
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//
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// 3. Neither the name of the copyright holder nor the names of its contributors may be
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// used to endorse or promote products derived from this software without specific
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// prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
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// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
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// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
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// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
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// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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#include <boost/optional/optional.hpp>
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#include <condition_variable>
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#include <cstddef>
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#include <functional>
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#include <thread>
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#include <utility>
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#include <vector>
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namespace tools
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{
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//! Manages zero or more threads for work dispatching
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class thread_group
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{
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public:
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//! Create `min(count, get_max_concurrency()) - 1` threads
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explicit thread_group(std::size_t count);
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thread_group(thread_group const&) = delete;
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thread_group(thread_group&&) = delete;
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//! Joins threads, but does not necessarily run all dispatched functions.
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~thread_group() = default;
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thread_group& operator=(thread_group const&) = delete;
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thread_group& operator=(thread_group&&) = delete;
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/*! Blocks until all functions provided to `dispatch` complete. Does not
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destroy threads. If a dispatched function calls `this->dispatch(...)`,
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`this->sync()` will continue to block until that new function completes. */
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void sync() noexcept {
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if (internal) {
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internal->sync();
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}
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}
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/*! Example usage:
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std::unique_ptr<thread_group, thread_group::lazy_sync> sync(std::addressof(group));
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which guarantees synchronization before the unique_ptr destructor returns. */
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struct lazy_sync {
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void operator()(thread_group* group) const noexcept {
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if (group != nullptr) {
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group->sync();
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}
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}
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};
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/*! `f` is invoked immediately if the thread_group is empty, otherwise
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execution of `f` is queued for next available thread. If `f` is queued, any
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exception leaving that function will result in process termination. Use
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std::packaged_task if exceptions need to be handled. */
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template<typename F>
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void dispatch(F&& f) {
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if (internal) {
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internal->dispatch(std::forward<F>(f));
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}
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else {
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f();
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}
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}
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private:
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class data {
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public:
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data(std::size_t count);
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~data() noexcept;
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void sync() noexcept;
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void dispatch(std::function<void()> f);
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private:
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struct work;
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struct node {
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node() = delete;
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std::unique_ptr<work> ptr;
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};
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struct work {
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work() = delete;
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std::function<void()> f;
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node next;
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};
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//! Requires lock on `mutex`.
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std::unique_ptr<work> get_next() noexcept;
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//! Blocks until destructor is invoked, only call from thread.
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void run() noexcept;
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private:
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std::vector<std::thread> threads;
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node head;
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node* last;
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std::size_t pending;
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std::condition_variable has_work;
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std::condition_variable finished_work;
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std::mutex mutex;
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bool stop;
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};
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private:
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// optionally construct elements, without separate heap allocation
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boost::optional<data> internal;
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};
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}
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