Lee Clagett
8 years ago
parent
d51f1af75f
commit
64094e5f4e
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// 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 "common/thread_group.h"
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#include <cassert>
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#include <limits>
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#include <stdexcept>
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#include "common/util.h"
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namespace tools
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{
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thread_group::thread_group(std::size_t count) : internal() {
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static_assert(
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std::numeric_limits<unsigned>::max() <= std::numeric_limits<std::size_t>::max(),
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"unexpected truncation"
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);
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count = std::min<std::size_t>(count, get_max_concurrency());
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count = count ? count - 1 : 0;
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if (count) {
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internal.emplace(count);
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}
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}
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thread_group::data::data(std::size_t count)
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: threads()
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, head{nullptr}
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, last(std::addressof(head))
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, pending(count)
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, mutex()
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, has_work()
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, finished_work()
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, stop(false) {
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threads.reserve(count);
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while (count--) {
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threads.push_back(std::thread(&thread_group::data::run, this));
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}
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}
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thread_group::data::~data() noexcept {
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{
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const std::unique_lock<std::mutex> lock(mutex);
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stop = true;
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}
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has_work.notify_all();
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finished_work.notify_all();
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for (auto& worker : threads) {
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try {
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worker.join();
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}
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catch(...) {}
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}
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}
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void thread_group::data::sync() noexcept {
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/* This function and `run()` can both throw when acquiring the lock, or in
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the dispatched function. It is tough to recover from either, particularly the
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lock case. These functions are marked as noexcept so that if either call
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throws, the entire process is terminated. Users of the `dispatch` call are
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expected to make their functions noexcept, or use std::packaged_task to copy
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exceptions so that the process will continue in all but the most pessimistic
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cases (std::bad_alloc). This was the existing behavior;
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`asio::io_service::run` propogates errors from dispatched calls, and uncaught
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exceptions on threads result in process termination. */
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assert(!threads.empty());
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bool not_first = false;
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while (true) {
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std::unique_ptr<work> next = nullptr;
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{
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std::unique_lock<std::mutex> lock(mutex);
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pending -= std::size_t(not_first);
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not_first = true;
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finished_work.notify_all();
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if (stop) {
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return;
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}
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next = get_next();
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if (next == nullptr) {
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finished_work.wait(lock, [this] { return pending == 0 || stop; });
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return;
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}
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}
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assert(next->f);
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next->f();
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}
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}
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std::unique_ptr<thread_group::data::work> thread_group::data::get_next() noexcept {
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std::unique_ptr<work> rc = std::move(head.ptr);
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if (rc != nullptr) {
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head.ptr = std::move(rc->next.ptr);
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if (head.ptr == nullptr) {
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last = std::addressof(head);
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}
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}
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return rc;
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}
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void thread_group::data::run() noexcept {
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// see `sync()` source for additional information
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while (true) {
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std::unique_ptr<work> next = nullptr;
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{
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std::unique_lock<std::mutex> lock(mutex);
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--pending;
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finished_work.notify_all();
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has_work.wait(lock, [this] { return head.ptr != nullptr || stop; });
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if (stop) {
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return;
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}
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next = get_next();
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}
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assert(next != nullptr);
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assert(next->f);
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next->f();
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}
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}
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void thread_group::data::dispatch(std::function<void()> f) {
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std::unique_ptr<work> latest(new work{std::move(f), node{nullptr}});
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node* const latest_node = std::addressof(latest->next);
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{
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const std::unique_lock<std::mutex> lock(mutex);
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assert(last != nullptr);
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assert(last->next == nullptr);
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if (pending == std::numeric_limits<std::size_t>::max()) {
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throw std::overflow_error("thread_group exceeded max queue depth");
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}
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last->ptr = std::move(latest);
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last = latest_node;
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++pending;
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}
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has_work.notify_one();
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}
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}
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@ -0,0 +1,133 @@
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// 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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