[英]Single producer, multiple parallel consumers implemented with boost fibers
我正在嘗試編寫一個生產者、多個消費者管道,其中消費者在並行線程中運行。 或者找到或分享一個簡單的例子。 Go 中的代碼相對簡單,output 清楚地顯示了消費者並行工作。 我認為它可能與 Boost 1.73 光纖類似,但我無法超越(不出所料)按順序工作的代碼:
#include <boost/fiber/buffered_channel.hpp>
#include <boost/fiber/fiber.hpp>
static void process(int item) {
std::cout << "consumer processing " << item << std::endl;
auto wasteOfTime = 0.;
for (auto s = 0.; s < item; s += 1e-7) {
wasteOfTime += sin(s);
}
if (wasteOfTime != 42) {
std::cout << "consumer processed " << item << std::endl;
}
}
static const std::uint32_t workers = 3;
int main() {
boost::fibers::buffered_channel<int> channel { 2 };
boost::fibers::fiber consumer[workers];
for (int i = 0; i < workers; ++i) {
consumer[i] = boost::fibers::fiber([&channel]() {
for (auto item : channel) {
process(item);
}
});
}
auto producer = boost::fibers::fiber([&channel]() {
std::cout << "producer starting" << std::endl;
channel.push(1);
channel.push(2);
channel.push(3);
channel.close();
std::cout << "producer ending" << std::endl;
});
producer.join();
for (int i = 0; i < workers; ++i) {
consumer[i].join();
}
return 0;
}
我嘗試插入許多代碼片段的變體來讓工作線程調度纖程,但它們總是按順序執行或根本不執行。 來自關於逆問題的問題的代碼似乎是朝着正確方向邁出的一步,雖然比 Go 復雜得多,但是(使用 -DM_1_PI=3.14 編譯時)該程序對我來說也只是閑置。
原來我誤解了 boost 用於調度光纖的代碼片段。 它似乎對我有用:
#include <boost/fiber/barrier.hpp>
#include <boost/fiber/buffered_channel.hpp>
#include <boost/fiber/fiber.hpp>
#include <boost/fiber/operations.hpp>
#include <boost/fiber/algo/work_stealing.hpp>
#include <optional>
static void process(int item) {
std::cout << "processing " << item << std::endl;
auto wasteOfTime = 0.;
for (auto s = 0.; s < 1; s += 3e-9) {
wasteOfTime += sin(s);
}
if (wasteOfTime != 42) {
std::cout << "processed " << item << std::endl;
}
}
static const std::uint32_t N_CONSUMING_FIBERS = 3;
void task() {
boost::fibers::buffered_channel<int> channel{ 2 };
boost::fibers::fiber fibers[1 + N_CONSUMING_FIBERS];
fibers[0] = boost::fibers::fiber([&channel]() {
std::cout << "producer starting" << std::endl;
channel.push(1);
channel.push(2);
channel.push(3);
channel.push(4);
channel.push(5);
channel.close();
std::cout << "producer ending" << std::endl;
});
auto start = boost::fibers::barrier(N_CONSUMING_FIBERS);
for (int i = 1; i <= N_CONSUMING_FIBERS; ++i) {
fibers[i] = boost::fibers::fiber([&start, &channel]() {
start.wait();
for (auto item : channel) {
process(item);
}
});
}
for (int i = 0; i <= N_CONSUMING_FIBERS; ++i) {
fibers[i].join();
}
}
class FiberExecutor {
static std::vector<std::thread > extra_threads;
static std::optional<boost::fibers::barrier> barrier;
public:
static void init() {
auto const N_THREADS = std::thread::hardware_concurrency();
barrier.emplace(N_THREADS);
extra_threads.reserve(N_THREADS - 1);
for (auto i = decltype(N_THREADS){0}; i < N_THREADS - 1; ++i) {
extra_threads.emplace_back([N_THREADS]() {
boost::fibers::use_scheduling_algorithm<boost::fibers::algo::work_stealing>(N_THREADS);
barrier->wait(); // start only after everyone has scheduled
barrier->wait(); // end after main thread says to
});
}
boost::fibers::use_scheduling_algorithm<boost::fibers::algo::work_stealing>(N_THREADS);
barrier->wait(); // start only after everyone has scheduled
}
static void exit() {
barrier->wait();
for (auto& thread : extra_threads) {
thread.join();
}
}
};
std::vector<std::thread> FiberExecutor::extra_threads;
std::optional<boost::fibers::barrier> FiberExecutor::barrier;
int Main() {
FiberExecutor::init();
std::cout << "Going once\n";
task();
std::cout << "Going twice\n";
task();
FiberExecutor::exit();
return 0;
}
請注意,這可能不正確。 它也不會將可靠的調度到所有線程上(至少在 Windows 上)。
實際上,它與關於逆問題的問題中的代碼幾乎相同,但需要更新。 另外,我發現使用條件變量而不是障礙是不可靠的,因為主線程可能會先於其他線程運行。
我沒有將 model 初始化和清理為 class,以避免產生可以多次實例化它的錯覺(按順序或並行)。 work_stealing
的構造函數使用全局變量。 你不能干凈地結束基於光纖的任務,然后啟動另一個基於光纖的任務,即使在臨時線程中編碼所有內容並且不以任何方式污染主線程也是如此。
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