我有std::vector
std::function<void()>
这样:
std::map<Event, std::vector<std::function<void()>>> observers_;
调用每个函数:
for (const auto& obs : observers_.at(event)) obs();
我想将其转换为并行for循环。由于我使用的是C++14
,并且无法访问std::execution::parallel
C++17
,因此我找到了一个允许我创建ThreadPool的小库。
如何将for (const auto& obs : observers_.at(event)) obs();
转换为并行调用observers_
中每个函数的版本?我似乎无法使语法正确。我试过,但这不起作用。
std::vector<std::function<void()>> vec = observers_.at(event);
ThreadPool::ParallelFor(0, vec.size(), [&](int i)
{
vec.at(i);
});
使用以下库的示例程序:
#include <iostream>
#include <mutex>
#include "ThreadPool.hpp"
////////////////////////////////////////////////////////////////////////////////
int main()
{
std::mutex critical;
ThreadPool::ParallelFor(0, 16, [&] (int i)
{
std::lock_guard<std::mutex> lock(critical);
std::cout << i << std::endl;
});
return 0;
}
ThreadPool库。
#ifndef THREADPOOL_HPP_INCLUDED
#define THREADPOOL_HPP_INCLUDED
////////////////////////////////////////////////////////////////////////////////
#include <thread>
#include <vector>
#include <cmath>
////////////////////////////////////////////////////////////////////////////////
class ThreadPool {
public:
template<typename Index, typename Callable>
static void ParallelFor(Index start, Index end, Callable func) {
// Estimate number of threads in the pool
const static unsigned nb_threads_hint = std::thread::hardware_concurrency();
const static unsigned nb_threads = (nb_threads_hint == 0u ? 8u : nb_threads_hint);
// Size of a slice for the range functions
Index n = end - start + 1;
Index slice = (Index) std::round(n / static_cast<double> (nb_threads));
slice = std::max(slice, Index(1));
// [Helper] Inner loop
auto launchRange = [&func] (int k1, int k2) {
for (Index k = k1; k < k2; k++) {
func(k);
}
};
// Create pool and launch jobs
std::vector<std::thread> pool;
pool.reserve(nb_threads);
Index i1 = start;
Index i2 = std::min(start + slice, end);
for (unsigned i = 0; i + 1 < nb_threads && i1 < end; ++i) {
pool.emplace_back(launchRange, i1, i2);
i1 = i2;
i2 = std::min(i2 + slice, end);
}
if (i1 < end) {
pool.emplace_back(launchRange, i1, end);
}
// Wait for jobs to finish
for (std::thread &t : pool) {
if (t.joinable()) {
t.join();
}
}
}
// Serial version for easy comparison
template<typename Index, typename Callable>
static void SequentialFor(Index start, Index end, Callable func) {
for (Index i = start; i < end; i++) {
func(i);
}
}
};
#endif // THREADPOOL_HPP_INCLUDED
答案 0 :(得分:3)
似乎你应该改变:
vec.at(i); // Only returns a reference to the element at index i
成:
vec.at(i)(); // The second () calls the function
--- OR ---
vec[i](); // Same
答案 1 :(得分:1)
提示:这是做什么的?
vec.at(i);
你想要做什么?
无意义的是,当您的意思是at()
时,您正在使用[]
。
答案 2 :(得分:-3)
这有效:
ThreadPool::ParallelFor(0, (int)vec.size(), [&] (int i)
{
vec[i]();
});