最佳做法是不要重复使用池（如果您不断创建新池，池的用途是什么？）。
如果您想确保将批次“计时”在一起，我建议在期货上使用 when_all：
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#define BOOST_THREAD_PROVIDES_FUTURE_WHEN_ALL_WHEN_ANY
#include <iostream>
#include <boost/bind.hpp>
#include <boost/asio.hpp>
#include <boost/thread.hpp>
uint64_t foo(uint64_t begin) {
uint64_t prev[] = {begin, 0};
for (uint64_t i = 0; i < 1000000000; ++i) {
const auto tmp = (prev[0] + prev[1]) % 1000;
prev[1] = prev[0];
prev[0] = tmp;
}
return prev[0];
}
void batch(boost::asio::thread_pool &pool, const uint64_t a[2])
{
using T = boost::packaged_task<uint64_t>;
T tasks[] {
T(boost::bind(foo, a[0])),
T(boost::bind(foo, a[1])),
};
auto all = boost::when_all(
tasks[0].get_future(),
tasks[1].get_future());
for (auto& t : tasks)
post(pool, std::move(t));
auto [r0, r1] = all.get();
std::cerr << "foo(" << a[0] << "): " << r0.get() << " foo(" << a[1] << "): " << r1.get() << std::endl;
}
int main() {
boost::asio::thread_pool pool(2);
const uint64_t a[] = {2, 4};
batch(pool, a);
const uint64_t b[] = {3, 5};
batch(pool, b);
const uint64_t c[] = {7, 9};
batch(pool, c);
}
打印
foo(2): 2 foo(4): 4
foo(3): 503 foo(5): 505
foo(7): 507 foo(9): 509
我会考虑
广义的
通过不对批量大小进行硬编码，使其更加灵活。毕竟，池大小已经固定，我们不需要“确保批次适合”之类的：
Live On Coliru
#define BOOST_THREAD_PROVIDES_FUTURE_WHEN_ALL_WHEN_ANY
#include <iostream>
#include <boost/bind.hpp>
#include <boost/asio.hpp>
#include <boost/thread.hpp>
#include <boost/thread/future.hpp>
struct Result { uint64_t begin, result; };
Result foo(uint64_t begin) {
uint64_t prev[] = {begin, 0};
for (uint64_t i = 0; i < 1000000000; ++i) {
const auto tmp = (prev[0] + prev[1]) % 1000;
prev[1] = prev[0];
prev[0] = tmp;
}
return { begin, prev[0] };
}
void batch(boost::asio::thread_pool &pool, std::vector<uint64_t> const a)
{
using T = boost::packaged_task<Result>;
std::vector<T> tasks;
tasks.reserve(a.size());
for(auto begin : a)
tasks.emplace_back(boost::bind(foo, begin));
std::vector<boost::unique_future<T::result_type> > futures;
for (auto& t : tasks) {
futures.push_back(t.get_future());
post(pool, std::move(t));
}
for (auto& fut : boost::when_all(futures.begin(), futures.end()).get()) {
auto r = fut.get();
std::cerr << "foo(" << r.begin << "): " << r.result << " ";
}
std::cout << std::endl;
}
int main() {
boost::asio::thread_pool pool(2);
batch(pool, {2});
batch(pool, {4, 3, 5});
batch(pool, {7, 9});
}
打印
foo(2): 2
foo(4): 4 foo(3): 503 foo(5): 505
foo(7): 507 foo(9): 509
Generalized2：可变参数简化
与普遍认为的相反（老实说，通常发生的情况），这次我们可以利用可变参数来摆脱所有中间向量（每一个）：
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void batch(boost::asio::thread_pool &pool, T... a)
{
auto launch = [&pool](uint64_t begin) {
boost::packaged_task<Result> pt(boost::bind(foo, begin));
auto fut = pt.get_future();
post(pool, std::move(pt));
return fut;
};
for (auto& r : {launch(a).get()...}) {
std::cerr << "foo(" << r.begin << "): " << r.result << " ";
}
std::cout << std::endl;
}
如果你坚持及时输出结果，你仍然可以在组合中添加when_all（需要更多的英雄来解包元组）：
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template <typename...T>
void batch(boost::asio::thread_pool &pool, T... a)
{
auto launch = [&pool](uint64_t begin) {
boost::packaged_task<Result> pt(boost::bind(foo, begin));
auto fut = pt.get_future();
post(pool, std::move(pt));
return fut;
};
std::apply([](auto&&... rfut) {
Result results[] {rfut.get()...};
for (auto& r : results) {
std::cerr << "foo(" << r.begin << "): " << r.result << " ";
}
}, boost::when_all(launch(a)...).get());
std::cout << std::endl;
}
两者仍然打印相同的结果
消息队列
这是非常自然的提升，并且可以跳过大多数复杂性。如果您还想按批次报告，则必须协调：
Live On Coliru
#include <iostream>
#include <boost/asio.hpp>
#include <memory>
struct Result { uint64_t begin, result; };
Result foo(uint64_t begin) {
uint64_t prev[] = {begin, 0};
for (uint64_t i = 0; i < 1000000000; ++i) {
const auto tmp = (prev[0] + prev[1]) % 1000;
prev[1] = prev[0];
prev[0] = tmp;
}
return { begin, prev[0] };
}
using Group = std::shared_ptr<size_t>;
void batch(boost::asio::thread_pool &pool, std::vector<uint64_t> begins) {
auto group = std::make_shared<std::vector<Result> >(begins.size());
for (size_t i=0; i < begins.size(); ++i) {
post(pool, [i,begin=begins.at(i),group] {
(*group)[i] = foo(begin);
if (group.unique()) {
for (auto& r : *group) {
std::cout << "foo(" << r.begin << "): " << r.result << " ";
std::cout << std::endl;
}
}
});
}
}
int main() {
boost::asio::thread_pool pool(2);
batch(pool, {2});
batch(pool, {4, 3, 5});
batch(pool, {7, 9});
pool.join();
}
请注意，这是对group 的并发访问，由于元素访问的限制，这是安全的。
打印：
foo(2): 2
foo(4): 4 foo(3): 503 foo(5): 505
foo(7): 507 foo(9): 509