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[英]How do I use Boost.Asio's spawn (stackful coroutines) so that it only depends on Boost.Context?
[英]How to wait for completion of all boost:asio's stackful coroutines?
我正在使用asio :: spawn開始一些協同程序,我想等到所有這些都完成后再做其他工作。 怎么做?
控制流程如下:
asio::spawn (io, [] (asio::yield_context yield) {
...
// starting few coroutines
asio::spawn (yield, [] (asio::yield_context yield2) { ... });
asio::spawn (yield, [] (asio::yield_context yield2) { ... });
asio::spawn (yield, [] (asio::yield_context yield2) { ... });
asio::spawn (yield, [] (asio::yield_context yield2) { ... });
// now I want to wait for all of them to finish before I do
// some other work?
...
});
io.run ();
UPDATE
下面是示例代碼
#include <boost/asio.hpp>
#include <boost/asio/spawn.hpp>
#include <boost/asio/steady_timer.hpp>
#include <chrono>
#include <iostream>
using namespace std;
int main ()
{
using namespace boost::asio;
io_service io;
spawn (io, [&] (yield_context yield) {
cout << "main coro starts\n";
auto lambda = [&] (yield_context yield)
{
cout << "in lambda inside subcoroutine - starts\n";
steady_timer t (io, std::chrono::seconds (1));
t.async_wait (yield);
cout << "in lambda inside subcoroutine - finishes\n";
};
// starting few coroutines
spawn (yield, lambda);
spawn (yield, lambda);
// now I want to wait for all of them to finish before I do
// some other work?
// ???
cout << "main coro finishes\n";
});
io.run ();
}
輸出是:
// main coro starts
// in lambda inside subcoroutine - starts
// in lambda inside subcoroutine - starts
// main coro finishes <----
// in lambda inside subcoroutine - finishes
// in lambda inside subcoroutine - finishes
雖然我期待:
// main coro starts
// in lambda inside subcoroutine - starts
// in lambda inside subcoroutine - starts
// in lambda inside subcoroutine - finishes
// in lambda inside subcoroutine - finishes
// main coro finishes
(參見“主要coro飾面”線的地方)
我找到了......一種解決方法。
我可以使用具有無限持續時間的計時器,並從最后的子協程中取消它。 這將喚醒主協程。
#include <boost/asio.hpp>
#include <boost/asio/spawn.hpp>
#include <boost/asio/steady_timer.hpp>
#include <iostream>
using namespace std;
int main ()
{
using namespace boost::asio;
io_service io;
spawn (io, [&] (yield_context yield) {
cout << "main coro starts\n";
steady_timer rendez_vous (io, steady_timer::clock_type::duration::max ());
/* volatile */ int counter = 2;
auto lambda = [&] (yield_context yield)
{
cout << "in lambda inside subcoroutine - starts\n";
steady_timer t (io, boost::chrono::seconds (1));
t.async_wait (yield);
cout << "in lambda inside subcoroutine - finishes\n";
if (--counter == 0)
rendez_vous.cancel ();
};
// starting few coroutines
spawn (yield, lambda);
spawn (yield, lambda);
// now I want to wait for all of them to finish before I do
// some other work?
// ???
boost::system::error_code ignored_ec;
rendez_vous.async_wait (yield [ignored_ec]);
// ignore errors here by reason.
cout << "main coro finishes\n";
});
io.run ();
}
坦率地說,我不喜歡這個解決方案,因為它濫用“計時器”的概念和對象,這可能會浪費系統資源。
更好的選擇是使用光纖(boost.fiber集成到boost.asio中)。 boost :: fiber是一個協程+調度程序+同步類(像std :: thread這樣的API),可以像coroutines一樣在boost.asio上下文中使用。
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