How to get return value outside visit function?

[sukeyisme]

No description provided.

[madmongo1]

You're going to have to provide some more context to your question.

[sukeyisme]

net::awaitable< void >
visit_site(http::connection_cache &cache, std::string url)

How get result from this function?

[madmongo1]

This function starts a corotuine that "returns" void.

To get it to return a value you'd have to modify the function.

For example:

blog-new-year-2021/src/http/connection_cache.hpp

Line 28 in 50f5f94

net::awaitable< response_type >

[sukeyisme]

But,how to get return value in a nomal function, you get the return in another coroutine.

[sukeyisme]

net::awaitable< void >
visit_site(http::connection_cache &cache, std::string url)
{
auto then = std::chrono::steady_clock::now();
try
{
auto result = co_await cache.call(http::verb::get, url);
auto time = std::chrono::duration_cast< std::chrono::milliseconds >(
std::chrono::steady_clock::now() - then);
std::cout << "GET " << url << " -> " << result->base().result_int()
<< " " << result->base().reason() << " in " << (time).count()
<< "ms\n";
}
catch (std::exception &e)
{
auto time = std::chrono::duration_cast< std::chrono::milliseconds >(
std::chrono::steady_clock::now() - then);
std::cout << "GET " << url << " -> "
<< " exception: " << e.what() << " in " << (time).count()
<< "ms\n";
}
}

net::awaitable< void >
crawl()
{
// build a connection cache
auto cache = http::connection_cache(co_await net::this_coro::executor);

// Build the async condition variable in order to know when all requests
// have completed
std::size_t pending_count = 0;
auto        cv = net::steady_timer(co_await net::this_coro::executor);
cv.expires_at(net::steady_timer::clock_type::time_point::max());

for (int i = 0; i < 5; ++i)
    for (auto &hostname : urls_large_data())
    {
        auto url = std::string("https://") + hostname + "/";
        ++pending_count;
        net::co_spawn(
            co_await net::this_coro::executor,
            visit_site(cache, std::move(url)),
            [&](std::exception_ptr) {
                if (--pending_count == 0)
                    cv.cancel_one();
            });
    }

std::cout << "waiting for " << pending_count << " requests\n";

while (pending_count)
    co_await cv.async_wait(
        asio::experimental::as_single(net::use_awaitable));

std::cout << "done\n";

}

int
main()
{
net::io_context ioctx;

net::co_spawn(
    ioctx.get_executor(), [] { return crawl(); }, net::detached);

ioctx.run();

}

[madmongo1]

This program is written in terms of asynchronous coroutines.