[core] Use single asio context along the IO path

[dentiny]

IIUC, we should use one single io_context, which represents one eventloop along the async operation path.

[dayshah]

would this call poll on the io_service in a different thread, and is this the main_io_context for the gcs. I actually just made the other pr with the concurrency hint for main_io_context which assumes io ops would only happen on a single thread

[dentiny]

Yes I understand the implication, please notice all other redis related operations are scheduled on the same eventloop.

[jjyao]

If I'm calling ResolveDNS from the io_service thread, will this be a problem (deadlock)?

[dentiny]

Not a problem, my test script.

#include <boost/asio.hpp>
#include <boost/asio/ip/tcp.hpp>
#include <iostream>
#include <memory>

void resolveAddress(boost::asio::io_context& io_context, const std::string& host, const std::string& port) {
    try {
        // Create a resolver
        boost::asio::ip::tcp::resolver resolver(io_context);

        // Resolve the address
        boost::asio::ip::tcp::resolver::results_type endpoints = resolver.resolve(host, port);

        std::cout << "Resolved endpoints:" << std::endl;
        for (const auto& endpoint : endpoints) {
            std::cout << endpoint.endpoint() << std::endl;
        }
    } catch (const std::exception& e) {
        std::cerr << "Error: " << e.what() << std::endl;
    }
}

int main() {
    try {
        boost::asio::io_context io_context;

        // Post a functor into the io_context
        io_context.post([&io_context]() {
            std::cout << "Functor running in io_context." << std::endl;

            // Use the io_context with a TCP resolver
            resolveAddress(io_context, "example.com", "80");
        });

        // Run the io_context
        io_context.run();
    } catch (const std::exception& e) {
        std::cerr << "Exception: " << e.what() << std::endl;
    }

    return 0;
}

[dentiny]

Output for the above code snippet.

Functor running in io_context.
Resolved endpoints:
93.184.215.14:80
[2606:2800:21f:cb07:6820:80da:af6b:8b2c]:80