Unable to process boost asio:- async read buffer's callback asynchronously - c++

Question

I'm using boost::asio::async_read() method to asynchronously get response from server which take 10 second to process request. I am able to read response successfully. but I am attaching callback to this function to process received response which take 10 seconds. I am unable to find how i can process that callback asynchronously.
void read_response(std::string data)
{
cout << data << endl;
sleep(10);
// if you think sleep works differently if i send another rest api request from here still this function blocks the processing
}
boost::asio::async_read(socket, boost::asio::buffer(buffer), [&](const boost::system::error_code&
error,
std::size_t bytes_transferred) {
io_context.post([&]() {
read_response(buffer.data());
//read_response is not processing asynchronously
});
});
I tried posting function to io_context, i tried using
std::async(std::launch::deferred, read_handler,error,bytes_transferred,buffer.data()).wait() ;
I am new to asyn programming and c++ programming.

Answer 1

Indeed, don't do blocking operations on the IO service. Or grow the thread pool to accomodate for the maximum number of concurrent tasks that must be supported.
In all circumstances, copy the message into your read handler, instead of passing the buffer directly (as you did) as that invites race conditions/stale references.
Let's demonstrate using httpbin.org/delay:
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#include <boost/asio.hpp>
#include <iomanip>
#include <iostream>
namespace asio = boost::asio;
using asio::ip::tcp;
using namespace std::chrono_literals;
std::string const request = "GET /delay/10 HTTP/1.1\r\nHost: httpbin.org\r\n\r\n";
void read_response(std::string data) {
std::cout << "Asynchronously received response: " << quoted(data) << std::endl;
sleep(10);
}
int main() {
asio::io_context ioc(1);
asio::thread_pool work(10); // support 10 tasks along-side async IO
tcp::socket conn(ioc);
connect(conn, tcp::resolver(ioc).resolve("httpbin.org", "80"));
write(conn, asio::buffer(request));
std::string buf;
async_read_until( //
conn, asio::dynamic_buffer(buf), "\r\n\r\n",
[&work, &buf](boost::system::error_code ec, size_t n) {
std::cout << "\n*** Completion " << ec.message() << ", " << n << std::endl;
post(work, [msg = buf.substr(0, n)] {
// NOTE: lambda owns msg, not a reference to `buf`
read_response(std::move(msg));
});
});
std::thread([&ioc] {
ioc.run();
std::cout << "\n*** IO complete" << std::endl;
}).detach();
for (int i = 0; i < 15; ++i) {
std::cout << "." << std::flush;
std::this_thread::sleep_for(1s);
}
work.join();
std::cout << "\n*** Work Done" << std::endl;
}
This shows work continuing, "asynchronously" (relative to IO) well after ioc completes: