As the commenter said, you need to handle exceptions - (Should the exception thrown by boost::asio::io_service::run() be caught?).
However from looking at the code, the problem seems more likely that you took io_service by reference and it potentially goes out of scope before IoServiceThreadGuard is destructed.
It seems a lot more natural to give them both the same lifetime:
Live On Coliru
#include <boost/asio.hpp>
#include <boost/thread.hpp>
#include <iostream>
namespace asio = boost::asio;
using namespace std::chrono_literals;
static std::ostream logger(std::clog.rdbuf());
static constexpr char const* info = "INFO ";
class IoServiceThreadGuard {
public:
explicit IoServiceThreadGuard(unsigned count) : threadCount_(count) {
for (unsigned int i = 0; i < threadCount_; ++i) {
threads_.create_thread([&]() {
asio::io_service::work work(ioService_);
ioService_.run();
});
}
}
~IoServiceThreadGuard() {
try {
if (not ioService_.stopped()) {
ioService_.stop();
}
threads_.join_all();
} catch (std::exception const& e) {
logger << ::info << "~IoServiceThreadGuard() throw error: " << e.what();
}
}
asio::io_service& get_service() { return ioService_; }
private:
asio::io_service ioService_;
boost::thread_group threads_; // note that destruction is in reverse order of declaration
unsigned threadCount_;
};
int main() {
{
IoServiceThreadGuard io(10);
asio::steady_timer timer(io.get_service(), 1s);
timer.async_wait([](auto ec) { logger << ::info << "timer " << ec.message() << "\n"; });
io.get_service().run_for(2s);
}
logger << "Done" << std::endl;
}
Even better, use the non-deprecated io_context: Live
Even better, drop the Boost Thread dependency and use asio::thread_pool directly.
Now it all works in just 5 lines of code, and it does the correct thing with exception handling as well!
Live On Coliru
#include <boost/asio.hpp>
#include <boost/thread.hpp>
#include <iostream>
namespace asio = boost::asio;
using namespace std::chrono_literals;
static std::ostream logger(std::clog.rdbuf());
static constexpr char const* info = "INFO ";
struct IoThreads {
explicit IoThreads(unsigned count) : ioc_(count) {}
asio::thread_pool& get_context() { return ioc_; }
private:
asio::thread_pool ioc_;
};
int main() {
for (auto time_allotted : {0.5s, 2.0s}) {
logger << "Using 4 threads for " << time_allotted / 1.s << "s" << std::endl;
IoThreads io(4);
asio::steady_timer timer(io.get_context(), 1s);
timer.async_wait([](auto ec) { logger << ::info << "timer " << ec.message() << "\n"; });
std::this_thread::sleep_for(time_allotted);
}
logger << "Done" << std::endl;
}
Prints (in total run time of 2.518s):
Using 4 threads for 0.5s
Using 4 threads for 2s
INFO timer Success
Done
Simplify, Generalize, De-couple
At this point, consider forgetting the redundant "guard" class, and also consider passing an executor (by value) instead of hardcoding asio::io_service&, asio::io_context& or asio::thread_pool&. The executor is a lightweight abstraction that decouples your asynchronous code from the execution context. For example, you might use a strand-executor in multi-threaded context, without the async code needing to know.
Live On Coliru
#include <boost/asio.hpp>
#include <boost/thread.hpp>
#include <iostream>
namespace asio = boost::asio;
using boost::core::demangle;
using namespace std::chrono_literals;
class Demo { // just a sample, this could be a network server/client
public:
Demo(asio::any_io_executor ex) : timer_(ex) {} // take an executor, don't care what type
void run_async_stuff() {
std::cout << "Demo on " << demangle(timer_.get_executor().target_type().name()) << std::endl;
timer_.expires_after(1s);
timer_.async_wait(on_completion); // or something like `asio::async_read` etc.
}
private:
static void on_completion(boost::system::error_code ec) {
std::cout << "async_stuff " << ec.message() << "\n";
}
asio::steady_timer timer_; // this could be tcp::socket or so
};
int main() {
{
asio::io_context io(1);
{
Demo demo(io.get_executor()); // no strand required
demo.run_async_stuff();
io.run_for(500ms);
} // ~Demo cancels uncompleted async operation
io.run(); // To see `operaion_aborted` completion
}
{
asio::thread_pool io(10);
Demo demo(make_strand(io)); // notice strand executor
demo.run_async_stuff();
std::this_thread::sleep_for(1.5s);
}
std::cout << "Done" << std::endl;
}
Prints e.g.
Demo on boost::asio::io_context::basic_executor_type<std::allocator<void>, 0ul>
async_stuff Operation canceled
Demo on boost::asio::strand<boost::asio::thread_pool::basic_executor_type<std::allocator<void>, 0u> >
async_stuff Success
Done
