Throwing Clear Exception in a Multithreaded Context with a proram STOP - c++

Question

I have a program that throws in another thread as follows:
#include <iostream>
#include <stdexcept>
#include <thread>
void op()
{
std::cout << "OP HELLO WORLD" << std::endl;
throw(std::runtime_error("OP ERROR"));
};
int main(int argc, char* argv[])
{
//throw(std::runtime_error("MAIN ERROR"));
std::thread t(op);
t.join();
std::cout << "MAIN HELLO WORLD" << std::endl;
};
I want my program to print a clear error message and stop. I know I can use std::abort or std::terminate, however the error message is not clear and does not contain the log "OP ERROR".
Could you please help me code a program that when fails exits and logs a clear error message. std::future does not work too when I tried a try, catch block?

Answer 1

Are you looking for something like this?
#include <iostream>
#include <stdexcept>
#include <thread>
#include <future>
void op()
{
std::cout << "OP HELLO WORLD" << std::endl;
throw(std::runtime_error("OP ERROR. File: " __FILE__ ", Line: "+ std::to_string(__LINE__)));
};
int main(int argc, char* argv[])
{
//throw(std::runtime_error("MAIN ERROR"));
auto res = std::async(op);
try {
res.get();
} catch(const std::exception& e) {
std::cerr << "Error: " << e.what() << std::endl;
return -1;
}
std::cout << "MAIN HELLO WORLD" << std::endl;
}
If you want to output errors for all threads without returning exceptions to main thread, you can setup your own version of terminate().
#include <iostream>
#include <cstdlib>
#include <exception>
#include <thread>
void op()
{
std::cout << "OP HELLO WORLD" << std::endl;
throw(std::runtime_error("OP ERROR"));
}
void my_terminate()
{
auto eptr = std::current_exception();
try {
if (eptr) {
std::rethrow_exception(eptr);
}
} catch(const std::exception& e) {
std::cerr << "Error: " << e.what() << std::endl;
}
std::abort();
}
int main(int argc, char* argv[])
{
std::set_terminate(my_terminate);
//throw(std::runtime_error("MAIN ERROR"));
std::thread t(op);
t.join();
std::cout << "MAIN HELLO WORLD" << std::endl;
}
For some reason MSVC uses per-thread handlers, and for it to work you need to call set_termnate() in every thread separatelly.

Answer 2

To avoid the call to std::terminate, make sure exceptions don't "leak" outside the thread function.
void op()
{
try {
std::cout << "OP HELLO WORLD" << std::endl;
throw std::runtime_error("OP ERROR");
} catch (const std::exception& e) {
std::cerr << "Exception: " << e.what() << std::endl;
exit(1);
}
}
If you want to automatically see the exception's file and line number, in C++ it is not generally possible.
If you want to catch all exceptions in a single place in the main thread, you need to catch them and pass them to the main thread. There's a useful wrapper utility std::packaged_task which gives back a future on which you can wait for the result or an exception.
#include <iostream>
#include <stdexcept>
#include <thread>
#include <future>
void op()
{
std::cout << "OP HELLO WORLD" << std::endl;
throw std::runtime_error("OP ERROR");
}
int main(int argc, char* argv[])
{
try {
std::packaged_task<void()> task{&op};
auto result = task.get_future();
std::thread t{std::move(task)};
t.join();
result.get();
std::cout << "MAIN HELLO WORLD" << std::endl;
} catch (const std::exception& e) {
std::cerr << "Exception: " << e.what() << std::endl;
}
}