A promise future implementation with continuation.
cfuture is header-only, and it only has a single file cfuture.hpp. It requires cpp14.
cfuture is aimed to provide a promise/future class which supports future::then to attach the continuations like a chain. I admit that async/await is a better practice than promise/future when writing the asynchronous codes. But there are still a lot of projects cannot use c++20 or higher standard. Or, sometimes, the promise/future is easier than coroutine.
The boost::future and std::experimental::future (in concurrency TS) both support then. But I hope to provide a light and easy-to-rely implementation. It isn't the cfuture's goal to be completely complied with the design of std::future or boost::future. But still, it will very close to them. It could be an alternate in most cases.
using namespace std::chrono_literals;
using namespace cfuture;
Promise<int> p;
std::cout << "the main thread is " << std::this_thread::get_id() << '\n';
std::thread th([&] {
std::cout << "run in thread " << std::this_thread::get_id() << '\n';
std::this_thread::sleep_for(100ms);
p.set_value(1);
});
Future<std::string> f;
f = p.get_future()
.then([](Future<int> v) {
Promise<int> p;
auto future = p.get_future();
std::thread th([v = v.get(), p = std::move(p)]() mutable {
std::cout << "run in thread " << std::this_thread::get_id() << '\n';
std::this_thread::sleep_for(100ms);
p.set_value(v + 2);
});
th.detach();
return future;
})
.then([](Future<int> v) -> long {
std::cout << "run in thread " << std::this_thread::get_id() << '\n';
std::this_thread::sleep_for(1ms);
return v.get() + 3;
})
.then([](Future<long> v) {
std::cout << "run in thread " << std::this_thread::get_id() << '\n';
std::this_thread::sleep_for(1ms);
return std::to_string(v.get() + 4);
});
std::cout << f.get() << '\n';
th.join();The possible output of the above codes is
the main thread is 0x7ff857913340
run in thread 0x70000da84000
run in thread 0x70000db07000
run in thread 0x70000db07000
run in thread 0x70000db07000
10