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oliverepper/senders_and_receivers.cpp

Last active November 27, 2022 19:19
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senders_and_receivers.cpp
/*
* This is all Eric Nieblers work, see: https://youtu.be/h-ExnuD6jms
*/
#include <thread>
#include <vector>
auto new_thread() {
return [](auto p) {
std::thread { [p=std::move(p)]() mutable {
p.set_value();
}}.detach();
};
}
auto async_algo(auto executor) {
return then(executor, []() {
return 42;
});
}
template <typename P, typename N>
struct then_sender {
P p;
N next;
void set_value(auto ...args) {
try {
p.set_value(next(args...));
} catch (...) {
p.set_error(std::current_exception());
}
}
void set_error(auto e) {
p.set_error(e);
}
};
auto then(auto task, auto next) {
return [=](auto p){
task(then_sender<decltype(p), decltype(next)>{p, next});
};
}
template <typename T>
struct shared {
std::mutex mtx;
std::condition_variable cv;
std::variant<std::monostate, std::exception_ptr, T> data;
};
template <typename T>
struct promise {
shared<T>* s;
// set
template <int I>
void _set(auto ...args) {
std::unique_lock lck{s->mtx};
s->data.template emplace<I>(args...);
s->cv.notify_one();
}
void set_value(auto ...args) {
_set<2>(args...);
}
void set_error(auto e) {
_set<1>(e);
}
};
template <typename T, typename Task>
T sync_wait(Task task) {
shared<T> s;
// start
task(promise<T>{&s});
// get
{
std::unique_lock lck{s.mtx};
s.cv.wait(lck, [&s]() { return s.data.index() != 0; });
}
if (s.data.index() == 1) std::rethrow_exception( std::get<1>(s.data) );
return std::move(std::get<2>(s.data));
}
int main() {
auto start = async_algo(new_thread());
auto next = then(start, [](int i) {
return i / 2;
});
printf("%d\n", sync_wait<int>(next));
return 0;
}
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