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#pragma once
#include <future>
#include <functional>
namespace nix {
/* A callback is a wrapper around a lambda that accepts a valid of
type T or an exception. (We abuse std::future<T> to pass the value or
exception.) */
template<typename T>
class Callback
{
std::function<void(std::future<T>)> fun;
std::atomic_flag done = ATOMIC_FLAG_INIT;
public:
Callback(std::function<void(std::future<T>)> fun) : fun(fun) { }
Callback(Callback && callback) : fun(std::move(callback.fun))
{
auto prev = callback.done.test_and_set();
if (prev) done.test_and_set();
}
void operator()(T && t) noexcept
{
auto prev = done.test_and_set();
assert(!prev);
std::promise<T> promise;
promise.set_value(std::move(t));
fun(promise.get_future());
}
void rethrow(const std::exception_ptr & exc = std::current_exception()) noexcept
{
auto prev = done.test_and_set();
assert(!prev);
std::promise<T> promise;
promise.set_exception(exc);
fun(promise.get_future());
}
};
}
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