examples

commit 8d22581197d69a18816496fb3693e16b8f04b350
parent f6636a139c4bc1c525fe9db4a1cc2eb07d4d4f50
Author: Henry Wilson <henry@henryandlizzy.uk>
Date:   Wed,  5 Jul 2023 08:27:12 +0000

coro-generator-consumer: add coroutine example for generating and consuming

Diffstat:
A
src/coro-generator-consumer.cpp
 | 
117
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

1 file changed, 117 insertions(+), 0 deletions(-)
diff --git a/src/coro-generator-consumer.cpp b/src/coro-generator-consumer.cpp
@@ -0,0 +1,117 @@
+#include <coroutine> // coroutine_handle noop_coroutine suspend_always suspend_never
+#include <exception> // terminate
+#include <iostream> // cout
+#include <optional> // optional
+#include <cassert> // assert
+#include <utility> // exchange
+
+struct sentry
+{
+	char const* msg;
+	sentry(char const* m) : msg(m) { std::cout << msg << " {\n"; }
+	~sentry() { std::cout << "} " << msg << '\n'; }
+};
+
+
+struct symmetric_transfer : std::suspend_always
+{
+	std::coroutine_handle<> await_suspend(std::coroutine_handle<>) { return h; }
+
+	std::coroutine_handle<> h;
+};
+
+struct generator
+{
+	struct promise_type;
+	~generator()
+	{
+		h.destroy();
+	}
+	promise_type& promise() { return h.promise(); }
+
+	std::coroutine_handle<promise_type> h;
+};
+
+struct generator::promise_type
+{
+	promise_type() { std::cout << __PRETTY_FUNCTION__ << '\n'; }
+	~promise_type() { std::cout << __PRETTY_FUNCTION__ << '\n'; }
+	generator get_return_object() { return {std::coroutine_handle<promise_type>::from_promise(*this)}; }
+	std::suspend_always initial_suspend() { return {}; }
+	symmetric_transfer yield_value(unsigned v)
+	{
+		assert(not yielded_value);
+		yielded_value = v;
+		if (yield_to)
+			return {{}, std::exchange(yield_to, {})};
+		else
+			return {{}, std::noop_coroutine()};
+	}
+	std::suspend_always final_suspend() noexcept { return {}; }
+
+	bool await_ready() { return yielded_value.has_value(); }
+	std::coroutine_handle<> await_suspend(std::coroutine_handle<> h)
+	{
+		assert(not yield_to);
+		yield_to = h;
+		return std::coroutine_handle<promise_type>::from_promise(*this);
+	}
+	unsigned await_resume() { return *std::exchange(yielded_value, {}); }
+	void unhandled_exception() { std::terminate(); }
+
+private:
+	std::optional<unsigned> yielded_value;
+	std::coroutine_handle<> yield_to;
+};
+
+
+generator number_generator(unsigned d)
+{
+	sentry s(__func__);
+	unsigned i = 0;
+	for (;;)
+		co_yield i += d;
+}
+
+struct consumer
+{
+	struct promise_type {
+		promise_type() { std::cout << __PRETTY_FUNCTION__ << '\n'; }
+		~promise_type() { std::cout << __PRETTY_FUNCTION__ << '\n'; }
+		consumer get_return_object() { return {std::coroutine_handle<promise_type>::from_promise(*this)}; }
+		std::suspend_never initial_suspend() { return {}; }
+		void return_value(unsigned x) { result = x; }
+		std::suspend_always final_suspend() noexcept { return {}; }
+		void unhandled_exception() { std::terminate(); }
+		unsigned result;
+	};
+
+	~consumer() {
+		h.destroy();
+	}
+	unsigned result() const {
+		return h.promise().result;
+	}
+
+	std::coroutine_handle<promise_type> h;
+};
+
+consumer number_consumer(generator::promise_type& g, unsigned i)
+{
+	sentry s(__func__);
+	unsigned total = 0;
+	while (i--)
+	{
+		unsigned x = co_await g;
+		std::cout << __func__ << ": " << x << '\n';
+		total += x;
+	}
+	co_return total;
+}
+
+int main()
+{
+	auto g = number_generator(2);
+	auto c = number_consumer(g.promise(), 5);
+	std::cout << __PRETTY_FUNCTION__ << ": " << c.result() << '\n';
+}