From b138f99f4c20ead0471358ed95de048e233a2c4e Mon Sep 17 00:00:00 2001
From: Myles Busig <mdbusig@gmail.com>
Date: Mon, 22 Jul 2024 18:43:08 -0600
Subject: [PATCH] Add fiber interface

---
 include/mtl/fiber.hpp | 164 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 164 insertions(+)
 create mode 100644 include/mtl/fiber.hpp

diff --git a/include/mtl/fiber.hpp b/include/mtl/fiber.hpp
new file mode 100644
index 0000000..be20222
--- /dev/null
+++ b/include/mtl/fiber.hpp
@@ -0,0 +1,164 @@
+#pragma once
+
+#include <cstddef>
+#include <cstdint>
+#include <tuple>
+
+#ifndef MTL_FIBER_MAX_ACTIVE
+#define MTL_FIBER_MAX_ACTIVE 4
+#endif
+
+#ifndef MTL_FIBER_MAX_QUEUE
+#define MTL_FIBER_MAX_QUEUE 256
+#endif
+
+#ifndef MTL_FIBER_MAX_QUEUE_LOW
+#define MTL_FIBER_MAX_QUEUE_LOW MTL_FIBER_MAX_QUEUE
+#endif
+
+#ifndef MTL_FIBER_MAX_QUEUE_MED
+#define MTL_FIBER_MAX_QUEUE_MED MTL_FIBER_MAX_QUEUE
+#endif
+
+#ifndef MTL_FIBER_MAX_QUEUE_HI
+#define MTL_FIBER_MAX_QUEUE_HI MTL_FIBER_MAX_QUEUE
+#endif
+
+#ifndef MTL_FIBER_STACK_SIZE
+#define MTL_FIBER_STACK_SIZE 4096
+#endif
+
+#ifndef MTL_FIBER_MAX_DEPENDENTS
+#define MTL_FIBER_MAX_DEPENDENTS 8
+#endif
+
+extern "C" void mtl_yield();
+
+namespace mtl {
+
+constexpr auto yield = mtl_yield;
+
+// TEMPORARY
+template <typename T, size_t N>
+class vector {
+public:
+	void push_back(T x) {}
+
+	T* begin() {return nullptr;}
+	T* end() { return nullptr;}
+	void clear();
+	constexpr size_t capacity() { return N; }
+	size_t size() { return 0; }
+};
+
+using fiber_stack = uint8_t[MTL_FIBER_STACK_SIZE];
+
+class ifiber;
+
+class ifiber_dependency {
+protected:
+	mtl::vector<ifiber*, MTL_FIBER_MAX_DEPENDENTS> m_dependents;
+	void clear();
+
+public:
+	void add_dependent(ifiber* dependent);
+};
+
+class fiber_trigger;
+
+extern ifiber* this_fiber;
+
+class ifiber : public ifiber_dependency {
+public:
+	enum class priority {
+		low,
+		med,
+		hi,
+	};
+
+protected:
+	friend class ifiber_dependency;
+
+	static mtl::vector<ifiber*, MTL_FIBER_MAX_QUEUE_LOW> s_queue_low;
+	static mtl::vector<ifiber*, MTL_FIBER_MAX_QUEUE_MED> s_queue_med;
+	static mtl::vector<ifiber*, MTL_FIBER_MAX_QUEUE_HI> s_queue_hi;
+
+	bool m_finished;
+	priority m_priority;
+	uint32_t m_dependencies;
+
+	ifiber(priority priority) : m_priority(priority), m_finished(false), m_dependencies(0) {
+		switch (priority) {
+		case priority::low:
+			// If the queue is already full, a currently running
+			// fiber must finish first to free room in the queue.
+			// If all currently running fibers are waiting for a
+			// dependency, we will throw an exception.
+			if (s_queue_low.size() == s_queue_low.capacity()) {
+				mtl::yield();
+			}
+			s_queue_low.push_back(this);
+			break;
+		case priority::med:
+			if (s_queue_med.size() == s_queue_med.capacity()) {
+				mtl::yield();
+			}
+			s_queue_med.push_back(this);
+			break;
+		case priority::hi:
+			if (s_queue_hi.size() == s_queue_hi.capacity()) {
+				mtl::yield();
+			}
+			s_queue_hi.push_back(this);
+			break;
+		}
+	}
+
+public:
+};
+
+class fiber_trigger : public ifiber_dependency {
+public:
+	void trigger() {
+		clear();
+	}
+};
+
+
+template <typename RetType, typename... ArgTypes>
+class fiber : public ifiber {
+public:
+	using FuncType = RetType(*)(ArgTypes...);
+
+private:
+	FuncType m_func;
+	std::tuple<ArgTypes...> m_args;
+
+public:
+	fiber(FuncType func, ArgTypes... args)
+		: ifiber(priority::med), m_func(func), m_args(args...) {}
+
+	fiber(FuncType func, ArgTypes... args, priority priority)
+		: ifiber(priority), m_func(func), m_args(args...) {}
+	
+	// TODO: Add priority+dependency constructors
+
+	fiber(FuncType func, ArgTypes... args, const ifiber_dependency& dep)
+		: ifiber(priority::med), m_func(func), m_args(args...) {
+		dep.add_dependent(this);
+	}
+
+	template <typename It>
+	fiber(FuncType func, ArgTypes... args, It begin, It end)
+		: ifiber(priority::med), m_func(func), m_args(args...) {
+		for (; begin != end; ++begin) {
+			begin->add_dependent(this);
+		}
+	}
+	
+	void join() {
+		this_fiber->add_dependent(this);
+	}
+};
+
+} // namespace mtl