gplib/include/gp/vfs/scheduling/simple_scheduling.hpp

#pragma once
#include "gp/vfs/system.hpp"

namespace gp{

	class simple_scheduling : public gp::scheduling_scheme {
		struct locked_circular_buffer {
			std::atomic_bool lock;
			gp::array<gp::topic_list::node_ptr, gp_config::limits::max_processes> processes;
			size_t read_idx = 0;
			size_t write_idx = 0;

			void push(gp::topic_list::node_ptr node) {
				bool t = true;
				bool f = false;
				while(not lock.compare_exchange_strong(f,t)){}
				{
					gp_config::assertion((write_idx + 1)%processes.size() != read_idx, "bad push to circular buffer");
					processes[write_idx] = node;
					write_idx=(write_idx+1)%processes.size();
				}
				while(not lock.compare_exchange_strong(t,f)){}
			}

			gp::topic_list::node_ptr pop() {
				bool t = true;
				bool f = false;
				gp::topic_list::node_ptr ret;
				while(not lock.compare_exchange_strong(f,t)){}
				{
					if(read_idx == write_idx) {
						ret = nullptr;
					} else {
						ret = processes[read_idx];
						read_idx=(read_idx+1)%processes.size();
					}
				}
				while(not lock.compare_exchange_strong(t,f)){}
				return ret;
			}
			
		};


		locked_circular_buffer running;
		locked_circular_buffer waiting;
		locked_circular_buffer to_clean;
		locked_circular_buffer naughty;
		system* sys = nullptr;

	public:
		simple_scheduling()
		{}

		virtual void link(system& value) {
			gp_config::assertion(!(sys), "Double linkage detected"); 
			sys = &value;

			sys->process_managers.emplace_back(*sys,0);
		}

		virtual gp::topic_list::node_ptr one(size_t) {
			auto v = running.pop();
			do{
				if(v) return v;
				v = running.pop();
			}while(true);
		}

		virtual void push(gp::topic_list::node_ptr node) {
			running.push(node);
		}

		virtual gp::topic_list::node_ptr next(size_t, gp::topic_list::node_ptr current) {
			switch(current->value->state) {
				case process_status::inactive:
				case process_status::running:
					running.push(current);
					break;
				case process_status::finished:
					to_clean.push(current);
					break;
				case process_status::zombie:
					naughty.push(current);
					break;
				case process_status::waiting:
					waiting.push(current);
					break;
			}
			return one(0);
		}

		virtual gp::scheduler& current_scheduler() {
			return sys->process_managers[0];
		}
	};
}