gplib/include/gp/vfs/system.hpp

#pragma once

#include "gp/algorithm/foreach.hpp"
#include "gp/algorithm/reference.hpp"
#include "gp/allocator/allocator.hpp"
#include "gp/vector.hpp"
#include "gp/vfs/file_description.hpp"
#include "gp/vfs/filesystem.hpp"
#include "gp/vfs/scheduler.hpp"

namespace gp{
// TODO: thread safety
class system {
	gp::reference_wrapper<gp::allocator> system_allocator;
	gp::vector<gp::filesystem*> filesystems{system_allocator};
	gp::vector<gp::scheduler> process_managers;
	gp::indexed_array<gp::process_data*, gp_config::limits::max_processes> processes;

	friend class scheduler;
public:
	system(allocator& v, size_t scheduler_count)
	: system_allocator{v}
	, process_managers{system_allocator}
	{
		gp_config::assertion(scheduler_count >= 1, "no scheduling in the system");
		process_managers.reserve(scheduler_count);
		gp::repeat(scheduler_count,[&](){
			process_managers.emplace_back(*this);
		});
	}

	size_t spawn(gp::function<void()> fn) {
		constexpr size_t stack_sz = gp_config::limits::process_stack;
		void* stack = system_allocator.get().allocate(stack_sz);
		gp_config::assertion(stack != nullptr, "failed to allocate a stack");
		process_data* created_process = (process_data*)system_allocator.get().allocate(sizeof(process_data));
		gp_config::assertion(stack != nullptr, "failed to allocate a process data");
		new(created_process) process_data(fn, stack, stack_sz);
		return processes.push(created_process);
	}

	void run_once() {
		(*process_managers.begin()).run_once();
		(*process_managers.begin()).cleanup(system_allocator);
	}
};

scheduler::scheduler(class system& v)
: sys(v){}

void scheduler::yield_to(size_t target_pid)
{
	auto& cur = current ? sys.processes[current-1]->specifics : root;
	auto& target = target_pid ? sys.processes[target_pid-1]->specifics : root;
	current = target_pid;
	cur.pull();
	if(target_pid)
	{
		no_inline_decl([&](scheduler* new_p)){
			auto& proc = *new_p->sys.processes[new_p->current-1];
			if(proc.state == gp::process_status::inactive) {
				proc.state = gp::process_status::running;
				proc.fn();
				proc.state = gp::process_status::finished;
				new_p->yield_to(0);
			}
		}(static_cast<scheduler*>(target.push(this)));
	} else {
		[[maybe_unused]] volatile scheduler* new_p = static_cast<scheduler*>(target.push(this));
	}
}


void scheduler::cleanup(allocator& alloc) {
	sys.processes.foreach(
		[&] (size_t pid, process_data* process) {
			if(
				process->state == process_status::finished
			) {
				process->fds.foreach([](size_t, file_description* fdes){
					fdes->close();
				});
				gp_config::assertion(alloc.deallocate(process->stack), "can't deallocate the stack");
				sys.processes.mark_for_removal(pid);
				gp_config::assertion(alloc.deallocate(process), "can't deallocate the process data");
			}
		}
	);
	sys.processes.sweep_removed();
}

void scheduler::run_once() {
	sys.processes.foreach(
		[&] (size_t pid, process_data* process) {
			if(
				process->state == process_status::inactive 
				|| process->state == process_status::running
			) {
				yield_to(pid+1);
			}
		}
	);
}

}