osdev/tasking.cpp

#include "tasking.hpp"

#include <array>

struct Task
{
    Registers regs;
    bool valid = false;
};

static std::array<Task, 4> tasks;
static int current = -1;

void schedule(Registers& regs)
{
    if (current < 0)
        return;

    tasks[current].regs = regs;

    do {
        if (++current >= tasks.size())
            current = 0;
    } while (!tasks[current].valid);

    regs = tasks[current].regs;
}

void tasking_initialize()
{
    tasks[0].valid = true;
    current = 0;
    asm volatile("int $0x20");
}

bool tasking_spawn(void (*entry)(), unsigned ssize)
{
    int i = -1;
    for (i = 0; i < tasks.size(); ++i) {
        if (!tasks[i].valid)
            break;
    }

    if (i < 0)
        return false;

    tasks[i] = Task();

    auto& r = tasks[i].regs;
    auto stack = reinterpret_cast<std::uint32_t>(new std::uint8_t[ssize]);
    r.ebp = stack + ssize;
    r.esp = r.ebp;
    r.eip = reinterpret_cast<std::uint32_t>(entry);
    r.cs = 0x8;
    r.eflags = tasks[current].regs.eflags;

    tasks[i].valid = true;
    return true;
}