Luna/kernel/src/thread/Thread.cpp

#include "thread/Thread.h"
#include "Log.h"
#include "arch/CPU.h"
#include "memory/MemoryManager.h"
#include "thread/Scheduler.h"
#include <bits/atfile.h>
#include <bits/open-flags.h>
#include <bits/signal.h>
#include <bits/waitpid.h>
#include <luna/Alloc.h>
#include <luna/Atomic.h>
#include <luna/PathParser.h>

static Atomic<pid_t> g_next_id;

LinkedList<Thread> g_threads;

void Thread::init()
{
    g_next_id = 2;
}

Result<Thread*> new_thread()
{
    Thread* const thread = TRY(make<Thread>());

    thread->id = g_next_id++;

    return thread;
}

pid_t next_thread_id()
{
    return g_next_id.load();
}

Result<int> Thread::allocate_fd(int min)
{
    if (min < 0 || min >= FD_MAX) return err(EINVAL);
    for (int i = min; i < FD_MAX; i++)
    {
        // FIXME: Possible race condition if multiple threads share a FileDescriptorTable? Let's not worry about it for
        // now, we're still a long way away from reaching that point.
        if (!fd_table[i].has_value()) { return i; }
    }

    return err(EMFILE);
}

Result<FileDescriptor*> Thread::resolve_fd(int fd)
{
    if (fd < 0 || fd >= FD_MAX) return err(EBADF);

    Option<FileDescriptor>& maybe_descriptor = fd_table[fd];

    if (!maybe_descriptor.has_value()) return err(EBADF);

    return maybe_descriptor.value_ptr();
}

Result<SharedPtr<VFS::Inode>> Thread::resolve_atfile(int dirfd, const String& path, bool allow_empty_path,
                                                     bool follow_last_symlink, SharedPtr<VFS::Inode>* parent_inode)
{
    if (parent_inode) *parent_inode = this->current_directory;

    if (PathParser::is_absolute(path.view()))
        return VFS::resolve_path(path.chars(), this->auth, &this->extra_groups, {}, follow_last_symlink);

    if (dirfd == AT_FDCWD)
        return VFS::resolve_path(path.chars(), this->auth, &this->extra_groups, this->current_directory,
                                 follow_last_symlink);

    auto descriptor = TRY(resolve_fd(dirfd));

    if (parent_inode) *parent_inode = descriptor->inode();

    if (path.is_empty() && allow_empty_path) return descriptor->inode();

    return VFS::resolve_path(path.chars(), this->auth, &this->extra_groups, descriptor->inode(), follow_last_symlink);
}

[[noreturn]] void Thread::exit_and_signal_parent(int _status)
{
#ifndef MOON_ENABLE_TESTING_FEATURES
    if (this->id == 1) fail("the init process exited");
#else
    if (this->id == 1) CPU::magic_exit(_status);
#endif
    if (is_kernel) state = ThreadState::Dying;
    else
    {
        Scheduler::for_each_child(this, [](Thread* child) {
            child->parent = Scheduler::init_thread();
            return true;
        });

        if (is_session_leader())
        {
            kinfoln("thread %d is exiting as a session leader, sending signals to session", id);
            // FIXME: Send SIGHUP only to the foreground process group if the session has a controlling terminal.
            Scheduler::for_each_in_session(sid, [this](Thread* thread) {
                if (thread == this) return true;
                thread->sid = 0;
                thread->controlling_terminal = {};
                thread->send_signal(SIGHUP);
                kinfoln("reparenting and sending SIGHUP to %d", thread->id);
                return true;
            });
        }

        if (parent)
        {
            if (parent->state == ThreadState::Waiting)
            {
                auto child = *parent->child_being_waited_for;
                if (child == -1 || child == id)
                {
                    parent->child_being_waited_for = id;
                    parent->wake_up();
                }
            }
            else
            {
                while (parent->pending_signals.get(SIGCHLD - 1)) kernel_yield();
                parent->send_signal(SIGCHLD);
            }
        }

        state = ThreadState::Exited;
    }
    status = _status;
    kernel_yield();
    unreachable();
}

enum class DefaultSignalAction
{
    Ignore,
    Terminate,
    Stop,
};

// FIXME: Implement coredumps for some signals.
static constexpr DefaultSignalAction default_actions[] = {
    DefaultSignalAction::Terminate, // SIGHUP
    DefaultSignalAction::Terminate, // SIGINT
    DefaultSignalAction::Terminate, // SIGQUIT (dump core)
    DefaultSignalAction::Terminate, // SIGILL  (dump core)
    DefaultSignalAction::Terminate, // SIGTRAP (dump core)
    DefaultSignalAction::Terminate, // SIGABRT (dump core)
    DefaultSignalAction::Ignore,    // SIGCHLD
    DefaultSignalAction::Terminate, // SIGFPE  (dump core)
    DefaultSignalAction::Terminate, // SIGKILL
    DefaultSignalAction::Stop,      // SIGSTOP
    DefaultSignalAction::Terminate, // SIGSEGV (dump core)
    DefaultSignalAction::Ignore,    // SIGCONT (Handled separately)
    DefaultSignalAction::Terminate, // SIGPIPE
    DefaultSignalAction::Terminate, // SIGALRM
    DefaultSignalAction::Terminate, // SIGTERM
    DefaultSignalAction::Terminate, // SIGTTIN
    DefaultSignalAction::Terminate, // SIGTTOU
    DefaultSignalAction::Ignore,    // SIGWINCH
};

void Thread::process_pending_signals(Registers* current_regs)
{
    interrupted = false;
    for (int i = 0; i < NSIG; i++)
    {
        int signo = i + 1;
        if (signo != SIGKILL && signo != SIGSTOP && signal_mask.get(i)) continue;
        if (pending_signals.get(i))
        {
            pending_signals.set(i, false);
            auto handler = signal_handlers[i];
            if (signo != SIGKILL && signo != SIGSTOP && handler.sa_handler == SIG_IGN) return;
            if (handler.sa_handler == SIG_DFL || signo == SIGKILL || signo == SIGSTOP)
            {
            default_signal:
                if (id == 1)
                {
                    kwarnln("signal: init got a signal it has no handler for, ignoring");
                    return;
                }

                auto action = default_actions[i];
                switch (action)
                {
                case DefaultSignalAction::Ignore: return;
                case DefaultSignalAction::Terminate: exit_and_signal_parent(signo | _SIGBIT);
                case DefaultSignalAction::Stop: stop();
                default: return;
                }
            }
            // If we fail to deliver the signal (usually because there's not enough space on the stack), execute the
            // default action.
            if (!deliver_signal(signo, current_regs)) goto default_signal;
            return;
        }
    }
}

bool Thread::will_ignore_pending_signal()
{
    for (int i = 0; i < NSIG; i++)
    {
        if (pending_signals.get(i))
        {
            int signo = i + 1;
            if (signo == SIGKILL || signo == SIGSTOP) return false;
            if (signal_mask.get(i)) continue;
            auto handler = signal_handlers[i];
            if (handler.sa_handler == SIG_IGN) return true;
            if (handler.sa_handler == SIG_DFL && default_actions[i] == DefaultSignalAction::Ignore) return true;
            return false;
        }
    }
    return false;
}

void Thread::send_signal(int signo)
{
    if (is_kernel) return;
    if (state == ThreadState::Exited || state == ThreadState::Dying) return;

    if (state == ThreadState::Stopped && signo == SIGCONT)
    {
        wake_up();
        return;
    }

    check(signo > 0 && signo <= NSIG);
    pending_signals.set(signo - 1, true);

    if (state == ThreadState::Waiting || state == ThreadState::Sleeping || is_in_kernel(&regs))
    {
        if (state == ThreadState::Stopped && signo != SIGKILL) return;
        interrupted = true;
        wake_up();
    }
}

void Thread::stop()
{
    state = ThreadState::Stopped;
    kernel_yield();
}