ladybird/Libraries/LibThreading/Thread.cpp

/*
 * Copyright (c) 2019-2020, Sergey Bugaev <bugaevc@serenityos.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <LibThreading/Thread.h>
#include <pthread.h>
#include <string.h>
#include <unistd.h>

namespace Threading {

Thread::Thread(Function<intptr_t()> action, StringView thread_name)
    : m_action(move(action))
    , m_thread_name(thread_name.is_null() ? ""sv : thread_name)
{
}

Thread::~Thread()
{
    if (needs_to_be_joined()) {
        dbgln("Destroying {} while it is still running undetached!", *this);
        [[maybe_unused]] auto res = join();
    }
}

ErrorOr<void> Thread::set_priority(int priority)
{
    // MacOS has an extra __opaque field, so list initialization will not compile on MacOS Lagom.
    sched_param scheduling_parameters {};
    scheduling_parameters.sched_priority = priority;
    int result = pthread_setschedparam(m_tid, 0, &scheduling_parameters);
    if (result != 0)
        return Error::from_errno(result);
    return {};
}

ErrorOr<int> Thread::get_priority() const
{
    sched_param scheduling_parameters {};
    int policy;
    int result = pthread_getschedparam(m_tid, &policy, &scheduling_parameters);
    if (result != 0)
        return Error::from_errno(result);
    return scheduling_parameters.sched_priority;
}

ByteString Thread::thread_name() const { return m_thread_name; }

pthread_t Thread::tid() const { return m_tid; }

ThreadState Thread::state() const { return m_state; }

bool Thread::is_started() const { return m_state != ThreadState::Startable; }

bool Threading::Thread::needs_to_be_joined() const
{
    auto state = m_state.load();
    return state == ThreadState::Running || state == ThreadState::Exited;
}

bool Threading::Thread::has_exited() const
{
    auto state = m_state.load();
    return state == ThreadState::Joined || state == ThreadState::Exited || state == ThreadState::DetachedExited;
}

void Thread::start()
{
    VERIFY(!is_started());

    // Set this first so that the other thread starts out seeing m_state == Running.
    m_state = Threading::ThreadState::Running;

    int rc = pthread_create(
        &m_tid,
        // FIXME: Use pthread_attr_t to start a thread detached if that was requested by the user before the call to start().
        nullptr,
        [](void* arg) -> void* {
            auto self = adopt_ref(*static_cast<Thread*>(arg));

            auto exit_code = self->m_action();

            auto expected = Threading::ThreadState::Running;
            // This code might race with a call to detach().
            if (!self->m_state.compare_exchange_strong(expected, Threading::ThreadState::Exited)) {
                // If the original state was Detached, we need to set to DetachedExited instead.
                if (expected == Threading::ThreadState::Detached) {
                    if (!self->m_state.compare_exchange_strong(expected, Threading::ThreadState::DetachedExited)) {
                        dbgln("Thread logic bug: Found thread state {} while trying to set ExitedDetached state!", expected);
                        VERIFY_NOT_REACHED();
                    }
                } else {
                    dbgln("Thread logic bug: Found thread state {} while trying to set Exited state!", expected);
                    VERIFY_NOT_REACHED();
                }
            }

            return reinterpret_cast<void*>(exit_code);
        },
        &NonnullRefPtr(*this).leak_ref());

    VERIFY(rc == 0);
}

void Thread::detach()
{
    auto expected = Threading::ThreadState::Running;
    // This code might race with the other thread exiting.
    if (!m_state.compare_exchange_strong(expected, Threading::ThreadState::Detached)) {
        if (expected == Threading::ThreadState::Exited)
            return;

        // Always report a precise error before crashing. These kinds of bugs are hard to reproduce.
        dbgln("Thread logic bug: trying to detach {} in state {}, which is neither Started nor Exited", this, expected);
        VERIFY_NOT_REACHED();
    }

    int rc = pthread_detach(m_tid);
    VERIFY(rc == 0);
}

}