serenity/Kernel/Syscalls/alarm.cpp

/*
 * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <Kernel/Tasks/Process.h>
#include <Kernel/Time/TimeManagement.h>
#include <Kernel/Time/TimerQueue.h>

namespace Kernel {

ErrorOr<FlatPtr> Process::sys$alarm(unsigned seconds)
{
    VERIFY_NO_PROCESS_BIG_LOCK(this);
    TRY(require_promise(Pledge::stdio));
    return m_alarm_timer.with([&](auto& timer) -> ErrorOr<FlatPtr> {
        unsigned previous_alarm_remaining = 0;
        if (timer) {
            bool was_in_use = false;
            if (TimerQueue::the().cancel_timer(*timer, &was_in_use)) {
                // The timer hasn't fired. Round up the remaining time (if any)
                Duration remaining = timer->remaining() + Duration::from_nanoseconds(999'999'999);
                previous_alarm_remaining = remaining.to_truncated_seconds();
            }
            // We had an existing alarm, must return a non-zero value here!
            if (was_in_use && previous_alarm_remaining == 0)
                previous_alarm_remaining = 1;
        }

        if (seconds > 0) {
            auto deadline = TimeManagement::the().current_time(CLOCK_REALTIME_COARSE);
            deadline = deadline + Duration::from_seconds(seconds);
            if (!timer) {
                timer = TRY(adopt_nonnull_ref_or_enomem(new (nothrow) Timer));
            }
            auto timer_was_added = TimerQueue::the().add_timer_without_id(*timer, CLOCK_REALTIME_COARSE, deadline, [this]() {
                MUST(send_signal(SIGALRM, nullptr));
            });
            if (!timer_was_added)
                return ENOMEM;
        }
        return previous_alarm_remaining;
    });
}

}