294 lines
6.6 KiB
C++
294 lines
6.6 KiB
C++
/*
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* \brief Timed event scheduler
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* \date 2005-10-24
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* \author Norman Feske
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*/
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/*
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* Copyright (C) 2005-2017 Genode Labs GmbH
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*
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* This file is part of the Genode OS framework, which is distributed
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* under the terms of the GNU Affero General Public License version 3.
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*/
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#include <base/log.h>
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#include <base/alarm.h>
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using namespace Genode;
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void Alarm_scheduler::_unsynchronized_enqueue(Alarm *alarm)
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{
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if (alarm->_active) {
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error("trying to insert the same alarm twice!");
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return;
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}
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alarm->_active++;
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/* if alarmlist is empty add first element */
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if (!_head) {
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alarm->_next = 0;
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_head = alarm;
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return;
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}
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/* if deadline is smaller than any other deadline, put it on the head */
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if (alarm->_raw.is_pending_at(_head->_raw.deadline, _head->_raw.deadline_period)) {
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alarm->_next = _head;
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_head = alarm;
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return;
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}
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/* find list element with a higher deadline */
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Alarm *curr = _head;
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while (curr->_next &&
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curr->_next->_raw.is_pending_at(alarm->_raw.deadline, alarm->_raw.deadline_period))
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{
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curr = curr->_next;
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}
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/* if end of list is reached, append new element */
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if (curr->_next == 0) {
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curr->_next = alarm;
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return;
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}
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/* insert element in middle of list */
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alarm->_next = curr->_next;
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curr->_next = alarm;
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}
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void Alarm_scheduler::_unsynchronized_dequeue(Alarm *alarm)
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{
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if (!_head) return;
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if (_head == alarm) {
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_head = alarm->_next;
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alarm->_reset();
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return;
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}
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/* find predecessor in alarm queue */
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Alarm *curr;
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for (curr = _head; curr && (curr->_next != alarm); curr = curr->_next);
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/* alarm is not enqueued */
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if (!curr) return;
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/* remove alarm from alarm queue */
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curr->_next = alarm->_next;
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alarm->_reset();
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}
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bool Alarm::Raw::is_pending_at(uint64_t time, bool time_period) const
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{
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return (time_period == deadline_period &&
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time >= deadline) ||
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(time_period != deadline_period &&
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time < deadline);
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}
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Alarm *Alarm_scheduler::_get_pending_alarm()
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{
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Lock::Guard lock_guard(_lock);
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if (!_head || !_head->_raw.is_pending_at(_now, _now_period)) {
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return nullptr; }
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/* remove alarm from head of the list */
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Alarm *pending_alarm = _head;
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_head = _head->_next;
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/*
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* Acquire dispatch lock to defer destruction until the call of 'on_alarm'
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* is finished
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*/
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pending_alarm->_dispatch_lock.lock();
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/* reset alarm object */
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pending_alarm->_next = nullptr;
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pending_alarm->_active--;
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return pending_alarm;
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}
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void Alarm_scheduler::handle(Alarm::Time curr_time)
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{
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/*
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* Raise the time counter and if it wraps, update also in which
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* period of the time counter we are.
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*/
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if (_now > curr_time) {
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_now_period = !_now_period;
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}
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_now = curr_time;
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if (!_min_handle_period.is_pending_at(_now, _now_period)) {
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return;
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}
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Alarm::Time const deadline = _now + _min_handle_period.period;
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_min_handle_period.deadline = deadline;
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_min_handle_period.deadline_period = _now > deadline ?
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!_now_period : _now_period;
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Alarm *curr;
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while ((curr = _get_pending_alarm())) {
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uint64_t triggered = 1;
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if (curr->_raw.period) {
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Alarm::Time deadline = curr->_raw.deadline;
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/* schedule next event */
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if (deadline == 0)
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deadline = curr_time;
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triggered += (curr_time - deadline) / curr->_raw.period;
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}
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/* do not reschedule if alarm function returns 0 */
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bool reschedule = curr->on_alarm(triggered);
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if (reschedule) {
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/*
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* At this point, the alarm deadline normally is somewhere near
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* the current time but If the alarm had no deadline by now,
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* initialize it with the current time.
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*/
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if (curr->_raw.deadline == 0) {
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curr->_raw.deadline = _now;
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curr->_raw.deadline_period = _now_period;
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}
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/*
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* Raise the deadline value by one period of the alarm and
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* if the deadline value wraps thereby, update also in which
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* period it is located.
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*/
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Alarm::Time const deadline = curr->_raw.deadline +
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triggered * curr->_raw.period;
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if (curr->_raw.deadline > deadline) {
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curr->_raw.deadline_period = !curr->_raw.deadline_period;
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}
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curr->_raw.deadline = deadline;
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/* synchronize enqueue operation */
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Lock::Guard lock_guard(_lock);
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_unsynchronized_enqueue(curr);
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}
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/* release alarm, resume concurrent destructor operation */
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curr->_dispatch_lock.unlock();
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}
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}
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void Alarm_scheduler::_setup_alarm(Alarm &alarm, Alarm::Time period, Alarm::Time deadline)
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{
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/*
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* If the alarm is already present in the queue, re-consider its queue
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* position because its deadline might have changed. I.e., if an alarm is
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* rescheduled with a new timeout before the original timeout triggered.
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*/
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if (alarm._active)
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_unsynchronized_dequeue(&alarm);
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alarm._assign(period, deadline, _now > deadline ? !_now_period : _now_period, this);
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_unsynchronized_enqueue(&alarm);
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}
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void Alarm_scheduler::schedule_absolute(Alarm *alarm, Alarm::Time timeout)
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{
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Lock::Guard alarm_list_lock_guard(_lock);
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_setup_alarm(*alarm, 0, timeout);
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}
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void Alarm_scheduler::schedule(Alarm *alarm, Alarm::Time period)
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{
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Lock::Guard alarm_list_lock_guard(_lock);
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/*
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* Refuse to schedule a periodic timeout of 0 because it would trigger
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* infinitely in the 'handle' function. To account for the case where the
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* alarm object was already scheduled, we make sure to remove it from the
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* queue.
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*/
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if (period == 0) {
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_unsynchronized_dequeue(alarm);
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return;
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}
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/* first deadline is overdue */
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_setup_alarm(*alarm, period, _now);
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}
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void Alarm_scheduler::discard(Alarm *alarm)
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{
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/*
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* Make sure that nobody is inside the '_get_pending_alarm' when
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* grabbing the '_dispatch_lock'. This is important when this function
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* is called from the 'Alarm' destructor. Without the '_dispatch_lock',
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* we could take the lock and proceed with destruction just before
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* '_get_pending_alarm' tries to grab the lock. When the destructor is
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* finished, '_get_pending_alarm' would proceed with operating on a
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* dangling pointer.
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*/
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Lock::Guard alarm_list_lock_guard(_lock);
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if (alarm) {
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Lock::Guard alarm_lock_guard(alarm->_dispatch_lock);
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_unsynchronized_dequeue(alarm);
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}
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}
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bool Alarm_scheduler::next_deadline(Alarm::Time *deadline)
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{
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Lock::Guard alarm_list_lock_guard(_lock);
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if (!_head) return false;
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if (deadline)
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*deadline = _head->_raw.deadline;
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if (deadline && *deadline < _min_handle_period.deadline) {
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*deadline = _min_handle_period.deadline;
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}
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return true;
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}
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Alarm_scheduler::~Alarm_scheduler()
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{
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Lock::Guard lock_guard(_lock);
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while (_head) {
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Alarm *next = _head->_next;
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/* reset alarm object */
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_head->_reset();
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/* remove from list */
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_head = next;
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}
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}
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Alarm::~Alarm()
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{
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if (_scheduler)
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_scheduler->discard(this);
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}
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