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// Copyright (c) 2013, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.
// part of "isolate_patch.dart";
// Timer heap implemented as a array-based binary heap[0].
// This allows for O(1) `first`, O(log(n)) `remove`/`removeFirst` and O(log(n))
// `add`.
//
// To ensure the timers are ordered by insertion time, the _Timer class has a
// `_id` field set when added to the heap.
//
// [0] http://en.wikipedia.org/wiki/Binary_heap
class _TimerHeap {
List<_Timer> _list;
int _used = 0;
_TimerHeap([int initSize = 7]) : _list = new List<_Timer>(initSize);
bool get isEmpty => _used == 0;
_Timer get first => _list[0];
bool isFirst(_Timer timer) => timer._indexOrNext == 0;
void add(_Timer timer) {
if (_used == _list.length) {
_resize();
}
timer._indexOrNext = _used++;
_list[timer._indexOrNext] = timer;
_bubbleUp(timer);
}
_Timer removeFirst() {
var f = first;
remove(f);
return f;
}
void remove(_Timer timer) {
_used--;
if (isEmpty) {
_list[0] = null;
timer._indexOrNext = null;
return;
}
var last = _list[_used];
if (!identical(last, timer)) {
last._indexOrNext = timer._indexOrNext;
_list[last._indexOrNext] = last;
if (last._compareTo(timer) < 0) {
_bubbleUp(last);
} else {
_bubbleDown(last);
}
}
_list[_used] = null;
timer._indexOrNext = null;
}
void _resize() {
var newList = new List<_Timer>(_list.length * 2 + 1);
newList.setRange(0, _used, _list);
_list = newList;
}
void _bubbleUp(_Timer timer) {
while (!isFirst(timer)) {
Timer parent = _parent(timer);
if (timer._compareTo(parent) < 0) {
_swap(timer, parent);
} else {
break;
}
}
}
void _bubbleDown(_Timer timer) {
while (true) {
int leftIndex = _leftChildIndex(timer._indexOrNext);
int rightIndex = _rightChildIndex(timer._indexOrNext);
_Timer newest = timer;
if (leftIndex < _used && _list[leftIndex]._compareTo(newest) < 0) {
newest = _list[leftIndex];
}
if (rightIndex < _used && _list[rightIndex]._compareTo(newest) < 0) {
newest = _list[rightIndex];
}
if (identical(newest, timer)) {
// We are where we should be, break.
break;
}
_swap(newest, timer);
}
}
void _swap(_Timer first, _Timer second) {
int tmp = first._indexOrNext;
first._indexOrNext = second._indexOrNext;
second._indexOrNext = tmp;
_list[first._indexOrNext] = first;
_list[second._indexOrNext] = second;
}
Timer _parent(_Timer timer) => _list[_parentIndex(timer._indexOrNext)];
Timer _leftChild(_Timer timer) => _list[_leftChildIndex(timer._indexOrNext)];
Timer _rightChild(_Timer timer) =>
_list[_rightChildIndex(timer._indexOrNext)];
static int _parentIndex(int index) => (index - 1) ~/ 2;
static int _leftChildIndex(int index) => 2 * index + 1;
static int _rightChildIndex(int index) => 2 * index + 2;
}
class _Timer implements Timer {
// Cancels the timer in the event handler.
static const _NO_TIMER = -1;
// We distinguish what kind of message arrived based on the value being sent.
static const _ZERO_EVENT = 1;
static const _TIMEOUT_EVENT = null;
// Timers are ordered by wakeup time. Timers with a timeout value of > 0 do
// end up on the TimerHeap. Timers with a timeout of 0 are queued in a list.
static final _heap = new _TimerHeap();
static _Timer _firstZeroTimer;
static _Timer _lastZeroTimer;
// We use an id to be able to sort timers with the same expiration time.
// ids are recycled after ID_MASK enqueues or when the timer queue is empty.
static const _ID_MASK = 0x1fffffff;
static int _idCount = 0;
static RawReceivePort _receivePort;
static SendPort _sendPort;
static int _scheduledWakeupTime;
static bool _handlingCallbacks = false;
Function _callback; // Closure to call when timer fires. null if canceled.
int _wakeupTime; // Expiration time.
final int _milliSeconds; // Duration specified at creation.
final bool _repeating; // Indicates periodic timers.
var _indexOrNext; // Index if part of the TimerHeap, link otherwise.
int _id; // Incrementing id to enable sorting of timers with same expiry.
int _tick = 0; // Backing for [tick],
// Get the next available id. We accept collisions and reordering when the
// _idCount overflows and the timers expire at the same millisecond.
static int _nextId() {
var result = _idCount;
_idCount = (_idCount + 1) & _ID_MASK;
return result;
}
_Timer._internal(
this._callback, this._wakeupTime, this._milliSeconds, this._repeating)
: _id = _nextId();
static Timer _createTimer(
void callback(Timer timer), int milliSeconds, bool repeating) {
// Negative timeouts are treated as if 0 timeout.
if (milliSeconds < 0) {
milliSeconds = 0;
}
// Add one because DateTime.now() is assumed to round down
// to nearest millisecond, not up, so that time + duration is before
// duration milliseconds from now. Using microsecond timers like
// Stopwatch allows detecting that the timer fires early.
int now = VMLibraryHooks.timerMillisecondClock();
int wakeupTime = (milliSeconds == 0) ? now : (now + 1 + milliSeconds);
_Timer timer =
new _Timer._internal(callback, wakeupTime, milliSeconds, repeating);
// Enqueue this newly created timer in the appropriate structure and
// notify if necessary.
timer._enqueue();
return timer;
}
factory _Timer(int milliSeconds, void callback(Timer timer)) {
return _createTimer(callback, milliSeconds, false);
}
factory _Timer.periodic(int milliSeconds, void callback(Timer timer)) {
return _createTimer(callback, milliSeconds, true);
}
bool get _isInHeap => _indexOrNext is int;
int _compareTo(_Timer other) {
int c = _wakeupTime - other._wakeupTime;
if (c != 0) return c;
return _id - other._id;
}
bool get isActive => _callback != null;
int get tick => _tick;
// Cancels a set timer. The timer is removed from the timer heap if it is a
// non-zero timer. Zero timers are kept in the list as they need to consume
// the corresponding pending message.
void cancel() {
_callback = null;
// Only heap timers are really removed. Zero timers need to consume their
// corresponding wakeup message so they are left in the queue.
if (!_isInHeap) return;
bool update = _heap.isFirst(this);
_heap.remove(this);
if (update) {
_notifyEventHandler();
}
}
void _advanceWakeupTime() {
// Recalculate the next wakeup time. For repeating timers with a 0 timeout
// the next wakeup time is now.
_id = _nextId();
if (_milliSeconds > 0) {
_wakeupTime += _milliSeconds;
} else {
_wakeupTime = VMLibraryHooks.timerMillisecondClock();
}
}
// Adds a timer to the heap or timer list. Timers with the same wakeup time
// are enqueued in order and notified in FIFO order.
void _enqueue() {
if (_milliSeconds == 0) {
if (_firstZeroTimer == null) {
_lastZeroTimer = this;
_firstZeroTimer = this;
} else {
_lastZeroTimer._indexOrNext = this;
_lastZeroTimer = this;
}
// Every zero timer gets its own event.
_notifyZeroHandler();
} else {
_heap.add(this);
if (_heap.isFirst(this)) {
_notifyEventHandler();
}
}
}
// Enqueue one message for each zero timer. To be able to distinguish from
// EventHandler messages we send a _ZERO_EVENT instead of a _TIMEOUT_EVENT.
static void _notifyZeroHandler() {
if (_sendPort == null) {
_createTimerHandler();
}
_sendPort.send(_ZERO_EVENT);
}
// Handle the notification of a zero timer. Make sure to also execute non-zero
// timers with a lower expiration time.
static List _queueFromZeroEvent() {
var pendingTimers = new List();
assert(_firstZeroTimer != null);
// Collect pending timers from the timer heap that have an expiration prior
// to the currently notified zero timer.
var timer;
while (!_heap.isEmpty && (_heap.first._compareTo(_firstZeroTimer) < 0)) {
timer = _heap.removeFirst();
pendingTimers.add(timer);
}
// Append the first zero timer to the pending timers.
timer = _firstZeroTimer;
_firstZeroTimer = timer._indexOrNext;
timer._indexOrNext = null;
pendingTimers.add(timer);
return pendingTimers;
}
static void _notifyEventHandler() {
if (_handlingCallbacks) {
// While we are already handling callbacks we will not notify the event
// handler. _handleTimeout will call _notifyEventHandler once all pending
// timers are processed.
return;
}
// If there are no pending timers. Close down the receive port.
if ((_firstZeroTimer == null) && _heap.isEmpty) {
// No pending timers: Close the receive port and let the event handler
// know.
if (_sendPort != null) {
_cancelWakeup();
_shutdownTimerHandler();
}
return;
} else if (_heap.isEmpty) {
// Only zero timers are left. Cancel any scheduled wakeups.
_cancelWakeup();
return;
}
// Only send a message if the requested wakeup time differs from the
// already scheduled wakeup time.
var wakeupTime = _heap.first._wakeupTime;
if ((_scheduledWakeupTime == null) ||
(wakeupTime != _scheduledWakeupTime)) {
_scheduleWakeup(wakeupTime);
}
}
static List _queueFromTimeoutEvent() {
var pendingTimers = new List();
if (_firstZeroTimer != null) {
// Collect pending timers from the timer heap that have an expiration
// prior to the next zero timer.
// By definition the first zero timer has been scheduled before the
// current time, meaning all timers which are "less than" the first zero
// timer are expired. The first zero timer will be dispatched when its
// corresponding message is delivered.
var timer;
while (!_heap.isEmpty && (_heap.first._compareTo(_firstZeroTimer) < 0)) {
timer = _heap.removeFirst();
pendingTimers.add(timer);
}
} else {
// Collect pending timers from the timer heap which have expired at this
// time.
var currentTime = VMLibraryHooks.timerMillisecondClock();
var timer;
while (!_heap.isEmpty && (_heap.first._wakeupTime <= currentTime)) {
timer = _heap.removeFirst();
pendingTimers.add(timer);
}
}
return pendingTimers;
}
static void _runTimers(List pendingTimers) {
// If there are no pending timers currently reset the id space before we
// have a chance to enqueue new timers.
if (_heap.isEmpty && (_firstZeroTimer == null)) {
_idCount = 0;
}
// Fast exit if no pending timers.
if (pendingTimers.length == 0) {
return;
}
// Trigger all of the pending timers. New timers added as part of the
// callbacks will be enqueued now and notified in the next spin at the
// earliest.
_handlingCallbacks = true;
var i = 0;
try {
for (; i < pendingTimers.length; i++) {
// Next pending timer.
var timer = pendingTimers[i];
timer._indexOrNext = null;
// One of the timers in the pending_timers list can cancel
// one of the later timers which will set the callback to
// null. Or the pending zero timer has been canceled earlier.
if (timer._callback != null) {
var callback = timer._callback;
if (!timer._repeating) {
// Mark timer as inactive.
timer._callback = null;
} else if (timer._milliSeconds > 0) {
var ms = timer._milliSeconds;
int overdue =
VMLibraryHooks.timerMillisecondClock() - timer._wakeupTime;
if (overdue > ms) {
int missedTicks = overdue ~/ ms;
timer._wakeupTime += missedTicks * ms;
timer._tick += missedTicks;
}
}
timer._tick += 1;
callback(timer);
// Re-insert repeating timer if not canceled.
if (timer._repeating && (timer._callback != null)) {
timer._advanceWakeupTime();
timer._enqueue();
}
// Execute pending micro tasks.
var immediateCallback = _removePendingImmediateCallback();
if (immediateCallback != null) {
immediateCallback();
}
}
}
} finally {
_handlingCallbacks = false;
// Re-queue timers we didn't get to.
for (i++; i < pendingTimers.length; i++) {
var timer = pendingTimers[i];
timer._enqueue();
}
_notifyEventHandler();
}
}
static void _handleMessage(msg) {
var pendingTimers;
if (msg == _ZERO_EVENT) {
pendingTimers = _queueFromZeroEvent();
assert(pendingTimers.length > 0);
} else {
assert(msg == _TIMEOUT_EVENT);
_scheduledWakeupTime = null; // Consumed the last scheduled wakeup now.
pendingTimers = _queueFromTimeoutEvent();
}
_runTimers(pendingTimers);
// Notify the event handler or shutdown the port if no more pending
// timers are present.
_notifyEventHandler();
}
// Tell the event handler to wake this isolate at a specific time.
static void _scheduleWakeup(int wakeupTime) {
if (_sendPort == null) {
_createTimerHandler();
}
VMLibraryHooks.eventHandlerSendData(null, _sendPort, wakeupTime);
_scheduledWakeupTime = wakeupTime;
}
// Cancel pending wakeups in the event handler.
static void _cancelWakeup() {
if (_sendPort != null) {
VMLibraryHooks.eventHandlerSendData(null, _sendPort, _NO_TIMER);
_scheduledWakeupTime = null;
}
}
// Create a receive port and register a message handler for the timer
// events.
static void _createTimerHandler() {
assert(_receivePort == null);
assert(_sendPort == null);
_receivePort = new RawReceivePort(_handleMessage);
_sendPort = _receivePort.sendPort;
_scheduledWakeupTime = null;
}
static void _shutdownTimerHandler() {
_receivePort.close();
_receivePort = null;
_sendPort = null;
_scheduledWakeupTime = null;
}
// The Timer factory registered with the dart:async library by the embedder.
static Timer _factory(
int milliSeconds, void callback(Timer timer), bool repeating) {
if (repeating) {
return new _Timer.periodic(milliSeconds, callback);
}
return new _Timer(milliSeconds, callback);
}
}
@pragma("vm:entry-point", "call")
_setupHooks() {
VMLibraryHooks.timerFactory = _Timer._factory;
}