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/*
* Copyright (C) 2006, 2008 Apple Inc. All rights reserved.
* Copyright (C) 2009 Google Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "config.h"
#include "Timer.h"
#include "SharedTimer.h"
#include "ThreadGlobalData.h"
#include "ThreadTimers.h"
#include <limits.h>
#include <limits>
#include <math.h>
#include <wtf/MainThread.h>
#include <wtf/Vector.h>
namespace WebCore {
class TimerHeapReference;
// Timers are stored in a heap data structure, used to implement a priority queue.
// This allows us to efficiently determine which timer needs to fire the soonest.
// Then we set a single shared system timer to fire at that time.
//
// When a timer's "next fire time" changes, we need to move it around in the priority queue.
static Vector<TimerBase*>& threadGlobalTimerHeap()
{
return threadGlobalData().threadTimers().timerHeap();
}
// ----------------
class TimerHeapPointer {
public:
TimerHeapPointer(TimerBase** pointer) : m_pointer(pointer) { }
TimerHeapReference operator*() const;
TimerBase* operator->() const { return *m_pointer; }
private:
TimerBase** m_pointer;
};
class TimerHeapReference {
public:
TimerHeapReference(TimerBase*& reference) : m_reference(reference) { }
operator TimerBase*() const { return m_reference; }
TimerHeapPointer operator&() const { return &m_reference; }
TimerHeapReference& operator=(TimerBase*);
TimerHeapReference& operator=(TimerHeapReference);
private:
TimerBase*& m_reference;
};
inline TimerHeapReference TimerHeapPointer::operator*() const
{
return *m_pointer;
}
inline TimerHeapReference& TimerHeapReference::operator=(TimerBase* timer)
{
m_reference = timer;
Vector<TimerBase*>& heap = timer->timerHeap();
if (&m_reference >= heap.data() && &m_reference < heap.data() + heap.size())
timer->m_heapIndex = &m_reference - heap.data();
return *this;
}
inline TimerHeapReference& TimerHeapReference::operator=(TimerHeapReference b)
{
TimerBase* timer = b;
return *this = timer;
}
inline void swap(TimerHeapReference a, TimerHeapReference b)
{
TimerBase* timerA = a;
TimerBase* timerB = b;
// Invoke the assignment operator, since that takes care of updating m_heapIndex.
a = timerB;
b = timerA;
}
// ----------------
// Class to represent iterators in the heap when calling the standard library heap algorithms.
// Uses a custom pointer and reference type that update indices for pointers in the heap.
class TimerHeapIterator : public std::iterator<std::random_access_iterator_tag, TimerBase*, ptrdiff_t, TimerHeapPointer, TimerHeapReference> {
public:
explicit TimerHeapIterator(TimerBase** pointer) : m_pointer(pointer) { checkConsistency(); }
TimerHeapIterator& operator++() { checkConsistency(); ++m_pointer; checkConsistency(); return *this; }
TimerHeapIterator operator++(int) { checkConsistency(1); return TimerHeapIterator(m_pointer++); }
TimerHeapIterator& operator--() { checkConsistency(); --m_pointer; checkConsistency(); return *this; }
TimerHeapIterator operator--(int) { checkConsistency(-1); return TimerHeapIterator(m_pointer--); }
TimerHeapIterator& operator+=(ptrdiff_t i) { checkConsistency(); m_pointer += i; checkConsistency(); return *this; }
TimerHeapIterator& operator-=(ptrdiff_t i) { checkConsistency(); m_pointer -= i; checkConsistency(); return *this; }
TimerHeapReference operator*() const { return TimerHeapReference(*m_pointer); }
TimerHeapReference operator[](ptrdiff_t i) const { return TimerHeapReference(m_pointer[i]); }
TimerBase* operator->() const { return *m_pointer; }
private:
void checkConsistency(ptrdiff_t offset = 0) const
{
ASSERT(m_pointer >= threadGlobalTimerHeap().data());
ASSERT(m_pointer <= threadGlobalTimerHeap().data() + threadGlobalTimerHeap().size());
ASSERT_UNUSED(offset, m_pointer + offset >= threadGlobalTimerHeap().data());
ASSERT_UNUSED(offset, m_pointer + offset <= threadGlobalTimerHeap().data() + threadGlobalTimerHeap().size());
}
friend bool operator==(TimerHeapIterator, TimerHeapIterator);
friend bool operator!=(TimerHeapIterator, TimerHeapIterator);
friend bool operator<(TimerHeapIterator, TimerHeapIterator);
friend bool operator>(TimerHeapIterator, TimerHeapIterator);
friend bool operator<=(TimerHeapIterator, TimerHeapIterator);
friend bool operator>=(TimerHeapIterator, TimerHeapIterator);
friend TimerHeapIterator operator+(TimerHeapIterator, size_t);
friend TimerHeapIterator operator+(size_t, TimerHeapIterator);
friend TimerHeapIterator operator-(TimerHeapIterator, size_t);
friend ptrdiff_t operator-(TimerHeapIterator, TimerHeapIterator);
TimerBase** m_pointer;
};
inline bool operator==(TimerHeapIterator a, TimerHeapIterator b) { return a.m_pointer == b.m_pointer; }
inline bool operator!=(TimerHeapIterator a, TimerHeapIterator b) { return a.m_pointer != b.m_pointer; }
inline bool operator<(TimerHeapIterator a, TimerHeapIterator b) { return a.m_pointer < b.m_pointer; }
inline bool operator>(TimerHeapIterator a, TimerHeapIterator b) { return a.m_pointer > b.m_pointer; }
inline bool operator<=(TimerHeapIterator a, TimerHeapIterator b) { return a.m_pointer <= b.m_pointer; }
inline bool operator>=(TimerHeapIterator a, TimerHeapIterator b) { return a.m_pointer >= b.m_pointer; }
inline TimerHeapIterator operator+(TimerHeapIterator a, size_t b) { return TimerHeapIterator(a.m_pointer + b); }
inline TimerHeapIterator operator+(size_t a, TimerHeapIterator b) { return TimerHeapIterator(a + b.m_pointer); }
inline TimerHeapIterator operator-(TimerHeapIterator a, size_t b) { return TimerHeapIterator(a.m_pointer - b); }
inline ptrdiff_t operator-(TimerHeapIterator a, TimerHeapIterator b) { return a.m_pointer - b.m_pointer; }
// ----------------
class TimerHeapLessThanFunction {
public:
bool operator()(const TimerBase*, const TimerBase*) const;
};
inline bool TimerHeapLessThanFunction::operator()(const TimerBase* a, const TimerBase* b) const
{
// The comparisons below are "backwards" because the heap puts the largest
// element first and we want the lowest time to be the first one in the heap.
MonotonicTime aFireTime = a->m_nextFireTime;
MonotonicTime bFireTime = b->m_nextFireTime;
if (bFireTime != aFireTime)
return bFireTime < aFireTime;
// We need to look at the difference of the insertion orders instead of comparing the two
// outright in case of overflow.
unsigned difference = a->m_heapInsertionOrder - b->m_heapInsertionOrder;
return difference < std::numeric_limits<unsigned>::max() / 2;
}
// ----------------
TimerBase::TimerBase()
{
}
TimerBase::~TimerBase()
{
RELEASE_ASSERT_WITH_SECURITY_IMPLICATION(canAccessThreadLocalDataForThread(m_thread.get()));
stop();
ASSERT(!inHeap());
m_wasDeleted = true;
}
void TimerBase::start(Seconds nextFireInterval, Seconds repeatInterval)
{
ASSERT(canAccessThreadLocalDataForThread(m_thread.get()));
m_repeatInterval = repeatInterval;
setNextFireTime(MonotonicTime::now() + nextFireInterval);
}
void TimerBase::stop()
{
ASSERT(canAccessThreadLocalDataForThread(m_thread.get()));
m_repeatInterval = 0_s;
setNextFireTime(MonotonicTime { });
ASSERT(!static_cast<bool>(m_nextFireTime));
ASSERT(m_repeatInterval == 0_s);
ASSERT(!inHeap());
}
Seconds TimerBase::nextFireInterval() const
{
ASSERT(isActive());
MonotonicTime current = MonotonicTime::now();
if (m_nextFireTime < current)
return 0_s;
return m_nextFireTime - current;
}
inline void TimerBase::checkHeapIndex() const
{
ASSERT(timerHeap() == threadGlobalTimerHeap());
ASSERT(!timerHeap().isEmpty());
ASSERT(m_heapIndex >= 0);
ASSERT(m_heapIndex < static_cast<int>(timerHeap().size()));
ASSERT(timerHeap()[m_heapIndex] == this);
}
inline void TimerBase::checkConsistency() const
{
// Timers should be in the heap if and only if they have a non-zero next fire time.
ASSERT(inHeap() == static_cast<bool>(m_nextFireTime));
if (inHeap())
checkHeapIndex();
}
void TimerBase::heapDecreaseKey()
{
ASSERT(static_cast<bool>(m_nextFireTime));
checkHeapIndex();
TimerBase** heapData = timerHeap().data();
push_heap(TimerHeapIterator(heapData), TimerHeapIterator(heapData + m_heapIndex + 1), TimerHeapLessThanFunction());
checkHeapIndex();
}
inline void TimerBase::heapDelete()
{
ASSERT(!static_cast<bool>(m_nextFireTime));
heapPop();
timerHeap().removeLast();
m_heapIndex = -1;
}
void TimerBase::heapDeleteMin()
{
ASSERT(!static_cast<bool>(m_nextFireTime));
heapPopMin();
timerHeap().removeLast();
m_heapIndex = -1;
}
inline void TimerBase::heapIncreaseKey()
{
ASSERT(static_cast<bool>(m_nextFireTime));
heapPop();
heapDecreaseKey();
}
inline void TimerBase::heapInsert()
{
ASSERT(!inHeap());
timerHeap().append(this);
m_heapIndex = timerHeap().size() - 1;
heapDecreaseKey();
}
inline void TimerBase::heapPop()
{
// Temporarily force this timer to have the minimum key so we can pop it.
MonotonicTime fireTime = m_nextFireTime;
m_nextFireTime = -MonotonicTime::infinity();
heapDecreaseKey();
heapPopMin();
m_nextFireTime = fireTime;
}
void TimerBase::heapPopMin()
{
ASSERT(this == timerHeap().first());
checkHeapIndex();
Vector<TimerBase*>& heap = timerHeap();
TimerBase** heapData = heap.data();
pop_heap(TimerHeapIterator(heapData), TimerHeapIterator(heapData + heap.size()), TimerHeapLessThanFunction());
checkHeapIndex();
ASSERT(this == timerHeap().last());
}
static inline bool parentHeapPropertyHolds(const TimerBase* current, const Vector<TimerBase*>& heap, unsigned currentIndex)
{
if (!currentIndex)
return true;
unsigned parentIndex = (currentIndex - 1) / 2;
TimerHeapLessThanFunction compareHeapPosition;
return compareHeapPosition(current, heap[parentIndex]);
}
static inline bool childHeapPropertyHolds(const TimerBase* current, const Vector<TimerBase*>& heap, unsigned childIndex)
{
if (childIndex >= heap.size())
return true;
TimerHeapLessThanFunction compareHeapPosition;
return compareHeapPosition(heap[childIndex], current);
}
bool TimerBase::hasValidHeapPosition() const
{
ASSERT(m_nextFireTime);
if (!inHeap())
return false;
// Check if the heap property still holds with the new fire time. If it does we don't need to do anything.
// This assumes that the STL heap is a standard binary heap. In an unlikely event it is not, the assertions
// in updateHeapIfNeeded() will get hit.
const Vector<TimerBase*>& heap = timerHeap();
if (!parentHeapPropertyHolds(this, heap, m_heapIndex))
return false;
unsigned childIndex1 = 2 * m_heapIndex + 1;
unsigned childIndex2 = childIndex1 + 1;
return childHeapPropertyHolds(this, heap, childIndex1) && childHeapPropertyHolds(this, heap, childIndex2);
}
void TimerBase::updateHeapIfNeeded(MonotonicTime oldTime)
{
if (m_nextFireTime && hasValidHeapPosition())
return;
#ifndef NDEBUG
int oldHeapIndex = m_heapIndex;
#endif
if (!oldTime)
heapInsert();
else if (!m_nextFireTime)
heapDelete();
else if (m_nextFireTime < oldTime)
heapDecreaseKey();
else
heapIncreaseKey();
ASSERT(m_heapIndex != oldHeapIndex);
ASSERT(!inHeap() || hasValidHeapPosition());
}
void TimerBase::setNextFireTime(MonotonicTime newTime)
{
ASSERT(canAccessThreadLocalDataForThread(m_thread.get()));
RELEASE_ASSERT_WITH_SECURITY_IMPLICATION(!m_wasDeleted);
if (m_unalignedNextFireTime != newTime)
m_unalignedNextFireTime = newTime;
// Accessing thread global data is slow. Cache the heap pointer.
if (!m_cachedThreadGlobalTimerHeap)
m_cachedThreadGlobalTimerHeap = &threadGlobalTimerHeap();
// Keep heap valid while changing the next-fire time.
MonotonicTime oldTime = m_nextFireTime;
// Don't realign zero-delay timers.
if (newTime) {
if (auto newAlignedTime = alignedFireTime(newTime))
newTime = newAlignedTime.value();
}
if (oldTime != newTime) {
m_nextFireTime = newTime;
// FIXME: This should be part of ThreadTimers, or another per-thread structure.
static std::atomic<unsigned> currentHeapInsertionOrder;
m_heapInsertionOrder = currentHeapInsertionOrder++;
bool wasFirstTimerInHeap = m_heapIndex == 0;
updateHeapIfNeeded(oldTime);
bool isFirstTimerInHeap = m_heapIndex == 0;
if (wasFirstTimerInHeap || isFirstTimerInHeap)
threadGlobalData().threadTimers().updateSharedTimer();
}
checkConsistency();
}
void TimerBase::fireTimersInNestedEventLoop()
{
// Redirect to ThreadTimers.
threadGlobalData().threadTimers().fireTimersInNestedEventLoop();
}
void TimerBase::didChangeAlignmentInterval()
{
setNextFireTime(m_unalignedNextFireTime);
}
Seconds TimerBase::nextUnalignedFireInterval() const
{
ASSERT(isActive());
return std::max(m_unalignedNextFireTime - MonotonicTime::now(), 0_s);
}
} // namespace WebCore