gecko-dev/xpcom/threads/TimerThread.cpp

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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#include "nsTimerImpl.h"
#include "TimerThread.h"
#include "nsThreadUtils.h"
#include "plarena.h"
#include "pratom.h"
#include "nsIObserverService.h"
#include "nsIServiceManager.h"
#include "mozilla/Services.h"
#include "mozilla/ChaosMode.h"
#include "mozilla/ArrayUtils.h"
#include "mozilla/BinarySearch.h"
#include <math.h>
using namespace mozilla;
#ifdef MOZ_TASK_TRACER
#include "GeckoTaskTracerImpl.h"
using namespace mozilla::tasktracer;
#endif
NS_IMPL_ISUPPORTS(TimerThread, nsIRunnable, nsIObserver)
TimerThread::TimerThread() :
mInitInProgress(false),
mInitialized(false),
mMonitor("TimerThread.mMonitor"),
mShutdown(false),
mWaiting(false),
mNotified(false),
mSleeping(false)
{
}
TimerThread::~TimerThread()
{
mThread = nullptr;
NS_ASSERTION(mTimers.IsEmpty(), "Timers remain in TimerThread::~TimerThread");
}
nsresult
TimerThread::InitLocks()
{
return NS_OK;
}
namespace {
class TimerObserverRunnable : public nsRunnable
{
public:
explicit TimerObserverRunnable(nsIObserver* aObserver)
: mObserver(aObserver)
{
}
NS_DECL_NSIRUNNABLE
private:
nsCOMPtr<nsIObserver> mObserver;
};
NS_IMETHODIMP
TimerObserverRunnable::Run()
{
nsCOMPtr<nsIObserverService> observerService =
mozilla::services::GetObserverService();
if (observerService) {
observerService->AddObserver(mObserver, "sleep_notification", false);
observerService->AddObserver(mObserver, "wake_notification", false);
observerService->AddObserver(mObserver, "suspend_process_notification", false);
observerService->AddObserver(mObserver, "resume_process_notification", false);
}
return NS_OK;
}
} // namespace
namespace {
// TimerEventAllocator is a thread-safe allocator used only for nsTimerEvents.
// It's needed to avoid contention over the default allocator lock when
// firing timer events (see bug 733277). The thread-safety is required because
// nsTimerEvent objects are allocated on the timer thread, and freed on another
// thread. Because TimerEventAllocator has its own lock, contention over that
// lock is limited to the allocation and deallocation of nsTimerEvent objects.
//
// Because this allocator is layered over PLArenaPool, it never shrinks -- even
// "freed" nsTimerEvents aren't truly freed, they're just put onto a free-list
// for later recycling. So the amount of memory consumed will always be equal
// to the high-water mark consumption. But nsTimerEvents are small and it's
// unusual to have more than a few hundred of them, so this shouldn't be a
// problem in practice.
class TimerEventAllocator
{
private:
struct FreeEntry
{
FreeEntry* mNext;
};
PLArenaPool mPool;
FreeEntry* mFirstFree;
mozilla::Monitor mMonitor;
public:
TimerEventAllocator()
: mFirstFree(nullptr)
, mMonitor("TimerEventAllocator")
{
PL_InitArenaPool(&mPool, "TimerEventPool", 4096, /* align = */ 0);
}
~TimerEventAllocator()
{
PL_FinishArenaPool(&mPool);
}
void* Alloc(size_t aSize);
void Free(void* aPtr);
};
} // namespace
// This is a nsICancelableRunnable because we can dispatch it to Workers and
// those can be shut down at any time, and in these cases, Cancel() is called
// instead of Run().
class nsTimerEvent : public nsCancelableRunnable
{
public:
NS_IMETHOD Run() override;
NS_IMETHOD Cancel() override
{
// Since nsTimerImpl is not thread-safe, we should release |mTimer|
// here in the target thread to avoid race condition. Otherwise,
// ~nsTimerEvent() which calls nsTimerImpl::Release() could run in the
// timer thread and result in race condition.
mTimer = nullptr;
return NS_OK;
}
nsTimerEvent()
: mTimer()
, mGeneration(0)
{
MOZ_COUNT_CTOR(nsTimerEvent);
// Note: We override operator new for this class, and the override is
// fallible!
sAllocatorUsers++;
}
TimeStamp mInitTime;
static void Init();
static void Shutdown();
static void DeleteAllocatorIfNeeded();
static void* operator new(size_t aSize) CPP_THROW_NEW
{
return sAllocator->Alloc(aSize);
}
void operator delete(void* aPtr)
{
sAllocator->Free(aPtr);
DeleteAllocatorIfNeeded();
}
already_AddRefed<nsTimerImpl> ForgetTimer()
{
return mTimer.forget();
}
void SetTimer(already_AddRefed<nsTimerImpl> aTimer)
{
mTimer = aTimer;
mGeneration = mTimer->GetGeneration();
}
private:
~nsTimerEvent()
{
MOZ_COUNT_DTOR(nsTimerEvent);
MOZ_ASSERT(!sCanDeleteAllocator || sAllocatorUsers > 0,
"This will result in us attempting to deallocate the nsTimerEvent allocator twice");
sAllocatorUsers--;
}
RefPtr<nsTimerImpl> mTimer;
int32_t mGeneration;
static TimerEventAllocator* sAllocator;
static Atomic<int32_t> sAllocatorUsers;
static bool sCanDeleteAllocator;
};
TimerEventAllocator* nsTimerEvent::sAllocator = nullptr;
Atomic<int32_t> nsTimerEvent::sAllocatorUsers;
bool nsTimerEvent::sCanDeleteAllocator = false;
namespace {
void*
TimerEventAllocator::Alloc(size_t aSize)
{
MOZ_ASSERT(aSize == sizeof(nsTimerEvent));
mozilla::MonitorAutoLock lock(mMonitor);
void* p;
if (mFirstFree) {
p = mFirstFree;
mFirstFree = mFirstFree->mNext;
} else {
PL_ARENA_ALLOCATE(p, &mPool, aSize);
if (!p) {
return nullptr;
}
}
return p;
}
void
TimerEventAllocator::Free(void* aPtr)
{
mozilla::MonitorAutoLock lock(mMonitor);
FreeEntry* entry = reinterpret_cast<FreeEntry*>(aPtr);
entry->mNext = mFirstFree;
mFirstFree = entry;
}
} // namespace
void
nsTimerEvent::Init()
{
sAllocator = new TimerEventAllocator();
}
void
nsTimerEvent::Shutdown()
{
sCanDeleteAllocator = true;
DeleteAllocatorIfNeeded();
}
void
nsTimerEvent::DeleteAllocatorIfNeeded()
{
if (sCanDeleteAllocator && sAllocatorUsers == 0) {
delete sAllocator;
sAllocator = nullptr;
}
}
NS_IMETHODIMP
nsTimerEvent::Run()
{
MOZ_ASSERT(mTimer);
if (mGeneration != mTimer->GetGeneration()) {
return NS_OK;
}
if (MOZ_LOG_TEST(GetTimerLog(), LogLevel::Debug)) {
TimeStamp now = TimeStamp::Now();
MOZ_LOG(GetTimerLog(), LogLevel::Debug,
("[this=%p] time between PostTimerEvent() and Fire(): %fms\n",
this, (now - mInitTime).ToMilliseconds()));
}
mTimer->Fire();
// We call Cancel() to correctly release mTimer.
// Read more in the Cancel() implementation.
return Cancel();
}
nsresult
TimerThread::Init()
{
MOZ_LOG(GetTimerLog(), LogLevel::Debug,
("TimerThread::Init [%d]\n", mInitialized));
if (mInitialized) {
if (!mThread) {
return NS_ERROR_FAILURE;
}
return NS_OK;
}
nsTimerEvent::Init();
if (mInitInProgress.exchange(true) == false) {
// We hold on to mThread to keep the thread alive.
nsresult rv = NS_NewThread(getter_AddRefs(mThread), this);
if (NS_FAILED(rv)) {
mThread = nullptr;
} else {
RefPtr<TimerObserverRunnable> r = new TimerObserverRunnable(this);
if (NS_IsMainThread()) {
r->Run();
} else {
NS_DispatchToMainThread(r);
}
}
{
MonitorAutoLock lock(mMonitor);
mInitialized = true;
mMonitor.NotifyAll();
}
} else {
MonitorAutoLock lock(mMonitor);
while (!mInitialized) {
mMonitor.Wait();
}
}
if (!mThread) {
return NS_ERROR_FAILURE;
}
return NS_OK;
}
nsresult
TimerThread::Shutdown()
{
MOZ_LOG(GetTimerLog(), LogLevel::Debug, ("TimerThread::Shutdown begin\n"));
if (!mThread) {
return NS_ERROR_NOT_INITIALIZED;
}
nsTArray<nsTimerImpl*> timers;
{
// lock scope
MonitorAutoLock lock(mMonitor);
mShutdown = true;
// notify the cond var so that Run() can return
if (mWaiting) {
mNotified = true;
mMonitor.Notify();
}
// Need to copy content of mTimers array to a local array
// because call to timers' ReleaseCallback() (and release its self)
// must not be done under the lock. Destructor of a callback
// might potentially call some code reentering the same lock
// that leads to unexpected behavior or deadlock.
// See bug 422472.
timers.AppendElements(mTimers);
mTimers.Clear();
}
uint32_t timersCount = timers.Length();
for (uint32_t i = 0; i < timersCount; i++) {
nsTimerImpl* timer = timers[i];
timer->ReleaseCallback();
ReleaseTimerInternal(timer);
}
mThread->Shutdown(); // wait for the thread to die
nsTimerEvent::Shutdown();
MOZ_LOG(GetTimerLog(), LogLevel::Debug, ("TimerThread::Shutdown end\n"));
return NS_OK;
}
#ifdef MOZ_NUWA_PROCESS
#include "ipc/Nuwa.h"
#endif
namespace {
struct MicrosecondsToInterval
{
PRIntervalTime operator[](size_t aMs) const {
return PR_MicrosecondsToInterval(aMs);
}
};
struct IntervalComparator
{
int operator()(PRIntervalTime aInterval) const {
return (0 < aInterval) ? -1 : 1;
}
};
} // namespace
NS_IMETHODIMP
TimerThread::Run()
{
PR_SetCurrentThreadName("Timer");
#ifdef MOZ_NUWA_PROCESS
if (IsNuwaProcess()) {
NuwaMarkCurrentThread(nullptr, nullptr);
}
#endif
MonitorAutoLock lock(mMonitor);
// We need to know how many microseconds give a positive PRIntervalTime. This
// is platform-dependent and we calculate it at runtime, finding a value |v|
// such that |PR_MicrosecondsToInterval(v) > 0| and then binary-searching in
// the range [0, v) to find the ms-to-interval scale.
uint32_t usForPosInterval = 1;
while (PR_MicrosecondsToInterval(usForPosInterval) == 0) {
usForPosInterval <<= 1;
}
size_t usIntervalResolution;
BinarySearchIf(MicrosecondsToInterval(), 0, usForPosInterval, IntervalComparator(), &usIntervalResolution);
MOZ_ASSERT(PR_MicrosecondsToInterval(usIntervalResolution - 1) == 0);
MOZ_ASSERT(PR_MicrosecondsToInterval(usIntervalResolution) == 1);
// Half of the amount of microseconds needed to get positive PRIntervalTime.
// We use this to decide how to round our wait times later
int32_t halfMicrosecondsIntervalResolution = usIntervalResolution / 2;
bool forceRunNextTimer = false;
while (!mShutdown) {
// Have to use PRIntervalTime here, since PR_WaitCondVar takes it
PRIntervalTime waitFor;
bool forceRunThisTimer = forceRunNextTimer;
forceRunNextTimer = false;
if (mSleeping
#ifdef MOZ_NUWA_PROCESS
|| IsNuwaProcess() // Don't fire timers or deadlock will result.
#endif
) {
// Sleep for 0.1 seconds while not firing timers.
uint32_t milliseconds = 100;
if (ChaosMode::isActive(ChaosFeature::TimerScheduling)) {
milliseconds = ChaosMode::randomUint32LessThan(200);
}
waitFor = PR_MillisecondsToInterval(milliseconds);
} else {
waitFor = PR_INTERVAL_NO_TIMEOUT;
TimeStamp now = TimeStamp::Now();
nsTimerImpl* timer = nullptr;
if (!mTimers.IsEmpty()) {
timer = mTimers[0];
if (now >= timer->mTimeout || forceRunThisTimer) {
next:
// NB: AddRef before the Release under RemoveTimerInternal to avoid
// mRefCnt passing through zero, in case all other refs than the one
// from mTimers have gone away (the last non-mTimers[i]-ref's Release
// must be racing with us, blocked in gThread->RemoveTimer waiting
// for TimerThread::mMonitor, under nsTimerImpl::Release.
RefPtr<nsTimerImpl> timerRef(timer);
RemoveTimerInternal(timer);
timer = nullptr;
MOZ_LOG(GetTimerLog(), LogLevel::Debug,
("Timer thread woke up %fms from when it was supposed to\n",
fabs((now - timerRef->mTimeout).ToMilliseconds())));
// We are going to let the call to PostTimerEvent here handle the
// release of the timer so that we don't end up releasing the timer
// on the TimerThread instead of on the thread it targets.
timerRef = PostTimerEvent(timerRef.forget());
if (timerRef) {
// We got our reference back due to an error.
// Unhook the nsRefPtr, and release manually so we can get the
// refcount.
nsrefcnt rc = timerRef.forget().take()->Release();
(void)rc;
// The nsITimer interface requires that its users keep a reference
// to the timers they use while those timers are initialized but
// have not yet fired. If this ever happens, it is a bug in the
// code that created and used the timer.
//
// Further, note that this should never happen even with a
// misbehaving user, because nsTimerImpl::Release checks for a
// refcount of 1 with an armed timer (a timer whose only reference
// is from the timer thread) and when it hits this will remove the
// timer from the timer thread and thus destroy the last reference,
// preventing this situation from occurring.
MOZ_ASSERT(rc != 0, "destroyed timer off its target thread!");
}
if (mShutdown) {
break;
}
// Update now, as PostTimerEvent plus the locking may have taken a
// tick or two, and we may goto next below.
now = TimeStamp::Now();
}
}
if (!mTimers.IsEmpty()) {
timer = mTimers[0];
TimeStamp timeout = timer->mTimeout;
// Don't wait at all (even for PR_INTERVAL_NO_WAIT) if the next timer
// is due now or overdue.
//
// Note that we can only sleep for integer values of a certain
// resolution. We use halfMicrosecondsIntervalResolution, calculated
// before, to do the optimal rounding (i.e., of how to decide what
// interval is so small we should not wait at all).
double microseconds = (timeout - now).ToMilliseconds() * 1000;
if (ChaosMode::isActive(ChaosFeature::TimerScheduling)) {
// The mean value of sFractions must be 1 to ensure that
// the average of a long sequence of timeouts converges to the
// actual sum of their times.
static const float sFractions[] = {
0.0f, 0.25f, 0.5f, 0.75f, 1.0f, 1.75f, 2.75f
};
microseconds *=
sFractions[ChaosMode::randomUint32LessThan(ArrayLength(sFractions))];
forceRunNextTimer = true;
}
if (microseconds < halfMicrosecondsIntervalResolution) {
forceRunNextTimer = false;
goto next; // round down; execute event now
}
waitFor = PR_MicrosecondsToInterval(
static_cast<uint32_t>(microseconds)); // Floor is accurate enough.
if (waitFor == 0) {
waitFor = 1; // round up, wait the minimum time we can wait
}
}
if (MOZ_LOG_TEST(GetTimerLog(), LogLevel::Debug)) {
if (waitFor == PR_INTERVAL_NO_TIMEOUT)
MOZ_LOG(GetTimerLog(), LogLevel::Debug,
("waiting for PR_INTERVAL_NO_TIMEOUT\n"));
else
MOZ_LOG(GetTimerLog(), LogLevel::Debug,
("waiting for %u\n", PR_IntervalToMilliseconds(waitFor)));
}
}
mWaiting = true;
mNotified = false;
mMonitor.Wait(waitFor);
if (mNotified) {
forceRunNextTimer = false;
}
mWaiting = false;
}
return NS_OK;
}
nsresult
TimerThread::AddTimer(nsTimerImpl* aTimer)
{
MonitorAutoLock lock(mMonitor);
// Add the timer to our list.
int32_t i = AddTimerInternal(aTimer);
if (i < 0) {
return NS_ERROR_OUT_OF_MEMORY;
}
// Awaken the timer thread.
if (mWaiting && i == 0) {
mNotified = true;
mMonitor.Notify();
}
return NS_OK;
}
nsresult
TimerThread::TimerDelayChanged(nsTimerImpl* aTimer)
{
MonitorAutoLock lock(mMonitor);
// Our caller has a strong ref to aTimer, so it can't go away here under
// ReleaseTimerInternal.
RemoveTimerInternal(aTimer);
int32_t i = AddTimerInternal(aTimer);
if (i < 0) {
return NS_ERROR_OUT_OF_MEMORY;
}
// Awaken the timer thread.
if (mWaiting && i == 0) {
mNotified = true;
mMonitor.Notify();
}
return NS_OK;
}
nsresult
TimerThread::RemoveTimer(nsTimerImpl* aTimer)
{
MonitorAutoLock lock(mMonitor);
// Remove the timer from our array. Tell callers that aTimer was not found
// by returning NS_ERROR_NOT_AVAILABLE. Unlike the TimerDelayChanged case
// immediately above, our caller may be passing a (now-)weak ref in via the
// aTimer param, specifically when nsTimerImpl::Release loses a race with
// TimerThread::Run, must wait for the mMonitor auto-lock here, and during the
// wait Run drops the only remaining ref to aTimer via RemoveTimerInternal.
if (!RemoveTimerInternal(aTimer)) {
return NS_ERROR_NOT_AVAILABLE;
}
// Awaken the timer thread.
if (mWaiting) {
mNotified = true;
mMonitor.Notify();
}
return NS_OK;
}
// This function must be called from within a lock
int32_t
TimerThread::AddTimerInternal(nsTimerImpl* aTimer)
{
mMonitor.AssertCurrentThreadOwns();
if (mShutdown) {
return -1;
}
TimeStamp now = TimeStamp::Now();
TimerAdditionComparator c(now, aTimer);
nsTimerImpl** insertSlot = mTimers.InsertElementSorted(aTimer, c);
if (!insertSlot) {
return -1;
}
aTimer->mArmed = true;
NS_ADDREF(aTimer);
#ifdef MOZ_TASK_TRACER
// Caller of AddTimer is the parent task of its timer event, so we store the
// TraceInfo here for later used.
aTimer->GetTLSTraceInfo();
#endif
return insertSlot - mTimers.Elements();
}
bool
TimerThread::RemoveTimerInternal(nsTimerImpl* aTimer)
{
mMonitor.AssertCurrentThreadOwns();
if (!mTimers.RemoveElement(aTimer)) {
return false;
}
ReleaseTimerInternal(aTimer);
return true;
}
void
TimerThread::ReleaseTimerInternal(nsTimerImpl* aTimer)
{
if (!mShutdown) {
// copied to a local array before releasing in shutdown
mMonitor.AssertCurrentThreadOwns();
}
// Order is crucial here -- see nsTimerImpl::Release.
aTimer->mArmed = false;
NS_RELEASE(aTimer);
}
already_AddRefed<nsTimerImpl>
TimerThread::PostTimerEvent(already_AddRefed<nsTimerImpl> aTimerRef)
{
mMonitor.AssertCurrentThreadOwns();
RefPtr<nsTimerImpl> timer(aTimerRef);
if (!timer->mEventTarget) {
NS_ERROR("Attempt to post timer event to NULL event target");
return timer.forget();
}
// XXX we may want to reuse this nsTimerEvent in the case of repeating timers.
// Since we already addref'd 'timer', we don't need to addref here.
// We will release either in ~nsTimerEvent(), or pass the reference back to
// the caller. We need to copy the generation number from this timer into the
// event, so we can avoid firing a timer that was re-initialized after being
// canceled.
RefPtr<nsTimerEvent> event = new nsTimerEvent;
if (!event) {
return timer.forget();
}
if (MOZ_LOG_TEST(GetTimerLog(), LogLevel::Debug)) {
event->mInitTime = TimeStamp::Now();
}
// If this is a repeating precise timer, we need to calculate the time for
// the next timer to fire before we make the callback. But don't re-arm.
if (timer->IsRepeatingPrecisely()) {
timer->SetDelayInternal(timer->mDelay);
}
#ifdef MOZ_TASK_TRACER
// During the dispatch of TimerEvent, we overwrite the current TraceInfo
// partially with the info saved in timer earlier, and restore it back by
// AutoSaveCurTraceInfo.
AutoSaveCurTraceInfo saveCurTraceInfo;
(timer->GetTracedTask()).SetTLSTraceInfo();
#endif
nsIEventTarget* target = timer->mEventTarget;
event->SetTimer(timer.forget());
nsresult rv;
{
// We release mMonitor around the Dispatch because if this timer is targeted
// at the TimerThread we'll deadlock.
MonitorAutoUnlock unlock(mMonitor);
rv = target->Dispatch(event, NS_DISPATCH_NORMAL);
}
if (NS_FAILED(rv)) {
timer = event->ForgetTimer();
RemoveTimerInternal(timer);
return timer.forget();
}
return nullptr;
}
void
TimerThread::DoBeforeSleep()
{
// Mainthread
MonitorAutoLock lock(mMonitor);
mSleeping = true;
}
// Note: wake may be notified without preceding sleep notification
void
TimerThread::DoAfterSleep()
{
// Mainthread
MonitorAutoLock lock(mMonitor);
mSleeping = false;
// Wake up the timer thread to re-process the array to ensure the sleep delay is correct,
// and fire any expired timers (perhaps quite a few)
mNotified = true;
mMonitor.Notify();
}
NS_IMETHODIMP
TimerThread::Observe(nsISupports* /* aSubject */, const char* aTopic,
const char16_t* /* aData */)
{
if (strcmp(aTopic, "sleep_notification") == 0 ||
strcmp(aTopic, "suspend_process_notification") == 0) {
DoBeforeSleep();
} else if (strcmp(aTopic, "wake_notification") == 0 ||
strcmp(aTopic, "resume_process_notification") == 0) {
DoAfterSleep();
}
return NS_OK;
}