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gecko-dev/xpcom/threads/nsTimerImpl.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 "nsAutoPtr.h"
#include "nsThreadManager.h"
#include "nsThreadUtils.h"
#include "plarena.h"
#include "GeckoProfiler.h"
using mozilla::TimeDuration;
using mozilla::TimeStamp;
static int32_t gGenerator = 0;
static TimerThread* gThread = nullptr;
#ifdef DEBUG_TIMERS
PRLogModuleInfo*
GetTimerLog()
{
static PRLogModuleInfo *sLog;
if (!sLog)
sLog = PR_NewLogModule("nsTimerImpl");
return sLog;
}
#include <math.h>
double nsTimerImpl::sDeltaSumSquared = 0;
double nsTimerImpl::sDeltaSum = 0;
double nsTimerImpl::sDeltaNum = 0;
static void
myNS_MeanAndStdDev(double n, double sumOfValues, double sumOfSquaredValues,
double *meanResult, double *stdDevResult)
{
double mean = 0.0, var = 0.0, stdDev = 0.0;
if (n > 0.0 && sumOfValues >= 0) {
mean = sumOfValues / n;
double temp = (n * sumOfSquaredValues) - (sumOfValues * sumOfValues);
if (temp < 0.0 || n <= 1)
var = 0.0;
else
var = temp / (n * (n - 1));
// for some reason, Windows says sqrt(0.0) is "-1.#J" (?!) so do this:
stdDev = var != 0.0 ? sqrt(var) : 0.0;
}
*meanResult = mean;
*stdDevResult = stdDev;
}
#endif
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);
};
} // anonymous namespace
class nsTimerEvent : public nsRunnable {
public:
NS_IMETHOD Run();
nsTimerEvent(nsTimerImpl *timer, int32_t generation)
: mTimer(timer), mGeneration(generation) {
// timer is already addref'd for us
MOZ_COUNT_CTOR(nsTimerEvent);
MOZ_ASSERT(gThread->IsOnTimerThread(),
"nsTimer must always be allocated on the timer thread");
PR_ATOMIC_INCREMENT(&sAllocatorUsers);
}
#ifdef DEBUG_TIMERS
TimeStamp mInitTime;
#endif
static void Init();
static void Shutdown();
static void DeleteAllocatorIfNeeded();
static void* operator new(size_t size) CPP_THROW_NEW {
return sAllocator->Alloc(size);
}
void operator delete(void* p) {
sAllocator->Free(p);
DeleteAllocatorIfNeeded();
}
private:
nsTimerEvent(); // Not implemented
~nsTimerEvent() {
#ifdef DEBUG
if (mTimer)
NS_WARNING("leaking reference to nsTimerImpl");
#endif
MOZ_COUNT_DTOR(nsTimerEvent);
MOZ_ASSERT(!sCanDeleteAllocator || sAllocatorUsers > 0,
"This will result in us attempting to deallocate the nsTimerEvent allocator twice");
PR_ATOMIC_DECREMENT(&sAllocatorUsers);
}
nsTimerImpl *mTimer;
int32_t mGeneration;
static TimerEventAllocator* sAllocator;
static int32_t sAllocatorUsers;
static bool sCanDeleteAllocator;
};
TimerEventAllocator* nsTimerEvent::sAllocator = nullptr;
int32_t nsTimerEvent::sAllocatorUsers = 0;
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;
}
} // anonymous namespace
NS_IMPL_THREADSAFE_QUERY_INTERFACE1(nsTimerImpl, nsITimer)
NS_IMPL_THREADSAFE_ADDREF(nsTimerImpl)
NS_IMETHODIMP_(nsrefcnt) nsTimerImpl::Release(void)
{
nsrefcnt count;
MOZ_ASSERT(int32_t(mRefCnt) > 0, "dup release");
count = NS_AtomicDecrementRefcnt(mRefCnt);
NS_LOG_RELEASE(this, count, "nsTimerImpl");
if (count == 0) {
mRefCnt = 1; /* stabilize */
/* enable this to find non-threadsafe destructors: */
/* NS_ASSERT_OWNINGTHREAD(nsTimerImpl); */
delete this;
return 0;
}
// If only one reference remains, and mArmed is set, then the ref must be
// from the TimerThread::mTimers array, so we Cancel this timer to remove
// the mTimers element, and return 0 if Cancel in fact disarmed the timer.
//
// We use an inlined version of nsTimerImpl::Cancel here to check for the
// NS_ERROR_NOT_AVAILABLE code returned by gThread->RemoveTimer when this
// timer is not found in the mTimers array -- i.e., when the timer was not
// in fact armed once we acquired TimerThread::mLock, in spite of mArmed
// being true here. That can happen if the armed timer is being fired by
// TimerThread::Run as we race and test mArmed just before it is cleared by
// the timer thread. If the RemoveTimer call below doesn't find this timer
// in the mTimers array, then the last ref to this timer is held manually
// and temporarily by the TimerThread, so we should fall through to the
// final return and return 1, not 0.
//
// The original version of this thread-based timer code kept weak refs from
// TimerThread::mTimers, removing this timer's weak ref in the destructor,
// but that leads to double-destructions in the race described above, and
// adding mArmed doesn't help, because destructors can't be deferred, once
// begun. But by combining reference-counting and a specialized Release
// method with "is this timer still in the mTimers array once we acquire
// the TimerThread's lock" testing, we defer destruction until we're sure
// that only one thread has its hot little hands on this timer.
//
// Note that both approaches preclude a timer creator, and everyone else
// except the TimerThread who might have a strong ref, from dropping all
// their strong refs without implicitly canceling the timer. Timers need
// non-mTimers-element strong refs to stay alive.
if (count == 1 && mArmed) {
mCanceled = true;
MOZ_ASSERT(gThread, "Armed timer exists after the thread timer stopped.");
if (NS_SUCCEEDED(gThread->RemoveTimer(this)))
return 0;
}
return count;
}
nsTimerImpl::nsTimerImpl() :
mClosure(nullptr),
mCallbackType(CALLBACK_TYPE_UNKNOWN),
mFiring(false),
mArmed(false),
mCanceled(false),
mGeneration(0),
mDelay(0)
{
// XXXbsmedberg: shouldn't this be in Init()?
mEventTarget = static_cast<nsIEventTarget*>(NS_GetCurrentThread());
mCallback.c = nullptr;
}
nsTimerImpl::~nsTimerImpl()
{
ReleaseCallback();
}
//static
nsresult
nsTimerImpl::Startup()
{
nsresult rv;
nsTimerEvent::Init();
gThread = new TimerThread();
if (!gThread) return NS_ERROR_OUT_OF_MEMORY;
NS_ADDREF(gThread);
rv = gThread->InitLocks();
if (NS_FAILED(rv)) {
NS_RELEASE(gThread);
}
return rv;
}
void nsTimerImpl::Shutdown()
{
#ifdef DEBUG_TIMERS
if (PR_LOG_TEST(GetTimerLog(), PR_LOG_DEBUG)) {
double mean = 0, stddev = 0;
myNS_MeanAndStdDev(sDeltaNum, sDeltaSum, sDeltaSumSquared, &mean, &stddev);
PR_LOG(GetTimerLog(), PR_LOG_DEBUG, ("sDeltaNum = %f, sDeltaSum = %f, sDeltaSumSquared = %f\n", sDeltaNum, sDeltaSum, sDeltaSumSquared));
PR_LOG(GetTimerLog(), PR_LOG_DEBUG, ("mean: %fms, stddev: %fms\n", mean, stddev));
}
#endif
if (!gThread)
return;
gThread->Shutdown();
NS_RELEASE(gThread);
nsTimerEvent::Shutdown();
}
nsresult nsTimerImpl::InitCommon(uint32_t aType, uint32_t aDelay)
{
nsresult rv;
NS_ENSURE_TRUE(gThread, NS_ERROR_NOT_INITIALIZED);
rv = gThread->Init();
NS_ENSURE_SUCCESS(rv, rv);
/**
* In case of re-Init, both with and without a preceding Cancel, clear the
* mCanceled flag and assign a new mGeneration. But first, remove any armed
* timer from the timer thread's list.
*
* If we are racing with the timer thread to remove this timer and we lose,
* the RemoveTimer call made here will fail to find this timer in the timer
* thread's list, and will return false harmlessly. We test mArmed here to
* avoid the small overhead in RemoveTimer of locking the timer thread and
* checking its list for this timer. It's safe to test mArmed even though
* it might be cleared on another thread in the next cycle (or even already
* be cleared by another CPU whose store hasn't reached our CPU's cache),
* because RemoveTimer is idempotent.
*/
if (mArmed)
gThread->RemoveTimer(this);
mCanceled = false;
mTimeout = TimeStamp();
mGeneration = PR_ATOMIC_INCREMENT(&gGenerator);
mType = (uint8_t)aType;
SetDelayInternal(aDelay);
return gThread->AddTimer(this);
}
NS_IMETHODIMP nsTimerImpl::InitWithFuncCallback(nsTimerCallbackFunc aFunc,
void *aClosure,
uint32_t aDelay,
uint32_t aType)
{
NS_ENSURE_ARG_POINTER(aFunc);
ReleaseCallback();
mCallbackType = CALLBACK_TYPE_FUNC;
mCallback.c = aFunc;
mClosure = aClosure;
return InitCommon(aType, aDelay);
}
NS_IMETHODIMP nsTimerImpl::InitWithCallback(nsITimerCallback *aCallback,
uint32_t aDelay,
uint32_t aType)
{
NS_ENSURE_ARG_POINTER(aCallback);
ReleaseCallback();
mCallbackType = CALLBACK_TYPE_INTERFACE;
mCallback.i = aCallback;
NS_ADDREF(mCallback.i);
return InitCommon(aType, aDelay);
}
NS_IMETHODIMP nsTimerImpl::Init(nsIObserver *aObserver,
uint32_t aDelay,
uint32_t aType)
{
NS_ENSURE_ARG_POINTER(aObserver);
ReleaseCallback();
mCallbackType = CALLBACK_TYPE_OBSERVER;
mCallback.o = aObserver;
NS_ADDREF(mCallback.o);
return InitCommon(aType, aDelay);
}
NS_IMETHODIMP nsTimerImpl::Cancel()
{
mCanceled = true;
if (gThread)
gThread->RemoveTimer(this);
ReleaseCallback();
return NS_OK;
}
NS_IMETHODIMP nsTimerImpl::SetDelay(uint32_t aDelay)
{
if (mCallbackType == CALLBACK_TYPE_UNKNOWN && mType == TYPE_ONE_SHOT) {
// This may happen if someone tries to re-use a one-shot timer
// by re-setting delay instead of reinitializing the timer.
NS_ERROR("nsITimer->SetDelay() called when the "
"one-shot timer is not set up.");
return NS_ERROR_NOT_INITIALIZED;
}
// If we're already repeating precisely, update mTimeout now so that the
// new delay takes effect in the future.
if (!mTimeout.IsNull() && mType == TYPE_REPEATING_PRECISE)
mTimeout = TimeStamp::Now();
SetDelayInternal(aDelay);
if (!mFiring && gThread)
gThread->TimerDelayChanged(this);
return NS_OK;
}
NS_IMETHODIMP nsTimerImpl::GetDelay(uint32_t* aDelay)
{
*aDelay = mDelay;
return NS_OK;
}
NS_IMETHODIMP nsTimerImpl::SetType(uint32_t aType)
{
mType = (uint8_t)aType;
// XXX if this is called, we should change the actual type.. this could effect
// repeating timers. we need to ensure in Fire() that if mType has changed
// during the callback that we don't end up with the timer in the queue twice.
return NS_OK;
}
NS_IMETHODIMP nsTimerImpl::GetType(uint32_t* aType)
{
*aType = mType;
return NS_OK;
}
NS_IMETHODIMP nsTimerImpl::GetClosure(void** aClosure)
{
*aClosure = mClosure;
return NS_OK;
}
NS_IMETHODIMP nsTimerImpl::GetCallback(nsITimerCallback **aCallback)
{
if (mCallbackType == CALLBACK_TYPE_INTERFACE)
NS_IF_ADDREF(*aCallback = mCallback.i);
else if (mTimerCallbackWhileFiring)
NS_ADDREF(*aCallback = mTimerCallbackWhileFiring);
else
*aCallback = nullptr;
return NS_OK;
}
NS_IMETHODIMP nsTimerImpl::GetTarget(nsIEventTarget** aTarget)
{
NS_IF_ADDREF(*aTarget = mEventTarget);
return NS_OK;
}
NS_IMETHODIMP nsTimerImpl::SetTarget(nsIEventTarget* aTarget)
{
NS_ENSURE_TRUE(mCallbackType == CALLBACK_TYPE_UNKNOWN,
NS_ERROR_ALREADY_INITIALIZED);
if (aTarget)
mEventTarget = aTarget;
else
mEventTarget = static_cast<nsIEventTarget*>(NS_GetCurrentThread());
return NS_OK;
}
void nsTimerImpl::Fire()
{
if (mCanceled)
return;
PROFILER_LABEL("Timer", "Fire");
TimeStamp now = TimeStamp::Now();
#ifdef DEBUG_TIMERS
if (PR_LOG_TEST(GetTimerLog(), PR_LOG_DEBUG)) {
TimeDuration a = now - mStart; // actual delay in intervals
TimeDuration b = TimeDuration::FromMilliseconds(mDelay); // expected delay in intervals
TimeDuration delta = (a > b) ? a - b : b - a;
uint32_t d = delta.ToMilliseconds(); // delta in ms
sDeltaSum += d;
sDeltaSumSquared += double(d) * double(d);
sDeltaNum++;
PR_LOG(GetTimerLog(), PR_LOG_DEBUG, ("[this=%p] expected delay time %4ums\n", this, mDelay));
PR_LOG(GetTimerLog(), PR_LOG_DEBUG, ("[this=%p] actual delay time %fms\n", this, a.ToMilliseconds()));
PR_LOG(GetTimerLog(), PR_LOG_DEBUG, ("[this=%p] (mType is %d) -------\n", this, mType));
PR_LOG(GetTimerLog(), PR_LOG_DEBUG, ("[this=%p] delta %4dms\n", this, (a > b) ? (int32_t)d : -(int32_t)d));
mStart = mStart2;
mStart2 = TimeStamp();
}
#endif
TimeStamp timeout = mTimeout;
if (IsRepeatingPrecisely()) {
// Precise repeating timers advance mTimeout by mDelay without fail before
// calling Fire().
timeout -= TimeDuration::FromMilliseconds(mDelay);
}
if (mCallbackType == CALLBACK_TYPE_INTERFACE)
mTimerCallbackWhileFiring = mCallback.i;
mFiring = true;
// Handle callbacks that re-init the timer, but avoid leaking.
// See bug 330128.
CallbackUnion callback = mCallback;
unsigned callbackType = mCallbackType;
if (callbackType == CALLBACK_TYPE_INTERFACE)
NS_ADDREF(callback.i);
else if (callbackType == CALLBACK_TYPE_OBSERVER)
NS_ADDREF(callback.o);
ReleaseCallback();
switch (callbackType) {
case CALLBACK_TYPE_FUNC:
callback.c(this, mClosure);
break;
case CALLBACK_TYPE_INTERFACE:
callback.i->Notify(this);
break;
case CALLBACK_TYPE_OBSERVER:
callback.o->Observe(static_cast<nsITimer*>(this),
NS_TIMER_CALLBACK_TOPIC,
nullptr);
break;
default:;
}
// If the callback didn't re-init the timer, and it's not a one-shot timer,
// restore the callback state.
if (mCallbackType == CALLBACK_TYPE_UNKNOWN &&
mType != TYPE_ONE_SHOT && !mCanceled) {
mCallback = callback;
mCallbackType = callbackType;
} else {
// The timer was a one-shot, or the callback was reinitialized.
if (callbackType == CALLBACK_TYPE_INTERFACE)
NS_RELEASE(callback.i);
else if (callbackType == CALLBACK_TYPE_OBSERVER)
NS_RELEASE(callback.o);
}
mFiring = false;
mTimerCallbackWhileFiring = nullptr;
#ifdef DEBUG_TIMERS
if (PR_LOG_TEST(GetTimerLog(), PR_LOG_DEBUG)) {
PR_LOG(GetTimerLog(), PR_LOG_DEBUG,
("[this=%p] Took %fms to fire timer callback\n",
this, (TimeStamp::Now() - now).ToMilliseconds()));
}
#endif
// Reschedule repeating timers, except REPEATING_PRECISE which already did
// that in PostTimerEvent, but make sure that we aren't armed already (which
// can happen if the callback reinitialized the timer).
if (IsRepeating() && mType != TYPE_REPEATING_PRECISE && !mArmed) {
if (mType == TYPE_REPEATING_SLACK)
SetDelayInternal(mDelay); // force mTimeout to be recomputed. For
// REPEATING_PRECISE_CAN_SKIP timers this has
// already happened.
if (gThread)
gThread->AddTimer(this);
}
}
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()
{
nsRefPtr<nsTimerImpl> timer;
timer.swap(mTimer);
if (mGeneration != timer->GetGeneration())
return NS_OK;
#ifdef DEBUG_TIMERS
if (PR_LOG_TEST(GetTimerLog(), PR_LOG_DEBUG)) {
TimeStamp now = TimeStamp::Now();
PR_LOG(GetTimerLog(), PR_LOG_DEBUG,
("[this=%p] time between PostTimerEvent() and Fire(): %fms\n",
this, (now - mInitTime).ToMilliseconds()));
}
#endif
timer->Fire();
return NS_OK;
}
nsresult nsTimerImpl::PostTimerEvent()
{
// XXX we may want to reuse this nsTimerEvent in the case of repeating timers.
// Since TimerThread addref'd 'this' for us, we don't need to addref here.
// We will release in destroyMyEvent. 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.
nsRefPtr<nsTimerEvent> event = new nsTimerEvent(this, mGeneration);
if (!event)
return NS_ERROR_OUT_OF_MEMORY;
#ifdef DEBUG_TIMERS
if (PR_LOG_TEST(GetTimerLog(), PR_LOG_DEBUG)) {
event->mInitTime = TimeStamp::Now();
}
#endif
// If this is a repeating precise timer, we need to calculate the time for
// the next timer to fire before we make the callback.
if (IsRepeatingPrecisely()) {
SetDelayInternal(mDelay);
// But only re-arm REPEATING_PRECISE timers.
if (gThread && mType == TYPE_REPEATING_PRECISE) {
nsresult rv = gThread->AddTimer(this);
if (NS_FAILED(rv))
return rv;
}
}
nsresult rv = mEventTarget->Dispatch(event, NS_DISPATCH_NORMAL);
if (NS_FAILED(rv) && gThread)
gThread->RemoveTimer(this);
return rv;
}
void nsTimerImpl::SetDelayInternal(uint32_t aDelay)
{
TimeDuration delayInterval = TimeDuration::FromMilliseconds(aDelay);
mDelay = aDelay;
TimeStamp now = TimeStamp::Now();
if (mTimeout.IsNull() || mType != TYPE_REPEATING_PRECISE)
mTimeout = now;
mTimeout += delayInterval;
#ifdef DEBUG_TIMERS
if (PR_LOG_TEST(GetTimerLog(), PR_LOG_DEBUG)) {
if (mStart.IsNull())
mStart = now;
else
mStart2 = now;
}
#endif
}
// NOT FOR PUBLIC CONSUMPTION!
nsresult
NS_NewTimer(nsITimer* *aResult, nsTimerCallbackFunc aCallback, void *aClosure,
uint32_t aDelay, uint32_t aType)
{
nsTimerImpl* timer = new nsTimerImpl();
if (timer == nullptr)
return NS_ERROR_OUT_OF_MEMORY;
NS_ADDREF(timer);
nsresult rv = timer->InitWithFuncCallback(aCallback, aClosure,
aDelay, aType);
if (NS_FAILED(rv)) {
NS_RELEASE(timer);
return rv;
}
*aResult = timer;
return NS_OK;
}
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