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gecko-dev/dom/base/CCGCScheduler.cpp

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/* 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 "CCGCScheduler.h"
#include "js/GCAPI.h"
#include "mozilla/StaticPrefs_javascript.h"
#include "mozilla/CycleCollectedJSRuntime.h"
#include "mozilla/ProfilerMarkers.h"
#include "mozilla/dom/ScriptSettings.h"
#include "mozilla/PerfStats.h"
#include "nsRefreshDriver.h"
/*
* GC Scheduling from Firefox
* ==========================
*
* See also GC Scheduling from SpiderMonkey's perspective here:
* https://searchfox.org/mozilla-central/source/js/src/gc/Scheduling.h
*
* From Firefox's perspective GCs can start in 5 different ways:
*
* * The JS engine just starts doing a GC for its own reasons (see above).
* Firefox finds out about these via a callback in nsJSEnvironment.cpp
* * PokeGC()
* * PokeFullGC()
* * PokeShrinkingGC()
* * memory-pressure GCs (via a listener in nsJSEnvironment.cpp).
*
* PokeGC
* ------
*
* void CCGCScheduler::PokeGC(JS::GCReason aReason, JSObject* aObj,
* TimeDuration aDelay)
*
* PokeGC provides a way for callers to say "Hey, there may be some memory
* associated with this object (via Zone) you can collect." PokeGC will:
* * add the zone to a set,
* * set flags including what kind of GC to run (SetWantMajorGC),
* * then creates the mGCRunner with a short delay.
*
* The delay can allow other calls to PokeGC to add their zones so they can
* be collected together.
*
* See below for what happens when mGCRunner fires.
*
* PokeFullGC
* ----------
*
* void CCGCScheduler::PokeFullGC()
*
* PokeFullGC will create a timer that will initiate a "full" (all zones)
* collection. This is usually used after a regular collection if a full GC
* seems like a good idea (to collect inter-zone references).
*
* When the timer fires it will:
* * set flags (SetWantMajorGC),
* * start the mGCRunner with zero delay.
*
* See below for when mGCRunner fires.
*
* PokeShrinkingGC
* ---------------
*
* void CCGCScheduler::PokeShrinkingGC()
*
* PokeShrinkingGC is called when Firefox's user is inactive.
* Like PokeFullGC, PokeShrinkingGC uses a timer, but the timeout is longer
* which should prevent the ShrinkingGC from starting if the user only
* glances away for a brief time. When the timer fires it will:
*
* * set flags (SetWantMajorGC),
* * create the mGCRunner.
*
* There is a check if the user is still inactive in GCRunnerFired), if the
* user has become active the shrinking GC is canceled and either a regular
* GC (if requested, see mWantAtLeastRegularGC) or no GC is run.
*
* When mGCRunner fires
* --------------------
*
* When mGCRunner fires it calls GCRunnerFired. This starts in the
* WaitToMajorGC state:
*
* * If this is a parent process it jumps to the next state
* * If this is a content process it will ask the parent if now is a good
* time to do a GC. (MayGCNow)
* * kill the mGCRunner
* * Exit
*
* Meanwhile the parent process will queue GC requests so that not too many
* are running in parallel overwhelming the CPU cores (see
* IdleSchedulerParent).
*
* When the promise from MayGCNow is resolved it will set some
* state (NoteReadyForMajorGC) and restore the mGCRunner.
*
* When the mGCRunner runs a second time (or this is the parent process and
* which jumped over the above logic. It will be in the StartMajorGC state.
* It will initiate the GC for real, usually. If it's a shrinking GC and the
* user is now active again it may abort. See GCRunnerFiredDoGC().
*
* The runner will then run the first slice of the garbage collection.
* Later slices are also run by the runner, the final slice kills the runner
* from the GC callback in nsJSEnvironment.cpp.
*
* There is additional logic in the code to handle concurrent requests of
* various kinds.
*/
namespace geckoprofiler::markers {
struct CCIntervalMarker {
static constexpr mozilla::Span<const char> MarkerTypeName() {
return mozilla::MakeStringSpan("CC");
}
static void StreamJSONMarkerData(
mozilla::baseprofiler::SpliceableJSONWriter& aWriter, bool aIsStart,
const mozilla::ProfilerString8View& aReason,
uint32_t aForgetSkippableBeforeCC, uint32_t aSuspectedAtCCStart,
uint32_t aRemovedPurples, const mozilla::CycleCollectorResults& aResults,
mozilla::TimeDuration aMaxSliceTime) {
if (aIsStart) {
aWriter.StringProperty("mReason", aReason);
aWriter.IntProperty("mSuspected", aSuspectedAtCCStart);
aWriter.IntProperty("mForgetSkippable", aForgetSkippableBeforeCC);
aWriter.IntProperty("mRemovedPurples", aRemovedPurples);
} else {
aWriter.TimeDoubleMsProperty("mMaxSliceTime",
aMaxSliceTime.ToMilliseconds());
aWriter.IntProperty("mSlices", aResults.mNumSlices);
aWriter.BoolProperty("mAnyManual", aResults.mAnyManual);
aWriter.BoolProperty("mForcedGC", aResults.mForcedGC);
aWriter.BoolProperty("mMergedZones", aResults.mMergedZones);
aWriter.IntProperty("mVisitedRefCounted", aResults.mVisitedRefCounted);
aWriter.IntProperty("mVisitedGCed", aResults.mVisitedGCed);
aWriter.IntProperty("mFreedRefCounted", aResults.mFreedRefCounted);
aWriter.IntProperty("mFreedGCed", aResults.mFreedGCed);
aWriter.IntProperty("mFreedJSZones", aResults.mFreedJSZones);
}
}
static mozilla::MarkerSchema MarkerTypeDisplay() {
using MS = mozilla::MarkerSchema;
MS schema{MS::Location::MarkerChart, MS::Location::MarkerTable,
MS::Location::TimelineMemory};
schema.AddStaticLabelValue(
"Description",
"Summary data for the core part of a cycle collection, possibly "
"encompassing a set of incremental slices. The main thread is not "
"blocked for the entire major CC interval, only for the individual "
"slices.");
schema.AddKeyLabelFormatSearchable("mReason", "Reason", MS::Format::String,
MS::Searchable::Searchable);
schema.AddKeyLabelFormat("mMaxSliceTime", "Max Slice Time",
MS::Format::Duration);
schema.AddKeyLabelFormat("mSuspected", "Suspected Objects",
MS::Format::Integer);
schema.AddKeyLabelFormat("mSlices", "Number of Slices",
MS::Format::Integer);
schema.AddKeyLabelFormat("mAnyManual", "Manually Triggered",
MS::Format::Integer);
schema.AddKeyLabelFormat("mForcedGC", "GC Forced", MS::Format::Integer);
schema.AddKeyLabelFormat("mMergedZones", "Zones Merged",
MS::Format::Integer);
schema.AddKeyLabelFormat("mForgetSkippable", "Forget Skippables",
MS::Format::Integer);
schema.AddKeyLabelFormat("mVisitedRefCounted", "Refcounted Objects Visited",
MS::Format::Integer);
schema.AddKeyLabelFormat("mVisitedGCed", "GC Objects Visited",
MS::Format::Integer);
schema.AddKeyLabelFormat("mFreedRefCounted", "Refcounted Objects Freed",
MS::Format::Integer);
schema.AddKeyLabelFormat("mFreedGCed", "GC Objects Freed",
MS::Format::Integer);
schema.AddKeyLabelFormat("mCollectedGCZones", "JS Zones Freed",
MS::Format::Integer);
schema.AddKeyLabelFormat("mRemovedPurples",
"Objects Removed From Purple Buffer",
MS::Format::Integer);
return schema;
}
};
} // namespace geckoprofiler::markers
namespace mozilla {
void CCGCScheduler::NoteGCBegin(JS::GCReason aReason) {
// Treat all GC as incremental here; non-incremental GC will just appear to
// be one slice.
mInIncrementalGC = true;
mReadyForMajorGC = !mAskParentBeforeMajorGC;
// Tell the parent process that we've started a GC (it might not know if
// we hit a threshold in the JS engine).
using mozilla::ipc::IdleSchedulerChild;
IdleSchedulerChild* child = IdleSchedulerChild::GetMainThreadIdleScheduler();
if (child) {
child->StartedGC();
}
// The reason might have come from mMajorReason, mEagerMajorGCReason, or
// in the case of an internally-generated GC, it might come from the
// internal logic (and be passed in here). It's easier to manage a single
// reason state variable, so merge all sources into mMajorGCReason.
MOZ_ASSERT(aReason != JS::GCReason::NO_REASON);
mMajorGCReason = aReason;
mEagerMajorGCReason = JS::GCReason::NO_REASON;
}
void CCGCScheduler::NoteGCEnd() {
mMajorGCReason = JS::GCReason::NO_REASON;
mEagerMajorGCReason = JS::GCReason::NO_REASON;
mEagerMinorGCReason = JS::GCReason::NO_REASON;
mInIncrementalGC = false;
mCCBlockStart = TimeStamp();
mReadyForMajorGC = !mAskParentBeforeMajorGC;
mWantAtLeastRegularGC = false;
mNeedsFullCC = CCReason::GC_FINISHED;
mHasRunGC = true;
mIsCompactingOnUserInactive = false;
mCleanupsSinceLastGC = 0;
mCCollectedWaitingForGC = 0;
mCCollectedZonesWaitingForGC = 0;
mLikelyShortLivingObjectsNeedingGC = 0;
using mozilla::ipc::IdleSchedulerChild;
IdleSchedulerChild* child = IdleSchedulerChild::GetMainThreadIdleScheduler();
if (child) {
child->DoneGC();
}
}
void CCGCScheduler::NoteGCSliceEnd(TimeStamp aStart, TimeStamp aEnd) {
if (mMajorGCReason == JS::GCReason::NO_REASON) {
// Internally-triggered GCs do not wait for the parent's permission to
// proceed. This flag won't be checked during an incremental GC anyway,
// but it better reflects reality.
mReadyForMajorGC = true;
}
// Subsequent slices should be INTER_SLICE_GC unless they are triggered by
// something else that provides its own reason.
mMajorGCReason = JS::GCReason::INTER_SLICE_GC;
MOZ_ASSERT(aEnd >= aStart);
TimeDuration sliceDuration = aEnd - aStart;
PerfStats::RecordMeasurement(PerfStats::Metric::MajorGC, sliceDuration);
// Compute how much GC time was spent in predicted-to-be-idle time. In the
// unlikely event that the slice started after the deadline had already
// passed, treat the entire slice as non-idle.
TimeDuration nonIdleDuration;
bool startedIdle = mTriggeredGCDeadline.isSome() &&
!mTriggeredGCDeadline->IsNull() &&
*mTriggeredGCDeadline > aStart;
if (!startedIdle) {
nonIdleDuration = sliceDuration;
} else {
if (*mTriggeredGCDeadline < aEnd) {
// Overran the idle deadline.
nonIdleDuration = aEnd - *mTriggeredGCDeadline;
}
}
PerfStats::RecordMeasurement(PerfStats::Metric::NonIdleMajorGC,
nonIdleDuration);
// Note the GC_SLICE_DURING_IDLE previously had a different definition: it was
// a histogram of percentages of externally-triggered slices. It is now a
// histogram of percentages of all slices. That means that now you might have
// a 4ms internal slice (0% during idle) followed by a 16ms external slice
// (15ms during idle), whereas before this would show up as a single record of
// a single slice with 75% of its time during idle (15 of 20ms).
TimeDuration idleDuration = sliceDuration - nonIdleDuration;
uint32_t percent =
uint32_t(idleDuration.ToSeconds() / sliceDuration.ToSeconds() * 100);
Telemetry::Accumulate(Telemetry::GC_SLICE_DURING_IDLE, percent);
mTriggeredGCDeadline.reset();
}
void CCGCScheduler::NoteCCBegin(CCReason aReason, TimeStamp aWhen,
uint32_t aNumForgetSkippables,
uint32_t aSuspected, uint32_t aRemovedPurples) {
CycleCollectorResults ignoredResults;
PROFILER_MARKER(
"CC", GCCC, MarkerOptions(MarkerTiming::IntervalStart(aWhen)),
CCIntervalMarker,
/* aIsStart */ true,
ProfilerString8View::WrapNullTerminatedString(CCReasonToString(aReason)),
aNumForgetSkippables, aSuspected, aRemovedPurples, ignoredResults,
TimeDuration());
mIsCollectingCycles = true;
}
void CCGCScheduler::NoteCCEnd(const CycleCollectorResults& aResults,
TimeStamp aWhen,
mozilla::TimeDuration aMaxSliceTime) {
mCCollectedWaitingForGC += aResults.mFreedGCed;
mCCollectedZonesWaitingForGC += aResults.mFreedJSZones;
PROFILER_MARKER("CC", GCCC, MarkerOptions(MarkerTiming::IntervalEnd(aWhen)),
CCIntervalMarker, /* aIsStart */ false, nullptr, 0, 0, 0,
aResults, aMaxSliceTime);
mIsCollectingCycles = false;
mLastCCEndTime = aWhen;
mNeedsFullCC = CCReason::NO_REASON;
}
void CCGCScheduler::NoteWontGC() {
mReadyForMajorGC = !mAskParentBeforeMajorGC;
mMajorGCReason = JS::GCReason::NO_REASON;
mEagerMajorGCReason = JS::GCReason::NO_REASON;
mWantAtLeastRegularGC = false;
// Don't clear the WantFullGC state, we will do a full GC the next time a
// GC happens for any other reason.
}
bool CCGCScheduler::GCRunnerFired(TimeStamp aDeadline) {
MOZ_ASSERT(!mDidShutdown, "GCRunner still alive during shutdown");
GCRunnerStep step = GetNextGCRunnerAction(aDeadline);
switch (step.mAction) {
case GCRunnerAction::None:
KillGCRunner();
return false;
case GCRunnerAction::MinorGC:
JS::MaybeRunNurseryCollection(CycleCollectedJSRuntime::Get()->Runtime(),
step.mReason);
NoteMinorGCEnd();
return HasMoreIdleGCRunnerWork();
case GCRunnerAction::WaitToMajorGC: {
MOZ_ASSERT(!mHaveAskedParent, "GCRunner alive after asking the parent");
RefPtr<CCGCScheduler::MayGCPromise> mbPromise =
CCGCScheduler::MayGCNow(step.mReason);
if (!mbPromise) {
// We can GC now.
break;
}
mHaveAskedParent = true;
KillGCRunner();
mbPromise->Then(
GetMainThreadSerialEventTarget(), __func__,
[this](bool aMayGC) {
mHaveAskedParent = false;
if (aMayGC) {
if (!NoteReadyForMajorGC()) {
// Another GC started and maybe completed while waiting.
return;
}
// Recreate the GC runner with a 0 delay. The new runner will
// continue in idle time.
KillGCRunner();
EnsureGCRunner(0);
} else if (!InIncrementalGC()) {
// We should kill the GC runner since we're done with it, but
// only if there's no incremental GC.
KillGCRunner();
NoteWontGC();
}
},
[this](mozilla::ipc::ResponseRejectReason r) {
mHaveAskedParent = false;
if (!InIncrementalGC()) {
KillGCRunner();
NoteWontGC();
}
});
return true;
}
case GCRunnerAction::StartMajorGC:
case GCRunnerAction::GCSlice:
break;
}
return GCRunnerFiredDoGC(aDeadline, step);
}
bool CCGCScheduler::GCRunnerFiredDoGC(TimeStamp aDeadline,
const GCRunnerStep& aStep) {
// Run a GC slice, possibly the first one of a major GC.
nsJSContext::IsShrinking is_shrinking = nsJSContext::NonShrinkingGC;
if (!InIncrementalGC() && aStep.mReason == JS::GCReason::USER_INACTIVE) {
bool do_gc = mWantAtLeastRegularGC;
if (!mUserIsActive) {
if (!nsRefreshDriver::IsRegularRateTimerTicking()) {
mIsCompactingOnUserInactive = true;
is_shrinking = nsJSContext::ShrinkingGC;
do_gc = true;
} else {
// Poke again to restart the timer.
PokeShrinkingGC();
}
}
if (!do_gc) {
using mozilla::ipc::IdleSchedulerChild;
IdleSchedulerChild* child =
IdleSchedulerChild::GetMainThreadIdleScheduler();
if (child) {
child->DoneGC();
}
NoteWontGC();
KillGCRunner();
return true;
}
}
// Note that we are triggering the following GC slice and recording whether
// it started in idle time, for use in the callback at the end of the slice.
mTriggeredGCDeadline = Some(aDeadline);
MOZ_ASSERT(mActiveIntersliceGCBudget);
TimeStamp startTimeStamp = TimeStamp::Now();
js::SliceBudget budget = ComputeInterSliceGCBudget(aDeadline, startTimeStamp);
nsJSContext::RunIncrementalGCSlice(aStep.mReason, is_shrinking, budget);
// If the GC doesn't have any more work to do on the foreground thread (and
// e.g. is waiting for background sweeping to finish) then return false to
// make IdleTaskRunner postpone the next call a bit.
JSContext* cx = dom::danger::GetJSContext();
return JS::IncrementalGCHasForegroundWork(cx);
}
RefPtr<CCGCScheduler::MayGCPromise> CCGCScheduler::MayGCNow(
JS::GCReason reason) {
using namespace mozilla::ipc;
// We ask the parent if we should GC for GCs that aren't too timely,
// with the exception of MEM_PRESSURE, in that case we ask the parent
// because GCing on too many processes at the same time when under
// memory pressure could be a very bad experience for the user.
switch (reason) {
case JS::GCReason::PAGE_HIDE:
case JS::GCReason::MEM_PRESSURE:
case JS::GCReason::USER_INACTIVE:
case JS::GCReason::FULL_GC_TIMER:
case JS::GCReason::CC_FINISHED: {
if (XRE_IsContentProcess()) {
IdleSchedulerChild* child =
IdleSchedulerChild::GetMainThreadIdleScheduler();
if (child) {
return child->MayGCNow();
}
}
// The parent process doesn't ask IdleSchedulerParent if it can GC.
break;
}
default:
break;
}
// We use synchronous task dispatch here to avoid a trip through the event
// loop if we're on the parent process or it's a GC reason that does not
// require permission to GC.
RefPtr<MayGCPromise::Private> p = MakeRefPtr<MayGCPromise::Private>(__func__);
p->UseSynchronousTaskDispatch(__func__);
p->Resolve(true, __func__);
return p;
}
void CCGCScheduler::RunNextCollectorTimer(JS::GCReason aReason,
mozilla::TimeStamp aDeadline) {
if (mDidShutdown) {
return;
}
// When we're in an incremental GC, we should always have an sGCRunner, so do
// not check CC timers. The CC timers won't do anything during a GC.
MOZ_ASSERT_IF(InIncrementalGC(), mGCRunner);
RefPtr<IdleTaskRunner> runner;
if (mGCRunner) {
SetWantMajorGC(aReason);
runner = mGCRunner;
} else if (mCCRunner) {
runner = mCCRunner;
}
if (runner) {
runner->SetIdleDeadline(aDeadline);
runner->Run();
}
}
void CCGCScheduler::PokeShrinkingGC() {
if (mShrinkingGCTimer || mDidShutdown) {
return;
}
NS_NewTimerWithFuncCallback(
&mShrinkingGCTimer,
[](nsITimer* aTimer, void* aClosure) {
CCGCScheduler* s = static_cast<CCGCScheduler*>(aClosure);
s->KillShrinkingGCTimer();
if (!s->mUserIsActive) {
if (!nsRefreshDriver::IsRegularRateTimerTicking()) {
s->SetWantMajorGC(JS::GCReason::USER_INACTIVE);
if (!s->mHaveAskedParent) {
s->EnsureGCRunner(0);
}
} else {
s->PokeShrinkingGC();
}
}
},
this, StaticPrefs::javascript_options_compact_on_user_inactive_delay(),
nsITimer::TYPE_ONE_SHOT_LOW_PRIORITY, "ShrinkingGCTimerFired");
}
void CCGCScheduler::PokeFullGC() {
if (!mFullGCTimer && !mDidShutdown) {
NS_NewTimerWithFuncCallback(
&mFullGCTimer,
[](nsITimer* aTimer, void* aClosure) {
CCGCScheduler* s = static_cast<CCGCScheduler*>(aClosure);
s->KillFullGCTimer();
// Even if the GC is denied by the parent process, because we've
// set that we want a full GC we will get one eventually.
s->SetNeedsFullGC();
s->SetWantMajorGC(JS::GCReason::FULL_GC_TIMER);
if (!s->mHaveAskedParent) {
s->EnsureGCRunner(0);
}
},
this, StaticPrefs::javascript_options_gc_delay_full(),
nsITimer::TYPE_ONE_SHOT_LOW_PRIORITY, "FullGCTimerFired");
}
}
void CCGCScheduler::PokeGC(JS::GCReason aReason, JSObject* aObj,
TimeDuration aDelay) {
MOZ_ASSERT(aReason != JS::GCReason::NO_REASON);
MOZ_ASSERT(aReason != JS::GCReason::EAGER_NURSERY_COLLECTION);
if (mDidShutdown) {
return;
}
// If a post-CC GC was pending, then we'll make sure one is happening.
mNeedsGCAfterCC = false;
if (aObj) {
JS::Zone* zone = JS::GetObjectZone(aObj);
CycleCollectedJSRuntime::Get()->AddZoneWaitingForGC(zone);
} else if (aReason != JS::GCReason::CC_FINISHED) {
SetNeedsFullGC();
}
if (mGCRunner || mHaveAskedParent) {
// There's already a GC runner, or there will be, so just return.
return;
}
SetWantMajorGC(aReason);
if (mCCRunner) {
// Make sure CC is called regardless of the size of the purple buffer, and
// GC after it.
EnsureCCThenGC(CCReason::GC_WAITING);
return;
}
// Wait for javascript.options.gc_delay (or delay_first) then start
// looking for idle time to run the initial GC slice.
static bool first = true;
TimeDuration delay =
aDelay ? aDelay
: TimeDuration::FromMilliseconds(
first ? StaticPrefs::javascript_options_gc_delay_first()
: StaticPrefs::javascript_options_gc_delay());
first = false;
EnsureGCRunner(delay);
}
void CCGCScheduler::PokeMinorGC(JS::GCReason aReason) {
MOZ_ASSERT(aReason != JS::GCReason::NO_REASON);
if (mDidShutdown) {
return;
}
SetWantEagerMinorGC(aReason);
if (mGCRunner || mHaveAskedParent || mCCRunner) {
// There's already a runner, or there will be, so just return.
return;
}
// Immediately start looking for idle time to run the minor GC.
EnsureGCRunner(0);
}
void CCGCScheduler::EnsureGCRunner(TimeDuration aDelay) {
if (mGCRunner) {
return;
}
TimeDuration minimumBudget = nsRefreshDriver::IsInHighRateMode()
? TimeDuration::FromMilliseconds(1)
: mActiveIntersliceGCBudget;
// Wait at most the interslice GC delay before forcing a run.
mGCRunner = IdleTaskRunner::Create(
[this](TimeStamp aDeadline) { return GCRunnerFired(aDeadline); },
"CCGCScheduler::EnsureGCRunner", aDelay,
TimeDuration::FromMilliseconds(
StaticPrefs::javascript_options_gc_delay_interslice()),
minimumBudget, true, [this] { return mDidShutdown; },
[this](uint32_t) {
PROFILER_MARKER_UNTYPED("GC Interrupt", GCCC);
mInterruptRequested = true;
});
}
// nsJSEnvironmentObserver observes the user-interaction-inactive notifications
// and triggers a shrinking a garbage collection if the user is still inactive
// after NS_SHRINKING_GC_DELAY ms later, if the appropriate pref is set.
void CCGCScheduler::UserIsInactive() {
mUserIsActive = false;
if (StaticPrefs::javascript_options_compact_on_user_inactive()) {
PokeShrinkingGC();
}
}
void CCGCScheduler::UserIsActive() {
mUserIsActive = true;
KillShrinkingGCTimer();
if (mIsCompactingOnUserInactive) {
mozilla::dom::AutoJSAPI jsapi;
jsapi.Init();
JS::AbortIncrementalGC(jsapi.cx());
}
MOZ_ASSERT(!mIsCompactingOnUserInactive);
}
void CCGCScheduler::KillShrinkingGCTimer() {
if (mShrinkingGCTimer) {
mShrinkingGCTimer->Cancel();
NS_RELEASE(mShrinkingGCTimer);
}
}
void CCGCScheduler::KillFullGCTimer() {
if (mFullGCTimer) {
mFullGCTimer->Cancel();
NS_RELEASE(mFullGCTimer);
}
}
void CCGCScheduler::KillGCRunner() {
// If we're in an incremental GC then killing the timer is only okay if
// we're shutting down.
MOZ_ASSERT(!(InIncrementalGC() && !mDidShutdown));
if (mGCRunner) {
mGCRunner->Cancel();
mGCRunner = nullptr;
}
}
void CCGCScheduler::EnsureCCRunner(TimeDuration aDelay, TimeDuration aBudget) {
MOZ_ASSERT(!mDidShutdown);
TimeDuration minimumBudget = nsRefreshDriver::IsInHighRateMode()
? TimeDuration::FromMilliseconds(1)
: aBudget;
if (!mCCRunner) {
mCCRunner = IdleTaskRunner::Create(
CCRunnerFired, "EnsureCCRunner::CCRunnerFired", 0, aDelay,
minimumBudget, true, [this] { return mDidShutdown; });
} else {
mCCRunner->SetMinimumUsefulBudget(minimumBudget.ToMilliseconds());
nsIEventTarget* target = mozilla::GetCurrentSerialEventTarget();
if (target) {
mCCRunner->SetTimer(aDelay, target);
}
}
}
void CCGCScheduler::MaybePokeCC(TimeStamp aNow, uint32_t aSuspectedCCObjects) {
if (mCCRunner || mDidShutdown) {
return;
}
CCReason reason = ShouldScheduleCC(aNow, aSuspectedCCObjects);
if (reason != CCReason::NO_REASON) {
// We can kill some objects before running forgetSkippable.
nsCycleCollector_dispatchDeferredDeletion();
if (!mCCRunner) {
InitCCRunnerStateMachine(CCRunnerState::ReducePurple, reason);
}
EnsureCCRunner(kCCSkippableDelay, kForgetSkippableSliceDuration);
}
}
void CCGCScheduler::KillCCRunner() {
UnblockCC();
DeactivateCCRunner();
if (mCCRunner) {
mCCRunner->Cancel();
mCCRunner = nullptr;
}
}
void CCGCScheduler::KillAllTimersAndRunners() {
KillShrinkingGCTimer();
KillCCRunner();
KillFullGCTimer();
KillGCRunner();
}
js::SliceBudget CCGCScheduler::ComputeCCSliceBudget(
TimeStamp aDeadline, TimeStamp aCCBeginTime, TimeStamp aPrevSliceEndTime,
TimeStamp aNow, bool* aPreferShorterSlices) const {
*aPreferShorterSlices =
aDeadline.IsNull() || (aDeadline - aNow) < kICCSliceBudget;
TimeDuration baseBudget =
aDeadline.IsNull() ? kICCSliceBudget : aDeadline - aNow;
if (aPrevSliceEndTime.IsNull()) {
// The first slice gets the standard slice time.
return js::SliceBudget(js::TimeBudget(baseBudget));
}
// Only run a limited slice if we're within the max running time.
MOZ_ASSERT(aNow >= aCCBeginTime);
TimeDuration runningTime = aNow - aCCBeginTime;
if (runningTime >= kMaxICCDuration) {
return js::SliceBudget::unlimited();
}
const TimeDuration maxSlice =
TimeDuration::FromMilliseconds(MainThreadIdlePeriod::GetLongIdlePeriod());
// Try to make up for a delay in running this slice.
MOZ_ASSERT(aNow >= aPrevSliceEndTime);
double sliceDelayMultiplier =
(aNow - aPrevSliceEndTime) / kICCIntersliceDelay;
TimeDuration delaySliceBudget =
std::min(baseBudget.MultDouble(sliceDelayMultiplier), maxSlice);
// Increase slice budgets up to |maxSlice| as we approach
// half way through the ICC, to avoid large sync CCs.
double percentToHalfDone =
std::min(2.0 * (runningTime / kMaxICCDuration), 1.0);
TimeDuration laterSliceBudget = maxSlice.MultDouble(percentToHalfDone);
// Note: We may have already overshot the deadline, in which case
// baseBudget will be negative and we will end up returning
// laterSliceBudget.
return js::SliceBudget(js::TimeBudget(
std::max({delaySliceBudget, laterSliceBudget, baseBudget})));
}
js::SliceBudget CCGCScheduler::ComputeInterSliceGCBudget(TimeStamp aDeadline,
TimeStamp aNow) {
// We use longer budgets when the CC has been locked out but the CC has
// tried to run since that means we may have a significant amount of
// garbage to collect and it's better to GC in several longer slices than
// in a very long one.
TimeDuration budget =
aDeadline.IsNull() ? mActiveIntersliceGCBudget * 2 : aDeadline - aNow;
if (!mCCBlockStart) {
return CreateGCSliceBudget(budget, !aDeadline.IsNull(), false);
}
TimeDuration blockedTime = aNow - mCCBlockStart;
TimeDuration maxSliceGCBudget = mActiveIntersliceGCBudget * 10;
double percentOfBlockedTime =
std::min(blockedTime / kMaxCCLockedoutTime, 1.0);
TimeDuration extendedBudget =
maxSliceGCBudget.MultDouble(percentOfBlockedTime);
if (budget >= extendedBudget) {
return CreateGCSliceBudget(budget, !aDeadline.IsNull(), false);
}
// If the budget is being extended, do not allow it to be interrupted.
auto result = js::SliceBudget(js::TimeBudget(extendedBudget), nullptr);
result.idle = !aDeadline.IsNull();
result.extended = true;
return result;
}
CCReason CCGCScheduler::ShouldScheduleCC(TimeStamp aNow,
uint32_t aSuspectedCCObjects) const {
if (!mHasRunGC) {
return CCReason::NO_REASON;
}
// Don't run consecutive CCs too often.
if (mCleanupsSinceLastGC && !mLastCCEndTime.IsNull()) {
if (aNow - mLastCCEndTime < kCCDelay) {
return CCReason::NO_REASON;
}
}
// If GC hasn't run recently and forget skippable only cycle was run,
// don't start a new cycle too soon.
if ((mCleanupsSinceLastGC > kMajorForgetSkippableCalls) &&
!mLastForgetSkippableCycleEndTime.IsNull()) {
if (aNow - mLastForgetSkippableCycleEndTime <
kTimeBetweenForgetSkippableCycles) {
return CCReason::NO_REASON;
}
}
return IsCCNeeded(aNow, aSuspectedCCObjects);
}
CCRunnerStep CCGCScheduler::AdvanceCCRunner(TimeStamp aDeadline, TimeStamp aNow,
uint32_t aSuspectedCCObjects) {
struct StateDescriptor {
// When in this state, should we first check to see if we still have
// enough reason to CC?
bool mCanAbortCC;
// If we do decide to abort the CC, should we still try to forget
// skippables one more time?
bool mTryFinalForgetSkippable;
};
// The state descriptors for Inactive and Canceled will never actually be
// used. We will never call this function while Inactive, and Canceled is
// handled specially at the beginning.
constexpr StateDescriptor stateDescriptors[] = {
{false, false}, /* CCRunnerState::Inactive */
{false, false}, /* CCRunnerState::ReducePurple */
{true, true}, /* CCRunnerState::CleanupChildless */
{true, false}, /* CCRunnerState::CleanupContentUnbinder */
{false, false}, /* CCRunnerState::CleanupDeferred */
{false, false}, /* CCRunnerState::StartCycleCollection */
{false, false}, /* CCRunnerState::CycleCollecting */
{false, false}}; /* CCRunnerState::Canceled */
static_assert(
ArrayLength(stateDescriptors) == size_t(CCRunnerState::NumStates),
"need one state descriptor per state");
const StateDescriptor& desc = stateDescriptors[int(mCCRunnerState)];
// Make sure we initialized the state machine.
MOZ_ASSERT(mCCRunnerState != CCRunnerState::Inactive);
if (mDidShutdown) {
return {CCRunnerAction::StopRunning, Yield};
}
if (mCCRunnerState == CCRunnerState::Canceled) {
// When we cancel a cycle, there may have been a final ForgetSkippable.
return {CCRunnerAction::StopRunning, Yield};
}
if (InIncrementalGC()) {
if (mCCBlockStart.IsNull()) {
BlockCC(aNow);
// If we have reached the CycleCollecting state, then ignore CC timer
// fires while incremental GC is running. (Running ICC during an IGC
// would cause us to synchronously finish the GC, which is bad.)
//
// If we have not yet started cycle collecting, then reset our state so
// that we run forgetSkippable often enough before CC. Because of reduced
// mCCDelay, forgetSkippable will be called just a few times.
//
// The kMaxCCLockedoutTime limit guarantees that we end up calling
// forgetSkippable and CycleCollectNow eventually.
if (mCCRunnerState != CCRunnerState::CycleCollecting) {
mCCRunnerState = CCRunnerState::ReducePurple;
mCCRunnerEarlyFireCount = 0;
mCCDelay = kCCDelay / int64_t(3);
}
return {CCRunnerAction::None, Yield};
}
if (GetCCBlockedTime(aNow) < kMaxCCLockedoutTime) {
return {CCRunnerAction::None, Yield};
}
// Locked out for too long, so proceed and finish the incremental GC
// synchronously.
}
// For states that aren't just continuations of previous states, check
// whether a CC is still needed (after doing various things to reduce the
// purple buffer).
if (desc.mCanAbortCC &&
IsCCNeeded(aNow, aSuspectedCCObjects) == CCReason::NO_REASON) {
// If we don't pass the threshold for wanting to cycle collect, stop now
// (after possibly doing a final ForgetSkippable).
mCCRunnerState = CCRunnerState::Canceled;
NoteForgetSkippableOnlyCycle(aNow);
// Preserve the previous code's idea of when to check whether a
// ForgetSkippable should be fired.
if (desc.mTryFinalForgetSkippable &&
ShouldForgetSkippable(aSuspectedCCObjects)) {
// The Canceled state will make us StopRunning after this action is
// performed (see conditional at top of function).
return {CCRunnerAction::ForgetSkippable, Yield, KeepChildless};
}
return {CCRunnerAction::StopRunning, Yield};
}
if (mEagerMinorGCReason != JS::GCReason::NO_REASON && !aDeadline.IsNull()) {
return {CCRunnerAction::MinorGC, Continue, mEagerMinorGCReason};
}
switch (mCCRunnerState) {
// ReducePurple: a GC ran (or we otherwise decided to try CC'ing). Wait
// for some amount of time (kCCDelay, or less if incremental GC blocked
// this CC) while firing regular ForgetSkippable actions before continuing
// on.
case CCRunnerState::ReducePurple:
++mCCRunnerEarlyFireCount;
if (IsLastEarlyCCTimer(mCCRunnerEarlyFireCount)) {
mCCRunnerState = CCRunnerState::CleanupChildless;
}
if (ShouldForgetSkippable(aSuspectedCCObjects)) {
return {CCRunnerAction::ForgetSkippable, Yield, KeepChildless};
}
if (aDeadline.IsNull()) {
return {CCRunnerAction::None, Yield};
}
// If we're called during idle time, try to find some work to do by
// advancing to the next state, effectively bypassing some possible forget
// skippable calls.
mCCRunnerState = CCRunnerState::CleanupChildless;
// Continue on to CleanupChildless, but only after checking IsCCNeeded
// again.
return {CCRunnerAction::None, Continue};
// CleanupChildless: do a stronger ForgetSkippable that removes nodes with
// no children in the cycle collector graph. This state is split into 3
// parts; the other Cleanup* actions will happen within the same callback
// (unless the ForgetSkippable shrinks the purple buffer enough for the CC
// to be skipped entirely.)
case CCRunnerState::CleanupChildless:
mCCRunnerState = CCRunnerState::CleanupContentUnbinder;
return {CCRunnerAction::ForgetSkippable, Yield, RemoveChildless};
// CleanupContentUnbinder: continuing cleanup, clear out the content
// unbinder.
case CCRunnerState::CleanupContentUnbinder:
if (aDeadline.IsNull()) {
// Non-idle (waiting) callbacks skip the rest of the cleanup, but still
// wait for another fire before the actual CC.
mCCRunnerState = CCRunnerState::StartCycleCollection;
return {CCRunnerAction::None, Yield};
}
// Running in an idle callback.
// The deadline passed, so go straight to CC in the next slice.
if (aNow >= aDeadline) {
mCCRunnerState = CCRunnerState::StartCycleCollection;
return {CCRunnerAction::None, Yield};
}
mCCRunnerState = CCRunnerState::CleanupDeferred;
return {CCRunnerAction::CleanupContentUnbinder, Continue};
// CleanupDeferred: continuing cleanup, do deferred deletion.
case CCRunnerState::CleanupDeferred:
MOZ_ASSERT(!aDeadline.IsNull(),
"Should only be in CleanupDeferred state when idle");
// Our efforts to avoid a CC have failed. Let the timer fire once more
// to trigger a CC.
mCCRunnerState = CCRunnerState::StartCycleCollection;
if (aNow >= aDeadline) {
// The deadline passed, go straight to CC in the next slice.
return {CCRunnerAction::None, Yield};
}
return {CCRunnerAction::CleanupDeferred, Yield};
// StartCycleCollection: start actually doing cycle collection slices.
case CCRunnerState::StartCycleCollection:
// We are in the final timer fire and still meet the conditions for
// triggering a CC. Let RunCycleCollectorSlice finish the current IGC if
// any, because that will allow us to include the GC time in the CC pause.
mCCRunnerState = CCRunnerState::CycleCollecting;
[[fallthrough]];
// CycleCollecting: continue running slices until done.
case CCRunnerState::CycleCollecting: {
CCRunnerStep step{CCRunnerAction::CycleCollect, Yield};
step.mParam.mCCReason = mCCReason;
mCCReason = CCReason::SLICE; // Set reason for following slices.
return step;
}
default:
MOZ_CRASH("Unexpected CCRunner state");
};
}
GCRunnerStep CCGCScheduler::GetNextGCRunnerAction(TimeStamp aDeadline) const {
if (InIncrementalGC()) {
MOZ_ASSERT(mMajorGCReason != JS::GCReason::NO_REASON);
return {GCRunnerAction::GCSlice, mMajorGCReason};
}
// Service a non-eager GC request first, even if it requires waiting.
if (mMajorGCReason != JS::GCReason::NO_REASON) {
return {mReadyForMajorGC ? GCRunnerAction::StartMajorGC
: GCRunnerAction::WaitToMajorGC,
mMajorGCReason};
}
// Now for eager requests, which are ignored unless we're idle.
if (!aDeadline.IsNull()) {
if (mEagerMajorGCReason != JS::GCReason::NO_REASON) {
return {mReadyForMajorGC ? GCRunnerAction::StartMajorGC
: GCRunnerAction::WaitToMajorGC,
mEagerMajorGCReason};
}
if (mEagerMinorGCReason != JS::GCReason::NO_REASON) {
return {GCRunnerAction::MinorGC, mEagerMinorGCReason};
}
}
return {GCRunnerAction::None, JS::GCReason::NO_REASON};
}
js::SliceBudget CCGCScheduler::ComputeForgetSkippableBudget(
TimeStamp aStartTimeStamp, TimeStamp aDeadline) {
if (mForgetSkippableFrequencyStartTime.IsNull()) {
mForgetSkippableFrequencyStartTime = aStartTimeStamp;
} else if (aStartTimeStamp - mForgetSkippableFrequencyStartTime >
kOneMinute) {
TimeStamp startPlusMinute = mForgetSkippableFrequencyStartTime + kOneMinute;
// If we had forget skippables only at the beginning of the interval, we
// still want to use the whole time, minute or more, for frequency
// calculation. mLastForgetSkippableEndTime is needed if forget skippable
// takes enough time to push the interval to be over a minute.
TimeStamp endPoint = std::max(startPlusMinute, mLastForgetSkippableEndTime);
// Duration in minutes.
double duration =
(endPoint - mForgetSkippableFrequencyStartTime).ToSeconds() / 60;
uint32_t frequencyPerMinute = uint32_t(mForgetSkippableCounter / duration);
Telemetry::Accumulate(Telemetry::FORGET_SKIPPABLE_FREQUENCY,
frequencyPerMinute);
mForgetSkippableCounter = 0;
mForgetSkippableFrequencyStartTime = aStartTimeStamp;
}
++mForgetSkippableCounter;
TimeDuration budgetTime =
aDeadline ? (aDeadline - aStartTimeStamp) : kForgetSkippableSliceDuration;
return js::SliceBudget(budgetTime);
}
} // namespace mozilla
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