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Marking.cpp
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Marking.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 "gc/Marking-inl.h"
#include "mozilla/DebugOnly.h"
#include "mozilla/IntegerRange.h"
#include "mozilla/ReentrancyGuard.h"
#include "mozilla/ScopeExit.h"
#include "mozilla/TypeTraits.h"
#include "jsfriendapi.h"
#include "builtin/ModuleObject.h"
#include "gc/GCInternals.h"
#include "gc/Policy.h"
#include "jit/IonCode.h"
#include "js/SliceBudget.h"
#include "vm/ArgumentsObject.h"
#include "vm/ArrayObject.h"
#ifdef ENABLE_BIGINT
#include "vm/BigIntType.h"
#endif
#include "vm/Debugger.h"
#include "vm/EnvironmentObject.h"
#include "vm/RegExpShared.h"
#include "vm/Scope.h"
#include "vm/Shape.h"
#include "vm/SymbolType.h"
#include "vm/TypedArrayObject.h"
#include "vm/UnboxedObject.h"
#include "wasm/WasmJS.h"
#include "gc/GC-inl.h"
#include "gc/Nursery-inl.h"
#include "gc/PrivateIterators-inl.h"
#include "gc/Zone-inl.h"
#include "vm/NativeObject-inl.h"
#include "vm/Realm-inl.h"
#include "vm/StringType-inl.h"
#include "vm/UnboxedObject-inl.h"
using namespace js;
using namespace js::gc;
using JS::MapTypeToTraceKind;
using mozilla::DebugOnly;
using mozilla::IntegerRange;
using mozilla::IsBaseOf;
using mozilla::IsSame;
using mozilla::PodCopy;
// [SMDOC] GC Tracing
//
// Tracing Overview
// ================
//
// Tracing, in this context, refers to an abstract visitation of some or all of
// the GC-controlled heap. The effect of tracing an edge of the graph depends
// on the subclass of the JSTracer on whose behalf we are tracing.
//
// Marking
// -------
//
// The primary JSTracer is the GCMarker. The marking tracer causes the target
// of each traversed edge to be marked black and the target edge's children to
// be marked either gray (in the gc algorithm sense) or immediately black.
//
// Callback
// --------
//
// The secondary JSTracer is the CallbackTracer. This simply invokes a callback
// on each edge in a child.
//
// The following is a rough outline of the general struture of the tracing
// internals.
//
/* clang-format off */
// //
// .---------. .---------. .--------------------------. .----------. //
// |TraceEdge| |TraceRoot| |TraceManuallyBarrieredEdge| ... |TraceRange| ... etc. //
// '---------' '---------' '--------------------------' '----------' //
// \ \ / / //
// \ \ .-----------------. / / //
// o------------->o-|TraceEdgeInternal|-o<----------------------o //
// '-----------------' //
// / \ //
// / \ //
// .---------. .----------. .-----------------. //
// |DoMarking| |DoCallback|-------> |<JSTraceCallback>|-----------> //
// '---------' '----------' '-----------------' //
// | //
// | //
// .--------. //
// o---------------->|traverse| . //
// /_\ '--------' ' . //
// | . . ' . //
// | . . ' . //
// | . . ' . //
// | .-----------. .-----------. ' . .--------------------. //
// | |markAndScan| |markAndPush| ' - |markAndTraceChildren|----> //
// | '-----------' '-----------' '--------------------' //
// | | \ //
// | | \ //
// | .----------------------. .----------------. //
// | |T::eagerlyMarkChildren| |pushMarkStackTop|<===Oo //
// | '----------------------' '----------------' || //
// | | || || //
// | | || || //
// | | || || //
// o<-----------------o<========================OO============Oo //
// //
// //
// Legend: //
// ------ Direct calls //
// . . . Static dispatch //
// ====== Dispatch through a manual stack. //
// //
/* clang-format on */
/*** Tracing Invariants *****************************************************/
#if defined(DEBUG)
template <typename T>
static inline bool IsThingPoisoned(T* thing) {
const uint8_t poisonBytes[] = {
JS_FRESH_NURSERY_PATTERN, JS_SWEPT_NURSERY_PATTERN,
JS_ALLOCATED_NURSERY_PATTERN, JS_FRESH_TENURED_PATTERN,
JS_MOVED_TENURED_PATTERN, JS_SWEPT_TENURED_PATTERN,
JS_ALLOCATED_TENURED_PATTERN, JS_FREED_HEAP_PTR_PATTERN,
JS_SWEPT_TI_PATTERN, JS_SWEPT_CODE_PATTERN,
JS_FREED_CHUNK_PATTERN};
const int numPoisonBytes = sizeof(poisonBytes) / sizeof(poisonBytes[0]);
uint32_t* p =
reinterpret_cast<uint32_t*>(reinterpret_cast<FreeSpan*>(thing) + 1);
// Note: all free patterns are odd to make the common, not-poisoned case a
// single test.
if ((*p & 1) == 0) {
return false;
}
for (int i = 0; i < numPoisonBytes; ++i) {
const uint8_t pb = poisonBytes[i];
const uint32_t pw = pb | (pb << 8) | (pb << 16) | (pb << 24);
if (*p == pw) {
return true;
}
}
return false;
}
static bool IsMovingTracer(JSTracer* trc) {
return trc->isCallbackTracer() && trc->asCallbackTracer()->getTracerKind() ==
JS::CallbackTracer::TracerKind::Moving;
}
#endif
bool ThingIsPermanentAtomOrWellKnownSymbol(JSString* str) {
return str->isPermanentAtom();
}
bool ThingIsPermanentAtomOrWellKnownSymbol(JSFlatString* str) {
return str->isPermanentAtom();
}
bool ThingIsPermanentAtomOrWellKnownSymbol(JSLinearString* str) {
return str->isPermanentAtom();
}
bool ThingIsPermanentAtomOrWellKnownSymbol(JSAtom* atom) {
return atom->isPermanent();
}
bool ThingIsPermanentAtomOrWellKnownSymbol(PropertyName* name) {
return name->isPermanent();
}
bool ThingIsPermanentAtomOrWellKnownSymbol(JS::Symbol* sym) {
return sym->isWellKnownSymbol();
}
template <typename T>
static inline bool IsOwnedByOtherRuntime(JSRuntime* rt, T thing) {
bool other = thing->runtimeFromAnyThread() != rt;
MOZ_ASSERT_IF(other, ThingIsPermanentAtomOrWellKnownSymbol(thing) ||
thing->zoneFromAnyThread()->isSelfHostingZone());
return other;
}
template <typename T>
void js::CheckTracedThing(JSTracer* trc, T* thing) {
#ifdef DEBUG
MOZ_ASSERT(trc);
MOZ_ASSERT(thing);
if (!trc->checkEdges()) {
return;
}
if (IsForwarded(thing)) {
thing = Forwarded(thing);
}
/* This function uses data that's not available in the nursery. */
if (IsInsideNursery(thing)) {
return;
}
MOZ_ASSERT_IF(!IsMovingTracer(trc) && !trc->isTenuringTracer(),
!IsForwarded(thing));
/*
* Permanent atoms and things in the self-hosting zone are not associated
* with this runtime, but will be ignored during marking.
*/
if (IsOwnedByOtherRuntime(trc->runtime(), thing)) {
return;
}
Zone* zone = thing->zoneFromAnyThread();
JSRuntime* rt = trc->runtime();
if (!IsMovingTracer(trc) && !IsBufferGrayRootsTracer(trc) &&
!IsClearEdgesTracer(trc)) {
MOZ_ASSERT(CurrentThreadCanAccessZone(zone));
MOZ_ASSERT(CurrentThreadCanAccessRuntime(rt));
}
MOZ_ASSERT(zone->runtimeFromAnyThread() == trc->runtime());
// It shouldn't be possible to trace into zones used by helper threads.
MOZ_ASSERT(!zone->usedByHelperThread());
MOZ_ASSERT(thing->isAligned());
MOZ_ASSERT(
MapTypeToTraceKind<typename mozilla::RemovePointer<T>::Type>::kind ==
thing->getTraceKind());
/*
* Do not check IsMarkingTracer directly -- it should only be used in paths
* where we cannot be the gray buffering tracer.
*/
bool isGcMarkingTracer = trc->isMarkingTracer();
MOZ_ASSERT_IF(zone->requireGCTracer(),
isGcMarkingTracer || IsBufferGrayRootsTracer(trc) ||
IsUnmarkGrayTracer(trc) || IsClearEdgesTracer(trc));
if (isGcMarkingTracer) {
GCMarker* gcMarker = GCMarker::fromTracer(trc);
MOZ_ASSERT_IF(gcMarker->shouldCheckCompartments(),
zone->isCollecting() || zone->isAtomsZone());
MOZ_ASSERT_IF(gcMarker->markColor() == MarkColor::Gray,
!zone->isGCMarkingBlack() || zone->isAtomsZone());
MOZ_ASSERT(!(zone->isGCSweeping() || zone->isGCFinished() ||
zone->isGCCompacting()));
}
/*
* Try to assert that the thing is allocated.
*
* We would like to assert that the thing is not in the free list, but this
* check is very slow. Instead we check whether the thing has been poisoned:
* if it has not then we assume it is allocated, but if it has then it is
* either free or uninitialized in which case we check the free list.
*
* Further complications are that background sweeping may be running and
* concurrently modifiying the free list and that tracing is done off
* thread during compacting GC and reading the contents of the thing by
* IsThingPoisoned would be racy in this case.
*/
MOZ_ASSERT_IF(JS::RuntimeHeapIsBusy() && !zone->isGCSweeping() &&
!zone->isGCFinished() && !zone->isGCCompacting(),
!IsThingPoisoned(thing) ||
!InFreeList(thing->asTenured().arena(), thing));
#endif
}
template <typename S>
struct CheckTracedFunctor : public VoidDefaultAdaptor<S> {
template <typename T>
void operator()(T* t, JSTracer* trc) {
CheckTracedThing(trc, t);
}
};
template <typename T>
void js::CheckTracedThing(JSTracer* trc, T thing) {
DispatchTyped(CheckTracedFunctor<T>(), thing, trc);
}
namespace js {
#define IMPL_CHECK_TRACED_THING(_, type, __) \
template void CheckTracedThing<type>(JSTracer*, type*);
JS_FOR_EACH_TRACEKIND(IMPL_CHECK_TRACED_THING);
#undef IMPL_CHECK_TRACED_THING
} // namespace js
static bool UnmarkGrayGCThing(JSRuntime* rt, JS::GCCellPtr thing);
static inline bool ShouldMarkCrossCompartment(GCMarker* marker, JSObject* src,
Cell* dstCell) {
MarkColor color = marker->markColor();
if (!dstCell->isTenured()) {
MOZ_ASSERT(color == MarkColor::Black);
return false;
}
TenuredCell& dst = dstCell->asTenured();
JS::Zone* dstZone = dst.zone();
if (!src->zone()->isGCMarking() && !dstZone->isGCMarking()) {
return false;
}
if (color == MarkColor::Black) {
/*
* Having black->gray edges violates our promise to the cycle
* collector. This can happen if we're collecting a compartment and it
* has an edge to an uncollected compartment: it's possible that the
* source and destination of the cross-compartment edge should be gray,
* but the source was marked black by the write barrier.
*/
if (dst.isMarkedGray()) {
MOZ_ASSERT(!dstZone->isCollecting());
UnmarkGrayGCThing(marker->runtime(),
JS::GCCellPtr(&dst, dst.getTraceKind()));
}
return dstZone->isGCMarking();
} else {
if (dstZone->isGCMarkingBlack()) {
/*
* The destination compartment is being not being marked gray now,
* but it will be later, so record the cell so it can be marked gray
* at the appropriate time.
*/
if (!dst.isMarkedAny()) {
DelayCrossCompartmentGrayMarking(src);
}
return false;
}
return dstZone->isGCMarkingGray();
}
}
static bool ShouldTraceCrossCompartment(JSTracer* trc, JSObject* src,
Cell* dstCell) {
if (!trc->isMarkingTracer()) {
return true;
}
return ShouldMarkCrossCompartment(GCMarker::fromTracer(trc), src, dstCell);
}
static bool ShouldTraceCrossCompartment(JSTracer* trc, JSObject* src,
const Value& val) {
return val.isGCThing() &&
ShouldTraceCrossCompartment(trc, src, val.toGCThing());
}
static void AssertShouldMarkInZone(Cell* thing) {
MOZ_ASSERT(thing->asTenured().zone()->shouldMarkInZone());
}
static void AssertShouldMarkInZone(JSString* str) {
#ifdef DEBUG
Zone* zone = str->zone();
MOZ_ASSERT(zone->shouldMarkInZone() || zone->isAtomsZone());
#endif
}
static void AssertShouldMarkInZone(JS::Symbol* sym) {
#ifdef DEBUG
Zone* zone = sym->asTenured().zone();
MOZ_ASSERT(zone->shouldMarkInZone() || zone->isAtomsZone());
#endif
}
#ifdef DEBUG
void js::gc::AssertRootMarkingPhase(JSTracer* trc) {
MOZ_ASSERT_IF(trc->isMarkingTracer(),
trc->runtime()->gc.state() == State::NotActive ||
trc->runtime()->gc.state() == State::MarkRoots);
}
#endif
/*** Tracing Interface ******************************************************/
template <typename T>
T DoCallback(JS::CallbackTracer* trc, T* thingp, const char* name);
template <typename T>
void DoMarking(GCMarker* gcmarker, T* thing);
template <typename T>
void DoMarking(GCMarker* gcmarker, const T& thing);
template <typename T>
void NoteWeakEdge(GCMarker* gcmarker, T** thingp);
template <typename T>
void NoteWeakEdge(GCMarker* gcmarker, T* thingp);
template <typename T>
JS_PUBLIC_API void js::gc::TraceExternalEdge(JSTracer* trc, T* thingp,
const char* name) {
MOZ_ASSERT(InternalBarrierMethods<T>::isMarkable(*thingp));
TraceEdgeInternal(trc, ConvertToBase(thingp), name);
}
template <typename T>
JS_PUBLIC_API void js::UnsafeTraceManuallyBarrieredEdge(JSTracer* trc,
T* thingp,
const char* name) {
TraceEdgeInternal(trc, ConvertToBase(thingp), name);
}
template <typename T>
JS_PUBLIC_API void JS::UnsafeTraceRoot(JSTracer* trc, T* thingp,
const char* name) {
MOZ_ASSERT(thingp);
js::TraceNullableRoot(trc, thingp, name);
}
// Instantiate a copy of the Tracing templates for each public GC pointer type.
#define INSTANTIATE_PUBLIC_TRACE_FUNCTIONS(type) \
template JS_PUBLIC_API void JS::UnsafeTraceRoot<type>(JSTracer*, type*, \
const char*); \
template JS_PUBLIC_API void js::UnsafeTraceManuallyBarrieredEdge<type>( \
JSTracer*, type*, const char*); \
template JS_PUBLIC_API void js::gc::TraceExternalEdge<type>( \
JSTracer*, type*, const char*);
FOR_EACH_PUBLIC_GC_POINTER_TYPE(INSTANTIATE_PUBLIC_TRACE_FUNCTIONS)
FOR_EACH_PUBLIC_TAGGED_GC_POINTER_TYPE(INSTANTIATE_PUBLIC_TRACE_FUNCTIONS)
#undef INSTANTIATE_PUBLIC_TRACE_FUNCTIONS
namespace js {
namespace gc {
#define INSTANTIATE_INTERNAL_TRACE_FUNCTIONS(type) \
template void TraceEdgeInternal<type>(JSTracer*, type*, const char*); \
template void TraceWeakEdgeInternal<type>(JSTracer*, type*, const char*); \
template void TraceRangeInternal<type>(JSTracer*, size_t len, type*, \
const char*);
#define INSTANTIATE_INTERNAL_TRACE_FUNCTIONS_FROM_TRACEKIND(_1, type, _2) \
INSTANTIATE_INTERNAL_TRACE_FUNCTIONS(type*)
JS_FOR_EACH_TRACEKIND(INSTANTIATE_INTERNAL_TRACE_FUNCTIONS_FROM_TRACEKIND)
FOR_EACH_PUBLIC_TAGGED_GC_POINTER_TYPE(INSTANTIATE_INTERNAL_TRACE_FUNCTIONS)
#undef INSTANTIATE_INTERNAL_TRACE_FUNCTIONS_FROM_TRACEKIND
#undef INSTANTIATE_INTERNAL_TRACE_FUNCTIONS
} // namespace gc
} // namespace js
template <typename T>
void js::TraceManuallyBarrieredCrossCompartmentEdge(JSTracer* trc,
JSObject* src, T* dst,
const char* name) {
if (ShouldTraceCrossCompartment(trc, src, *dst)) {
TraceEdgeInternal(trc, dst, name);
}
}
template void js::TraceManuallyBarrieredCrossCompartmentEdge<JSObject*>(
JSTracer*, JSObject*, JSObject**, const char*);
template void js::TraceManuallyBarrieredCrossCompartmentEdge<JSScript*>(
JSTracer*, JSObject*, JSScript**, const char*);
template void js::TraceManuallyBarrieredCrossCompartmentEdge<LazyScript*>(
JSTracer*, JSObject*, LazyScript**, const char*);
void js::TraceCrossCompartmentEdge(JSTracer* trc, JSObject* src,
WriteBarrieredBase<Value>* dst,
const char* name) {
if (ShouldTraceCrossCompartment(trc, src, dst->get())) {
TraceEdgeInternal(trc, dst->unsafeUnbarrieredForTracing(), name);
}
}
template <typename T>
void js::TraceProcessGlobalRoot(JSTracer* trc, T* thing, const char* name) {
AssertRootMarkingPhase(trc);
MOZ_ASSERT(ThingIsPermanentAtomOrWellKnownSymbol(thing));
// We have to mark permanent atoms and well-known symbols through a special
// method because the default DoMarking implementation automatically skips
// them. Fortunately, atoms (permanent and non) cannot refer to other GC
// things so they do not need to go through the mark stack and may simply
// be marked directly. Moreover, well-known symbols can refer only to
// permanent atoms, so likewise require no subsquent marking.
CheckTracedThing(trc, *ConvertToBase(&thing));
if (trc->isMarkingTracer()) {
thing->asTenured().markIfUnmarked(gc::MarkColor::Black);
} else {
DoCallback(trc->asCallbackTracer(), ConvertToBase(&thing), name);
}
}
template void js::TraceProcessGlobalRoot<JSAtom>(JSTracer*, JSAtom*,
const char*);
template void js::TraceProcessGlobalRoot<JS::Symbol>(JSTracer*, JS::Symbol*,
const char*);
// A typed functor adaptor for TraceRoot.
struct TraceRootFunctor {
template <typename T>
void operator()(JSTracer* trc, Cell** thingp, const char* name) {
TraceRoot(trc, reinterpret_cast<T**>(thingp), name);
}
};
void js::TraceGenericPointerRoot(JSTracer* trc, Cell** thingp,
const char* name) {
MOZ_ASSERT(thingp);
if (!*thingp) {
return;
}
TraceRootFunctor f;
DispatchTraceKindTyped(f, (*thingp)->getTraceKind(), trc, thingp, name);
}
// A typed functor adaptor for TraceManuallyBarrieredEdge.
struct TraceManuallyBarrieredEdgeFunctor {
template <typename T>
void operator()(JSTracer* trc, Cell** thingp, const char* name) {
TraceManuallyBarrieredEdge(trc, reinterpret_cast<T**>(thingp), name);
}
};
void js::TraceManuallyBarrieredGenericPointerEdge(JSTracer* trc, Cell** thingp,
const char* name) {
MOZ_ASSERT(thingp);
if (!*thingp) {
return;
}
TraceManuallyBarrieredEdgeFunctor f;
DispatchTraceKindTyped(f, (*thingp)->getTraceKind(), trc, thingp, name);
}
// This method is responsible for dynamic dispatch to the real tracer
// implementation. Consider replacing this choke point with virtual dispatch:
// a sufficiently smart C++ compiler may be able to devirtualize some paths.
template <typename T>
void js::gc::TraceEdgeInternal(JSTracer* trc, T* thingp, const char* name) {
#define IS_SAME_TYPE_OR(name, type, _) mozilla::IsSame<type*, T>::value ||
static_assert(JS_FOR_EACH_TRACEKIND(IS_SAME_TYPE_OR)
mozilla::IsSame<T, JS::Value>::value ||
mozilla::IsSame<T, jsid>::value ||
mozilla::IsSame<T, TaggedProto>::value,
"Only the base cell layout types are allowed into "
"marking/tracing internals");
#undef IS_SAME_TYPE_OR
if (trc->isMarkingTracer()) {
return DoMarking(GCMarker::fromTracer(trc), *thingp);
}
if (trc->isTenuringTracer()) {
return static_cast<TenuringTracer*>(trc)->traverse(thingp);
}
MOZ_ASSERT(trc->isCallbackTracer());
DoCallback(trc->asCallbackTracer(), thingp, name);
}
template <typename T>
void js::gc::TraceWeakEdgeInternal(JSTracer* trc, T* thingp, const char* name) {
if (!trc->isMarkingTracer()) {
// Non-marking tracers can select whether or not they see weak edges.
if (trc->traceWeakEdges()) {
TraceEdgeInternal(trc, thingp, name);
}
return;
}
NoteWeakEdge(GCMarker::fromTracer(trc), thingp);
}
template <typename T>
void js::gc::TraceRangeInternal(JSTracer* trc, size_t len, T* vec,
const char* name) {
JS::AutoTracingIndex index(trc);
for (auto i : IntegerRange(len)) {
if (InternalBarrierMethods<T>::isMarkable(vec[i])) {
TraceEdgeInternal(trc, &vec[i], name);
}
++index;
}
}
/*** GC Marking Interface ***************************************************/
namespace js {
typedef bool HasNoImplicitEdgesType;
template <typename T>
struct ImplicitEdgeHolderType {
typedef HasNoImplicitEdgesType Type;
};
// For now, we only handle JSObject* and JSScript* keys, but the linear time
// algorithm can be easily extended by adding in more types here, then making
// GCMarker::traverse<T> call markPotentialEphemeronKey.
template <>
struct ImplicitEdgeHolderType<JSObject*> {
typedef JSObject* Type;
};
template <>
struct ImplicitEdgeHolderType<JSScript*> {
typedef JSScript* Type;
};
void GCMarker::markEphemeronValues(gc::Cell* markedCell,
WeakEntryVector& values) {
size_t initialLen = values.length();
for (size_t i = 0; i < initialLen; i++) {
values[i].weakmap->markEntry(this, markedCell, values[i].key);
}
// The vector should not be appended to during iteration because the key is
// already marked, and even in cases where we have a multipart key, we
// should only be inserting entries for the unmarked portions.
MOZ_ASSERT(values.length() == initialLen);
}
template <typename T>
void GCMarker::markImplicitEdgesHelper(T markedThing) {
if (!isWeakMarkingTracer()) {
return;
}
Zone* zone = gc::TenuredCell::fromPointer(markedThing)->zone();
MOZ_ASSERT(zone->isGCMarking());
MOZ_ASSERT(!zone->isGCSweeping());
auto p = zone->gcWeakKeys().get(JS::GCCellPtr(markedThing));
if (!p) {
return;
}
WeakEntryVector& markables = p->value;
markEphemeronValues(markedThing, markables);
markables.clear(); // If key address is reused, it should do nothing
}
template <>
void GCMarker::markImplicitEdgesHelper(HasNoImplicitEdgesType) {}
template <typename T>
void GCMarker::markImplicitEdges(T* thing) {
markImplicitEdgesHelper<typename ImplicitEdgeHolderType<T*>::Type>(thing);
}
template void GCMarker::markImplicitEdges(JSObject*);
template void GCMarker::markImplicitEdges(JSScript*);
template void GCMarker::markImplicitEdges(LazyScript*);
} // namespace js
template <typename T>
static inline bool ShouldMark(GCMarker* gcmarker, T thing) {
// Don't trace things that are owned by another runtime.
if (IsOwnedByOtherRuntime(gcmarker->runtime(), thing)) {
return false;
}
// Don't mark things outside a zone if we are in a per-zone GC.
return thing->zone()->shouldMarkInZone();
}
template <>
bool ShouldMark<JSObject*>(GCMarker* gcmarker, JSObject* obj) {
// Don't trace things that are owned by another runtime.
if (IsOwnedByOtherRuntime(gcmarker->runtime(), obj)) {
return false;
}
// We may mark a Nursery thing outside the context of the
// MinorCollectionTracer because of a pre-barrier. The pre-barrier is not
// needed in this case because we perform a minor collection before each
// incremental slice.
if (IsInsideNursery(obj)) {
return false;
}
// Don't mark things outside a zone if we are in a per-zone GC. It is
// faster to check our own arena, which we can do since we know that
// the object is tenured.
return obj->asTenured().zone()->shouldMarkInZone();
}
// JSStrings can also be in the nursery. See ShouldMark<JSObject*> for comments.
template <>
bool ShouldMark<JSString*>(GCMarker* gcmarker, JSString* str) {
if (IsOwnedByOtherRuntime(gcmarker->runtime(), str)) {
return false;
}
if (IsInsideNursery(str)) {
return false;
}
return str->asTenured().zone()->shouldMarkInZone();
}
template <typename T>
void DoMarking(GCMarker* gcmarker, T* thing) {
// Do per-type marking precondition checks.
if (!ShouldMark(gcmarker, thing)) {
return;
}
CheckTracedThing(gcmarker, thing);
gcmarker->traverse(thing);
// Mark the compartment as live.
SetMaybeAliveFlag(thing);
}
template <typename S>
struct DoMarkingFunctor : public VoidDefaultAdaptor<S> {
template <typename T>
void operator()(T* t, GCMarker* gcmarker) {
DoMarking(gcmarker, t);
}
};
template <typename T>
void DoMarking(GCMarker* gcmarker, const T& thing) {
DispatchTyped(DoMarkingFunctor<T>(), thing, gcmarker);
}
template <typename T>
void NoteWeakEdge(GCMarker* gcmarker, T** thingp) {
// Do per-type marking precondition checks.
if (!ShouldMark(gcmarker, *thingp)) {
return;
}
CheckTracedThing(gcmarker, *thingp);
// If the target is already marked, there's no need to store the edge.
if (IsMarkedUnbarriered(gcmarker->runtime(), thingp)) {
return;
}
gcmarker->noteWeakEdge(thingp);
}
template <typename T>
void NoteWeakEdge(GCMarker* gcmarker, T* thingp) {
MOZ_CRASH("the gc does not support tagged pointers as weak edges");
}
template <typename T>
void js::GCMarker::noteWeakEdge(T* edge) {
static_assert(IsBaseOf<Cell, typename mozilla::RemovePointer<T>::Type>::value,
"edge must point to a GC pointer");
MOZ_ASSERT((*edge)->isTenured());
// Note: we really want the *source* Zone here. The edge may start in a
// non-gc heap location, however, so we use the fact that cross-zone weak
// references are not allowed and use the *target's* zone.
JS::Zone::WeakEdges& weakRefs = (*edge)->asTenured().zone()->gcWeakRefs();
AutoEnterOOMUnsafeRegion oomUnsafe;
if (!weakRefs.append(reinterpret_cast<TenuredCell**>(edge))) {
oomUnsafe.crash("Failed to record a weak edge for sweeping.");
}
}
// The simplest traversal calls out to the fully generic traceChildren function
// to visit the child edges. In the absence of other traversal mechanisms, this
// function will rapidly grow the stack past its bounds and crash the process.
// Thus, this generic tracing should only be used in cases where subsequent
// tracing will not recurse.
template <typename T>
void js::GCMarker::markAndTraceChildren(T* thing) {
if (ThingIsPermanentAtomOrWellKnownSymbol(thing)) {
return;
}
if (mark(thing)) {
thing->traceChildren(this);
}
}
namespace js {
template <>
void GCMarker::traverse(BaseShape* thing) {
markAndTraceChildren(thing);
}
template <>
void GCMarker::traverse(JS::Symbol* thing) {
markAndTraceChildren(thing);
}
#ifdef ENABLE_BIGINT
template <>
void GCMarker::traverse(JS::BigInt* thing) {
markAndTraceChildren(thing);
}
#endif
template <>
void GCMarker::traverse(RegExpShared* thing) {
markAndTraceChildren(thing);
}
} // namespace js
// Strings, LazyScripts, Shapes, and Scopes are extremely common, but have
// simple patterns of recursion. We traverse trees of these edges immediately,
// with aggressive, manual inlining, implemented by eagerlyTraceChildren.
template <typename T>
void js::GCMarker::markAndScan(T* thing) {
if (ThingIsPermanentAtomOrWellKnownSymbol(thing)) {
return;
}
if (mark(thing)) {
eagerlyMarkChildren(thing);
}
}
namespace js {
template <>
void GCMarker::traverse(JSString* thing) {
markAndScan(thing);
}
template <>
void GCMarker::traverse(LazyScript* thing) {
markAndScan(thing);
}
template <>
void GCMarker::traverse(Shape* thing) {
markAndScan(thing);
}
template <>
void GCMarker::traverse(js::Scope* thing) {
markAndScan(thing);
}
} // namespace js
// Object and ObjectGroup are extremely common and can contain arbitrarily
// nested graphs, so are not trivially inlined. In this case we use a mark
// stack to control recursion. JitCode shares none of these properties, but is
// included for historical reasons. JSScript normally cannot recurse, but may
// be used as a weakmap key and thereby recurse into weakmapped values.
template <typename T>
void js::GCMarker::markAndPush(T* thing) {
if (!mark(thing)) {
return;
}
pushTaggedPtr(thing);
}
namespace js {
template <>
void GCMarker::traverse(JSObject* thing) {
markAndPush(thing);
}
template <>
void GCMarker::traverse(ObjectGroup* thing) {
markAndPush(thing);
}
template <>
void GCMarker::traverse(jit::JitCode* thing) {
markAndPush(thing);
}
template <>
void GCMarker::traverse(JSScript* thing) {
markAndPush(thing);
}
} // namespace js
namespace js {
template <>
void GCMarker::traverse(AccessorShape* thing) {
MOZ_CRASH("AccessorShape must be marked as a Shape");
}
} // namespace js
template <typename S, typename T>
static void CheckTraversedEdge(S source, T* target) {
// Atoms and Symbols do not have or mark their internal pointers,
// respectively.
MOZ_ASSERT(!ThingIsPermanentAtomOrWellKnownSymbol(source));
// The Zones must match, unless the target is an atom.
MOZ_ASSERT_IF(
!ThingIsPermanentAtomOrWellKnownSymbol(target),
target->zone()->isAtomsZone() || target->zone() == source->zone());
// If we are marking an atom, that atom must be marked in the source zone's
// atom bitmap.
MOZ_ASSERT_IF(!ThingIsPermanentAtomOrWellKnownSymbol(target) &&
target->zone()->isAtomsZone() &&
!source->zone()->isAtomsZone(),
target->runtimeFromAnyThread()->gc.atomMarking.atomIsMarked(
source->zone(), reinterpret_cast<TenuredCell*>(target)));
// Atoms and Symbols do not have access to a compartment pointer, or we'd need
// to adjust the subsequent check to catch that case.
MOZ_ASSERT_IF(ThingIsPermanentAtomOrWellKnownSymbol(target),
!target->maybeCompartment());
MOZ_ASSERT_IF(target->zoneFromAnyThread()->isAtomsZone(),
!target->maybeCompartment());
// If we have access to a compartment pointer for both things, they must
// match.
MOZ_ASSERT_IF(source->maybeCompartment() && target->maybeCompartment(),
source->maybeCompartment() == target->maybeCompartment());
}
template <typename S, typename T>
void js::GCMarker::traverseEdge(S source, T* target) {
CheckTraversedEdge(source, target);
traverse(target);
}
template <typename V, typename S>
struct TraverseEdgeFunctor : public VoidDefaultAdaptor<V> {
template <typename T>
void operator()(T t, GCMarker* gcmarker, S s) {
return gcmarker->traverseEdge(s, t);
}
};
template <typename S, typename T>
void js::GCMarker::traverseEdge(S source, const T& thing) {
DispatchTyped(TraverseEdgeFunctor<T, S>(), thing, this, source);
}
namespace {
template <typename T>
struct TypeParticipatesInCC {};
#define EXPAND_PARTICIPATES_IN_CC(_, type, addToCCKind) \
template <> \
struct TypeParticipatesInCC<type> { \
static const bool value = addToCCKind; \
};
JS_FOR_EACH_TRACEKIND(EXPAND_PARTICIPATES_IN_CC)
#undef EXPAND_PARTICIPATES_IN_CC
struct ParticipatesInCCFunctor {
template <typename T>
bool operator()() {
return TypeParticipatesInCC<T>::value;
}
};
} // namespace
static bool TraceKindParticipatesInCC(JS::TraceKind kind) {
return DispatchTraceKindTyped(ParticipatesInCCFunctor(), kind);
}
template <typename T>
bool js::GCMarker::mark(T* thing) {
if (IsInsideNursery(thing)) {
return false;
}
AssertShouldMarkInZone(thing);
TenuredCell* cell = TenuredCell::fromPointer(thing);
if (!TypeParticipatesInCC<T>::value) {
return cell->markIfUnmarked(MarkColor::Black);
}
return cell->markIfUnmarked(markColor());
}
/*** Inline, Eager GC Marking ***********************************************/
// Each of the eager, inline marking paths is directly preceeded by the
// out-of-line, generic tracing code for comparison. Both paths must end up
// traversing equivalent subgraphs.
void LazyScript::traceChildren(JSTracer* trc) {
if (script_) {
TraceWeakEdge(trc, &script_, "script");
}
if (function_) {
TraceEdge(trc, &function_, "function");
}
if (sourceObject_) {
TraceEdge(trc, &sourceObject_, "sourceObject");
}
if (enclosingLazyScriptOrScope_) {
TraceGenericPointerRoot(
trc,
reinterpret_cast<Cell**>(
enclosingLazyScriptOrScope_.unsafeUnbarrieredForTracing()),
"enclosingScope or enclosingLazyScript");
}
// We rely on the fact that atoms are always tenured.
JSAtom** closedOverBindings = this->closedOverBindings();
for (auto i : IntegerRange(numClosedOverBindings())) {
if (closedOverBindings[i]) {
TraceManuallyBarrieredEdge(trc, &closedOverBindings[i],
"closedOverBinding");
}
}
GCPtrFunction* innerFunctions = this->innerFunctions();
for (auto i : IntegerRange(numInnerFunctions())) {
TraceEdge(trc, &innerFunctions[i], "lazyScriptInnerFunction");
}
if (trc->isMarkingTracer()) {
return GCMarker::fromTracer(trc)->markImplicitEdges(this);