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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
* vim: set ts=8 sw=2 et 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 */
#ifndef gc_Nursery_h
#define gc_Nursery_h
#include "mozilla/EnumeratedArray.h"
#include "mozilla/TimeStamp.h"
#include <tuple>
#include "ds/LifoAlloc.h"
#include "gc/GCEnum.h"
#include "gc/GCProbes.h"
#include "gc/Heap.h"
#include "gc/MallocedBlockCache.h"
#include "gc/Pretenuring.h"
#include "js/AllocPolicy.h"
#include "js/Class.h"
#include "js/GCAPI.h"
#include "js/GCVector.h"
#include "js/HeapAPI.h"
#include "js/TypeDecls.h"
#include "js/UniquePtr.h"
#include "js/Utility.h"
#include "js/Vector.h"
/* Key Header text */ \
_(Total, "total") \
_(TraceValues, "mkVals") \
_(TraceCells, "mkClls") \
_(TraceSlots, "mkSlts") \
_(TraceWasmAnyRefs, "mkWars") \
_(TraceWholeCells, "mcWCll") \
_(TraceGenericEntries, "mkGnrc") \
_(CheckHashTables, "ckTbls") \
_(MarkRuntime, "mkRntm") \
_(MarkDebugger, "mkDbgr") \
_(SweepCaches, "swpCch") \
_(CollectToObjFP, "colObj") \
_(CollectToStrFP, "colStr") \
_(ObjectsTenuredCallback, "tenCB") \
_(Sweep, "sweep") \
_(UpdateJitActivations, "updtIn") \
_(FreeMallocedBuffers, "frSlts") \
_(FreeTrailerBlocks, "frTrBs") \
_(ClearNursery, "clear") \
_(PurgeStringToAtomCache, "pStoA") \
_(Pretenure, "pretnr")
template <typename T>
class SharedMem;
namespace mozilla {
class StringBuffer;
namespace js {
struct StringStats;
class AutoLockGCBgAlloc;
class ObjectElements;
struct NurseryChunk;
class HeapSlot;
class JSONPrinter;
class MapObject;
class SetObject;
class JS_PUBLIC_API Sprinter;
namespace gc {
class AutoGCSession;
struct Cell;
class GCSchedulingTunables;
class StoreBuffer;
class TenuringTracer;
// A set of cells that need to be swept at the end of a minor GC,
// represented as a linked list of ArenaCellSet structs extracted from a
// WholeCellBuffer.
struct CellSweepSet {
UniquePtr<LifoAlloc> storage_;
ArenaCellSet* head_ = nullptr;
// Fixup the tenured dependent strings stored in the ArenaCellSet list.
void sweep();
} // namespace gc
class Nursery {
explicit Nursery(gc::GCRuntime* gc);
[[nodiscard]] bool init(AutoLockGCBgAlloc& lock);
void enable();
void disable();
bool isEnabled() const { return capacity() != 0; }
void enableStrings();
void disableStrings();
bool canAllocateStrings() const { return canAllocateStrings_; }
void enableBigInts();
void disableBigInts();
bool canAllocateBigInts() const { return canAllocateBigInts_; }
void setSemispaceEnabled(bool enabled);
bool semispaceEnabled() const { return semispaceEnabled_; }
// Return true if no allocations have been made since the last collection.
bool isEmpty() const;
// Check whether an arbitrary pointer is within the nursery. This is
// slower than IsInsideNursery(Cell*), but works on all types of pointers.
bool isInside(gc::Cell* cellp) const = delete;
inline bool isInside(const void* p) const;
template <typename T>
inline bool isInside(const SharedMem<T>& p) const;
// Allocate and return a pointer to a new GC thing. Returns nullptr if the
// Nursery is full.
void* allocateCell(gc::AllocSite* site, size_t size, JS::TraceKind kind);
// Allocate and return a pointer to a new GC thing. Returns nullptr if the
// handleAllocationFailure() needs to be called before retrying.
inline void* tryAllocateCell(gc::AllocSite* site, size_t size,
JS::TraceKind kind);
// Attempt to handle the failure of tryAllocate. Returns a GCReason if minor
// GC is required, or NO_REASON if the failure was handled and allocation will
// now succeed.
[[nodiscard]] JS::GCReason handleAllocationFailure();
static size_t nurseryCellHeaderSize() {
return sizeof(gc::NurseryCellHeader);
// Allocate a buffer for a given zone, using the nursery if possible. Returns
// <buffer, isMalloced> so the caller can register the buffer if
// needed. Returns false in |isMalloced| if the allocation fails.
// Use the following API if the owning Cell is already known.
std::tuple<void*, bool> allocateBuffer(JS::Zone* zone, size_t nbytes,
arena_id_t arenaId);
// Like allocateBuffer, but returns nullptr if the buffer can't be allocated
// in the nursery.
void* tryAllocateNurseryBuffer(JS::Zone* zone, size_t nbytes,
arena_id_t arenaId);
// Allocate a buffer for a given Cell, using the nursery if possible and
// owner is in the nursery.
void* allocateBuffer(JS::Zone* zone, gc::Cell* owner, size_t nbytes,
arena_id_t arenaId);
// Allocate a buffer for a given Cell, always using the nursery if |owner| is
// in the nursery. The requested size must be less than or equal to
// MaxNurseryBufferSize.
void* allocateBufferSameLocation(gc::Cell* owner, size_t nbytes,
arena_id_t arenaId);
// Allocate a zero-initialized buffer for a given zone, using the nursery if
// possible. If the buffer isn't allocated in the nursery, the given arena is
// used. Returns <buffer, isMalloced>. Returns false in |isMalloced| if the
// allocation fails.
std::tuple<void*, bool> allocateZeroedBuffer(JS::Zone* zone, size_t nbytes,
arena_id_t arena);
// Allocate a zero-initialized buffer for a given Cell, using the nursery if
// possible and |owner| is in the nursery. If the buffer isn't allocated in
// the nursery, the given arena is used.
void* allocateZeroedBuffer(gc::Cell* owner, size_t nbytes, arena_id_t arena);
// Resize an existing buffer.
void* reallocateBuffer(JS::Zone* zone, gc::Cell* cell, void* oldBuffer,
size_t oldBytes, size_t newBytes, arena_id_t arena);
// Free an object buffer.
void freeBuffer(void* buffer, size_t nbytes);
// The maximum number of bytes allowed to reside in nursery buffers.
static const size_t MaxNurseryBufferSize = 1024;
// Do a minor collection.
void collect(JS::GCOptions options, JS::GCReason reason);
// If the thing at |*ref| in the Nursery has been forwarded, set |*ref| to
// the new location and return true. Otherwise return false and leave
// |*ref| unset.
[[nodiscard]] MOZ_ALWAYS_INLINE static bool getForwardedPointer(
js::gc::Cell** ref);
// Forward a slots/elements pointer stored in an Ion frame.
void forwardBufferPointer(uintptr_t* pSlotsElems);
inline void maybeSetForwardingPointer(JSTracer* trc, void* oldData,
void* newData, bool direct);
inline void setForwardingPointerWhileTenuring(void* oldData, void* newData,
bool direct);
// Handle an external buffer when a cell is promoted. Updates the pointer to
// the (possibly moved) buffer and returns whether it was moved.
enum WasBufferMoved : bool { BufferNotMoved = false, BufferMoved = true };
WasBufferMoved maybeMoveRawBufferOnPromotion(void** bufferp, gc::Cell* owner,
size_t nbytes, MemoryUse use,
arena_id_t arena);
template <typename T>
WasBufferMoved maybeMoveBufferOnPromotion(T** bufferp, gc::Cell* owner,
size_t nbytes, MemoryUse use,
arena_id_t arena) {
return maybeMoveRawBufferOnPromotion(reinterpret_cast<void**>(bufferp),
owner, nbytes, use, arena);
template <typename T>
WasBufferMoved maybeMoveBufferOnPromotion(T** bufferp, gc::Cell* owner,
size_t nbytes, MemoryUse use) {
return maybeMoveBufferOnPromotion(bufferp, owner, nbytes, use, MallocArena);
// Register a malloced buffer that is held by a nursery object, which
// should be freed at the end of a minor GC. Buffers are unregistered when
// their owning objects are tenured.
[[nodiscard]] bool registerMallocedBuffer(void* buffer, size_t nbytes);
// Mark a malloced buffer as no longer needing to be freed.
void removeMallocedBuffer(void* buffer, size_t nbytes) {
MOZ_ASSERT(nbytes > 0);
MOZ_ASSERT(toSpace.mallocedBufferBytes >= nbytes);
toSpace.mallocedBufferBytes -= nbytes;
// Mark a malloced buffer as no longer needing to be freed during minor
// GC. There's no need to account for the size here since all remaining
// buffers will soon be freed.
void removeMallocedBufferDuringMinorGC(void* buffer) {
[[nodiscard]] bool addedUniqueIdToCell(gc::Cell* cell) {
return cellsWithUid_.append(cell);
[[nodiscard]] inline bool addStringBuffer(JSLinearString* s);
size_t sizeOfMallocedBuffers(mozilla::MallocSizeOf mallocSizeOf) const;
// Wasm "trailer" (C++-heap-allocated) blocks.
// All involved blocks are allocated/deallocated via this nursery's
// `mallocedBlockCache_`. Hence we must store both the block address and
// its freelist ID, wrapped up in a PointerAndUint7.
// Trailer blocks registered here are added to `trailersAdded_`. Those that
// are later deregistered as a result of `obj_moved` calls that indicate
// tenuring, should be added to `trailersRemoved_`.
// Unfortunately ::unregisterTrailer cannot be allowed to OOM. To get
// around this we rely on the observation that all deregistered blocks
// should previously have been registered, so the deregistered set can never
// be larger than the registered set. Hence ::registerTrailer effectively
// preallocates space in `trailersRemoved_` so as to ensure that, in the
// worst case, all registered blocks can be handed to ::unregisterTrailer
// without needing to resize `trailersRemoved_` in ::unregisterTrailer.
// The downside is that most of the space in `trailersRemoved_` is wasted in
// the case where there are few blocks deregistered. This is unfortunate
// but it's hard to see how to avoid it.
// At the end of a minor collection, all blocks in the set `trailersAdded_ -
// trailersRemoved_[0 .. trailersRemovedUsed_ - 1]` are handed back to the
// `mallocedBlockCache_`.
[[nodiscard]] inline bool registerTrailer(PointerAndUint7 blockAndListID,
size_t nBytes);
inline void unregisterTrailer(void* block);
size_t sizeOfTrailerBlockSets(mozilla::MallocSizeOf mallocSizeOf) const;
size_t totalCapacity() const;
size_t totalCommitted() const;
#ifdef JS_GC_ZEAL
void enterZealMode();
void leaveZealMode();
// Write profile time JSON on JSONPrinter.
void renderProfileJSON(JSONPrinter& json) const;
// Print header line for profile times.
void printProfileHeader();
// Print total profile times on shutdown.
void printTotalProfileTimes();
void* addressOfPosition() const { return (void**)&toSpace.position_; }
static constexpr int32_t offsetOfCurrentEndFromPosition() {
return offsetof(Nursery, toSpace.currentEnd_) -
offsetof(Nursery, toSpace.position_);
void* addressOfNurseryAllocatedSites() {
return pretenuringNursery.addressOfAllocatedSites();
void requestMinorGC(JS::GCReason reason);
bool minorGCRequested() const {
return minorGCTriggerReason_ != JS::GCReason::NO_REASON;
JS::GCReason minorGCTriggerReason() const { return minorGCTriggerReason_; }
bool wantEagerCollection() const;
bool enableProfiling() const { return enableProfiling_; }
bool addMapWithNurseryMemory(MapObject* obj) {
mapsWithNurseryMemory_.back() != obj);
return mapsWithNurseryMemory_.append(obj);
bool addSetWithNurseryMemory(SetObject* obj) {
setsWithNurseryMemory_.back() != obj);
return setsWithNurseryMemory_.append(obj);
void joinDecommitTask();
mozilla::TimeStamp collectionStartTime() {
return startTimes_[ProfileKey::Total];
bool canCreateAllocSite() { return pretenuringNursery.canCreateAllocSite(); }
void noteAllocSiteCreated() { pretenuringNursery.noteAllocSiteCreated(); }
bool reportPretenuring() const { return pretenuringReportFilter_.enabled; }
void maybeStopPretenuring(gc::GCRuntime* gc) {
void setAllocFlagsForZone(JS::Zone* zone);
bool shouldTenureEverything(JS::GCReason reason);
inline bool inCollectedRegion(gc::Cell* cell) const;
inline bool inCollectedRegion(void* ptr) const;
void trackMallocedBufferOnPromotion(void* buffer, gc::Cell* owner,
size_t nbytes, MemoryUse use);
void trackTrailerOnPromotion(void* buffer, gc::Cell* owner, size_t nbytes,
size_t overhead, MemoryUse use);
// Round a size in bytes to the nearest valid nursery size.
static size_t roundSize(size_t size);
// The malloc'd block cache.
gc::MallocedBlockCache& mallocedBlockCache() { return mallocedBlockCache_; }
size_t sizeOfMallocedBlockCache(mozilla::MallocSizeOf mallocSizeOf) const {
return mallocedBlockCache_.sizeOfExcludingThis(mallocSizeOf);
mozilla::TimeStamp lastCollectionEndTime() const;
struct Space;
enum class ProfileKey {
#define DEFINE_TIME_KEY(name, text) name,
using ProfileTimes = mozilla::EnumeratedArray<ProfileKey, mozilla::TimeStamp,
using ProfileDurations =
mozilla::EnumeratedArray<ProfileKey, mozilla::TimeDuration,
size_t capacity() const { return capacity_; }
// Total number of chunks and the capacity of the current nursery
// space. Chunks will be lazily allocated and added to the chunks array up to
// this limit. After that the nursery must be collected. This limit may be
// changed at the end of collection by maybeResizeNursery.
uint32_t maxChunkCount() const {
return toSpace.maxChunkCount_;
// Number of allocated (ready to use) chunks.
unsigned allocatedChunkCount() const { return toSpace.chunks_.length(); }
uint32_t currentChunk() const { return toSpace.currentChunk_; }
uint32_t startChunk() const { return toSpace.startChunk_; }
uintptr_t startPosition() const { return toSpace.startPosition_; }
// Used and free space both include chunk headers for that part of the
// nursery.
MOZ_ALWAYS_INLINE size_t usedSpace() const {
return capacity() - freeSpace();
MOZ_ALWAYS_INLINE size_t freeSpace() const {
MOZ_ASSERT(currentChunk() < maxChunkCount());
return (currentEnd() - position()) +
(maxChunkCount() - currentChunk() - 1) * gc::ChunkSize;
// Calculate the promotion rate of the most recent minor GC.
// The valid_for_tenuring parameter is used to return whether this
// promotion rate is accurate enough (the nursery was full enough) to be
// used for tenuring and other decisions.
// Must only be called if the previousGC data is initialised.
double calcPromotionRate(bool* validForTenuring) const;
void freeTrailerBlocks(JS::GCOptions options, JS::GCReason reason);
NurseryChunk& chunk(unsigned index) const { return *toSpace.chunks_[index]; }
// Set the allocation position to the start of a chunk. This sets
// currentChunk_, position_ and currentEnd_ values as appropriate.
void moveToStartOfChunk(unsigned chunkno);
bool initFirstChunk(AutoLockGCBgAlloc& lock);
void setCapacity(size_t newCapacity);
void poisonAndInitCurrentChunk();
void setCurrentEnd();
void setStartToCurrentPosition();
// Allocate another chunk.
[[nodiscard]] bool allocateNextChunk(AutoLockGCBgAlloc& lock);
uintptr_t position() const { return toSpace.position_; }
uintptr_t currentEnd() const { return toSpace.currentEnd_; }
MOZ_ALWAYS_INLINE bool isSubChunkMode() const;
JSRuntime* runtime() const;
gcstats::Statistics& stats() const;
const js::gc::GCSchedulingTunables& tunables() const;
void getAllocFlagsForZone(JS::Zone* zone, bool* allocObjectsOut,
bool* allocStringsOut, bool* allocBigIntsOut);
void updateAllZoneAllocFlags();
void updateAllocFlagsForZone(JS::Zone* zone);
void discardCodeAndSetJitFlagsForZone(JS::Zone* zone);
void* allocate(size_t size);
// Common internal allocator function. If this fails, call
// handleAllocationFailure to see whether it's possible to retry.
inline void* tryAllocate(size_t size);
[[nodiscard]] bool moveToNextChunk();
bool freeSpaceIsBelowEagerThreshold() const;
bool isUnderused() const;
struct CollectionResult {
size_t tenuredBytes;
size_t tenuredCells;
CollectionResult doCollection(gc::AutoGCSession& session,
JS::GCOptions options, JS::GCReason reason);
void swapSpaces();
void traceRoots(gc::AutoGCSession& session, gc::TenuringTracer& mover);
size_t doPretenuring(JSRuntime* rt, JS::GCReason reason,
bool validPromotionRate, double promotionRate);
// Handle relocation of slots/elements pointers stored in Ion frames.
inline void setForwardingPointer(void* oldData, void* newData, bool direct);
inline void setDirectForwardingPointer(void* oldData, void* newData);
void setIndirectForwardingPointer(void* oldData, void* newData);
inline void setSlotsForwardingPointer(HeapSlot* oldSlots, HeapSlot* newSlots,
uint32_t nslots);
inline void setElementsForwardingPointer(ObjectElements* oldHeader,
ObjectElements* newHeader,
uint32_t capacity);
#ifdef DEBUG
bool checkForwardingPointerInsideNursery(void* ptr);
// Updates pointers to nursery objects that have been tenured and discards
// pointers to objects that have been freed.
void sweep();
// In a minor GC, resets the start and end positions, the current chunk and
// current position.
void setNewExtentAndPosition();
// the nursery on debug & nightly builds.
void clear();
void clearMapAndSetNurseryRanges();
void sweepMapAndSetObjects();
// Allocate a buffer for a given zone, using the nursery if possible.
void* allocateBuffer(JS::Zone* zone, size_t nbytes);
// Get per-space size limits.
size_t maxSpaceSize() const;
size_t minSpaceSize() const;
// Change the allocable space provided by the nursery.
void maybeResizeNursery(JS::GCOptions options, JS::GCReason reason);
size_t targetSize(JS::GCOptions options, JS::GCReason reason);
void clearRecentGrowthData();
void growAllocableSpace(size_t newCapacity);
void shrinkAllocableSpace(size_t newCapacity);
void minimizeAllocableSpace();
// Free the chunks starting at firstFreeChunk until the end of the chunks
// vector. Shrinks the vector but does not update maxChunkCount().
void freeChunksFrom(Space& space, unsigned firstFreeChunk);
inline bool shouldTenure(gc::Cell* cell);
void sendTelemetry(JS::GCReason reason, mozilla::TimeDuration totalTime,
bool wasEmpty, double promotionRate,
size_t sitesPretenured);
void printCollectionProfile(JS::GCReason reason, double promotionRate);
void printDeduplicationData(js::StringStats& prev, js::StringStats& curr);
// Profile recording and printing.
void maybeClearProfileDurations();
void startProfile(ProfileKey key);
void endProfile(ProfileKey key);
static void printProfileDurations(const ProfileDurations& times,
Sprinter& sprinter);
mozilla::TimeStamp collectionStartTime() const;
using BufferRelocationOverlay = void*;
using BufferSet = HashSet<void*, PointerHasher<void*>, SystemAllocPolicy>;
struct Space {
// Fields used during allocation fast path go first:
// Pointer to the first unallocated byte in the nursery.
uintptr_t position_ = 0;
// Pointer to the last byte of space in the current chunk.
uintptr_t currentEnd_ = 0;
// Vector of allocated chunks to allocate from.
Vector<NurseryChunk*, 0, SystemAllocPolicy> chunks_;
// The index of the chunk that is currently being allocated from.
uint32_t currentChunk_ = 0;
// The maximum number of chunks to allocate based on capacity_.
uint32_t maxChunkCount_ = 0;
// These fields refer to the beginning of the nursery. They're normally 0
// and chunk(0).start() respectively. Except when a generational GC zeal
// mode is active, then they may be arbitrary (see Nursery::clear()).
uint32_t startChunk_ = 0;
uintptr_t startPosition_ = 0;
// The set of malloced-allocated buffers owned by nursery objects. Any
// buffers that do not belong to a promoted thing at the end of a minor GC
// must be freed.
BufferSet mallocedBuffers;
size_t mallocedBufferBytes = 0;
// Wasm "trailer" (C++-heap-allocated) blocks. See comments above on
// ::registerTrailer and ::unregisterTrailer.
Vector<PointerAndUint7, 0, SystemAllocPolicy> trailersAdded_;
Vector<void*, 0, SystemAllocPolicy> trailersRemoved_;
size_t trailersRemovedUsed_ = 0;
size_t trailerBytes_ = 0;
gc::ChunkKind kind;
explicit Space(gc::ChunkKind kind);
inline bool isEmpty() const;
inline bool isInside(const void* p) const;
// Return the logical offset within the nursery of an address in a nursery
// chunk (chunks are discontiguous in memory).
inline size_t offsetFromAddress(uintptr_t addr) const;
inline size_t offsetFromExclusiveAddress(uintptr_t addr) const;
void setKind(gc::ChunkKind newKind);
void clear(Nursery* nursery);
void moveToStartOfChunk(Nursery* nursery, unsigned chunkno);
void setCurrentEnd(Nursery* nursery);
void setStartToCurrentPosition();
bool commitSubChunkRegion(size_t oldCapacity, size_t newCapacity);
void decommitSubChunkRegion(Nursery* nursery, size_t oldCapacity,
size_t newCapacity);
void freeTrailerBlocks(gc::MallocedBlockCache& mallocedBlockCache);
#ifdef DEBUG
void checkKind(gc::ChunkKind expected) const;
size_t findChunkIndex(uintptr_t chunkAddr) const;
Space toSpace;
Space fromSpace;
gc::GCRuntime* const gc;
// The current nursery capacity measured in bytes. It may grow up to this
// value without a collection, allocating chunks on demand. This limit may be
// changed by maybeResizeNursery() each collection. It includes chunk headers.
size_t capacity_;
uintptr_t tenureThreshold_ = 0;
gc::PretenuringNursery pretenuringNursery;
mozilla::TimeDuration timeInChunkAlloc_;
// Report minor collections taking at least this long, if enabled.
bool enableProfiling_ = false;
bool profileWorkers_ = false;
mozilla::TimeDuration profileThreshold_;
// Whether to use semispace collection.
bool semispaceEnabled_;
// Whether we will nursery-allocate strings.
bool canAllocateStrings_;
// Whether we will nursery-allocate BigInts.
bool canAllocateBigInts_;
// Report how many strings were deduplicated.
bool reportDeduplications_;
#ifdef JS_GC_ZEAL
// Report on the kinds of things promoted.
bool reportPromotion_;
// Whether to report information on pretenuring, and if so the allocation
// threshold at which to report details of each allocation site.
gc::AllocSiteFilter pretenuringReportFilter_;
// Whether and why a collection of this nursery has been requested. When this
// happens |prevPosition_| is set to the current position and |position_| set
// to the end of the chunk to force the next allocation to fail.
JS::GCReason minorGCTriggerReason_;
uintptr_t prevPosition_;
// Profiling data.
ProfileTimes startTimes_;
ProfileDurations profileDurations_;
ProfileDurations totalDurations_;
// Data about the previous collection.
struct PreviousGC {
JS::GCReason reason = JS::GCReason::NO_REASON;
size_t nurseryCapacity = 0;
size_t nurseryCommitted = 0;
size_t nurseryUsedBytes = 0;
size_t nurseryUsedChunkCount = 0;
size_t tenuredBytes = 0;
size_t tenuredCells = 0;
mozilla::TimeStamp endTime;
PreviousGC previousGC;
bool hasRecentGrowthData;
double smoothedTargetSize;
// During a collection most hoisted slot and element buffers indicate their
// new location with a forwarding pointer at the base. This does not work
// for buffers whose length is less than pointer width, or when different
// buffers might overlap each other. For these, an entry in the following
// table is used.
using ForwardedBufferMap =
HashMap<void*, void*, PointerHasher<void*>, SystemAllocPolicy>;
ForwardedBufferMap forwardedBuffers;
gc::CellSweepSet cellsToSweep;
// When we assign a unique id to cell in the nursery, that almost always
// means that the cell will be in a hash table, and thus, held live,
// automatically moving the uid from the nursery to its new home in
// tenured. It is possible, if rare, for an object that acquired a uid to
// be dead before the next collection, in which case we need to know to
// remove it when we sweep.
// Note: we store the pointers as Cell* here, resulting in an ugly cast in
// sweep. This is because this structure is used to help implement
// stable object hashing and we have to break the cycle somehow.
using CellsWithUniqueIdVector = JS::GCVector<gc::Cell*, 8, SystemAllocPolicy>;
CellsWithUniqueIdVector cellsWithUid_;
// Lists of map and set objects allocated in the nursery or with iterators
// allocated there. Such objects need to be swept after minor GC.
using MapObjectVector = Vector<MapObject*, 0, SystemAllocPolicy>;
MapObjectVector mapsWithNurseryMemory_;
using SetObjectVector = Vector<SetObject*, 0, SystemAllocPolicy>;
SetObjectVector setsWithNurseryMemory_;
// List of strings with StringBuffers allocated in the nursery. References
// to the buffers are dropped after minor GC. The list stores both the JS
// string and the StringBuffer to simplify interaction with AtomRefs and
// string deduplication.
using StringAndBuffer = std::pair<JSLinearString*, mozilla::StringBuffer*>;
using StringBufferVector =
JS::GCVector<StringAndBuffer, 8, SystemAllocPolicy>;
StringBufferVector stringBuffers_;
UniquePtr<NurseryDecommitTask> decommitTask;
// A cache of small C++-heap allocated blocks associated with this Nursery.
// This provided so as to provide cheap allocation/deallocation of
// out-of-line storage areas as used by WasmStructObject and
// WasmArrayObject, although the mechanism is general and not specific to
// these object types. Regarding lifetimes, because the cache holds only
// blocks that are not currently in use, it can be flushed at any point with
// no correctness impact, only a performance impact.
gc::MallocedBlockCache mallocedBlockCache_;
// Whether the previous collection tenured everything. This may be false if
// semispace is in use.
bool tenuredEverything;
friend class gc::GCRuntime;
friend class gc::TenuringTracer;
friend struct NurseryChunk;
MOZ_ALWAYS_INLINE bool Nursery::isInside(const void* p) const {
// TODO: Split this into separate methods.
// TODO: Do we ever need to check both?
return toSpace.isInside(p) || fromSpace.isInside(p);
MOZ_ALWAYS_INLINE bool Nursery::Space::isInside(const void* p) const {
for (auto* chunk : chunks_) {
if (uintptr_t(p) - uintptr_t(chunk) < gc::ChunkSize) {
return true;
return false;
} // namespace js
#endif // gc_Nursery_h