author Paul Bone <pbone@mozilla.com>
Thu, 11 Oct 2018 16:29:55 +1100
changeset 499863 a49f77c868163991c7d1bee5d73dd6716bbca577
parent 498386 d4ccb5aa7b1412d931779d1a1c3ea7d04394d105
child 503756 881a67c2941279c07463c782d5aa65e49e96d281
permissions -rw-r--r--
Bug 1498095 - Only poison the portion of the nursery we used r=jonco We have to do this both for sweeping and when setting the current chunk. We set the current chunk after sweeping so to have an effect when there's only one chunk (the main reason for this code) we need to do this correctly then also.

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * vim: set ts=8 sw=4 et tw=78:
 * 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/. */

#ifndef gc_Nursery_h
#define gc_Nursery_h

#include "mozilla/EnumeratedArray.h"
#include "mozilla/TimeStamp.h"

#include "js/Class.h"
#include "js/HeapAPI.h"
#include "js/TracingAPI.h"
#include "js/TypeDecls.h"
#include "js/Vector.h"

#define FOR_EACH_NURSERY_PROFILE_TIME(_)                                      \
   /* Key                       Header text */                                \
    _(Total,                    "total")                                      \
    _(CancelIonCompilations,    "canIon")                                     \
    _(TraceValues,              "mkVals")                                     \
    _(TraceCells,               "mkClls")                                     \
    _(TraceSlots,               "mkSlts")                                     \
    _(TraceWholeCells,          "mcWCll")                                     \
    _(TraceGenericEntries,      "mkGnrc")                                     \
    _(CheckHashTables,          "ckTbls")                                     \
    _(MarkRuntime,              "mkRntm")                                     \
    _(MarkDebugger,             "mkDbgr")                                     \
    _(SweepCaches,              "swpCch")                                     \
    _(CollectToFP,              "collct")                                     \
    _(ObjectsTenuredCallback,   "tenCB")                                      \
    _(Sweep,                    "sweep")                                      \
    _(UpdateJitActivations,     "updtIn")                                     \
    _(FreeMallocedBuffers,      "frSlts")                                     \
    _(ClearStoreBuffer,         "clrSB")                                      \
    _(ClearNursery,             "clear")                                      \
    _(Pretenure,                "pretnr")

template<typename T> class SharedMem;

namespace js {

class AutoLockGCBgAlloc;
class ObjectElements;
class PlainObject;
class NativeObject;
class Nursery;
struct NurseryChunk;
class HeapSlot;
class JSONPrinter;
class MapObject;
class SetObject;

namespace gc {
class AutoMaybeStartBackgroundAllocation;
class AutoTraceSession;
struct Cell;
class MinorCollectionTracer;
class RelocationOverlay;
struct TenureCountCache;
enum class AllocKind : uint8_t;
class TenuredCell;
} /* namespace gc */

namespace jit {
class MacroAssembler;
} // namespace jit

class TenuringTracer : public JSTracer
    friend class Nursery;
    Nursery& nursery_;

    // Amount of data moved to the tenured generation during collection.
    size_t tenuredSize;
    // Number of cells moved to the tenured generation.
    size_t tenuredCells;

    // These lists are threaded through the Nursery using the space from
    // already moved things. The lists are used to fix up the moved things and
    // to find things held live by intra-Nursery pointers.
    gc::RelocationOverlay* objHead;
    gc::RelocationOverlay** objTail;
    gc::RelocationOverlay* stringHead;
    gc::RelocationOverlay** stringTail;

    TenuringTracer(JSRuntime* rt, Nursery* nursery);

    Nursery& nursery() { return nursery_; }

    template <typename T> void traverse(T** thingp);
    template <typename T> void traverse(T* thingp);

    // The store buffers need to be able to call these directly.
    void traceObject(JSObject* src);
    void traceObjectSlots(NativeObject* nobj, uint32_t start, uint32_t length);
    void traceSlots(JS::Value* vp, uint32_t nslots);
    void traceString(JSString* src);

    inline void insertIntoObjectFixupList(gc::RelocationOverlay* entry);
    inline void insertIntoStringFixupList(gc::RelocationOverlay* entry);

    template <typename T>
    inline T* allocTenured(JS::Zone* zone, gc::AllocKind kind);

    inline JSObject* movePlainObjectToTenured(PlainObject* src);
    JSObject* moveToTenuredSlow(JSObject* src);
    JSString* moveToTenured(JSString* src);

    size_t moveElementsToTenured(NativeObject* dst, NativeObject* src, gc::AllocKind dstKind);
    size_t moveSlotsToTenured(NativeObject* dst, NativeObject* src);
    size_t moveStringToTenured(JSString* dst, JSString* src, gc::AllocKind dstKind);

    void traceSlots(JS::Value* vp, JS::Value* end);

 * Classes with JSCLASS_SKIP_NURSERY_FINALIZE or Wrapper classes with
 * CROSS_COMPARTMENT flags will not have their finalizer called if they are
 * nursery allocated and not promoted to the tenured heap. The finalizers for
 * these classes must do nothing except free data which was allocated via
 * Nursery::allocateBuffer.
inline bool
CanNurseryAllocateFinalizedClass(const js::Class* const clasp)
    return clasp->flags & JSCLASS_SKIP_NURSERY_FINALIZE;

class Nursery
    static const size_t Alignment = gc::ChunkSize;
    static const size_t ChunkShift = gc::ChunkShift;

    struct alignas(gc::CellAlignBytes) CellAlignedByte {
        char byte;

    struct StringLayout {
        JS::Zone* zone;
        CellAlignedByte cell;

    explicit Nursery(JSRuntime* rt);

    MOZ_MUST_USE bool init(uint32_t maxNurseryBytes, AutoLockGCBgAlloc& lock);

    unsigned chunkCountLimit() const { return chunkCountLimit_; }

    // Number of allocated (ready to use) chunks.
    unsigned allocatedChunkCount() const { return chunks_.length(); }

    // Total number of chunks and the capacity of the nursery. Chunks will be
    // lazilly allocated and added to the chunks array up to this limit, after
    // that the nursery must be collected, this limit may be raised during
    // collection.
    unsigned maxChunkCount() const { return maxChunkCount_; }

    bool exists() const { return chunkCountLimit() != 0; }

    void enable();
    void disable();
    bool isEnabled() const { return maxChunkCount() != 0; }

    void enableStrings();
    void disableStrings();
    bool canAllocateStrings() const { return canAllocateStrings_; }

    /* 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.
    MOZ_ALWAYS_INLINE bool isInside(gc::Cell* cellp) const = delete;
    MOZ_ALWAYS_INLINE bool isInside(const void* p) const {
        for (auto chunk : chunks_) {
            if (uintptr_t(p) - uintptr_t(chunk) < gc::ChunkSize) {
                return true;
        return false;

    template<typename T>
    inline bool isInside(const SharedMem<T>& p) const;

     * Allocate and return a pointer to a new GC object with its |slots|
     * pointer pre-filled. Returns nullptr if the Nursery is full.
    JSObject* allocateObject(JSContext* cx, size_t size, size_t numDynamic, const js::Class* clasp);

     * Allocate and return a pointer to a new string. Returns nullptr if the
     * Nursery is full.
    gc::Cell* allocateString(JS::Zone* zone, size_t size, gc::AllocKind kind);

     * String zones are stored just before the string in nursery memory.
    static JS::Zone* getStringZone(const JSString* str) {
#ifdef DEBUG
        auto cell = reinterpret_cast<const js::gc::Cell*>(str); // JSString type is incomplete here
        MOZ_ASSERT(js::gc::IsInsideNursery(cell), "getStringZone must be passed a nursery string");

        auto layout = reinterpret_cast<const uint8_t*>(str) - offsetof(StringLayout, cell);
        return reinterpret_cast<const StringLayout*>(layout)->zone;

    static size_t stringHeaderSize() {
        return offsetof(StringLayout, cell);

    /* Allocate a buffer for a given zone, using the nursery if possible. */
    void* allocateBuffer(JS::Zone* zone, size_t nbytes);

     * Allocate a buffer for a given object, using the nursery if possible and
     * obj is in the nursery.
    void* allocateBuffer(JSObject* obj, size_t nbytes);

     * Allocate a buffer for a given object, always using the nursery if obj is
     * in the nursery. The requested size must be less than or equal to
     * MaxNurseryBufferSize.
    void* allocateBufferSameLocation(JSObject* obj, size_t nbytes);

    /* Resize an existing object buffer. */
    void* reallocateBuffer(JSObject* obj, void* oldBuffer,
                           size_t oldBytes, size_t newBytes);

    /* Free an object buffer. */
    void freeBuffer(void* buffer);

    /* The maximum number of bytes allowed to reside in nursery buffers. */
    static const size_t MaxNurseryBufferSize = 1024;

    /* Do a minor collection. */
    void collect(JS::gcreason::Reason 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.
    MOZ_ALWAYS_INLINE MOZ_MUST_USE static bool getForwardedPointer(js::gc::Cell** ref);

    /* Forward a slots/elements pointer stored in an Ion frame. */
    void forwardBufferPointer(HeapSlot** pSlotsElems);

    inline void maybeSetForwardingPointer(JSTracer* trc, void* oldData, void* newData, bool direct);
    inline void setForwardingPointerWhileTenuring(void* oldData, void* newData, bool direct);

     * 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.
    bool registerMallocedBuffer(void* buffer);

    /* Mark a malloced buffer as no longer needing to be freed. */
    void removeMallocedBuffer(void* buffer) {

    void waitBackgroundFreeEnd();

    MOZ_MUST_USE bool addedUniqueIdToCell(gc::Cell* cell) {
        return cellsWithUid_.append(cell);

    MOZ_MUST_USE bool queueDictionaryModeObjectToSweep(NativeObject* obj);

    size_t sizeOfHeapCommitted() const {
        return allocatedChunkCount() * gc::ChunkSize;
    size_t sizeOfMallocedBuffers(mozilla::MallocSizeOf mallocSizeOf) const {
        size_t total = 0;
        for (MallocedBuffersSet::Range r = mallocedBuffers.all(); !r.empty(); r.popFront()) {
            total += mallocSizeOf(r.front());
        total += mallocedBuffers.shallowSizeOfExcludingThis(mallocSizeOf);
        return total;

    // The number of bytes from the start position to the end of the nursery.
    // pass maxChunkCount(), allocatedChunkCount() or chunkCountLimit()
    // to calculate the nursery size, current lazy-allocated size or nursery
    // limit respectively.
    size_t spaceToEnd(unsigned chunkCount) const;

    // Free space remaining, not counting chunk trailers.
    MOZ_ALWAYS_INLINE size_t freeSpace() const {
        MOZ_ASSERT(currentEnd_ - position_ <= NurseryChunkUsableSize);
        return (currentEnd_ - position_) +
               (maxChunkCount() - currentChunk_ - 1) * NurseryChunkUsableSize;

#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. */
    static void printProfileHeader();

    /* Print total profile times on shutdown. */
    void printTotalProfileTimes();

    void* addressOfPosition() const { return (void**)&position_; }
    const void* addressOfCurrentEnd() const { return (void**)&currentEnd_; }
    const void* addressOfCurrentStringEnd() const {
        return (void*)&currentStringEnd_;

    void requestMinorGC(JS::gcreason::Reason reason) const;

    bool minorGCRequested() const { return minorGCTriggerReason_ != JS::gcreason::NO_REASON; }
    JS::gcreason::Reason minorGCTriggerReason() const { return minorGCTriggerReason_; }
    void clearMinorGCRequest() { minorGCTriggerReason_ = JS::gcreason::NO_REASON; }

    bool needIdleTimeCollection() 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);

    /* The amount of space in the mapped nursery available to allocations. */
    static const size_t NurseryChunkUsableSize = gc::ChunkSize - gc::ChunkTrailerSize;

    JSRuntime* runtime_;

    /* Vector of allocated chunks to allocate from. */
    Vector<NurseryChunk*, 0, SystemAllocPolicy> chunks_;

    /* Pointer to the first unallocated byte in the nursery. */
    uintptr_t position_;

    /* Pointer to the logical start of the Nursery. */
    unsigned currentStartChunk_;
    uintptr_t currentStartPosition_;

    /* Pointer to the last byte of space in the current chunk. */
    uintptr_t currentEnd_;

     * Pointer to the last byte of space in the current chunk, or nullptr if we
     * are not allocating strings in the nursery.
    uintptr_t currentStringEnd_;

    /* The index of the chunk that is currently being allocated from. */
    unsigned currentChunk_;

     * The nursery may grow the chunks_ vector up to this size without a
     * collection.  This allows the nursery to grow lazilly.  This limit may
     * change during maybeResizeNursery() each collection.
    unsigned maxChunkCount_;

     * This limit is fixed by configuration.  It represents the maximum size
     * the nursery is permitted to tune itself to in maybeResizeNursery();
    unsigned chunkCountLimit_;

    mozilla::TimeDuration timeInChunkAlloc_;

    /* Report minor collections taking at least this long, if enabled. */
    mozilla::TimeDuration profileThreshold_;
    bool enableProfiling_;

    /* Whether we will nursery-allocate strings. */
    bool canAllocateStrings_;

    /* Report ObjectGroups with at least this many instances tenured. */
    int64_t reportTenurings_;

     * Whether and why a collection of this nursery has been requested. This is
     * mutable as it is set by the store buffer, which otherwise cannot modify
     * anything in the nursery.
    mutable JS::gcreason::Reason minorGCTriggerReason_;

    /* Profiling data. */

    enum class ProfileKey
#define DEFINE_TIME_KEY(name, text)                                           \

    using ProfileTimes =
        mozilla::EnumeratedArray<ProfileKey, ProfileKey::KeyCount, mozilla::TimeStamp>;
    using ProfileDurations =
        mozilla::EnumeratedArray<ProfileKey, ProfileKey::KeyCount, mozilla::TimeDuration>;

    ProfileTimes startTimes_;
    ProfileDurations profileDurations_;
    ProfileDurations totalDurations_;

    struct {
        JS::gcreason::Reason reason = JS::gcreason::NO_REASON;
        size_t nurseryCapacity = 0;
        size_t nurseryLazyCapacity = 0;
        size_t nurseryUsedBytes = 0;
        size_t tenuredBytes = 0;
        size_t tenuredCells = 0;
    } previousGC;

     * 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.
    calcPromotionRate(bool *validForTenuring) const;

     * The set of externally malloced buffers potentially kept live by objects
     * stored in the nursery. Any external buffers that do not belong to a
     * tenured thing at the end of a minor GC must be freed.
    typedef HashSet<void*, PointerHasher<void*>, SystemAllocPolicy> MallocedBuffersSet;
    MallocedBuffersSet mallocedBuffers;

    /* A task structure used to free the malloced bufers on a background thread. */
    struct FreeMallocedBuffersTask;
    FreeMallocedBuffersTask* freeMallocedBuffersTask;

     * 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.
    typedef HashMap<void*, void*, PointerHasher<void*>, SystemAllocPolicy> ForwardedBufferMap;
    ForwardedBufferMap forwardedBuffers;

     * 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 = Vector<gc::Cell*, 8, SystemAllocPolicy>;
    CellsWithUniqueIdVector cellsWithUid_;

    using NativeObjectVector = Vector<NativeObject*, 0, SystemAllocPolicy>;
    NativeObjectVector dictionaryModeObjects_;

     * Lists of map and set objects allocated in the nursery or with iterators
     * allocated there. Such objects need to be swept after minor GC.
    Vector<MapObject*, 0, SystemAllocPolicy> mapsWithNurseryMemory_;
    Vector<SetObject*, 0, SystemAllocPolicy> setsWithNurseryMemory_;

#ifdef JS_GC_ZEAL
    struct Canary;
    Canary* lastCanary_;

    NurseryChunk& chunk(unsigned index) const {
        return *chunks_[index];

     * Set the current chunk. This updates the currentChunk_, position_
     * currentEnd_ and currentStringEnd_ values as approprite. It'll also
     * poison the chunk, either a portion of the chunk if it is already the
     * current chunk, or the whole chunk if fullPoison is true or it is not
     * the current chunk.
    void setCurrentChunk(unsigned chunkno, bool fullPoison = false);
    void setStartPosition();

     * Allocate the next chunk, or the first chunk for initialization.
     * Callers will probably want to call setCurrentChunk(0) next.
    MOZ_MUST_USE bool allocateNextChunk(unsigned chunkno,
        AutoLockGCBgAlloc& lock);

    MOZ_ALWAYS_INLINE uintptr_t currentEnd() const;

    uintptr_t position() const { return position_; }

    JSRuntime* runtime() const { return runtime_; }

    /* Common internal allocator function. */
    void* allocate(size_t size);

    void doCollection(JS::gcreason::Reason reason, gc::TenureCountCache& tenureCounts);

     * Move the object at |src| in the Nursery to an already-allocated cell
     * |dst| in Tenured.
    void collectToFixedPoint(TenuringTracer& trc, gc::TenureCountCache& tenureCounts);

    /* 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);

    /* Free malloced pointers owned by freed things in the nursery. */
    void freeMallocedBuffers();

     * Updates pointers to nursery objects that have been tenured and discards
     * pointers to objects that have been freed.
    void sweep(JSTracer* trc);

     * Frees all non-live nursery-allocated things at the end of a minor
     * collection.
    void clear();

    void sweepDictionaryModeObjects();
    void sweepMapAndSetObjects();

    /* Change the allocable space provided by the nursery. */
    void maybeResizeNursery(JS::gcreason::Reason reason);
    void growAllocableSpace();
    void shrinkAllocableSpace(unsigned newCount);
    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(unsigned firstFreeChunk);

    /* Profile recording and printing. */
    void maybeClearProfileDurations();
    void startProfile(ProfileKey key);
    void endProfile(ProfileKey key);
    static void printProfileDurations(const ProfileDurations& times);

    friend class TenuringTracer;
    friend class gc::MinorCollectionTracer;
    friend class jit::MacroAssembler;
    friend struct NurseryChunk;

} /* namespace js */

#endif /* gc_Nursery_h */