/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * vim: set ts=8 sts=4 et sw=4 tw=99:
 * 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/. */

/* JS Garbage Collector. */

#ifndef jsgc_h
#define jsgc_h

#include "mozilla/Atomics.h"
#include "mozilla/DebugOnly.h"
#include "mozilla/MemoryReporting.h"

#include "jslock.h"
#include "jsobj.h"

#include "js/GCAPI.h"
#include "js/SliceBudget.h"
#include "js/Vector.h"

class JSAtom;
struct JSCompartment;
class JSFlatString;
class JSLinearString;

namespace js {

class ArgumentsObject;
class ArrayBufferObject;
class ArrayBufferViewObject;
class SharedArrayBufferObject;
class BaseShape;
class DebugScopeObject;
class GlobalObject;
class LazyScript;
class Nursery;
class PropertyName;
class ScopeObject;
class Shape;
class UnownedBaseShape;

unsigned GetCPUCount();

enum HeapState {
    Idle,             // doing nothing with the GC heap
    Tracing,          // tracing the GC heap without collecting, e.g. IterateCompartments()
    MajorCollecting,  // doing a GC of the major heap
    MinorCollecting   // doing a GC of the minor heap (nursery)
};

namespace jit {
    class JitCode;
}

namespace gc {

enum State {
    NO_INCREMENTAL,
    MARK_ROOTS,
    MARK,
    SWEEP,
    INVALID
};

class ChunkPool {
    Chunk   *emptyChunkListHead;
    size_t  emptyCount;

  public:
    ChunkPool()
      : emptyChunkListHead(nullptr),
        emptyCount(0) { }

    size_t getEmptyCount() const {
        return emptyCount;
    }

    /* Must be called with the GC lock taken. */
    inline Chunk *get(JSRuntime *rt);

    /* Must be called either during the GC or with the GC lock taken. */
    inline void put(Chunk *chunk);

    /*
     * Return the list of chunks that can be released outside the GC lock.
     * Must be called either during the GC or with the GC lock taken.
     */
    Chunk *expire(JSRuntime *rt, bool shrinkBuffers, bool releaseAll);

    /* Must be called with the GC lock taken. */
    void expireAndFree(JSRuntime *rt, bool releaseAll);
};

static inline JSGCTraceKind
MapAllocToTraceKind(AllocKind kind)
{
    static const JSGCTraceKind map[] = {
        JSTRACE_OBJECT,     /* FINALIZE_OBJECT0 */
        JSTRACE_OBJECT,     /* FINALIZE_OBJECT0_BACKGROUND */
        JSTRACE_OBJECT,     /* FINALIZE_OBJECT2 */
        JSTRACE_OBJECT,     /* FINALIZE_OBJECT2_BACKGROUND */
        JSTRACE_OBJECT,     /* FINALIZE_OBJECT4 */
        JSTRACE_OBJECT,     /* FINALIZE_OBJECT4_BACKGROUND */
        JSTRACE_OBJECT,     /* FINALIZE_OBJECT8 */
        JSTRACE_OBJECT,     /* FINALIZE_OBJECT8_BACKGROUND */
        JSTRACE_OBJECT,     /* FINALIZE_OBJECT12 */
        JSTRACE_OBJECT,     /* FINALIZE_OBJECT12_BACKGROUND */
        JSTRACE_OBJECT,     /* FINALIZE_OBJECT16 */
        JSTRACE_OBJECT,     /* FINALIZE_OBJECT16_BACKGROUND */
        JSTRACE_SCRIPT,     /* FINALIZE_SCRIPT */
        JSTRACE_LAZY_SCRIPT,/* FINALIZE_LAZY_SCRIPT */
        JSTRACE_SHAPE,      /* FINALIZE_SHAPE */
        JSTRACE_BASE_SHAPE, /* FINALIZE_BASE_SHAPE */
        JSTRACE_TYPE_OBJECT,/* FINALIZE_TYPE_OBJECT */
        JSTRACE_STRING,     /* FINALIZE_FAT_INLINE_STRING */
        JSTRACE_STRING,     /* FINALIZE_STRING */
        JSTRACE_STRING,     /* FINALIZE_EXTERNAL_STRING */
        JSTRACE_JITCODE,    /* FINALIZE_JITCODE */
    };
    JS_STATIC_ASSERT(JS_ARRAY_LENGTH(map) == FINALIZE_LIMIT);
    return map[kind];
}

template <typename T> struct MapTypeToTraceKind {};
template <> struct MapTypeToTraceKind<ObjectImpl>       { static const JSGCTraceKind kind = JSTRACE_OBJECT; };
template <> struct MapTypeToTraceKind<JSObject>         { static const JSGCTraceKind kind = JSTRACE_OBJECT; };
template <> struct MapTypeToTraceKind<JSFunction>       { static const JSGCTraceKind kind = JSTRACE_OBJECT; };
template <> struct MapTypeToTraceKind<ArgumentsObject>  { static const JSGCTraceKind kind = JSTRACE_OBJECT; };
template <> struct MapTypeToTraceKind<ArrayBufferObject>{ static const JSGCTraceKind kind = JSTRACE_OBJECT; };
template <> struct MapTypeToTraceKind<ArrayBufferViewObject>{ static const JSGCTraceKind kind = JSTRACE_OBJECT; };
template <> struct MapTypeToTraceKind<SharedArrayBufferObject>{ static const JSGCTraceKind kind = JSTRACE_OBJECT; };
template <> struct MapTypeToTraceKind<DebugScopeObject> { static const JSGCTraceKind kind = JSTRACE_OBJECT; };
template <> struct MapTypeToTraceKind<GlobalObject>     { static const JSGCTraceKind kind = JSTRACE_OBJECT; };
template <> struct MapTypeToTraceKind<ScopeObject>      { static const JSGCTraceKind kind = JSTRACE_OBJECT; };
template <> struct MapTypeToTraceKind<JSScript>         { static const JSGCTraceKind kind = JSTRACE_SCRIPT; };
template <> struct MapTypeToTraceKind<LazyScript>       { static const JSGCTraceKind kind = JSTRACE_LAZY_SCRIPT; };
template <> struct MapTypeToTraceKind<Shape>            { static const JSGCTraceKind kind = JSTRACE_SHAPE; };
template <> struct MapTypeToTraceKind<BaseShape>        { static const JSGCTraceKind kind = JSTRACE_BASE_SHAPE; };
template <> struct MapTypeToTraceKind<UnownedBaseShape> { static const JSGCTraceKind kind = JSTRACE_BASE_SHAPE; };
template <> struct MapTypeToTraceKind<types::TypeObject>{ static const JSGCTraceKind kind = JSTRACE_TYPE_OBJECT; };
template <> struct MapTypeToTraceKind<JSAtom>           { static const JSGCTraceKind kind = JSTRACE_STRING; };
template <> struct MapTypeToTraceKind<JSString>         { static const JSGCTraceKind kind = JSTRACE_STRING; };
template <> struct MapTypeToTraceKind<JSFlatString>     { static const JSGCTraceKind kind = JSTRACE_STRING; };
template <> struct MapTypeToTraceKind<JSLinearString>   { static const JSGCTraceKind kind = JSTRACE_STRING; };
template <> struct MapTypeToTraceKind<PropertyName>     { static const JSGCTraceKind kind = JSTRACE_STRING; };
template <> struct MapTypeToTraceKind<jit::JitCode>     { static const JSGCTraceKind kind = JSTRACE_JITCODE; };

/* Return a printable string for the given kind, for diagnostic purposes. */
const char *
TraceKindAsAscii(JSGCTraceKind kind);

/* Map from C++ type to finalize kind. JSObject does not have a 1:1 mapping, so must use Arena::thingSize. */
template <typename T> struct MapTypeToFinalizeKind {};
template <> struct MapTypeToFinalizeKind<JSScript>          { static const AllocKind kind = FINALIZE_SCRIPT; };
template <> struct MapTypeToFinalizeKind<LazyScript>        { static const AllocKind kind = FINALIZE_LAZY_SCRIPT; };
template <> struct MapTypeToFinalizeKind<Shape>             { static const AllocKind kind = FINALIZE_SHAPE; };
template <> struct MapTypeToFinalizeKind<BaseShape>         { static const AllocKind kind = FINALIZE_BASE_SHAPE; };
template <> struct MapTypeToFinalizeKind<types::TypeObject> { static const AllocKind kind = FINALIZE_TYPE_OBJECT; };
template <> struct MapTypeToFinalizeKind<JSFatInlineString> { static const AllocKind kind = FINALIZE_FAT_INLINE_STRING; };
template <> struct MapTypeToFinalizeKind<JSString>          { static const AllocKind kind = FINALIZE_STRING; };
template <> struct MapTypeToFinalizeKind<JSExternalString>  { static const AllocKind kind = FINALIZE_EXTERNAL_STRING; };
template <> struct MapTypeToFinalizeKind<jit::JitCode>      { static const AllocKind kind = FINALIZE_JITCODE; };

#if defined(JSGC_GENERATIONAL) || defined(DEBUG)
static inline bool
IsNurseryAllocable(AllocKind kind)
{
    JS_ASSERT(kind >= 0 && unsigned(kind) < FINALIZE_LIMIT);
    static const bool map[] = {
        false,     /* FINALIZE_OBJECT0 */
        true,      /* FINALIZE_OBJECT0_BACKGROUND */
        false,     /* FINALIZE_OBJECT2 */
        true,      /* FINALIZE_OBJECT2_BACKGROUND */
        false,     /* FINALIZE_OBJECT4 */
        true,      /* FINALIZE_OBJECT4_BACKGROUND */
        false,     /* FINALIZE_OBJECT8 */
        true,      /* FINALIZE_OBJECT8_BACKGROUND */
        false,     /* FINALIZE_OBJECT12 */
        true,      /* FINALIZE_OBJECT12_BACKGROUND */
        false,     /* FINALIZE_OBJECT16 */
        true,      /* FINALIZE_OBJECT16_BACKGROUND */
        false,     /* FINALIZE_SCRIPT */
        false,     /* FINALIZE_LAZY_SCRIPT */
        false,     /* FINALIZE_SHAPE */
        false,     /* FINALIZE_BASE_SHAPE */
        false,     /* FINALIZE_TYPE_OBJECT */
        false,     /* FINALIZE_FAT_INLINE_STRING */
        false,     /* FINALIZE_STRING */
        false,     /* FINALIZE_EXTERNAL_STRING */
        false,     /* FINALIZE_JITCODE */
    };
    JS_STATIC_ASSERT(JS_ARRAY_LENGTH(map) == FINALIZE_LIMIT);
    return map[kind];
}
#endif

static inline bool
IsBackgroundFinalized(AllocKind kind)
{
    JS_ASSERT(kind >= 0 && unsigned(kind) < FINALIZE_LIMIT);
    static const bool map[] = {
        false,     /* FINALIZE_OBJECT0 */
        true,      /* FINALIZE_OBJECT0_BACKGROUND */
        false,     /* FINALIZE_OBJECT2 */
        true,      /* FINALIZE_OBJECT2_BACKGROUND */
        false,     /* FINALIZE_OBJECT4 */
        true,      /* FINALIZE_OBJECT4_BACKGROUND */
        false,     /* FINALIZE_OBJECT8 */
        true,      /* FINALIZE_OBJECT8_BACKGROUND */
        false,     /* FINALIZE_OBJECT12 */
        true,      /* FINALIZE_OBJECT12_BACKGROUND */
        false,     /* FINALIZE_OBJECT16 */
        true,      /* FINALIZE_OBJECT16_BACKGROUND */
        false,     /* FINALIZE_SCRIPT */
        false,     /* FINALIZE_LAZY_SCRIPT */
        true,      /* FINALIZE_SHAPE */
        true,      /* FINALIZE_BASE_SHAPE */
        true,      /* FINALIZE_TYPE_OBJECT */
        true,      /* FINALIZE_FAT_INLINE_STRING */
        true,      /* FINALIZE_STRING */
        false,     /* FINALIZE_EXTERNAL_STRING */
        false,     /* FINALIZE_JITCODE */
    };
    JS_STATIC_ASSERT(JS_ARRAY_LENGTH(map) == FINALIZE_LIMIT);
    return map[kind];
}

static inline bool
CanBeFinalizedInBackground(gc::AllocKind kind, const Class *clasp)
{
    JS_ASSERT(kind <= gc::FINALIZE_OBJECT_LAST);
    /* If the class has no finalizer or a finalizer that is safe to call on
     * a different thread, we change the finalize kind. For example,
     * FINALIZE_OBJECT0 calls the finalizer on the main thread,
     * FINALIZE_OBJECT0_BACKGROUND calls the finalizer on the gcHelperThread.
     * IsBackgroundFinalized is called to prevent recursively incrementing
     * the finalize kind; kind may already be a background finalize kind.
     */
    return (!gc::IsBackgroundFinalized(kind) &&
            (!clasp->finalize || (clasp->flags & JSCLASS_BACKGROUND_FINALIZE)));
}

inline JSGCTraceKind
GetGCThingTraceKind(const void *thing);

/* Capacity for slotsToThingKind */
const size_t SLOTS_TO_THING_KIND_LIMIT = 17;

extern const AllocKind slotsToThingKind[];

/* Get the best kind to use when making an object with the given slot count. */
static inline AllocKind
GetGCObjectKind(size_t numSlots)
{
    if (numSlots >= SLOTS_TO_THING_KIND_LIMIT)
        return FINALIZE_OBJECT16;
    return slotsToThingKind[numSlots];
}

/* As for GetGCObjectKind, but for dense array allocation. */
static inline AllocKind
GetGCArrayKind(size_t numSlots)
{
    /*
     * Dense arrays can use their fixed slots to hold their elements array
     * (less two Values worth of ObjectElements header), but if more than the
     * maximum number of fixed slots is needed then the fixed slots will be
     * unused.
     */
    JS_STATIC_ASSERT(ObjectElements::VALUES_PER_HEADER == 2);
    if (numSlots > JSObject::NELEMENTS_LIMIT || numSlots + 2 >= SLOTS_TO_THING_KIND_LIMIT)
        return FINALIZE_OBJECT2;
    return slotsToThingKind[numSlots + 2];
}

static inline AllocKind
GetGCObjectFixedSlotsKind(size_t numFixedSlots)
{
    JS_ASSERT(numFixedSlots < SLOTS_TO_THING_KIND_LIMIT);
    return slotsToThingKind[numFixedSlots];
}

static inline AllocKind
GetBackgroundAllocKind(AllocKind kind)
{
    JS_ASSERT(!IsBackgroundFinalized(kind));
    JS_ASSERT(kind <= FINALIZE_OBJECT_LAST);
    return (AllocKind) (kind + 1);
}

/*
 * Try to get the next larger size for an object, keeping BACKGROUND
 * consistent.
 */
static inline bool
TryIncrementAllocKind(AllocKind *kindp)
{
    size_t next = size_t(*kindp) + 2;
    if (next >= size_t(FINALIZE_OBJECT_LIMIT))
        return false;
    *kindp = AllocKind(next);
    return true;
}

/* Get the number of fixed slots and initial capacity associated with a kind. */
static inline size_t
GetGCKindSlots(AllocKind thingKind)
{
    /* Using a switch in hopes that thingKind will usually be a compile-time constant. */
    switch (thingKind) {
      case FINALIZE_OBJECT0:
      case FINALIZE_OBJECT0_BACKGROUND:
        return 0;
      case FINALIZE_OBJECT2:
      case FINALIZE_OBJECT2_BACKGROUND:
        return 2;
      case FINALIZE_OBJECT4:
      case FINALIZE_OBJECT4_BACKGROUND:
        return 4;
      case FINALIZE_OBJECT8:
      case FINALIZE_OBJECT8_BACKGROUND:
        return 8;
      case FINALIZE_OBJECT12:
      case FINALIZE_OBJECT12_BACKGROUND:
        return 12;
      case FINALIZE_OBJECT16:
      case FINALIZE_OBJECT16_BACKGROUND:
        return 16;
      default:
        MOZ_ASSUME_UNREACHABLE("Bad object finalize kind");
    }
}

static inline size_t
GetGCKindSlots(AllocKind thingKind, const Class *clasp)
{
    size_t nslots = GetGCKindSlots(thingKind);

    /* An object's private data uses the space taken by its last fixed slot. */
    if (clasp->flags & JSCLASS_HAS_PRIVATE) {
        JS_ASSERT(nslots > 0);
        nslots--;
    }

    /*
     * Functions have a larger finalize kind than FINALIZE_OBJECT to reserve
     * space for the extra fields in JSFunction, but have no fixed slots.
     */
    if (clasp == FunctionClassPtr)
        nslots = 0;

    return nslots;
}

// Class to assist in triggering background chunk allocation. This cannot be done
// while holding the GC or worker thread state lock due to lock ordering issues.
// As a result, the triggering is delayed using this class until neither of the
// above locks is held.
class AutoMaybeStartBackgroundAllocation;

/*
 * Arena lists have a head and a cursor. The cursor conceptually lies on arena
 * boundaries, i.e. before the first arena, between two arenas, or after the
 * last arena.
 *
 * Normally the arena following the cursor is the first arena in the list with
 * some free things and all arenas before the cursor are fully allocated. (And
 * if the cursor is at the end of the list, then all the arenas are full.)
 *
 * However, the arena currently being allocated from is considered full while
 * its list of free spans is moved into the freeList. Therefore, during GC or
 * cell enumeration, when an unallocated freeList is moved back to the arena,
 * we can see an arena with some free cells before the cursor.
 *
 * Arenas following the cursor should not be full.
 */
class ArenaList {
    // The cursor is implemented via an indirect pointer, |cursorp_|, to allow
    // for efficient list insertion at the cursor point and other list
    // manipulations.
    //
    // - If the list is empty: |head| is null, |cursorp_| points to |head|, and
    //   therefore |*cursorp_| is null.
    //
    // - If the list is not empty: |head| is non-null, and...
    //
    //   - If the cursor is at the start of the list: |cursorp_| points to
    //     |head|, and therefore |*cursorp_| points to the first arena.
    //
    //   - If cursor is at the end of the list: |cursorp_| points to the |next|
    //     field of the last arena, and therefore |*cursorp_| is null.
    //
    //   - If the cursor is at neither the start nor the end of the list:
    //     |cursorp_| points to the |next| field of the arena preceding the
    //     cursor, and therefore |*cursorp_| points to the arena following the
    //     cursor.
    //
    // |cursorp_| is never null.
    //
    ArenaHeader     *head_;
    ArenaHeader     **cursorp_;

  public:
    ArenaList() {
        clear();
    }

    // This does checking just of |head_| and |cursorp_|.
    void check() const {
#ifdef DEBUG
        // If the list is empty, it must have this form.
        JS_ASSERT_IF(!head_, cursorp_ == &head_);

        // If there's an arena following the cursor, it must not be full.
        ArenaHeader *cursor = *cursorp_;
        JS_ASSERT_IF(cursor, cursor->hasFreeThings());
#endif
    }

    // This does checking involving all the arenas in the list.
    void deepCheck() const {
#ifdef DEBUG
        check();
        // All full arenas must precede all non-full arenas.
        //
        // XXX: this is currently commented out because it fails moderately
        // often. I'm not sure if this is because (a) it's not true that all
        // full arenas must precede all non-full arenas, or (b) we have some
        // defective list-handling code.
        //
//      bool havePassedFullArenas = false;
//      for (ArenaHeader *aheader = head_; aheader; aheader = aheader->next) {
//          if (havePassedFullArenas) {
//              JS_ASSERT(aheader->hasFreeThings());
//          } else if (aheader->hasFreeThings()) {
//              havePassedFullArenas = true;
//          }
//      }
#endif
    }

    void clear() {
        head_ = nullptr;
        cursorp_ = &head_;
        check();
    }

    bool isEmpty() const {
        check();
        return !head_;
    }

    // This returns nullptr if the list is empty.
    ArenaHeader *head() const {
        check();
        return head_;
    }

    bool isCursorAtEnd() const {
        check();
        return !*cursorp_;
    }

    // This can return nullptr.
    ArenaHeader *arenaAfterCursor() const {
        check();
        return *cursorp_;
    }

    // This moves the cursor past |aheader|. |aheader| must be an arena within
    // this list.
    void moveCursorPast(ArenaHeader *aheader) {
        cursorp_ = &aheader->next;
        check();
    }

    // This does two things.
    // - Inserts |a| at the cursor.
    // - Leaves the cursor sitting just before |a|, if |a| is not full, or just
    //   after |a|, if |a| is full.
    //
    void insertAtCursor(ArenaHeader *a) {
        check();
        a->next = *cursorp_;
        *cursorp_ = a;
        // At this point, the cursor is sitting before |a|. Move it after |a|
        // if necessary.
        if (!a->hasFreeThings())
            cursorp_ = &a->next;
        check();
    }

    // This inserts |a| at the start of the list, and doesn't change the
    // cursor.
    void insertAtStart(ArenaHeader *a) {
        check();
        a->next = head_;
        if (isEmpty())
            cursorp_ = &a->next;        // The cursor remains null.
        head_ = a;
        check();
    }

    // Appends |list|. |this|'s cursor must be at the end.
    void appendToListWithCursorAtEnd(ArenaList &other) {
        JS_ASSERT(isCursorAtEnd());
        deepCheck();
        other.deepCheck();
        if (!other.isEmpty()) {
            // Because |this|'s cursor is at the end, |cursorp_| points to the
            // list-ending null. So this assignment appends |other| to |this|.
            *cursorp_ = other.head_;

            // If |other|'s cursor isn't at the start of the list, then update
            // |this|'s cursor accordingly.
            if (other.cursorp_ != &other.head_)
                cursorp_ = other.cursorp_;
        }
        deepCheck();
    }
};

class ArenaLists
{
    /*
     * For each arena kind its free list is represented as the first span with
     * free things. Initially all the spans are initialized as empty. After we
     * find a new arena with available things we move its first free span into
     * the list and set the arena as fully allocated. way we do not need to
     * update the arena header after the initial allocation. When starting the
     * GC we only move the head of the of the list of spans back to the arena
     * only for the arena that was not fully allocated.
     */
    FreeList       freeLists[FINALIZE_LIMIT];

    ArenaList      arenaLists[FINALIZE_LIMIT];

    /*
     * The background finalization adds the finalized arenas to the list at
     * the cursor position. backgroundFinalizeState controls the interaction
     * between the GC lock and the access to the list from the allocation
     * thread.
     *
     * BFS_DONE indicates that the finalizations is not running or cannot
     * affect this arena list. The allocation thread can access the list
     * outside the GC lock.
     *
     * In BFS_RUN and BFS_JUST_FINISHED the allocation thread must take the
     * lock. The former indicates that the finalization still runs. The latter
     * signals that finalization just added to the list finalized arenas. In
     * that case the lock effectively serves as a read barrier to ensure that
     * the allocation thread sees all the writes done during finalization.
     */
    enum BackgroundFinalizeStateEnum {
        BFS_DONE,
        BFS_RUN,
        BFS_JUST_FINISHED
    };

    typedef mozilla::Atomic<BackgroundFinalizeStateEnum, mozilla::ReleaseAcquire>
        BackgroundFinalizeState;

    BackgroundFinalizeState backgroundFinalizeState[FINALIZE_LIMIT];

  public:
    /* For each arena kind, a list of arenas remaining to be swept. */
    ArenaHeader *arenaListsToSweep[FINALIZE_LIMIT];

    /* Shape arenas to be swept in the foreground. */
    ArenaHeader *gcShapeArenasToSweep;

  public:
    ArenaLists() {
        for (size_t i = 0; i != FINALIZE_LIMIT; ++i)
            freeLists[i].initAsEmpty();
        for (size_t i = 0; i != FINALIZE_LIMIT; ++i)
            backgroundFinalizeState[i] = BFS_DONE;
        for (size_t i = 0; i != FINALIZE_LIMIT; ++i)
            arenaListsToSweep[i] = nullptr;
        gcShapeArenasToSweep = nullptr;
    }

    ~ArenaLists() {
        for (size_t i = 0; i != FINALIZE_LIMIT; ++i) {
            /*
             * We can only call this during the shutdown after the last GC when
             * the background finalization is disabled.
             */
            JS_ASSERT(backgroundFinalizeState[i] == BFS_DONE);
            ArenaHeader *next;
            for (ArenaHeader *aheader = arenaLists[i].head(); aheader; aheader = next) {
                // Copy aheader->next before releasing.
                next = aheader->next;
                aheader->chunk()->releaseArena(aheader);
            }
        }
    }

    static uintptr_t getFreeListOffset(AllocKind thingKind) {
        uintptr_t offset = offsetof(ArenaLists, freeLists);
        return offset + thingKind * sizeof(FreeList);
    }

    const FreeList *getFreeList(AllocKind thingKind) const {
        return &freeLists[thingKind];
    }

    ArenaHeader *getFirstArena(AllocKind thingKind) const {
        return arenaLists[thingKind].head();
    }

    ArenaHeader *getFirstArenaToSweep(AllocKind thingKind) const {
        return arenaListsToSweep[thingKind];
    }

    bool arenaListsAreEmpty() const {
        for (size_t i = 0; i != FINALIZE_LIMIT; ++i) {
            /*
             * The arena cannot be empty if the background finalization is not yet
             * done.
             */
            if (backgroundFinalizeState[i] != BFS_DONE)
                return false;
            if (!arenaLists[i].isEmpty())
                return false;
        }
        return true;
    }

    void unmarkAll() {
        for (size_t i = 0; i != FINALIZE_LIMIT; ++i) {
            /* The background finalization must have stopped at this point. */
            JS_ASSERT(backgroundFinalizeState[i] == BFS_DONE ||
                      backgroundFinalizeState[i] == BFS_JUST_FINISHED);
            for (ArenaHeader *aheader = arenaLists[i].head(); aheader; aheader = aheader->next) {
                uintptr_t *word = aheader->chunk()->bitmap.arenaBits(aheader);
                memset(word, 0, ArenaBitmapWords * sizeof(uintptr_t));
            }
        }
    }

    bool doneBackgroundFinalize(AllocKind kind) const {
        return backgroundFinalizeState[kind] == BFS_DONE ||
               backgroundFinalizeState[kind] == BFS_JUST_FINISHED;
    }

    bool needBackgroundFinalizeWait(AllocKind kind) const {
        return backgroundFinalizeState[kind] != BFS_DONE;
    }

    /*
     * Return the free list back to the arena so the GC finalization will not
     * run the finalizers over unitialized bytes from free things.
     */
    void purge() {
        for (size_t i = 0; i != FINALIZE_LIMIT; ++i)
            purge(AllocKind(i));
    }

    void purge(AllocKind i) {
        FreeList *freeList = &freeLists[i];
        if (!freeList->isEmpty()) {
            ArenaHeader *aheader = freeList->arenaHeader();
            aheader->setFirstFreeSpan(freeList->getHead());
            freeList->initAsEmpty();
        }
    }

    inline void prepareForIncrementalGC(JSRuntime *rt);

    /*
     * Temporarily copy the free list heads to the arenas so the code can see
     * the proper value in ArenaHeader::freeList when accessing the latter
     * outside the GC.
     */
    void copyFreeListsToArenas() {
        for (size_t i = 0; i != FINALIZE_LIMIT; ++i)
            copyFreeListToArena(AllocKind(i));
    }

    void copyFreeListToArena(AllocKind thingKind) {
        FreeList *freeList = &freeLists[thingKind];
        if (!freeList->isEmpty()) {
            ArenaHeader *aheader = freeList->arenaHeader();
            JS_ASSERT(!aheader->hasFreeThings());
            aheader->setFirstFreeSpan(freeList->getHead());
        }
    }

    /*
     * Clear the free lists in arenas that were temporarily set there using
     * copyToArenas.
     */
    void clearFreeListsInArenas() {
        for (size_t i = 0; i != FINALIZE_LIMIT; ++i)
            clearFreeListInArena(AllocKind(i));
    }


    void clearFreeListInArena(AllocKind kind) {
        FreeList *freeList = &freeLists[kind];
        if (!freeList->isEmpty()) {
            ArenaHeader *aheader = freeList->arenaHeader();
            JS_ASSERT(freeList->isSameNonEmptySpan(aheader->getFirstFreeSpan()));
            aheader->setAsFullyUsed();
        }
    }

    /*
     * Check that the free list is either empty or were synchronized with the
     * arena using copyToArena().
     */
    bool isSynchronizedFreeList(AllocKind kind) {
        FreeList *freeList = &freeLists[kind];
        if (freeList->isEmpty())
            return true;
        ArenaHeader *aheader = freeList->arenaHeader();
        if (aheader->hasFreeThings()) {
            /*
             * If the arena has a free list, it must be the same as one in
             * lists.
             */
            JS_ASSERT(freeList->isSameNonEmptySpan(aheader->getFirstFreeSpan()));
            return true;
        }
        return false;
    }

    MOZ_ALWAYS_INLINE void *allocateFromFreeList(AllocKind thingKind, size_t thingSize) {
        return freeLists[thingKind].allocate(thingSize);
    }

    template <AllowGC allowGC>
    static void *refillFreeList(ThreadSafeContext *cx, AllocKind thingKind);

    /*
     * Moves all arenas from |fromArenaLists| into |this|.  In
     * parallel blocks, we temporarily create one ArenaLists per
     * parallel thread.  When the parallel block ends, we move
     * whatever allocations may have been performed back into the
     * compartment's main arena list using this function.
     */
    void adoptArenas(JSRuntime *runtime, ArenaLists *fromArenaLists);

    /* True if the ArenaHeader in question is found in this ArenaLists */
    bool containsArena(JSRuntime *runtime, ArenaHeader *arenaHeader);

    void checkEmptyFreeLists() {
#ifdef DEBUG
        for (size_t i = 0; i < mozilla::ArrayLength(freeLists); ++i)
            JS_ASSERT(freeLists[i].isEmpty());
#endif
    }

    void checkEmptyFreeList(AllocKind kind) {
        JS_ASSERT(freeLists[kind].isEmpty());
    }

    void queueObjectsForSweep(FreeOp *fop);
    void queueStringsForSweep(FreeOp *fop);
    void queueShapesForSweep(FreeOp *fop);
    void queueScriptsForSweep(FreeOp *fop);
    void queueJitCodeForSweep(FreeOp *fop);

    bool foregroundFinalize(FreeOp *fop, AllocKind thingKind, SliceBudget &sliceBudget);
    static void backgroundFinalize(FreeOp *fop, ArenaHeader *listHead, bool onBackgroundThread);

    void wipeDuringParallelExecution(JSRuntime *rt);

  private:
    inline void finalizeNow(FreeOp *fop, AllocKind thingKind);
    inline void forceFinalizeNow(FreeOp *fop, AllocKind thingKind);
    inline void queueForForegroundSweep(FreeOp *fop, AllocKind thingKind);
    inline void queueForBackgroundSweep(FreeOp *fop, AllocKind thingKind);

    void *allocateFromArena(JS::Zone *zone, AllocKind thingKind);
    inline void *allocateFromArenaInline(JS::Zone *zone, AllocKind thingKind,
                                         AutoMaybeStartBackgroundAllocation &maybeStartBackgroundAllocation);

    inline void normalizeBackgroundFinalizeState(AllocKind thingKind);

    friend class js::Nursery;
};

/*
 * Initial allocation size for data structures holding chunks is set to hold
 * chunks with total capacity of 16MB to avoid buffer resizes during browser
 * startup.
 */
const size_t INITIAL_CHUNK_CAPACITY = 16 * 1024 * 1024 / ChunkSize;

/* The number of GC cycles an empty chunk can survive before been released. */
const size_t MAX_EMPTY_CHUNK_AGE = 4;

} /* namespace gc */

typedef enum JSGCRootType {
    JS_GC_ROOT_VALUE_PTR,
    JS_GC_ROOT_STRING_PTR,
    JS_GC_ROOT_OBJECT_PTR,
    JS_GC_ROOT_SCRIPT_PTR
} JSGCRootType;

struct RootInfo {
    RootInfo() {}
    RootInfo(const char *name, JSGCRootType type) : name(name), type(type) {}
    const char *name;
    JSGCRootType type;
};

typedef js::HashMap<void *,
                    RootInfo,
                    js::DefaultHasher<void *>,
                    js::SystemAllocPolicy> RootedValueMap;

extern bool
AddValueRoot(JSContext *cx, js::Value *vp, const char *name);

extern bool
AddValueRootRT(JSRuntime *rt, js::Value *vp, const char *name);

extern bool
AddStringRoot(JSContext *cx, JSString **rp, const char *name);

extern bool
AddObjectRoot(JSContext *cx, JSObject **rp, const char *name);

extern bool
AddObjectRoot(JSRuntime *rt, JSObject **rp, const char *name);

extern bool
AddScriptRoot(JSContext *cx, JSScript **rp, const char *name);

extern void
RemoveRoot(JSRuntime *rt, void *rp);

} /* namespace js */

extern bool
js_InitGC(JSRuntime *rt, uint32_t maxbytes);

extern void
js_FinishGC(JSRuntime *rt);

namespace js {

class InterpreterFrame;

extern void
MarkCompartmentActive(js::InterpreterFrame *fp);

extern void
TraceRuntime(JSTracer *trc);

/* Must be called with GC lock taken. */
extern bool
TriggerGC(JSRuntime *rt, JS::gcreason::Reason reason);

/* Must be called with GC lock taken. */
extern bool
TriggerZoneGC(Zone *zone, JS::gcreason::Reason reason);

extern void
MaybeGC(JSContext *cx);

extern void
ReleaseAllJITCode(FreeOp *op);

/*
 * Kinds of js_GC invocation.
 */
typedef enum JSGCInvocationKind {
    /* Normal invocation. */
    GC_NORMAL           = 0,

    /* Minimize GC triggers and release empty GC chunks right away. */
    GC_SHRINK             = 1
} JSGCInvocationKind;

extern void
GC(JSRuntime *rt, JSGCInvocationKind gckind, JS::gcreason::Reason reason);

extern void
GCSlice(JSRuntime *rt, JSGCInvocationKind gckind, JS::gcreason::Reason reason, int64_t millis = 0);

extern void
GCFinalSlice(JSRuntime *rt, JSGCInvocationKind gckind, JS::gcreason::Reason reason);

extern void
GCDebugSlice(JSRuntime *rt, bool limit, int64_t objCount);

extern void
PrepareForDebugGC(JSRuntime *rt);

extern void
MinorGC(JSRuntime *rt, JS::gcreason::Reason reason);

extern void
MinorGC(JSContext *cx, JS::gcreason::Reason reason);

/* Functions for managing cross compartment gray pointers. */

extern void
DelayCrossCompartmentGrayMarking(JSObject *src);

extern void
NotifyGCNukeWrapper(JSObject *o);

extern unsigned
NotifyGCPreSwap(JSObject *a, JSObject *b);

extern void
NotifyGCPostSwap(JSObject *a, JSObject *b, unsigned preResult);

/*
 * Helper state for use when JS helper threads sweep and allocate GC thing kinds
 * that can be swept and allocated off the main thread.
 *
 * In non-threadsafe builds, all actual sweeping and allocation is performed
 * on the main thread, but GCHelperState encapsulates this from clients as
 * much as possible.
 */
class GCHelperState
{
    enum State {
        IDLE,
        SWEEPING,
        ALLOCATING,
        CANCEL_ALLOCATION
    };

    /*
     * During the finalization we do not free immediately. Rather we add the
     * corresponding pointers to a buffer which we later release on a
     * separated thread.
     *
     * The buffer is implemented as a vector of 64K arrays of pointers, not as
     * a simple vector, to avoid realloc calls during the vector growth and to
     * not bloat the binary size of the inlined freeLater method. Any OOM
     * during buffer growth results in the pointer being freed immediately.
     */
    static const size_t FREE_ARRAY_SIZE = size_t(1) << 16;
    static const size_t FREE_ARRAY_LENGTH = FREE_ARRAY_SIZE / sizeof(void *);

    // Associated runtime.
    JSRuntime *const rt;

    // Condvar for notifying the main thread when work has finished. This is
    // associated with the runtime's GC lock --- the worker thread state
    // condvars can't be used here due to lock ordering issues.
    PRCondVar *done;

    // Activity for the helper to do, protected by the GC lock.
    State state_;

    // Thread which work is being performed on, or null.
    PRThread *thread;

    void startBackgroundThread(State newState);
    void waitForBackgroundThread();

    State state();
    void setState(State state);

    bool              sweepFlag;
    bool              shrinkFlag;

    Vector<void **, 16, js::SystemAllocPolicy> freeVector;
    void            **freeCursor;
    void            **freeCursorEnd;

    bool              backgroundAllocation;

    friend class js::gc::ArenaLists;

    void
    replenishAndFreeLater(void *ptr);

    static void freeElementsAndArray(void **array, void **end) {
        JS_ASSERT(array <= end);
        for (void **p = array; p != end; ++p)
            js_free(*p);
        js_free(array);
    }

    /* Must be called with the GC lock taken. */
    void doSweep();

  public:
    explicit GCHelperState(JSRuntime *rt)
      : rt(rt),
        done(nullptr),
        state_(IDLE),
        thread(nullptr),
        sweepFlag(false),
        shrinkFlag(false),
        freeCursor(nullptr),
        freeCursorEnd(nullptr),
        backgroundAllocation(true)
    { }

    bool init();
    void finish();

    void work();

    /* Must be called with the GC lock taken. */
    void startBackgroundSweep(bool shouldShrink);

    /* Must be called with the GC lock taken. */
    void startBackgroundShrink();

    /* Must be called without the GC lock taken. */
    void waitBackgroundSweepEnd();

    /* Must be called without the GC lock taken. */
    void waitBackgroundSweepOrAllocEnd();

    /* Must be called with the GC lock taken. */
    void startBackgroundAllocationIfIdle();

    bool canBackgroundAllocate() const {
        return backgroundAllocation;
    }

    void disableBackgroundAllocation() {
        backgroundAllocation = false;
    }

    bool onBackgroundThread();

    /*
     * Outside the GC lock may give true answer when in fact the sweeping has
     * been done.
     */
    bool isBackgroundSweeping() const {
        return state_ == SWEEPING;
    }

    bool shouldShrink() const {
        JS_ASSERT(isBackgroundSweeping());
        return shrinkFlag;
    }

    void freeLater(void *ptr) {
        JS_ASSERT(!isBackgroundSweeping());
        if (freeCursor != freeCursorEnd)
            *freeCursor++ = ptr;
        else
            replenishAndFreeLater(ptr);
    }
};

struct GCChunkHasher {
    typedef gc::Chunk *Lookup;

    /*
     * Strip zeros for better distribution after multiplying by the golden
     * ratio.
     */
    static HashNumber hash(gc::Chunk *chunk) {
        JS_ASSERT(!(uintptr_t(chunk) & gc::ChunkMask));
        return HashNumber(uintptr_t(chunk) >> gc::ChunkShift);
    }

    static bool match(gc::Chunk *k, gc::Chunk *l) {
        JS_ASSERT(!(uintptr_t(k) & gc::ChunkMask));
        JS_ASSERT(!(uintptr_t(l) & gc::ChunkMask));
        return k == l;
    }
};

typedef HashSet<js::gc::Chunk *, GCChunkHasher, SystemAllocPolicy> GCChunkSet;

struct GrayRoot {
    void *thing;
    JSGCTraceKind kind;
#ifdef DEBUG
    JSTraceNamePrinter debugPrinter;
    const void *debugPrintArg;
    size_t debugPrintIndex;
#endif

    GrayRoot(void *thing, JSGCTraceKind kind)
        : thing(thing), kind(kind) {}
};

void
MarkStackRangeConservatively(JSTracer *trc, Value *begin, Value *end);

typedef void (*IterateChunkCallback)(JSRuntime *rt, void *data, gc::Chunk *chunk);
typedef void (*IterateZoneCallback)(JSRuntime *rt, void *data, JS::Zone *zone);
typedef void (*IterateArenaCallback)(JSRuntime *rt, void *data, gc::Arena *arena,
                                     JSGCTraceKind traceKind, size_t thingSize);
typedef void (*IterateCellCallback)(JSRuntime *rt, void *data, void *thing,
                                    JSGCTraceKind traceKind, size_t thingSize);

/*
 * This function calls |zoneCallback| on every zone, |compartmentCallback| on
 * every compartment, |arenaCallback| on every in-use arena, and |cellCallback|
 * on every in-use cell in the GC heap.
 */
extern void
IterateZonesCompartmentsArenasCells(JSRuntime *rt, void *data,
                                    IterateZoneCallback zoneCallback,
                                    JSIterateCompartmentCallback compartmentCallback,
                                    IterateArenaCallback arenaCallback,
                                    IterateCellCallback cellCallback);

/*
 * This function is like IterateZonesCompartmentsArenasCells, but does it for a
 * single zone.
 */
extern void
IterateZoneCompartmentsArenasCells(JSRuntime *rt, Zone *zone, void *data,
                                   IterateZoneCallback zoneCallback,
                                   JSIterateCompartmentCallback compartmentCallback,
                                   IterateArenaCallback arenaCallback,
                                   IterateCellCallback cellCallback);

/*
 * Invoke chunkCallback on every in-use chunk.
 */
extern void
IterateChunks(JSRuntime *rt, void *data, IterateChunkCallback chunkCallback);

typedef void (*IterateScriptCallback)(JSRuntime *rt, void *data, JSScript *script);

/*
 * Invoke scriptCallback on every in-use script for
 * the given compartment or for all compartments if it is null.
 */
extern void
IterateScripts(JSRuntime *rt, JSCompartment *compartment,
               void *data, IterateScriptCallback scriptCallback);

} /* namespace js */

extern void
js_FinalizeStringRT(JSRuntime *rt, JSString *str);

namespace js {

JSCompartment *
NewCompartment(JSContext *cx, JS::Zone *zone, JSPrincipals *principals,
               const JS::CompartmentOptions &options);

namespace gc {

extern void
GCIfNeeded(JSContext *cx);

/* Tries to run a GC no matter what (used for GC zeal). */
void
RunDebugGC(JSContext *cx);

/* Wait for the background thread to finish sweeping if it is running. */
void
FinishBackgroundFinalize(JSRuntime *rt);

/*
 * Merge all contents of source into target. This can only be used if source is
 * the only compartment in its zone.
 */
void
MergeCompartments(JSCompartment *source, JSCompartment *target);

const int ZealPokeValue = 1;
const int ZealAllocValue = 2;
const int ZealFrameGCValue = 3;
const int ZealVerifierPreValue = 4;
const int ZealFrameVerifierPreValue = 5;
const int ZealStackRootingValue = 6;
const int ZealGenerationalGCValue = 7;
const int ZealIncrementalRootsThenFinish = 8;
const int ZealIncrementalMarkAllThenFinish = 9;
const int ZealIncrementalMultipleSlices = 10;
const int ZealVerifierPostValue = 11;
const int ZealFrameVerifierPostValue = 12;
const int ZealCheckHashTablesOnMinorGC = 13;
const int ZealLimit = 13;

enum VerifierType {
    PreBarrierVerifier,
    PostBarrierVerifier
};

#ifdef JS_GC_ZEAL

/* Check that write barriers have been used correctly. See jsgc.cpp. */
void
VerifyBarriers(JSRuntime *rt, VerifierType type);

void
MaybeVerifyBarriers(JSContext *cx, bool always = false);

#else

static inline void
VerifyBarriers(JSRuntime *rt, VerifierType type)
{
}

static inline void
MaybeVerifyBarriers(JSContext *cx, bool always = false)
{
}

#endif

/*
 * Instances of this class set the |JSRuntime::suppressGC| flag for the duration
 * that they are live. Use of this class is highly discouraged. Please carefully
 * read the comment in jscntxt.h above |suppressGC| and take all appropriate
 * precautions before instantiating this class.
 */
class AutoSuppressGC
{
    int32_t &suppressGC_;

  public:
    explicit AutoSuppressGC(ExclusiveContext *cx);
    explicit AutoSuppressGC(JSCompartment *comp);
    explicit AutoSuppressGC(JSRuntime *rt);

    ~AutoSuppressGC()
    {
        suppressGC_--;
    }
};

#ifdef DEBUG
/* Disable OOM testing in sections which are not OOM safe. */
class AutoEnterOOMUnsafeRegion
{
    uint32_t saved_;

  public:
    AutoEnterOOMUnsafeRegion() : saved_(OOM_maxAllocations) {
        OOM_maxAllocations = UINT32_MAX;
    }
    ~AutoEnterOOMUnsafeRegion() {
        OOM_maxAllocations = saved_;
    }
};
#else
class AutoEnterOOMUnsafeRegion {};
#endif /* DEBUG */

} /* namespace gc */

#ifdef DEBUG
/* Use this to avoid assertions when manipulating the wrapper map. */
class AutoDisableProxyCheck
{
    MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER;
    uintptr_t &count;

  public:
    explicit AutoDisableProxyCheck(JSRuntime *rt
                                   MOZ_GUARD_OBJECT_NOTIFIER_PARAM);

    ~AutoDisableProxyCheck() {
        count--;
    }
};
#else
struct AutoDisableProxyCheck
{
    explicit AutoDisableProxyCheck(JSRuntime *rt) {}
};
#endif

void
PurgeJITCaches(JS::Zone *zone);

// This is the same as IsInsideNursery, but not inlined.
bool
UninlinedIsInsideNursery(const gc::Cell *cell);

} /* namespace js */

#endif /* jsgc_h */