/* -*- 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/EnumeratedArray.h"
#include "mozilla/MemoryReporting.h"
#include "mozilla/TypeTraits.h"
#include "jslock.h"
#include "js/GCAPI.h"
#include "js/SliceBudget.h"
#include "js/Vector.h"
#include "vm/NativeObject.h"
namespace js {
unsigned GetCPUCount();
enum ThreadType
{
MainThread,
BackgroundThread
};
namespace gcstats {
struct Statistics;
} // namespace gcstats
class Nursery;
namespace gc {
struct FinalizePhase;
enum State {
NO_INCREMENTAL,
MARK_ROOTS,
MARK,
SWEEP,
COMPACT
};
// Expand the given macro D for each valid GC reference type.
#define FOR_EACH_GC_POINTER_TYPE(D) \
D(AccessorShape*) \
D(BaseShape*) \
D(UnownedBaseShape*) \
D(jit::JitCode*) \
D(NativeObject*) \
D(ArrayObject*) \
D(ArgumentsObject*) \
D(ArrayBufferObject*) \
D(ArrayBufferObjectMaybeShared*) \
D(ArrayBufferViewObject*) \
D(DebugScopeObject*) \
D(GlobalObject*) \
D(JSObject*) \
D(JSFunction*) \
D(ModuleObject*) \
D(ModuleEnvironmentObject*) \
D(NestedScopeObject*) \
D(PlainObject*) \
D(SavedFrame*) \
D(ScopeObject*) \
D(ScriptSourceObject*) \
D(SharedArrayBufferObject*) \
D(SharedTypedArrayObject*) \
D(ImportEntryObject*) \
D(ExportEntryObject*) \
D(JSScript*) \
D(LazyScript*) \
D(Shape*) \
D(JSAtom*) \
D(JSString*) \
D(JSFlatString*) \
D(JSLinearString*) \
D(PropertyName*) \
D(JS::Symbol*) \
D(js::ObjectGroup*) \
D(Value) \
D(jsid) \
D(TaggedProto)
/* Map from C++ type to alloc 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 = AllocKind::SCRIPT; };
template <> struct MapTypeToFinalizeKind<LazyScript> { static const AllocKind kind = AllocKind::LAZY_SCRIPT; };
template <> struct MapTypeToFinalizeKind<Shape> { static const AllocKind kind = AllocKind::SHAPE; };
template <> struct MapTypeToFinalizeKind<AccessorShape> { static const AllocKind kind = AllocKind::ACCESSOR_SHAPE; };
template <> struct MapTypeToFinalizeKind<BaseShape> { static const AllocKind kind = AllocKind::BASE_SHAPE; };
template <> struct MapTypeToFinalizeKind<ObjectGroup> { static const AllocKind kind = AllocKind::OBJECT_GROUP; };
template <> struct MapTypeToFinalizeKind<JSFatInlineString> { static const AllocKind kind = AllocKind::FAT_INLINE_STRING; };
template <> struct MapTypeToFinalizeKind<JSString> { static const AllocKind kind = AllocKind::STRING; };
template <> struct MapTypeToFinalizeKind<JSExternalString> { static const AllocKind kind = AllocKind::EXTERNAL_STRING; };
template <> struct MapTypeToFinalizeKind<JS::Symbol> { static const AllocKind kind = AllocKind::SYMBOL; };
template <> struct MapTypeToFinalizeKind<jit::JitCode> { static const AllocKind kind = AllocKind::JITCODE; };
template <typename T> struct ParticipatesInCC {};
#define EXPAND_PARTICIPATES_IN_CC(_, type, addToCCKind) \
template <> struct ParticipatesInCC<type> { static const bool value = addToCCKind; };
JS_FOR_EACH_TRACEKIND(EXPAND_PARTICIPATES_IN_CC)
#undef EXPAND_PARTICIPATES_IN_CC
static inline bool
IsNurseryAllocable(AllocKind kind)
{
MOZ_ASSERT(IsValidAllocKind(kind));
static const bool map[] = {
true, /* AllocKind::FUNCTION */
true, /* AllocKind::FUNCTION_EXTENDED */
false, /* AllocKind::OBJECT0 */
true, /* AllocKind::OBJECT0_BACKGROUND */
false, /* AllocKind::OBJECT2 */
true, /* AllocKind::OBJECT2_BACKGROUND */
false, /* AllocKind::OBJECT4 */
true, /* AllocKind::OBJECT4_BACKGROUND */
false, /* AllocKind::OBJECT8 */
true, /* AllocKind::OBJECT8_BACKGROUND */
false, /* AllocKind::OBJECT12 */
true, /* AllocKind::OBJECT12_BACKGROUND */
false, /* AllocKind::OBJECT16 */
true, /* AllocKind::OBJECT16_BACKGROUND */
false, /* AllocKind::SCRIPT */
false, /* AllocKind::LAZY_SCRIPT */
false, /* AllocKind::SHAPE */
false, /* AllocKind::ACCESSOR_SHAPE */
false, /* AllocKind::BASE_SHAPE */
false, /* AllocKind::OBJECT_GROUP */
false, /* AllocKind::FAT_INLINE_STRING */
false, /* AllocKind::STRING */
false, /* AllocKind::EXTERNAL_STRING */
false, /* AllocKind::SYMBOL */
false, /* AllocKind::JITCODE */
};
JS_STATIC_ASSERT(JS_ARRAY_LENGTH(map) == size_t(AllocKind::LIMIT));
return map[size_t(kind)];
}
static inline bool
IsBackgroundFinalized(AllocKind kind)
{
MOZ_ASSERT(IsValidAllocKind(kind));
static const bool map[] = {
true, /* AllocKind::FUNCTION */
true, /* AllocKind::FUNCTION_EXTENDED */
false, /* AllocKind::OBJECT0 */
true, /* AllocKind::OBJECT0_BACKGROUND */
false, /* AllocKind::OBJECT2 */
true, /* AllocKind::OBJECT2_BACKGROUND */
false, /* AllocKind::OBJECT4 */
true, /* AllocKind::OBJECT4_BACKGROUND */
false, /* AllocKind::OBJECT8 */
true, /* AllocKind::OBJECT8_BACKGROUND */
false, /* AllocKind::OBJECT12 */
true, /* AllocKind::OBJECT12_BACKGROUND */
false, /* AllocKind::OBJECT16 */
true, /* AllocKind::OBJECT16_BACKGROUND */
false, /* AllocKind::SCRIPT */
false, /* AllocKind::LAZY_SCRIPT */
true, /* AllocKind::SHAPE */
true, /* AllocKind::ACCESSOR_SHAPE */
true, /* AllocKind::BASE_SHAPE */
true, /* AllocKind::OBJECT_GROUP */
true, /* AllocKind::FAT_INLINE_STRING */
true, /* AllocKind::STRING */
false, /* AllocKind::EXTERNAL_STRING */
true, /* AllocKind::SYMBOL */
false, /* AllocKind::JITCODE */
};
JS_STATIC_ASSERT(JS_ARRAY_LENGTH(map) == size_t(AllocKind::LIMIT));
return map[size_t(kind)];
}
static inline bool
CanBeFinalizedInBackground(AllocKind kind, const Class* clasp)
{
MOZ_ASSERT(IsObjectAllocKind(kind));
/* If the class has no finalizer or a finalizer that is safe to call on
* a different thread, we change the alloc kind. For example,
* AllocKind::OBJECT0 calls the finalizer on the main thread,
* AllocKind::OBJECT0_BACKGROUND calls the finalizer on the gcHelperThread.
* IsBackgroundFinalized is called to prevent recursively incrementing
* the alloc kind; kind may already be a background finalize kind.
*/
return (!IsBackgroundFinalized(kind) &&
(!clasp->finalize || (clasp->flags & JSCLASS_BACKGROUND_FINALIZE)));
}
/* 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 AllocKind::OBJECT16;
return slotsToThingKind[numSlots];
}
/* As for GetGCObjectKind, but for dense array allocation. */
static inline AllocKind
GetGCArrayKind(size_t numElements)
{
/*
* 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 (numElements > NativeObject::MAX_DENSE_ELEMENTS_COUNT ||
numElements + ObjectElements::VALUES_PER_HEADER >= SLOTS_TO_THING_KIND_LIMIT)
{
return AllocKind::OBJECT2;
}
return slotsToThingKind[numElements + ObjectElements::VALUES_PER_HEADER];
}
static inline AllocKind
GetGCObjectFixedSlotsKind(size_t numFixedSlots)
{
MOZ_ASSERT(numFixedSlots < SLOTS_TO_THING_KIND_LIMIT);
return slotsToThingKind[numFixedSlots];
}
// Get the best kind to use when allocating an object that needs a specific
// number of bytes.
static inline AllocKind
GetGCObjectKindForBytes(size_t nbytes)
{
MOZ_ASSERT(nbytes <= JSObject::MAX_BYTE_SIZE);
if (nbytes <= sizeof(NativeObject))
return AllocKind::OBJECT0;
nbytes -= sizeof(NativeObject);
size_t dataSlots = AlignBytes(nbytes, sizeof(Value)) / sizeof(Value);
MOZ_ASSERT(nbytes <= dataSlots * sizeof(Value));
return GetGCObjectKind(dataSlots);
}
static inline AllocKind
GetBackgroundAllocKind(AllocKind kind)
{
MOZ_ASSERT(!IsBackgroundFinalized(kind));
MOZ_ASSERT(IsObjectAllocKind(kind));
return AllocKind(size_t(kind) + 1);
}
/* 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 AllocKind::FUNCTION:
case AllocKind::OBJECT0:
case AllocKind::OBJECT0_BACKGROUND:
return 0;
case AllocKind::FUNCTION_EXTENDED:
case AllocKind::OBJECT2:
case AllocKind::OBJECT2_BACKGROUND:
return 2;
case AllocKind::OBJECT4:
case AllocKind::OBJECT4_BACKGROUND:
return 4;
case AllocKind::OBJECT8:
case AllocKind::OBJECT8_BACKGROUND:
return 8;
case AllocKind::OBJECT12:
case AllocKind::OBJECT12_BACKGROUND:
return 12;
case AllocKind::OBJECT16:
case AllocKind::OBJECT16_BACKGROUND:
return 16;
default:
MOZ_CRASH("Bad object alloc 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) {
MOZ_ASSERT(nslots > 0);
nslots--;
}
/*
* Functions have a larger alloc kind than AllocKind::OBJECT to reserve
* space for the extra fields in JSFunction, but have no fixed slots.
*/
if (clasp == FunctionClassPtr)
nslots = 0;
return nslots;
}
static inline size_t
GetGCKindBytes(AllocKind thingKind)
{
return sizeof(JSObject_Slots0) + GetGCKindSlots(thingKind) * sizeof(Value);
}
// 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;
/*
* A single segment of a SortedArenaList. Each segment has a head and a tail,
* which track the start and end of a segment for O(1) append and concatenation.
*/
struct SortedArenaListSegment
{
ArenaHeader* head;
ArenaHeader** tailp;
void clear() {
head = nullptr;
tailp = &head;
}
bool isEmpty() const {
return tailp == &head;
}
// Appends |aheader| to this segment.
void append(ArenaHeader* aheader) {
MOZ_ASSERT(aheader);
MOZ_ASSERT_IF(head, head->getAllocKind() == aheader->getAllocKind());
*tailp = aheader;
tailp = &aheader->next;
}
// Points the tail of this segment at |aheader|, which may be null. Note
// that this does not change the tail itself, but merely which arena
// follows it. This essentially turns the tail into a cursor (see also the
// description of ArenaList), but from the perspective of a SortedArenaList
// this makes no difference.
void linkTo(ArenaHeader* aheader) {
*tailp = aheader;
}
};
/*
* 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_;
void copy(const ArenaList& other) {
other.check();
head_ = other.head_;
cursorp_ = other.isCursorAtHead() ? &head_ : other.cursorp_;
check();
}
public:
ArenaList() {
clear();
}
ArenaList(const ArenaList& other) {
copy(other);
}
ArenaList& operator=(const ArenaList& other) {
copy(other);
return *this;
}
explicit ArenaList(const SortedArenaListSegment& segment) {
head_ = segment.head;
cursorp_ = segment.isEmpty() ? &head_ : segment.tailp;
check();
}
// This does checking just of |head_| and |cursorp_|.
void check() const {
#ifdef DEBUG
// If the list is empty, it must have this form.
MOZ_ASSERT_IF(!head_, cursorp_ == &head_);
// If there's an arena following the cursor, it must not be full.
ArenaHeader* cursor = *cursorp_;
MOZ_ASSERT_IF(cursor, cursor->hasFreeThings());
#endif
}
void clear() {
head_ = nullptr;
cursorp_ = &head_;
check();
}
ArenaList copyAndClear() {
ArenaList result = *this;
clear();
return result;
}
bool isEmpty() const {
check();
return !head_;
}
// This returns nullptr if the list is empty.
ArenaHeader* head() const {
check();
return head_;
}
bool isCursorAtHead() const {
check();
return cursorp_ == &head_;
}
bool isCursorAtEnd() const {
check();
return !*cursorp_;
}
// This can return nullptr.
ArenaHeader* arenaAfterCursor() const {
check();
return *cursorp_;
}
// This returns the arena after the cursor and moves the cursor past it.
ArenaHeader* takeNextArena() {
check();
ArenaHeader* aheader = *cursorp_;
if (!aheader)
return nullptr;
cursorp_ = &aheader->next;
check();
return aheader;
}
// 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 |other|, which must be full, at the cursor of |this|.
ArenaList& insertListWithCursorAtEnd(const ArenaList& other) {
check();
other.check();
MOZ_ASSERT(other.isCursorAtEnd());
if (other.isCursorAtHead())
return *this;
// Insert the full arenas of |other| after those of |this|.
*other.cursorp_ = *cursorp_;
*cursorp_ = other.head_;
cursorp_ = other.cursorp_;
check();
return *this;
}
ArenaHeader* removeRemainingArenas(ArenaHeader** arenap);
ArenaHeader** pickArenasToRelocate(size_t& arenaTotalOut, size_t& relocTotalOut);
ArenaHeader* relocateArenas(ArenaHeader* toRelocate, ArenaHeader* relocated,
SliceBudget& sliceBudget, gcstats::Statistics& stats);
};
/*
* A class that holds arenas in sorted order by appending arenas to specific
* segments. Each segment has a head and a tail, which can be linked up to
* other segments to create a contiguous ArenaList.
*/
class SortedArenaList
{
public:
// The minimum size, in bytes, of a GC thing.
static const size_t MinThingSize = 16;
static_assert(ArenaSize <= 4096, "When increasing the Arena size, please consider how"\
" this will affect the size of a SortedArenaList.");
static_assert(MinThingSize >= 16, "When decreasing the minimum thing size, please consider"\
" how this will affect the size of a SortedArenaList.");
private:
// The maximum number of GC things that an arena can hold.
static const size_t MaxThingsPerArena = (ArenaSize - sizeof(ArenaHeader)) / MinThingSize;
size_t thingsPerArena_;
SortedArenaListSegment segments[MaxThingsPerArena + 1];
// Convenience functions to get the nth head and tail.
ArenaHeader* headAt(size_t n) { return segments[n].head; }
ArenaHeader** tailAt(size_t n) { return segments[n].tailp; }
public:
explicit SortedArenaList(size_t thingsPerArena = MaxThingsPerArena) {
reset(thingsPerArena);
}
void setThingsPerArena(size_t thingsPerArena) {
MOZ_ASSERT(thingsPerArena && thingsPerArena <= MaxThingsPerArena);
thingsPerArena_ = thingsPerArena;
}
// Resets the first |thingsPerArena| segments of this list for further use.
void reset(size_t thingsPerArena = MaxThingsPerArena) {
setThingsPerArena(thingsPerArena);
// Initialize the segments.
for (size_t i = 0; i <= thingsPerArena; ++i)
segments[i].clear();
}
// Inserts a header, which has room for |nfree| more things, in its segment.
void insertAt(ArenaHeader* aheader, size_t nfree) {
MOZ_ASSERT(nfree <= thingsPerArena_);
segments[nfree].append(aheader);
}
// Remove all empty arenas, inserting them as a linked list.
void extractEmpty(ArenaHeader** empty) {
SortedArenaListSegment& segment = segments[thingsPerArena_];
if (segment.head) {
*segment.tailp = *empty;
*empty = segment.head;
segment.clear();
}
}
// Links up the tail of each non-empty segment to the head of the next
// non-empty segment, creating a contiguous list that is returned as an
// ArenaList. This is not a destructive operation: neither the head nor tail
// of any segment is modified. However, note that the ArenaHeaders in the
// resulting ArenaList should be treated as read-only unless the
// SortedArenaList is no longer needed: inserting or removing arenas would
// invalidate the SortedArenaList.
ArenaList toArenaList() {
// Link the non-empty segment tails up to the non-empty segment heads.
size_t tailIndex = 0;
for (size_t headIndex = 1; headIndex <= thingsPerArena_; ++headIndex) {
if (headAt(headIndex)) {
segments[tailIndex].linkTo(headAt(headIndex));
tailIndex = headIndex;
}
}
// Point the tail of the final non-empty segment at null. Note that if
// the list is empty, this will just set segments[0].head to null.
segments[tailIndex].linkTo(nullptr);
// Create an ArenaList with head and cursor set to the head and tail of
// the first segment (if that segment is empty, only the head is used).
return ArenaList(segments[0]);
}
};
class ArenaLists
{
JSRuntime* runtime_;
/*
* 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.
*/
AllAllocKindArray<FreeList> freeLists;
AllAllocKindArray<ArenaList> arenaLists;
enum BackgroundFinalizeStateEnum { BFS_DONE, BFS_RUN };
typedef mozilla::Atomic<BackgroundFinalizeStateEnum, mozilla::ReleaseAcquire>
BackgroundFinalizeState;
/* The current background finalization state, accessed atomically. */
AllAllocKindArray<BackgroundFinalizeState> backgroundFinalizeState;
/* For each arena kind, a list of arenas remaining to be swept. */
AllAllocKindArray<ArenaHeader*> arenaListsToSweep;
/* During incremental sweeping, a list of the arenas already swept. */
AllocKind incrementalSweptArenaKind;
ArenaList incrementalSweptArenas;
// Arena lists which have yet to be swept, but need additional foreground
// processing before they are swept.
ArenaHeader* gcShapeArenasToUpdate;
ArenaHeader* gcAccessorShapeArenasToUpdate;
ArenaHeader* gcScriptArenasToUpdate;
ArenaHeader* gcObjectGroupArenasToUpdate;
// While sweeping type information, these lists save the arenas for the
// objects which have already been finalized in the foreground (which must
// happen at the beginning of the GC), so that type sweeping can determine
// which of the object pointers are marked.
ObjectAllocKindArray<ArenaList> savedObjectArenas;
ArenaHeader* savedEmptyObjectArenas;
public:
explicit ArenaLists(JSRuntime* rt) : runtime_(rt) {
for (auto i : AllAllocKinds())
freeLists[i].initAsEmpty();
for (auto i : AllAllocKinds())
backgroundFinalizeState[i] = BFS_DONE;
for (auto i : AllAllocKinds())
arenaListsToSweep[i] = nullptr;
incrementalSweptArenaKind = AllocKind::LIMIT;
gcShapeArenasToUpdate = nullptr;
gcAccessorShapeArenasToUpdate = nullptr;
gcScriptArenasToUpdate = nullptr;
gcObjectGroupArenasToUpdate = nullptr;
savedEmptyObjectArenas = nullptr;
}
~ArenaLists();
static uintptr_t getFreeListOffset(AllocKind thingKind) {
uintptr_t offset = offsetof(ArenaLists, freeLists);
return offset + size_t(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];
}
ArenaHeader* getFirstSweptArena(AllocKind thingKind) const {
if (thingKind != incrementalSweptArenaKind)
return nullptr;
return incrementalSweptArenas.head();
}
ArenaHeader* getArenaAfterCursor(AllocKind thingKind) const {
return arenaLists[thingKind].arenaAfterCursor();
}
bool arenaListsAreEmpty() const {
for (auto i : AllAllocKinds()) {
/*
* 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 (auto i : AllAllocKinds()) {
/* The background finalization must have stopped at this point. */
MOZ_ASSERT(backgroundFinalizeState[i] == BFS_DONE);
for (ArenaHeader* aheader = arenaLists[i].head(); aheader; aheader = aheader->next)
aheader->unmarkAll();
}
}
bool doneBackgroundFinalize(AllocKind kind) const {
return backgroundFinalizeState[kind] == BFS_DONE;
}
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 (auto i : AllAllocKinds())
purge(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 (auto i : AllAllocKinds())
copyFreeListToArena(i);
}
void copyFreeListToArena(AllocKind thingKind) {
FreeList* freeList = &freeLists[thingKind];
if (!freeList->isEmpty()) {
ArenaHeader* aheader = freeList->arenaHeader();
MOZ_ASSERT(!aheader->hasFreeThings());
aheader->setFirstFreeSpan(freeList->getHead());
}
}
/*
* Clear the free lists in arenas that were temporarily set there using
* copyToArenas.
*/
void clearFreeListsInArenas() {
for (auto i : AllAllocKinds())
clearFreeListInArena(i);
}
void clearFreeListInArena(AllocKind kind) {
FreeList* freeList = &freeLists[kind];
if (!freeList->isEmpty()) {
ArenaHeader* aheader = freeList->arenaHeader();
MOZ_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.
*/
MOZ_ASSERT(freeList->isSameNonEmptySpan(aheader->getFirstFreeSpan()));
return true;
}
return false;
}
/* Check if |aheader|'s arena is in use. */
bool arenaIsInUse(ArenaHeader* aheader, AllocKind kind) const {
MOZ_ASSERT(aheader);
const FreeList& freeList = freeLists[kind];
if (freeList.isEmpty())
return false;
return aheader == freeList.arenaHeader();
}
MOZ_ALWAYS_INLINE TenuredCell* allocateFromFreeList(AllocKind thingKind, size_t thingSize) {
return freeLists[thingKind].allocate(thingSize);
}
/*
* Moves all arenas from |fromArenaLists| into |this|.
*/
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 (auto i : AllAllocKinds())
checkEmptyFreeList(i);
#endif
}
void checkEmptyFreeList(AllocKind kind) {
MOZ_ASSERT(freeLists[kind].isEmpty());
}
bool relocateArenas(Zone* zone, ArenaHeader*& relocatedListOut, JS::gcreason::Reason reason,
SliceBudget& sliceBudget, gcstats::Statistics& stats);
void queueForegroundObjectsForSweep(FreeOp* fop);
void queueForegroundThingsForSweep(FreeOp* fop);
void mergeForegroundSweptObjectArenas();
bool foregroundFinalize(FreeOp* fop, AllocKind thingKind, SliceBudget& sliceBudget,
SortedArenaList& sweepList);
static void backgroundFinalize(FreeOp* fop, ArenaHeader* listHead, ArenaHeader** empty);
// When finalizing arenas, whether to keep empty arenas on the list or
// release them immediately.
enum KeepArenasEnum {
RELEASE_ARENAS,
KEEP_ARENAS
};
private:
inline void finalizeNow(FreeOp* fop, const FinalizePhase& phase);
inline void queueForForegroundSweep(FreeOp* fop, const FinalizePhase& phase);
inline void queueForBackgroundSweep(FreeOp* fop, const FinalizePhase& phase);
inline void finalizeNow(FreeOp* fop, AllocKind thingKind,
KeepArenasEnum keepArenas, ArenaHeader** empty = nullptr);
inline void forceFinalizeNow(FreeOp* fop, AllocKind thingKind,
KeepArenasEnum keepArenas, ArenaHeader** empty = nullptr);
inline void queueForForegroundSweep(FreeOp* fop, AllocKind thingKind);
inline void queueForBackgroundSweep(FreeOp* fop, AllocKind thingKind);
inline void mergeSweptArenas(AllocKind thingKind);
TenuredCell* allocateFromArena(JS::Zone* zone, AllocKind thingKind,
AutoMaybeStartBackgroundAllocation& maybeStartBGAlloc);
enum ArenaAllocMode { HasFreeThings = true, IsEmpty = false };
template <ArenaAllocMode hasFreeThings>
TenuredCell* allocateFromArenaInner(JS::Zone* zone, ArenaHeader* aheader, AllocKind kind);
inline void normalizeBackgroundFinalizeState(AllocKind thingKind);
friend class GCRuntime;
friend class js::Nursery;
friend class js::TenuringTracer;
};
/* The number of GC cycles an empty chunk can survive before been released. */
const size_t MAX_EMPTY_CHUNK_AGE = 4;
} /* namespace gc */
extern bool
InitGC(JSRuntime* rt, uint32_t maxbytes);
extern void
FinishGC(JSRuntime* rt);
class InterpreterFrame;
extern void
MarkCompartmentActive(js::InterpreterFrame* fp);
extern void
TraceRuntime(JSTracer* trc);
extern void
ReleaseAllJITCode(FreeOp* op);
extern void
PrepareForDebugGC(JSRuntime* rt);
/* 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
};
// 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 shrinkFlag;
friend class js::gc::ArenaLists;
static void freeElementsAndArray(void** array, void** end) {
MOZ_ASSERT(array <= end);
for (void** p = array; p != end; ++p)
js_free(*p);
js_free(array);
}
void doSweep(AutoLockGC& lock);
public:
explicit GCHelperState(JSRuntime* rt)
: rt(rt),
done(nullptr),
state_(IDLE),
thread(nullptr),
shrinkFlag(false)
{ }
bool init();
void finish();
void work();
void maybeStartBackgroundSweep(const AutoLockGC& lock);
void startBackgroundShrink(const AutoLockGC& lock);
/* Must be called without the GC lock taken. */
void waitBackgroundSweepEnd();
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 {
MOZ_ASSERT(isBackgroundSweeping());
return shrinkFlag;
}
};
// A generic task used to dispatch work to the helper thread system.
// Users should derive from GCParallelTask add what data they need and
// override |run|.
class GCParallelTask
{
// The state of the parallel computation.
enum TaskState {
NotStarted,
Dispatched,
Finished,
} state;
// Amount of time this task took to execute.
uint64_t duration_;
protected:
// A flag to signal a request for early completion of the off-thread task.
mozilla::Atomic<bool> cancel_;
virtual void run() = 0;
public:
GCParallelTask() : state(NotStarted), duration_(0) {}
// Derived classes must override this to ensure that join() gets called
// before members get destructed.
virtual ~GCParallelTask();
// Time spent in the most recent invocation of this task.
int64_t duration() const { return duration_; }
// The simple interface to a parallel task works exactly like pthreads.
bool start();
void join();
// If multiple tasks are to be started or joined at once, it is more
// efficient to take the helper thread lock once and use these methods.
bool startWithLockHeld();
void joinWithLockHeld();
// Instead of dispatching to a helper, run the task on the main thread.
void runFromMainThread(JSRuntime* rt);
// Dispatch a cancelation request.
enum CancelMode { CancelNoWait, CancelAndWait};
void cancel(CancelMode mode = CancelNoWait) {
cancel_ = true;
if (mode == CancelAndWait)
join();
}
// Check if a task is actively running.
bool isRunning() const;
// This should be friended to HelperThread, but cannot be because it
// would introduce several circular dependencies.
public:
virtual void runFromHelperThread();
};
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,
JS::TraceKind traceKind, size_t thingSize);
typedef void (*IterateCellCallback)(JSRuntime* rt, void* data, void* thing,
JS::TraceKind 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);
extern void
FinalizeStringRT(JSRuntime* rt, JSString* str);
JSCompartment*
NewCompartment(JSContext* cx, JS::Zone* zone, JSPrincipals* principals,
const JS::CompartmentOptions& options);
namespace gc {
/*
* 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);
/*
* This structure overlays a Cell in the Nursery and re-purposes its memory
* for managing the Nursery collection process.
*/
class RelocationOverlay
{
/* The low bit is set so this should never equal a normal pointer. */
static const uintptr_t Relocated = uintptr_t(0xbad0bad1);
// Arrange the fields of the RelocationOverlay so that JSObject's group
// pointer is not overwritten during compacting.
/* A list entry to track all relocated things. */
RelocationOverlay* next_;
/* Set to Relocated when moved. */
uintptr_t magic_;
/* The location |this| was moved to. */
Cell* newLocation_;
public:
static RelocationOverlay* fromCell(Cell* cell) {
return reinterpret_cast<RelocationOverlay*>(cell);
}
bool isForwarded() const {
return magic_ == Relocated;
}
Cell* forwardingAddress() const {
MOZ_ASSERT(isForwarded());
return newLocation_;
}
void forwardTo(Cell* cell) {
MOZ_ASSERT(!isForwarded());
static_assert(offsetof(JSObject, group_) == offsetof(RelocationOverlay, next_),
"next pointer and group should be at same location, "
"so that group is not overwritten during compacting");
newLocation_ = cell;
magic_ = Relocated;
}
RelocationOverlay*& nextRef() {
MOZ_ASSERT(isForwarded());
return next_;
}
RelocationOverlay* next() const {
MOZ_ASSERT(isForwarded());
return next_;
}
static bool isCellForwarded(Cell* cell) {
return fromCell(cell)->isForwarded();
}
};
/* Functions for checking and updating things that might be moved by compacting GC. */
template <typename T>
struct MightBeForwarded
{
static_assert(mozilla::IsBaseOf<Cell, T>::value,
"T must derive from Cell");
static_assert(!mozilla::IsSame<Cell, T>::value && !mozilla::IsSame<TenuredCell, T>::value,
"T must not be Cell or TenuredCell");
static const bool value = mozilla::IsBaseOf<JSObject, T>::value;
};
template <typename T>
inline bool
IsForwarded(T* t)
{
RelocationOverlay* overlay = RelocationOverlay::fromCell(t);
if (!MightBeForwarded<T>::value) {
MOZ_ASSERT(!overlay->isForwarded());
return false;
}
return overlay->isForwarded();
}
struct IsForwardedFunctor : public BoolDefaultAdaptor<Value, false> {
template <typename T> bool operator()(T* t) { return IsForwarded(t); }
};
inline bool
IsForwarded(const JS::Value& value)
{
return DispatchTyped(IsForwardedFunctor(), value);
}
template <typename T>
inline T*
Forwarded(T* t)
{
RelocationOverlay* overlay = RelocationOverlay::fromCell(t);
MOZ_ASSERT(overlay->isForwarded());
return reinterpret_cast<T*>(overlay->forwardingAddress());
}
struct ForwardedFunctor : public IdentityDefaultAdaptor<Value> {
template <typename T> inline Value operator()(T* t) {
return js::gc::RewrapTaggedPointer<Value, T*>::wrap(Forwarded(t));
}
};
inline Value
Forwarded(const JS::Value& value)
{
return DispatchTyped(ForwardedFunctor(), value);
}
template <typename T>
inline T
MaybeForwarded(T t)
{
return IsForwarded(t) ? Forwarded(t) : t;
}
#ifdef JSGC_HASH_TABLE_CHECKS
template <typename T>
inline void
CheckGCThingAfterMovingGC(T* t)
{
if (t) {
MOZ_RELEASE_ASSERT(!IsInsideNursery(t));
MOZ_RELEASE_ASSERT(!RelocationOverlay::isCellForwarded(t));
}
}
template <typename T>
inline void
CheckGCThingAfterMovingGC(const ReadBarriered<T*>& t)
{
CheckGCThingAfterMovingGC(t.unbarrieredGet());
}
struct CheckValueAfterMovingGCFunctor : public VoidDefaultAdaptor<Value> {
template <typename T> void operator()(T* t) { CheckGCThingAfterMovingGC(t); }
};
inline void
CheckValueAfterMovingGC(const JS::Value& value)
{
DispatchTyped(CheckValueAfterMovingGCFunctor(), value);
}
#endif // JSGC_HASH_TABLE_CHECKS
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 ZealCheckHashTablesOnMinorGC = 13;
const int ZealCompactValue = 14;
const int ZealLimit = 14;
enum VerifierType {
PreBarrierVerifier
};
#ifdef JS_GC_ZEAL
extern const char* ZealModeHelpText;
/* 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 vm/Runtime.h above |suppressGC| and take all appropriate
* precautions before instantiating this class.
*/
class MOZ_RAII AutoSuppressGC
{
int32_t& suppressGC_;
public:
explicit AutoSuppressGC(ExclusiveContext* cx);
explicit AutoSuppressGC(JSCompartment* comp);
explicit AutoSuppressGC(JSRuntime* rt);
~AutoSuppressGC()
{
suppressGC_--;
}
};
// A singly linked list of zones.
class ZoneList
{
static Zone * const End;
Zone* head;
Zone* tail;
public:
ZoneList();
~ZoneList();
bool isEmpty() const;
Zone* front() const;
void append(Zone* zone);
void transferFrom(ZoneList& other);
void removeFront();
void clear();
private:
explicit ZoneList(Zone* singleZone);
void check() const;
ZoneList(const ZoneList& other) = delete;
ZoneList& operator=(const ZoneList& other) = delete;
};
JSObject*
NewMemoryStatisticsObject(JSContext* cx);
} /* namespace gc */
#ifdef DEBUG
/* Use this to avoid assertions when manipulating the wrapper map. */
class MOZ_RAII AutoDisableProxyCheck
{
gc::GCRuntime& gc;
public:
explicit AutoDisableProxyCheck(JSRuntime* rt);
~AutoDisableProxyCheck();
};
#else
struct MOZ_RAII AutoDisableProxyCheck
{
explicit AutoDisableProxyCheck(JSRuntime* rt) {}
};
#endif
struct MOZ_RAII AutoDisableCompactingGC
{
explicit AutoDisableCompactingGC(JSRuntime* rt);
~AutoDisableCompactingGC();
private:
gc::GCRuntime& gc;
};
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 */