/* -*- 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/. */
#ifndef gc_Barrier_h
#define gc_Barrier_h
#include "NamespaceImports.h"
#include "gc/Heap.h"
#include "gc/StoreBuffer.h"
#include "js/HeapAPI.h"
#include "js/Id.h"
#include "js/RootingAPI.h"
#include "js/Value.h"
/*
* A write barrier is a mechanism used by incremental or generation GCs to
* ensure that every value that needs to be marked is marked. In general, the
* write barrier should be invoked whenever a write can cause the set of things
* traced through by the GC to change. This includes:
* - writes to object properties
* - writes to array slots
* - writes to fields like JSObject::shape_ that we trace through
* - writes to fields in private data
* - writes to non-markable fields like JSObject::private that point to
* markable data
* The last category is the trickiest. Even though the private pointers does not
* point to a GC thing, changing the private pointer may change the set of
* objects that are traced by the GC. Therefore it needs a write barrier.
*
* Every barriered write should have the following form:
* <pre-barrier>
* obj->field = value; // do the actual write
* <post-barrier>
* The pre-barrier is used for incremental GC and the post-barrier is for
* generational GC.
*
* PRE-BARRIER
*
* To understand the pre-barrier, let's consider how incremental GC works. The
* GC itself is divided into "slices". Between each slice, JS code is allowed to
* run. Each slice should be short so that the user doesn't notice the
* interruptions. In our GC, the structure of the slices is as follows:
*
* 1. ... JS work, which leads to a request to do GC ...
* 2. [first GC slice, which performs all root marking and possibly more marking]
* 3. ... more JS work is allowed to run ...
* 4. [GC mark slice, which runs entirely in drainMarkStack]
* 5. ... more JS work ...
* 6. [GC mark slice, which runs entirely in drainMarkStack]
* 7. ... more JS work ...
* 8. [GC marking finishes; sweeping done non-incrementally; GC is done]
* 9. ... JS continues uninterrupted now that GC is finishes ...
*
* Of course, there may be a different number of slices depending on how much
* marking is to be done.
*
* The danger inherent in this scheme is that the JS code in steps 3, 5, and 7
* might change the heap in a way that causes the GC to collect an object that
* is actually reachable. The write barrier prevents this from happening. We use
* a variant of incremental GC called "snapshot at the beginning." This approach
* guarantees the invariant that if an object is reachable in step 2, then we
* will mark it eventually. The name comes from the idea that we take a
* theoretical "snapshot" of all reachable objects in step 2; all objects in
* that snapshot should eventually be marked. (Note that the write barrier
* verifier code takes an actual snapshot.)
*
* The basic correctness invariant of a snapshot-at-the-beginning collector is
* that any object reachable at the end of the GC (step 9) must either:
* (1) have been reachable at the beginning (step 2) and thus in the snapshot
* (2) or must have been newly allocated, in steps 3, 5, or 7.
* To deal with case (2), any objects allocated during an incremental GC are
* automatically marked black.
*
* This strategy is actually somewhat conservative: if an object becomes
* unreachable between steps 2 and 8, it would be safe to collect it. We won't,
* mainly for simplicity. (Also, note that the snapshot is entirely
* theoretical. We don't actually do anything special in step 2 that we wouldn't
* do in a non-incremental GC.
*
* It's the pre-barrier's job to maintain the snapshot invariant. Consider the
* write "obj->field = value". Let the prior value of obj->field be
* value0. Since it's possible that value0 may have been what obj->field
* contained in step 2, when the snapshot was taken, the barrier marks
* value0. Note that it only does this if we're in the middle of an incremental
* GC. Since this is rare, the cost of the write barrier is usually just an
* extra branch.
*
* In practice, we implement the pre-barrier differently based on the type of
* value0. E.g., see JSObject::writeBarrierPre, which is used if obj->field is
* a JSObject*. It takes value0 as a parameter.
*
* READ-BARRIER
*
* Incremental GC requires that weak pointers have read barriers. The problem
* happens when, during an incremental GC, some code reads a weak pointer and
* writes it somewhere on the heap that has been marked black in a previous
* slice. Since the weak pointer will not otherwise be marked and will be swept
* and finalized in the last slice, this will leave the pointer just written
* dangling after the GC. To solve this, we immediately mark black all weak
* pointers that get read between slices so that it is safe to store them in an
* already marked part of the heap, e.g. in Rooted.
*
* POST-BARRIER
*
* For generational GC, we want to be able to quickly collect the nursery in a
* minor collection. Part of the way this is achieved is to only mark the
* nursery itself; tenured things, which may form the majority of the heap, are
* not traced through or marked. This leads to the problem of what to do about
* tenured objects that have pointers into the nursery: if such things are not
* marked, they may be discarded while there are still live objects which
* reference them. The solution is to maintain information about these pointers,
* and mark their targets when we start a minor collection.
*
* The pointers can be thought of as edges in object graph, and the set of edges
* from the tenured generation into the nursery is know as the remembered set.
* Post barriers are used to track this remembered set.
*
* Whenever a slot which could contain such a pointer is written, we use a write
* barrier to check if the edge created is in the remembered set, and if so we
* insert it into the store buffer, which is the collector's representation of
* the remembered set. This means than when we come to do a minor collection we
* can examine the contents of the store buffer and mark any edge targets that
* are in the nursery.
*
* IMPLEMENTATION DETAILS
*
* Since it would be awkward to change every write to memory into a function
* call, this file contains a bunch of C++ classes and templates that use
* operator overloading to take care of barriers automatically. In many cases,
* all that's necessary to make some field be barriered is to replace
* Type* field;
* with
* GCPtr<Type> field;
*
* One additional note: not all object writes need to be pre-barriered. Writes
* to newly allocated objects do not need a pre-barrier. In these cases, we use
* the "obj->field.init(value)" method instead of "obj->field = value". We use
* the init naming idiom in many places to signify that a field is being
* assigned for the first time.
*
* This file implements four classes, illustrated here:
*
* BarrieredBase base class of all barriers
* | |
* | WriteBarrieredBase base class which provides common write operations
* | | | | |
* | | | | PreBarriered provides pre-barriers only
* | | | |
* | | | GCPtr provides pre- and post-barriers
* | | |
* | | HeapPtr provides pre- and post-barriers; is relocatable
* | | and deletable for use inside C++ managed memory
* | |
* | HeapSlot similar to GCPtr, but tailored to slots storage
* |
* ReadBarrieredBase base class which provides common read operations
* |
* ReadBarriered provides read barriers only
*
*
* The implementation of the barrier logic is implemented on T::writeBarrier.*,
* via:
*
* WriteBarrieredBase<T>::pre
* -> InternalBarrierMethods<T*>::preBarrier
* -> T::writeBarrierPre
* -> InternalBarrierMethods<Value>::preBarrier
* -> InternalBarrierMethods<jsid>::preBarrier
* -> InternalBarrierMethods<T*>::preBarrier
* -> T::writeBarrierPre
*
* GCPtr<T>::post and HeapPtr<T>::post
* -> InternalBarrierMethods<T*>::postBarrier
* -> T::writeBarrierPost
* -> InternalBarrierMethods<Value>::postBarrier
* -> StoreBuffer::put
*
* These classes are designed to be used by the internals of the JS engine.
* Barriers designed to be used externally are provided in js/RootingAPI.h.
* These external barriers call into the same post-barrier implementations at
* InternalBarrierMethods<T>::post via an indirect call to Heap(.+)Barrier.
*
* These clases are designed to be used to wrap GC thing pointers or values that
* act like them (i.e. JS::Value and jsid). It is possible to use them for
* other types by supplying the necessary barrier implementations but this
* is not usually necessary and should be done with caution.
*/
class JSAtom;
struct JSCompartment;
class JSFlatString;
class JSLinearString;
namespace JS {
class Symbol;
} // namespace JS
namespace js {
class AccessorShape;
class ArrayObject;
class ArgumentsObject;
class ArrayBufferObjectMaybeShared;
class ArrayBufferObject;
class ArrayBufferViewObject;
class SharedArrayBufferObject;
class BaseShape;
class DebugEnvironmentProxy;
class GlobalObject;
class LazyScript;
class ModuleObject;
class ModuleEnvironmentObject;
class ModuleNamespaceObject;
class NativeObject;
class PlainObject;
class PropertyName;
class SavedFrame;
class EnvironmentObject;
class ScriptSourceObject;
class Shape;
class UnownedBaseShape;
class ObjectGroup;
namespace jit {
class JitCode;
} // namespace jit
#ifdef DEBUG
// Barriers can't be triggered during backend Ion compilation, which may run on
// a helper thread.
bool
CurrentThreadIsIonCompiling();
bool
CurrentThreadIsIonCompilingSafeForMinorGC();
bool
CurrentThreadIsGCSweeping();
bool
IsMarkedBlack(NativeObject* obj);
#endif
namespace gc {
// Marking.h depends on these barrier definitions, so we need a separate
// entry point for marking to implement the pre-barrier.
void MarkValueForBarrier(JSTracer* trc, Value* v, const char* name);
void MarkIdForBarrier(JSTracer* trc, jsid* idp, const char* name);
} // namespace gc
template <typename T>
struct InternalBarrierMethods {};
template <typename T>
struct InternalBarrierMethods<T*>
{
static bool isMarkable(T* v) { return v != nullptr; }
static bool isMarkableTaggedPointer(T* v) { return !IsNullTaggedPointer(v); }
static void preBarrier(T* v) { T::writeBarrierPre(v); }
static void postBarrier(T** vp, T* prev, T* next) { T::writeBarrierPost(vp, prev, next); }
static void readBarrier(T* v) { T::readBarrier(v); }
};
template <typename S> struct PreBarrierFunctor : public VoidDefaultAdaptor<S> {
template <typename T> void operator()(T* t);
};
template <typename S> struct ReadBarrierFunctor : public VoidDefaultAdaptor<S> {
template <typename T> void operator()(T* t);
};
template <>
struct InternalBarrierMethods<Value>
{
static bool isMarkable(const Value& v) { return v.isGCThing(); }
static bool isMarkableTaggedPointer(const Value& v) { return isMarkable(v); }
static void preBarrier(const Value& v) {
DispatchTyped(PreBarrierFunctor<Value>(), v);
}
static void postBarrier(Value* vp, const Value& prev, const Value& next) {
MOZ_ASSERT(!CurrentThreadIsIonCompiling());
MOZ_ASSERT(vp);
// If the target needs an entry, add it.
js::gc::StoreBuffer* sb;
if (next.isObject() && (sb = reinterpret_cast<gc::Cell*>(&next.toObject())->storeBuffer())) {
// If we know that the prev has already inserted an entry, we can
// skip doing the lookup to add the new entry. Note that we cannot
// safely assert the presence of the entry because it may have been
// added via a different store buffer.
if (prev.isObject() && reinterpret_cast<gc::Cell*>(&prev.toObject())->storeBuffer())
return;
sb->putValue(vp);
return;
}
// Remove the prev entry if the new value does not need it.
if (prev.isObject() && (sb = reinterpret_cast<gc::Cell*>(&prev.toObject())->storeBuffer()))
sb->unputValue(vp);
}
static void readBarrier(const Value& v) {
DispatchTyped(ReadBarrierFunctor<Value>(), v);
}
};
template <>
struct InternalBarrierMethods<jsid>
{
static bool isMarkable(jsid id) { return JSID_IS_GCTHING(id); }
static bool isMarkableTaggedPointer(jsid id) { return isMarkable(id); }
static void preBarrier(jsid id) { DispatchTyped(PreBarrierFunctor<jsid>(), id); }
static void postBarrier(jsid* idp, jsid prev, jsid next) {}
};
// Barrier classes can use Mixins to add methods to a set of barrier
// instantiations, to make the barriered thing look and feel more like the
// thing itself.
template <typename T>
class BarrieredBaseMixins {};
// Base class of all barrier types.
//
// This is marked non-memmovable since post barriers added by derived classes
// can add pointers to class instances to the store buffer.
template <typename T>
class MOZ_NON_MEMMOVABLE BarrieredBase : public BarrieredBaseMixins<T>
{
protected:
// BarrieredBase is not directly instantiable.
explicit BarrieredBase(const T& v) : value(v) {}
// Storage for all barrier classes. |value| must be a GC thing reference
// type: either a direct pointer to a GC thing or a supported tagged
// pointer that can reference GC things, such as JS::Value or jsid. Nested
// barrier types are NOT supported. See assertTypeConstraints.
T value;
public:
// Note: this is public because C++ cannot friend to a specific template instantiation.
// Friending to the generic template leads to a number of unintended consequences, including
// template resolution ambiguity and a circular dependency with Tracing.h.
T* unsafeUnbarrieredForTracing() { return &value; }
};
// Base class for barriered pointer types that intercept only writes.
template <class T>
class WriteBarrieredBase : public BarrieredBase<T>
{
protected:
// WriteBarrieredBase is not directly instantiable.
explicit WriteBarrieredBase(const T& v) : BarrieredBase<T>(v) {}
public:
DECLARE_POINTER_COMPARISON_OPS(T);
DECLARE_POINTER_CONSTREF_OPS(T);
// Use this if the automatic coercion to T isn't working.
const T& get() const { return this->value; }
// Use this if you want to change the value without invoking barriers.
// Obviously this is dangerous unless you know the barrier is not needed.
void unsafeSet(const T& v) { this->value = v; }
// For users who need to manually barrier the raw types.
static void writeBarrierPre(const T& v) { InternalBarrierMethods<T>::preBarrier(v); }
protected:
void pre() { InternalBarrierMethods<T>::preBarrier(this->value); }
void post(const T& prev, const T& next) {
InternalBarrierMethods<T>::postBarrier(&this->value, prev, next);
}
};
/*
* PreBarriered only automatically handles pre-barriers. Post-barriers must be
* manually implemented when using this class. GCPtr and HeapPtr should be used
* in all cases that do not require explicit low-level control of moving
* behavior, e.g. for HashMap keys.
*/
template <class T>
class PreBarriered : public WriteBarrieredBase<T>
{
public:
PreBarriered() : WriteBarrieredBase<T>(JS::GCPolicy<T>::initial()) {}
/*
* Allow implicit construction for use in generic contexts, such as
* DebuggerWeakMap::markKeys.
*/
MOZ_IMPLICIT PreBarriered(const T& v) : WriteBarrieredBase<T>(v) {}
explicit PreBarriered(const PreBarriered<T>& v) : WriteBarrieredBase<T>(v.value) {}
~PreBarriered() { this->pre(); }
void init(const T& v) {
this->value = v;
}
/* Use to set the pointer to nullptr. */
void clear() {
this->pre();
this->value = nullptr;
}
DECLARE_POINTER_ASSIGN_OPS(PreBarriered, T);
private:
void set(const T& v) {
this->pre();
this->value = v;
}
};
/*
* A pre- and post-barriered heap pointer, for use inside the JS engine.
*
* It must only be stored in memory that has GC lifetime. GCPtr must not be
* used in contexts where it may be implicitly moved or deleted, e.g. most
* containers.
*
* The post-barriers implemented by this class are faster than those
* implemented by js::HeapPtr<T> or JS::Heap<T> at the cost of not
* automatically handling deletion or movement.
*/
template <class T>
class GCPtr : public WriteBarrieredBase<T>
{
public:
GCPtr() : WriteBarrieredBase<T>(JS::GCPolicy<T>::initial()) {}
explicit GCPtr(const T& v) : WriteBarrieredBase<T>(v) {
this->post(JS::GCPolicy<T>::initial(), v);
}
explicit GCPtr(const GCPtr<T>& v) : WriteBarrieredBase<T>(v) {
this->post(JS::GCPolicy<T>::initial(), v);
}
#ifdef DEBUG
~GCPtr() {
// No prebarrier necessary as this only happens when we are sweeping or
// after we have just collected the nursery. Note that the wrapped
// pointer may already have been freed by this point.
MOZ_ASSERT(CurrentThreadIsGCSweeping());
Poison(this, JS_FREED_HEAP_PTR_PATTERN, sizeof(*this));
}
#endif
void init(const T& v) {
this->value = v;
this->post(JS::GCPolicy<T>::initial(), v);
}
DECLARE_POINTER_ASSIGN_OPS(GCPtr, T);
T unbarrieredGet() const {
return this->value;
}
private:
void set(const T& v) {
this->pre();
T tmp = this->value;
this->value = v;
this->post(tmp, this->value);
}
/*
* Unlike HeapPtr<T>, GCPtr<T> must be managed with GC lifetimes.
* Specifically, the memory used by the pointer itself must be live until
* at least the next minor GC. For that reason, move semantics are invalid
* and are deleted here. Please note that not all containers support move
* semantics, so this does not completely prevent invalid uses.
*/
GCPtr(GCPtr<T>&&) = delete;
GCPtr<T>& operator=(GCPtr<T>&&) = delete;
};
/*
* A pre- and post-barriered heap pointer, for use inside the JS engine. These
* heap pointers can be stored in C++ containers like GCVector and GCHashMap.
*
* The GC sometimes keeps pointers to pointers to GC things --- for example, to
* track references into the nursery. However, C++ containers like GCVector and
* GCHashMap usually reserve the right to relocate their elements any time
* they're modified, invalidating all pointers to the elements. HeapPtr
* has a move constructor which knows how to keep the GC up to date if it is
* moved to a new location.
*
* However, because of this additional communication with the GC, HeapPtr
* is somewhat slower, so it should only be used in contexts where this ability
* is necessary.
*
* Obviously, JSObjects, JSStrings, and the like get tenured and compacted, so
* whatever pointers they contain get relocated, in the sense used here.
* However, since the GC itself is moving those values, it takes care of its
* internal pointers to those pointers itself. HeapPtr is only necessary
* when the relocation would otherwise occur without the GC's knowledge.
*/
template <class T>
class HeapPtr : public WriteBarrieredBase<T>
{
public:
HeapPtr() : WriteBarrieredBase<T>(JS::GCPolicy<T>::initial()) {}
// Implicitly adding barriers is a reasonable default.
MOZ_IMPLICIT HeapPtr(const T& v) : WriteBarrieredBase<T>(v) {
this->post(JS::GCPolicy<T>::initial(), this->value);
}
/*
* For HeapPtr, move semantics are equivalent to copy semantics. In
* C++, a copy constructor taking const-ref is the way to get a single
* function that will be used for both lvalue and rvalue copies, so we can
* simply omit the rvalue variant.
*/
MOZ_IMPLICIT HeapPtr(const HeapPtr<T>& v) : WriteBarrieredBase<T>(v) {
this->post(JS::GCPolicy<T>::initial(), this->value);
}
~HeapPtr() {
this->pre();
this->post(this->value, JS::GCPolicy<T>::initial());
}
void init(const T& v) {
this->value = v;
this->post(JS::GCPolicy<T>::initial(), this->value);
}
DECLARE_POINTER_ASSIGN_OPS(HeapPtr, T);
/* Make this friend so it can access pre() and post(). */
template <class T1, class T2>
friend inline void
BarrieredSetPair(Zone* zone,
HeapPtr<T1*>& v1, T1* val1,
HeapPtr<T2*>& v2, T2* val2);
protected:
void set(const T& v) {
this->pre();
postBarrieredSet(v);
}
void postBarrieredSet(const T& v) {
T tmp = this->value;
this->value = v;
this->post(tmp, this->value);
}
};
// Base class for barriered pointer types that intercept reads and writes.
template <typename T>
class ReadBarrieredBase : public BarrieredBase<T>
{
protected:
// ReadBarrieredBase is not directly instantiable.
explicit ReadBarrieredBase(const T& v) : BarrieredBase<T>(v) {}
protected:
void read() const { InternalBarrierMethods<T>::readBarrier(this->value); }
void post(const T& prev, const T& next) {
InternalBarrierMethods<T>::postBarrier(&this->value, prev, next);
}
};
// Incremental GC requires that weak pointers have read barriers. See the block
// comment at the top of Barrier.h for a complete discussion of why.
//
// Note that this class also has post-barriers, so is safe to use with nursery
// pointers. However, when used as a hashtable key, care must still be taken to
// insert manual post-barriers on the table for rekeying if the key is based in
// any way on the address of the object.
template <typename T>
class ReadBarriered : public ReadBarrieredBase<T>
{
public:
ReadBarriered() : ReadBarrieredBase<T>(JS::GCPolicy<T>::initial()) {}
// It is okay to add barriers implicitly.
MOZ_IMPLICIT ReadBarriered(const T& v) : ReadBarrieredBase<T>(v) {
this->post(JS::GCPolicy<T>::initial(), v);
}
// Copy is creating a new edge, so we must read barrier the source edge.
explicit ReadBarriered(const ReadBarriered& v) : ReadBarrieredBase<T>(v) {
this->post(JS::GCPolicy<T>::initial(), v.get());
}
// Move retains the lifetime status of the source edge, so does not fire
// the read barrier of the defunct edge.
ReadBarriered(ReadBarriered&& v)
: ReadBarrieredBase<T>(mozilla::Move(v))
{
this->post(JS::GCPolicy<T>::initial(), v.value);
}
~ReadBarriered() {
this->post(this->value, JS::GCPolicy<T>::initial());
}
ReadBarriered& operator=(const ReadBarriered& v) {
T prior = this->value;
this->value = v.value;
this->post(prior, v.value);
return *this;
}
const T get() const {
if (!InternalBarrierMethods<T>::isMarkable(this->value))
return JS::GCPolicy<T>::initial();
this->read();
return this->value;
}
const T unbarrieredGet() const {
return this->value;
}
explicit operator bool() const {
return bool(this->value);
}
operator const T() const { return get(); }
const T operator->() const { return get(); }
T* unsafeGet() { return &this->value; }
T const* unsafeGet() const { return &this->value; }
void set(const T& v)
{
T tmp = this->value;
this->value = v;
this->post(tmp, v);
}
};
// A WeakRef pointer does not hold its target live and is automatically nulled
// out when the GC discovers that it is not reachable from any other path.
template <typename T>
using WeakRef = ReadBarriered<T>;
// Add Value operations to all Barrier types. Note, this must be defined before
// HeapSlot for HeapSlot's base to get these operations.
template <>
class BarrieredBaseMixins<JS::Value> : public ValueOperations<WriteBarrieredBase<JS::Value>>
{};
// A pre- and post-barriered Value that is specialized to be aware that it
// resides in a slots or elements vector. This allows it to be relocated in
// memory, but with substantially less overhead than a HeapPtr.
class HeapSlot : public WriteBarrieredBase<Value>
{
public:
enum Kind {
Slot = 0,
Element = 1
};
void init(NativeObject* owner, Kind kind, uint32_t slot, const Value& v) {
value = v;
post(owner, kind, slot, v);
}
void destroy() {
pre();
}
#ifdef DEBUG
bool preconditionForSet(NativeObject* owner, Kind kind, uint32_t slot) const;
bool preconditionForWriteBarrierPost(NativeObject* obj, Kind kind, uint32_t slot,
const Value& target) const;
#endif
void set(NativeObject* owner, Kind kind, uint32_t slot, const Value& v) {
MOZ_ASSERT(preconditionForSet(owner, kind, slot));
pre();
value = v;
post(owner, kind, slot, v);
}
private:
void post(NativeObject* owner, Kind kind, uint32_t slot, const Value& target) {
MOZ_ASSERT(preconditionForWriteBarrierPost(owner, kind, slot, target));
if (this->value.isObject()) {
gc::Cell* cell = reinterpret_cast<gc::Cell*>(&this->value.toObject());
if (cell->storeBuffer())
cell->storeBuffer()->putSlot(owner, kind, slot, 1);
}
}
};
class HeapSlotArray
{
HeapSlot* array;
// Whether writes may be performed to the slots in this array. This helps
// to control how object elements which may be copy on write are used.
#ifdef DEBUG
bool allowWrite_;
#endif
public:
explicit HeapSlotArray(HeapSlot* array, bool allowWrite)
: array(array)
#ifdef DEBUG
, allowWrite_(allowWrite)
#endif
{}
operator const Value*() const {
JS_STATIC_ASSERT(sizeof(GCPtr<Value>) == sizeof(Value));
JS_STATIC_ASSERT(sizeof(HeapSlot) == sizeof(Value));
return reinterpret_cast<const Value*>(array);
}
operator HeapSlot*() const { MOZ_ASSERT(allowWrite()); return array; }
HeapSlotArray operator +(int offset) const { return HeapSlotArray(array + offset, allowWrite()); }
HeapSlotArray operator +(uint32_t offset) const { return HeapSlotArray(array + offset, allowWrite()); }
private:
bool allowWrite() const {
#ifdef DEBUG
return allowWrite_;
#else
return true;
#endif
}
};
/*
* This is a hack for RegExpStatics::updateFromMatch. It allows us to do two
* barriers with only one branch to check if we're in an incremental GC.
*/
template <class T1, class T2>
static inline void
BarrieredSetPair(Zone* zone,
HeapPtr<T1*>& v1, T1* val1,
HeapPtr<T2*>& v2, T2* val2)
{
if (T1::needWriteBarrierPre(zone)) {
v1.pre();
v2.pre();
}
v1.postBarrieredSet(val1);
v2.postBarrieredSet(val2);
}
/*
* ImmutableTenuredPtr is designed for one very narrow case: replacing
* immutable raw pointers to GC-managed things, implicitly converting to a
* handle type for ease of use. Pointers encapsulated by this type must:
*
* be immutable (no incremental write barriers),
* never point into the nursery (no generational write barriers), and
* be traced via MarkRuntime (we use fromMarkedLocation).
*
* In short: you *really* need to know what you're doing before you use this
* class!
*/
template <typename T>
class ImmutableTenuredPtr
{
T value;
public:
operator T() const { return value; }
T operator->() const { return value; }
operator Handle<T>() const {
return Handle<T>::fromMarkedLocation(&value);
}
void init(T ptr) {
MOZ_ASSERT(ptr->isTenured());
value = ptr;
}
T get() const { return value; }
const T* address() { return &value; }
};
template <typename T>
struct MovableCellHasher<PreBarriered<T>>
{
using Key = PreBarriered<T>;
using Lookup = T;
static bool hasHash(const Lookup& l) { return MovableCellHasher<T>::hasHash(l); }
static bool ensureHash(const Lookup& l) { return MovableCellHasher<T>::ensureHash(l); }
static HashNumber hash(const Lookup& l) { return MovableCellHasher<T>::hash(l); }
static bool match(const Key& k, const Lookup& l) { return MovableCellHasher<T>::match(k, l); }
static void rekey(Key& k, const Key& newKey) { k.unsafeSet(newKey); }
};
template <typename T>
struct MovableCellHasher<HeapPtr<T>>
{
using Key = HeapPtr<T>;
using Lookup = T;
static bool hasHash(const Lookup& l) { return MovableCellHasher<T>::hasHash(l); }
static bool ensureHash(const Lookup& l) { return MovableCellHasher<T>::ensureHash(l); }
static HashNumber hash(const Lookup& l) { return MovableCellHasher<T>::hash(l); }
static bool match(const Key& k, const Lookup& l) { return MovableCellHasher<T>::match(k, l); }
static void rekey(Key& k, const Key& newKey) { k.unsafeSet(newKey); }
};
template <typename T>
struct MovableCellHasher<ReadBarriered<T>>
{
using Key = ReadBarriered<T>;
using Lookup = T;
static bool hasHash(const Lookup& l) { return MovableCellHasher<T>::hasHash(l); }
static bool ensureHash(const Lookup& l) { return MovableCellHasher<T>::ensureHash(l); }
static HashNumber hash(const Lookup& l) { return MovableCellHasher<T>::hash(l); }
static bool match(const Key& k, const Lookup& l) {
return MovableCellHasher<T>::match(k.unbarrieredGet(), l);
}
static void rekey(Key& k, const Key& newKey) { k.unsafeSet(newKey); }
};
/* Useful for hashtables with a GCPtr as key. */
template <class T>
struct GCPtrHasher
{
typedef GCPtr<T> Key;
typedef T Lookup;
static HashNumber hash(Lookup obj) { return DefaultHasher<T>::hash(obj); }
static bool match(const Key& k, Lookup l) { return k.get() == l; }
static void rekey(Key& k, const Key& newKey) { k.unsafeSet(newKey); }
};
/* Specialized hashing policy for GCPtrs. */
template <class T>
struct DefaultHasher<GCPtr<T>> : GCPtrHasher<T> {};
template <class T>
struct PreBarrieredHasher
{
typedef PreBarriered<T> Key;
typedef T Lookup;
static HashNumber hash(Lookup obj) { return DefaultHasher<T>::hash(obj); }
static bool match(const Key& k, Lookup l) { return k.get() == l; }
static void rekey(Key& k, const Key& newKey) { k.unsafeSet(newKey); }
};
template <class T>
struct DefaultHasher<PreBarriered<T>> : PreBarrieredHasher<T> { };
/* Useful for hashtables with a ReadBarriered as key. */
template <class T>
struct ReadBarrieredHasher
{
typedef ReadBarriered<T> Key;
typedef T Lookup;
static HashNumber hash(Lookup obj) { return DefaultHasher<T>::hash(obj); }
static bool match(const Key& k, Lookup l) { return k.unbarrieredGet() == l; }
static void rekey(Key& k, const Key& newKey) { k.set(newKey.unbarrieredGet()); }
};
/* Specialized hashing policy for ReadBarriereds. */
template <class T>
struct DefaultHasher<ReadBarriered<T>> : ReadBarrieredHasher<T> { };
class ArrayObject;
class ArrayBufferObject;
class GlobalObject;
class Scope;
class ScriptSourceObject;
class Shape;
class BaseShape;
class UnownedBaseShape;
class WasmInstanceObject;
class WasmTableObject;
namespace jit {
class JitCode;
} // namespace jit
typedef PreBarriered<JSObject*> PreBarrieredObject;
typedef PreBarriered<JSScript*> PreBarrieredScript;
typedef PreBarriered<jit::JitCode*> PreBarrieredJitCode;
typedef PreBarriered<JSString*> PreBarrieredString;
typedef PreBarriered<JSAtom*> PreBarrieredAtom;
typedef GCPtr<NativeObject*> GCPtrNativeObject;
typedef GCPtr<ArrayObject*> GCPtrArrayObject;
typedef GCPtr<ArrayBufferObjectMaybeShared*> GCPtrArrayBufferObjectMaybeShared;
typedef GCPtr<ArrayBufferObject*> GCPtrArrayBufferObject;
typedef GCPtr<BaseShape*> GCPtrBaseShape;
typedef GCPtr<JSAtom*> GCPtrAtom;
typedef GCPtr<JSFlatString*> GCPtrFlatString;
typedef GCPtr<JSFunction*> GCPtrFunction;
typedef GCPtr<JSLinearString*> GCPtrLinearString;
typedef GCPtr<JSObject*> GCPtrObject;
typedef GCPtr<JSScript*> GCPtrScript;
typedef GCPtr<JSString*> GCPtrString;
typedef GCPtr<ModuleObject*> GCPtrModuleObject;
typedef GCPtr<ModuleEnvironmentObject*> GCPtrModuleEnvironmentObject;
typedef GCPtr<ModuleNamespaceObject*> GCPtrModuleNamespaceObject;
typedef GCPtr<PlainObject*> GCPtrPlainObject;
typedef GCPtr<PropertyName*> GCPtrPropertyName;
typedef GCPtr<Shape*> GCPtrShape;
typedef GCPtr<UnownedBaseShape*> GCPtrUnownedBaseShape;
typedef GCPtr<jit::JitCode*> GCPtrJitCode;
typedef GCPtr<ObjectGroup*> GCPtrObjectGroup;
typedef GCPtr<Scope*> GCPtrScope;
typedef PreBarriered<Value> PreBarrieredValue;
typedef GCPtr<Value> GCPtrValue;
typedef PreBarriered<jsid> PreBarrieredId;
typedef GCPtr<jsid> GCPtrId;
typedef ImmutableTenuredPtr<PropertyName*> ImmutablePropertyNamePtr;
typedef ImmutableTenuredPtr<JS::Symbol*> ImmutableSymbolPtr;
typedef ReadBarriered<DebugEnvironmentProxy*> ReadBarrieredDebugEnvironmentProxy;
typedef ReadBarriered<GlobalObject*> ReadBarrieredGlobalObject;
typedef ReadBarriered<JSObject*> ReadBarrieredObject;
typedef ReadBarriered<JSFunction*> ReadBarrieredFunction;
typedef ReadBarriered<JSScript*> ReadBarrieredScript;
typedef ReadBarriered<ScriptSourceObject*> ReadBarrieredScriptSourceObject;
typedef ReadBarriered<Shape*> ReadBarrieredShape;
typedef ReadBarriered<jit::JitCode*> ReadBarrieredJitCode;
typedef ReadBarriered<ObjectGroup*> ReadBarrieredObjectGroup;
typedef ReadBarriered<JS::Symbol*> ReadBarrieredSymbol;
typedef ReadBarriered<WasmInstanceObject*> ReadBarrieredWasmInstanceObject;
typedef ReadBarriered<WasmTableObject*> ReadBarrieredWasmTableObject;
typedef ReadBarriered<Value> ReadBarrieredValue;
} /* namespace js */
#endif /* gc_Barrier_h */