fune/js/src/gc/Tenuring.h

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 * vim: set ts=8 sts=2 et sw=2 tw=80:
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef gc_Tenuring_h
#define gc_Tenuring_h

#include "mozilla/Maybe.h"

#include "gc/AllocKind.h"
#include "js/GCAPI.h"
#include "js/TracingAPI.h"
#include "util/Text.h"

namespace js {

class NativeObject;
class Nursery;
class PlainObject;

namespace wasm {
class AnyRef;
}  // namespace wasm

namespace gc {

class AllocSite;
class ArenaCellSet;
class RelocationOverlay;
class StringRelocationOverlay;

template <typename Key>
struct DeduplicationStringHasher {
  using Lookup = Key;
  static inline HashNumber hash(const Lookup& lookup);
  static MOZ_ALWAYS_INLINE bool match(const Key& key, const Lookup& lookup);
};

class TenuringTracer final : public JSTracer {
  Nursery& nursery_;

  // Size of data promoted during collection.
  size_t promotedSize = 0;
  // Number of cells promoted during collection.
  size_t promotedCells = 0;

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

  using StringDeDupSet =
      HashSet<JSString*, DeduplicationStringHasher<JSString*>,
              SystemAllocPolicy>;

  // deDupSet is emplaced at the beginning of the nursery collection and reset
  // at the end of the nursery collection. It can also be reset during nursery
  // collection when out of memory to insert new entries.
  mozilla::Maybe<StringDeDupSet> stringDeDupSet;

  bool tenureEverything;

  // A flag set when a GC thing is promoted to the next nursery generation (as
  // opposed to the tenured heap). This is used to check when we need to add an
  // edge to the remembered set during nursery collection.
  bool promotedToNursery = false;

#define DEFINE_ON_EDGE_METHOD(name, type, _1, _2) \
  void on##name##Edge(type** thingp, const char* name) override;
  JS_FOR_EACH_TRACEKIND(DEFINE_ON_EDGE_METHOD)
#undef DEFINE_ON_EDGE_METHOD

 public:
  TenuringTracer(JSRuntime* rt, Nursery* nursery, bool tenureEverything);

  Nursery& nursery() { return nursery_; }

  // Promote all live objects and everything they can reach. Called after all
  // roots have been traced.
  void collectToObjectFixedPoint();

  // Promote all live strings and all strings they can reach, and additionally
  // do any fixups for when strings are pointing into memory that was
  // deduplicated. Called after collectToObjectFixedPoint().
  void collectToStringFixedPoint();

  size_t getPromotedSize() const;
  size_t getPromotedCells() const;

  void traverse(JS::Value* thingp);
  void traverse(wasm::AnyRef* thingp);

  // The store buffers need to be able to call these directly.
  void traceObject(JSObject* obj);
  void traceObjectSlots(NativeObject* nobj, uint32_t start, uint32_t end);
  void traceObjectElements(JS::Value* vp, uint32_t count);
  void traceString(JSString* str);
  void traceBigInt(JS::BigInt* bi);

  // Methods to promote a live cell or get the pointer to its new location if
  // that has already happened. The store buffers call these.
  JSObject* promoteOrForward(JSObject* obj);
  JSString* promoteOrForward(JSString* str);
  JS::BigInt* promoteOrForward(JS::BigInt* bip);

  // Returns whether any cells in the arena require sweeping.
  template <typename T>
  bool traceBufferedCells(Arena* arena, ArenaCellSet* cells);

  class AutoPromotedAnyToNursery;

 private:
  MOZ_ALWAYS_INLINE JSObject* onNonForwardedNurseryObject(JSObject* obj);
  MOZ_ALWAYS_INLINE JSString* onNonForwardedNurseryString(JSString* str);
  MOZ_ALWAYS_INLINE JS::BigInt* onNonForwardedNurseryBigInt(JS::BigInt* bi);

  // The dependent string chars needs to be relocated if the base which it's
  // using chars from has been deduplicated.
  template <typename CharT>
  void relocateDependentStringChars(JSDependentString* tenuredDependentStr,
                                    JSLinearString* baseOrRelocOverlay,
                                    size_t* offset,
                                    bool* rootBaseNotYetForwarded,
                                    JSLinearString** rootBase);

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

  template <typename T>
  T* alloc(JS::Zone* zone, gc::AllocKind kind, gc::Cell* src);
  template <JS::TraceKind traceKind>
  void* allocCell(JS::Zone* zone, gc::AllocKind allocKind, gc::AllocSite* site,
                  gc::Cell* src);
  JSString* allocString(JSString* src, JS::Zone* zone, gc::AllocKind dstKind);

  bool shouldTenure(Zone* zone, JS::TraceKind traceKind, Cell* cell);

  inline JSObject* promotePlainObject(PlainObject* src);
  JSObject* promoteObjectSlow(JSObject* src);
  JSString* promoteString(JSString* src);
  JS::BigInt* promoteBigInt(JS::BigInt* src);

  size_t moveElements(NativeObject* dst, NativeObject* src,
                      gc::AllocKind dstKind);
  size_t moveSlots(NativeObject* dst, NativeObject* src);
  size_t moveString(JSString* dst, JSString* src, gc::AllocKind dstKind);
  size_t moveBigInt(JS::BigInt* dst, JS::BigInt* src, gc::AllocKind dstKind);

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

}  // namespace gc
}  // namespace js

#endif  // gc_Tenuring_h