src/objects/js-weak-refs-inl.h

// Copyright 2018 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef V8_OBJECTS_JS_WEAK_REFS_INL_H_
#define V8_OBJECTS_JS_WEAK_REFS_INL_H_

#include "src/objects/js-weak-refs.h"

#include "src/api/api-inl.h"
#include "src/heap/heap-write-barrier-inl.h"
#include "src/objects/microtask-inl.h"
#include "src/objects/smi-inl.h"

// Has to be the last include (doesn't have include guards):
#include "src/objects/object-macros.h"

namespace v8 {
namespace internal {

OBJECT_CONSTRUCTORS_IMPL(WeakCell, HeapObject)
OBJECT_CONSTRUCTORS_IMPL(JSWeakRef, JSObject)
OBJECT_CONSTRUCTORS_IMPL(JSFinalizationGroup, JSObject)
OBJECT_CONSTRUCTORS_IMPL(JSFinalizationGroupCleanupIterator, JSObject)
OBJECT_CONSTRUCTORS_IMPL(FinalizationGroupCleanupJobTask, Microtask)

ACCESSORS(JSFinalizationGroup, native_context, NativeContext,
          kNativeContextOffset)
ACCESSORS(JSFinalizationGroup, cleanup, Object, kCleanupOffset)
ACCESSORS(JSFinalizationGroup, active_cells, Object, kActiveCellsOffset)
ACCESSORS(JSFinalizationGroup, cleared_cells, Object, kClearedCellsOffset)
ACCESSORS(JSFinalizationGroup, key_map, Object, kKeyMapOffset)
SMI_ACCESSORS(JSFinalizationGroup, flags, kFlagsOffset)
ACCESSORS(JSFinalizationGroup, next, Object, kNextOffset)
CAST_ACCESSOR(JSFinalizationGroup)

ACCESSORS(WeakCell, finalization_group, Object, kFinalizationGroupOffset)
ACCESSORS(WeakCell, target, HeapObject, kTargetOffset)
ACCESSORS(WeakCell, holdings, Object, kHoldingsOffset)
ACCESSORS(WeakCell, next, Object, kNextOffset)
ACCESSORS(WeakCell, prev, Object, kPrevOffset)
ACCESSORS(WeakCell, key, Object, kKeyOffset)
ACCESSORS(WeakCell, key_list_next, Object, kKeyListNextOffset)
ACCESSORS(WeakCell, key_list_prev, Object, kKeyListPrevOffset)
CAST_ACCESSOR(WeakCell)

CAST_ACCESSOR(JSWeakRef)
ACCESSORS(JSWeakRef, target, HeapObject, kTargetOffset)

ACCESSORS(JSFinalizationGroupCleanupIterator, finalization_group,
          JSFinalizationGroup, kFinalizationGroupOffset)
CAST_ACCESSOR(JSFinalizationGroupCleanupIterator)

ACCESSORS(FinalizationGroupCleanupJobTask, finalization_group,
          JSFinalizationGroup, kFinalizationGroupOffset)
CAST_ACCESSOR(FinalizationGroupCleanupJobTask)

void JSFinalizationGroup::Register(
    Handle<JSFinalizationGroup> finalization_group, Handle<JSReceiver> target,
    Handle<Object> holdings, Handle<Object> key, Isolate* isolate) {
  Handle<WeakCell> weak_cell = isolate->factory()->NewWeakCell();
  weak_cell->set_finalization_group(*finalization_group);
  weak_cell->set_target(*target);
  weak_cell->set_holdings(*holdings);
  weak_cell->set_prev(ReadOnlyRoots(isolate).undefined_value());
  weak_cell->set_next(ReadOnlyRoots(isolate).undefined_value());
  weak_cell->set_key(*key);
  weak_cell->set_key_list_prev(ReadOnlyRoots(isolate).undefined_value());
  weak_cell->set_key_list_next(ReadOnlyRoots(isolate).undefined_value());

  // Add to active_cells.
  weak_cell->set_next(finalization_group->active_cells());
  if (finalization_group->active_cells().IsWeakCell()) {
    WeakCell::cast(finalization_group->active_cells()).set_prev(*weak_cell);
  }
  finalization_group->set_active_cells(*weak_cell);

  if (!key->IsUndefined(isolate)) {
    Handle<ObjectHashTable> key_map;
    if (finalization_group->key_map().IsUndefined(isolate)) {
      key_map = ObjectHashTable::New(isolate, 1);
    } else {
      key_map =
          handle(ObjectHashTable::cast(finalization_group->key_map()), isolate);
    }

    Object value = key_map->Lookup(key);
    if (value.IsWeakCell()) {
      WeakCell existing_weak_cell = WeakCell::cast(value);
      existing_weak_cell.set_key_list_prev(*weak_cell);
      weak_cell->set_key_list_next(existing_weak_cell);
    } else {
      DCHECK(value.IsTheHole(isolate));
    }
    key_map = ObjectHashTable::Put(key_map, key, weak_cell);
    finalization_group->set_key_map(*key_map);
  }
}

bool JSFinalizationGroup::Unregister(
    Handle<JSFinalizationGroup> finalization_group,
    Handle<JSReceiver> unregister_token, Isolate* isolate) {
  // Iterate through the doubly linked list of WeakCells associated with the
  // key. Each WeakCell will be in the "active_cells" or "cleared_cells" list of
  // its FinalizationGroup; remove it from there.
  if (!finalization_group->key_map().IsUndefined(isolate)) {
    Handle<ObjectHashTable> key_map =
        handle(ObjectHashTable::cast(finalization_group->key_map()), isolate);
    Object value = key_map->Lookup(unregister_token);
    Object undefined = ReadOnlyRoots(isolate).undefined_value();
    while (value.IsWeakCell()) {
      WeakCell weak_cell = WeakCell::cast(value);
      weak_cell.RemoveFromFinalizationGroupCells(isolate);
      value = weak_cell.key_list_next();
      weak_cell.set_key_list_prev(undefined);
      weak_cell.set_key_list_next(undefined);
    }
    bool was_present;
    key_map = ObjectHashTable::Remove(isolate, key_map, unregister_token,
                                      &was_present);
    finalization_group->set_key_map(*key_map);
    return was_present;
  }

  return false;
}

bool JSFinalizationGroup::NeedsCleanup() const {
  return cleared_cells().IsWeakCell();
}

bool JSFinalizationGroup::scheduled_for_cleanup() const {
  return ScheduledForCleanupField::decode(flags());
}

void JSFinalizationGroup::set_scheduled_for_cleanup(
    bool scheduled_for_cleanup) {
  set_flags(ScheduledForCleanupField::update(flags(), scheduled_for_cleanup));
}

Object JSFinalizationGroup::PopClearedCellHoldings(
    Handle<JSFinalizationGroup> finalization_group, Isolate* isolate) {
  Handle<WeakCell> weak_cell =
      handle(WeakCell::cast(finalization_group->cleared_cells()), isolate);
  DCHECK(weak_cell->prev().IsUndefined(isolate));
  finalization_group->set_cleared_cells(weak_cell->next());
  weak_cell->set_next(ReadOnlyRoots(isolate).undefined_value());

  if (finalization_group->cleared_cells().IsWeakCell()) {
    WeakCell cleared_cells_head =
        WeakCell::cast(finalization_group->cleared_cells());
    DCHECK_EQ(cleared_cells_head.prev(), *weak_cell);
    cleared_cells_head.set_prev(ReadOnlyRoots(isolate).undefined_value());
  } else {
    DCHECK(finalization_group->cleared_cells().IsUndefined(isolate));
  }

  // Also remove the WeakCell from the key_map (if it's there).
  if (!weak_cell->key().IsUndefined(isolate)) {
    if (weak_cell->key_list_prev().IsUndefined(isolate) &&
        weak_cell->key_list_next().IsUndefined(isolate)) {
      // weak_cell is the only one associated with its key; remove the key
      // from the hash table.
      Handle<ObjectHashTable> key_map =
          handle(ObjectHashTable::cast(finalization_group->key_map()), isolate);
      Handle<Object> key = handle(weak_cell->key(), isolate);
      bool was_present;
      key_map = ObjectHashTable::Remove(isolate, key_map, key, &was_present);
      DCHECK(was_present);
      finalization_group->set_key_map(*key_map);
    } else if (weak_cell->key_list_prev().IsUndefined()) {
      // weak_cell is the list head for its key; we need to change the value of
      // the key in the hash table.
      Handle<ObjectHashTable> key_map =
          handle(ObjectHashTable::cast(finalization_group->key_map()), isolate);
      Handle<Object> key = handle(weak_cell->key(), isolate);
      Handle<WeakCell> next =
          handle(WeakCell::cast(weak_cell->key_list_next()), isolate);
      DCHECK_EQ(next->key_list_prev(), *weak_cell);
      next->set_key_list_prev(ReadOnlyRoots(isolate).undefined_value());
      weak_cell->set_key_list_next(ReadOnlyRoots(isolate).undefined_value());
      key_map = ObjectHashTable::Put(key_map, key, next);
      finalization_group->set_key_map(*key_map);
    } else {
      // weak_cell is somewhere in the middle of its key list.
      WeakCell prev = WeakCell::cast(weak_cell->key_list_prev());
      prev.set_key_list_next(weak_cell->key_list_next());
      if (!weak_cell->key_list_next().IsUndefined()) {
        WeakCell next = WeakCell::cast(weak_cell->key_list_next());
        next.set_key_list_prev(weak_cell->key_list_prev());
      }
    }
  }

  return weak_cell->holdings();
}

void WeakCell::Nullify(
    Isolate* isolate,
    std::function<void(HeapObject object, ObjectSlot slot, Object target)>
        gc_notify_updated_slot) {
  // Remove from the WeakCell from the "active_cells" list of its
  // JSFinalizationGroup and insert it into the "cleared_cells" list. This is
  // only called for WeakCells which haven't been unregistered yet, so they will
  // be in the active_cells list. (The caller must guard against calling this
  // for unregistered WeakCells by checking that the target is not undefined.)
  DCHECK(target().IsJSReceiver());
  set_target(ReadOnlyRoots(isolate).undefined_value());

  JSFinalizationGroup fg = JSFinalizationGroup::cast(finalization_group());
  if (prev().IsWeakCell()) {
    DCHECK_NE(fg.active_cells(), *this);
    WeakCell prev_cell = WeakCell::cast(prev());
    prev_cell.set_next(next());
    gc_notify_updated_slot(prev_cell, prev_cell.RawField(WeakCell::kNextOffset),
                           next());
  } else {
    DCHECK_EQ(fg.active_cells(), *this);
    fg.set_active_cells(next());
    gc_notify_updated_slot(
        fg, fg.RawField(JSFinalizationGroup::kActiveCellsOffset), next());
  }
  if (next().IsWeakCell()) {
    WeakCell next_cell = WeakCell::cast(next());
    next_cell.set_prev(prev());
    gc_notify_updated_slot(next_cell, next_cell.RawField(WeakCell::kPrevOffset),
                           prev());
  }

  set_prev(ReadOnlyRoots(isolate).undefined_value());
  Object cleared_head = fg.cleared_cells();
  if (cleared_head.IsWeakCell()) {
    WeakCell cleared_head_cell = WeakCell::cast(cleared_head);
    cleared_head_cell.set_prev(*this);
    gc_notify_updated_slot(cleared_head_cell,
                           cleared_head_cell.RawField(WeakCell::kPrevOffset),
                           *this);
  }
  set_next(fg.cleared_cells());
  gc_notify_updated_slot(*this, RawField(WeakCell::kNextOffset), next());
  fg.set_cleared_cells(*this);
  gc_notify_updated_slot(
      fg, fg.RawField(JSFinalizationGroup::kClearedCellsOffset), *this);
}

void WeakCell::RemoveFromFinalizationGroupCells(Isolate* isolate) {
  // Remove the WeakCell from the list it's in (either "active_cells" or
  // "cleared_cells" of its JSFinalizationGroup).

  // It's important to set_target to undefined here. This guards that we won't
  // call Nullify (which assumes that the WeakCell is in active_cells).
  DCHECK(target().IsUndefined() || target().IsJSReceiver());
  set_target(ReadOnlyRoots(isolate).undefined_value());

  JSFinalizationGroup fg = JSFinalizationGroup::cast(finalization_group());
  if (fg.active_cells() == *this) {
    DCHECK(prev().IsUndefined(isolate));
    fg.set_active_cells(next());
  } else if (fg.cleared_cells() == *this) {
    DCHECK(!prev().IsWeakCell());
    fg.set_cleared_cells(next());
  } else {
    DCHECK(prev().IsWeakCell());
    WeakCell prev_cell = WeakCell::cast(prev());
    prev_cell.set_next(next());
  }
  if (next().IsWeakCell()) {
    WeakCell next_cell = WeakCell::cast(next());
    next_cell.set_prev(prev());
  }
  set_prev(ReadOnlyRoots(isolate).undefined_value());
  set_next(ReadOnlyRoots(isolate).undefined_value());
}

}  // namespace internal
}  // namespace v8

#include "src/objects/object-macros-undef.h"

#endif  // V8_OBJECTS_JS_WEAK_REFS_INL_H_