sdk/runtime/vm/field_table.h

// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

#ifndef RUNTIME_VM_FIELD_TABLE_H_
#define RUNTIME_VM_FIELD_TABLE_H_

#include "platform/assert.h"
#include "platform/atomic.h"

#include "vm/bitfield.h"
#include "vm/class_id.h"
#include "vm/globals.h"
#include "vm/growable_array.h"
#include "vm/tagged_pointer.h"

namespace dart {

class Isolate;
class Field;
class FieldInvalidator;

class FieldTable {
 public:
  explicit FieldTable(Isolate* isolate, IsolateGroup* isolate_group = nullptr)
      : top_(0),
        capacity_(0),
        free_head_(-1),
        table_(nullptr),
        old_tables_(new MallocGrowableArray<ObjectPtr*>()),
        isolate_(isolate),
        isolate_group_(isolate_group),
        is_ready_to_use_(isolate == nullptr) {}

  ~FieldTable();

  bool IsReadyToUse() const;
  void MarkReadyToUse();

  intptr_t NumFieldIds() const { return top_; }
  intptr_t Capacity() const { return capacity_; }

  ObjectPtr* table() { return table_; }

  void FreeOldTables();

  // Used by the generated code.
  static intptr_t FieldOffsetFor(intptr_t field_id);

  bool IsValidIndex(intptr_t index) const { return index >= 0 && index < top_; }

  // Returns whether registering this field caused a growth in the backing
  // store.
  bool Register(const Field& field, intptr_t expected_field_id = -1);
  void AllocateIndex(intptr_t index);

  // Static field elements are being freed only during isolate reload
  // when initially created static field have to get remapped to point
  // to an existing static field value.
  void Free(intptr_t index);

  ObjectPtr At(intptr_t index, bool concurrent_use = false) const {
    ASSERT(IsValidIndex(index));
    if (concurrent_use) {
      ObjectPtr* table =
          std::atomic_ref(table_).load(std::memory_order::acquire);
      return std::atomic_ref(table[index]).load(std::memory_order_acquire);
    } else {
      // There is no concurrent access expected for this field, so we avoid
      // using atomics. This will allow us to detect via TSAN if there are
      // racy uses.
      return table_[index];
    }
  }

  void SetAt(intptr_t index,
             ObjectPtr raw_instance,
             bool concurrent_use = false) {
    ASSERT(index < capacity_);
    ObjectPtr* slot = &table_[index];
    if (concurrent_use) {
      reinterpret_cast<AcqRelAtomic<ObjectPtr>*>(slot)->store(raw_instance);
    } else {
      // There is no concurrent access expected for this field, so we avoid
      // using atomics. This will allow us to detect via TSAN if there are
      // racy uses.
      *slot = raw_instance;
    }
  }

  FieldTable* Clone(Isolate* for_isolate,
                    IsolateGroup* for_isolate_group = nullptr);

  void VisitObjectPointers(ObjectPointerVisitor* visitor);

  static constexpr int kInitialCapacity = 512;
  static constexpr int kCapacityIncrement = 256;

 private:
  void Grow(intptr_t new_capacity);

  intptr_t top_;
  intptr_t capacity_;
  // -1 if free list is empty, otherwise index of first empty element. Empty
  // elements are organized into linked list - they contain index of next
  // element, last element contains -1.
  intptr_t free_head_;

  // Mutable for atomic_ref in At.
  mutable ObjectPtr* table_;
  // When table_ grows and have to reallocated, keep the old one here
  // so it will get freed when its are no longer in use.
  MallocGrowableArray<ObjectPtr*>* old_tables_;

  // If non-null, it will specify the isolate this field table belongs to.
  // Growing the field table will keep the cached field table on the isolate's
  // mutator thread up-to-date.
  Isolate* isolate_;
  IsolateGroup* isolate_group_;

  // Whether this field table is ready to use by e.g. registering new static
  // fields.
  bool is_ready_to_use_ = false;

  DISALLOW_COPY_AND_ASSIGN(FieldTable);
};

}  // namespace dart

#endif  // RUNTIME_VM_FIELD_TABLE_H_