src/stack_indirect_reference_table.h

/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef ART_SRC_STACK_INDIRECT_REFERENCE_TABLE_H_
#define ART_SRC_STACK_INDIRECT_REFERENCE_TABLE_H_

#include "logging.h"
#include "macros.h"
#include "thread.h"

namespace art {

class Object;

// Stack allocated indirect reference table. It can allocated within
// the bridge frame between managed and native code backed by stack
// storage or manually allocated by SirtRef to hold one reference.
class StackIndirectReferenceTable {
 public:
  explicit StackIndirectReferenceTable(Object* object) {
    number_of_references_ = 1;
    references_[0] = object;
    Thread::Current()->PushSirt(this);
  }

  ~StackIndirectReferenceTable() {
    StackIndirectReferenceTable* sirt = Thread::Current()->PopSirt();
    CHECK_EQ(this, sirt);
  }

  // Number of references contained within this SIRT
  size_t NumberOfReferences() const {
    return number_of_references_;
  }

  // Link to previous SIRT or NULL
  StackIndirectReferenceTable* GetLink() const {
    return link_;
  }

  void SetLink(StackIndirectReferenceTable* sirt) {
    DCHECK_NE(this, sirt);
    link_ = sirt;
  }

  Object* GetReference(size_t i) const {
    DCHECK_LT(i, number_of_references_);
    return references_[i];
  }

  void SetReference(size_t i, Object* object) {
    DCHECK_LT(i, number_of_references_);
    references_[i] = object;
  }

  bool Contains(Object** sirt_entry) const {
    // A SIRT should always contain something. One created by the
    // jni_compiler should have a jobject/jclass as a native method is
    // passed in a this pointer or a class
    DCHECK_GT(number_of_references_, 0U);
    return ((&references_[0] <= sirt_entry)
            && (sirt_entry <= (&references_[number_of_references_ - 1])));
  }

  // Offset of length within SIRT, used by generated code
  static size_t NumberOfReferencesOffset() {
    return OFFSETOF_MEMBER(StackIndirectReferenceTable, number_of_references_);
  }

  // Offset of link within SIRT, used by generated code
  static size_t LinkOffset() {
    return OFFSETOF_MEMBER(StackIndirectReferenceTable, link_);
  }

 private:
  StackIndirectReferenceTable() {}

  size_t number_of_references_;
  StackIndirectReferenceTable* link_;

  // number_of_references_ are available if this is allocated and filled in by jni_compiler.
  Object* references_[1];

  DISALLOW_COPY_AND_ASSIGN(StackIndirectReferenceTable);
};

template<class T>
class SirtRef {
 public:
  explicit SirtRef(T* object) : sirt_(object) {}
  ~SirtRef() {}

  T& operator*() const { return *get(); }
  T* operator->() const { return get(); }
  T* get() const {
    return down_cast<T*>(sirt_.GetReference(0));
  }

  void reset(T* object = NULL) {
    sirt_.SetReference(0, object);
  }

 private:
  StackIndirectReferenceTable sirt_;

  DISALLOW_COPY_AND_ASSIGN(SirtRef);
};

}  // namespace art

#endif  // ART_SRC_STACK_INDIRECT_REFERENCE_TABLE_H_