runtime/class_table.h

/*
 * Copyright (C) 2015 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_RUNTIME_CLASS_TABLE_H_
#define ART_RUNTIME_CLASS_TABLE_H_

#include <string>
#include <utility>
#include <vector>

#include "base/allocator.h"
#include "base/hash_set.h"
#include "base/macros.h"
#include "base/mutex.h"
#include "dex_file.h"
#include "gc_root.h"
#include "object_callbacks.h"
#include "runtime.h"

namespace art {

namespace mirror {
  class ClassLoader;
}  // namespace mirror

// Each loader has a ClassTable
class ClassTable {
 public:
  class ClassDescriptorHashEquals {
   public:
    // uint32_t for cross compilation.
    uint32_t operator()(const GcRoot<mirror::Class>& root) const NO_THREAD_SAFETY_ANALYSIS;
    // Same class loader and descriptor.
    bool operator()(const GcRoot<mirror::Class>& a, const GcRoot<mirror::Class>& b) const
        NO_THREAD_SAFETY_ANALYSIS;;
    // Same descriptor.
    bool operator()(const GcRoot<mirror::Class>& a, const char* descriptor) const
        NO_THREAD_SAFETY_ANALYSIS;
    // uint32_t for cross compilation.
    uint32_t operator()(const char* descriptor) const NO_THREAD_SAFETY_ANALYSIS;
  };
  class GcRootEmptyFn {
   public:
    void MakeEmpty(GcRoot<mirror::Class>& item) const {
      item = GcRoot<mirror::Class>();
    }
    bool IsEmpty(const GcRoot<mirror::Class>& item) const {
      return item.IsNull();
    }
  };
  // hash set which hashes class descriptor, and compares descriptors and class loaders. Results
  // should be compared for a matching Class descriptor and class loader.
  typedef HashSet<GcRoot<mirror::Class>, GcRootEmptyFn, ClassDescriptorHashEquals,
      ClassDescriptorHashEquals, TrackingAllocator<GcRoot<mirror::Class>, kAllocatorTagClassTable>>
      ClassSet;

  ClassTable();

  // Used by image writer for checking.
  bool Contains(mirror::Class* klass)
      REQUIRES(!lock_)
      SHARED_REQUIRES(Locks::mutator_lock_);

  // Freeze the current class tables by allocating a new table and never updating or modifying the
  // existing table. This helps prevents dirty pages after caused by inserting after zygote fork.
  void FreezeSnapshot()
      REQUIRES(!lock_)
      SHARED_REQUIRES(Locks::mutator_lock_);

  // Returns the number of classes in previous snapshots.
  size_t NumZygoteClasses() const REQUIRES(!lock_);

  // Returns all off the classes in the lastest snapshot.
  size_t NumNonZygoteClasses() const REQUIRES(!lock_);

  // Update a class in the table with the new class. Returns the existing class which was replaced.
  mirror::Class* UpdateClass(const char* descriptor, mirror::Class* new_klass, size_t hash)
      REQUIRES(!lock_)
      SHARED_REQUIRES(Locks::mutator_lock_);

  // NO_THREAD_SAFETY_ANALYSIS for object marking requiring heap bitmap lock.
  template<class Visitor>
  void VisitRoots(Visitor& visitor)
      NO_THREAD_SAFETY_ANALYSIS
      REQUIRES(!lock_)
      SHARED_REQUIRES(Locks::mutator_lock_);

  template<class Visitor>
  void VisitRoots(const Visitor& visitor)
      NO_THREAD_SAFETY_ANALYSIS
      REQUIRES(!lock_)
      SHARED_REQUIRES(Locks::mutator_lock_);

  // Stops visit if the visitor returns false.
  template <typename Visitor>
  bool Visit(Visitor& visitor)
      REQUIRES(!lock_)
      SHARED_REQUIRES(Locks::mutator_lock_);

  // Return the first class that matches the descriptor. Returns null if there are none.
  mirror::Class* Lookup(const char* descriptor, size_t hash)
      REQUIRES(!lock_)
      SHARED_REQUIRES(Locks::mutator_lock_);

  // Return the first class that matches the descriptor of klass. Returns null if there are none.
  mirror::Class* LookupByDescriptor(mirror::Class* klass)
      REQUIRES(!lock_)
      SHARED_REQUIRES(Locks::mutator_lock_);

  void Insert(mirror::Class* klass)
      REQUIRES(!lock_)
      SHARED_REQUIRES(Locks::mutator_lock_);

  void InsertWithHash(mirror::Class* klass, size_t hash)
      REQUIRES(!lock_)
      SHARED_REQUIRES(Locks::mutator_lock_);

  // Returns true if the class was found and removed, false otherwise.
  bool Remove(const char* descriptor)
      REQUIRES(!lock_)
      SHARED_REQUIRES(Locks::mutator_lock_);

  // Return true if we inserted the strong root, false if it already exists.
  bool InsertStrongRoot(mirror::Object* obj)
      REQUIRES(!lock_)
      SHARED_REQUIRES(Locks::mutator_lock_);

  // Combines all of the tables into one class set.
  size_t WriteToMemory(uint8_t* ptr) const
      REQUIRES(!lock_)
      SHARED_REQUIRES(Locks::mutator_lock_);

  // Read a table from ptr and put it at the front of the class set.
  size_t ReadFromMemory(uint8_t* ptr)
      REQUIRES(!lock_)
      SHARED_REQUIRES(Locks::mutator_lock_);

  // Add a class set to the front of classes.
  void AddClassSet(ClassSet&& set)
      REQUIRES(!lock_)
      SHARED_REQUIRES(Locks::mutator_lock_);

  // Clear strong roots (other than classes themselves).
  void ClearStrongRoots()
      REQUIRES(!lock_)
      SHARED_REQUIRES(Locks::mutator_lock_);

  ReaderWriterMutex& GetLock() {
    return lock_;
  }

 private:
  // Lock to guard inserting and removing.
  mutable ReaderWriterMutex lock_;
  // We have a vector to help prevent dirty pages after the zygote forks by calling FreezeSnapshot.
  std::vector<ClassSet> classes_ GUARDED_BY(lock_);
  // Extra strong roots that can be either dex files or dex caches. Dex files used by the class
  // loader which may not be owned by the class loader must be held strongly live. Also dex caches
  // are held live to prevent them being unloading once they have classes in them.
  std::vector<GcRoot<mirror::Object>> strong_roots_ GUARDED_BY(lock_);
};

}  // namespace art

#endif  // ART_RUNTIME_CLASS_TABLE_H_