runtime/jni/jni_id_manager.h

/*
 * Copyright (C) 2019 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_JNI_JNI_ID_MANAGER_H_
#define ART_RUNTIME_JNI_JNI_ID_MANAGER_H_

#include <atomic>
#include <jni.h>
#include <vector>

#include "art_field.h"
#include "art_method.h"
#include "base/mutex.h"
#include "jni_id_type.h"

namespace art {
namespace jni {

class ScopedEnableSuspendAllJniIdQueries;
class JniIdManager {
 public:
  class IdVisitor {
   public:
    virtual ~IdVisitor() {}
    virtual void VisitMethodId(jmethodID id, ArtMethod** method) = 0;
    virtual void VisitFieldId(jfieldID id, ArtField** field) = 0;
    virtual bool ShouldVisitFields() = 0;
    virtual bool ShouldVisitMethods() = 0;
  };

  template <typename T,
            typename = typename std::enable_if<std::is_same_v<T, jmethodID> ||
                                               std::is_same_v<T, jfieldID>>>
  static constexpr bool IsIndexId(T val) {
    return val == nullptr || reinterpret_cast<uintptr_t>(val) % 2 == 1;
  }

  ArtMethod* DecodeMethodId(jmethodID method) REQUIRES(!Locks::jni_id_lock_);
  ArtField* DecodeFieldId(jfieldID field) REQUIRES(!Locks::jni_id_lock_);
  jmethodID EncodeMethodId(ArtMethod* method) REQUIRES(!Locks::jni_id_lock_)
      REQUIRES_SHARED(Locks::mutator_lock_);
  jfieldID EncodeFieldId(ArtField* field) REQUIRES(!Locks::jni_id_lock_)
      REQUIRES_SHARED(Locks::mutator_lock_);

  void VisitIds(Thread* self, IdVisitor* visitor);

  template<typename MethodVisitor, typename FieldVisitor>
  void VisitIds(Thread* self, MethodVisitor m, FieldVisitor f) REQUIRES(!Locks::jni_id_lock_) {
    struct FuncVisitor : public IdVisitor {
     public:
      FuncVisitor(MethodVisitor m, FieldVisitor f) : m_(m), f_(f) {}
      bool ShouldVisitFields() override {
        return true;
      }
      bool ShouldVisitMethods() override {
        return true;
      }
      void VisitMethodId(jmethodID mid, ArtMethod** am) NO_THREAD_SAFETY_ANALYSIS override {
        m_(mid, am);
      }
      void VisitFieldId(jfieldID fid, ArtField** af) NO_THREAD_SAFETY_ANALYSIS override {
        f_(fid, af);
      }

     private:
      MethodVisitor m_;
      FieldVisitor f_;
    };
    FuncVisitor fv(m, f);
    VisitIds(self, &fv);
  }

 private:
  template <typename ArtType>
  uintptr_t EncodeGenericId(ArtType* t) REQUIRES(!Locks::jni_id_lock_)
      REQUIRES_SHARED(Locks::mutator_lock_);
  template <typename ArtType>
  ArtType* DecodeGenericId(uintptr_t input) REQUIRES(!Locks::jni_id_lock_);
  template <typename ArtType> std::vector<ArtType*>& GetGenericMap() REQUIRES(Locks::jni_id_lock_);
  template <typename ArtType>
  uintptr_t GetNextId(JniIdType id, ArtType* t) REQUIRES(Locks::jni_id_lock_);
  template <typename ArtType>
  size_t GetLinearSearchStartId(ArtType* t) REQUIRES(Locks::jni_id_lock_);

  void StartDefer() REQUIRES(!Locks::jni_id_lock_) REQUIRES_SHARED(Locks::mutator_lock_);
  void EndDefer() REQUIRES(!Locks::jni_id_lock_) REQUIRES_SHARED(Locks::mutator_lock_);

  uintptr_t next_method_id_ GUARDED_BY(Locks::jni_id_lock_) = 1u;
  std::vector<ArtMethod*> method_id_map_ GUARDED_BY(Locks::jni_id_lock_);
  uintptr_t next_field_id_ GUARDED_BY(Locks::jni_id_lock_) = 1u;
  std::vector<ArtField*> field_id_map_ GUARDED_BY(Locks::jni_id_lock_);

  // If non-zero indicates that some thread is trying to allocate ids without being able to update
  // the method->id mapping (due to not being able to allocate or something). In this case decode
  // and encode need to do a linear scan of the lists. The ScopedEnableSuspendAllJniIdQueries struct
  // will deal with fixing everything up.
  size_t deferred_allocation_refcount_ GUARDED_BY(Locks::jni_id_lock_) = 0;
  // min jmethodID that might not have it's method->id mapping filled in.
  uintptr_t deferred_allocation_method_id_start_ GUARDED_BY(Locks::jni_id_lock_) = 0u;
  // min jfieldID that might not have it's field->id mapping filled in.
  uintptr_t deferred_allocation_field_id_start_ GUARDED_BY(Locks::jni_id_lock_) = 0u;

  friend class ScopedEnableSuspendAllJniIdQueries;
};

// A scope that will enable using the Encode/Decode JNI id functions with all threads suspended.
// This is required since normally we need to be able to allocate to encode new ids. This should
// only be used when absolutely required, for example to invoke user-callbacks during heap walking
// or similar.
class ScopedEnableSuspendAllJniIdQueries {
 public:
  ScopedEnableSuspendAllJniIdQueries() REQUIRES_SHARED(Locks::mutator_lock_);
  ~ScopedEnableSuspendAllJniIdQueries() REQUIRES_SHARED(Locks::mutator_lock_);

 private:
  JniIdManager* manager_;
};

}  // namespace jni
}  // namespace art

#endif  // ART_RUNTIME_JNI_JNI_ID_MANAGER_H_