naiveproxy/base/android/scoped_java_ref.h
2018-08-14 22:19:20 +00:00

286 lines
9.6 KiB
C++

// Copyright (c) 2012 The Chromium 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 BASE_ANDROID_SCOPED_JAVA_REF_H_
#define BASE_ANDROID_SCOPED_JAVA_REF_H_
#include <jni.h>
#include <stddef.h>
#include <type_traits>
#include <utility>
#include "base/base_export.h"
#include "base/logging.h"
#include "base/macros.h"
namespace base {
namespace android {
// Creates a new local reference frame, in which at least a given number of
// local references can be created. Note that local references already created
// in previous local frames are still valid in the current local frame.
class BASE_EXPORT ScopedJavaLocalFrame {
public:
explicit ScopedJavaLocalFrame(JNIEnv* env);
ScopedJavaLocalFrame(JNIEnv* env, int capacity);
~ScopedJavaLocalFrame();
private:
// This class is only good for use on the thread it was created on so
// it's safe to cache the non-threadsafe JNIEnv* inside this object.
JNIEnv* env_;
DISALLOW_COPY_AND_ASSIGN(ScopedJavaLocalFrame);
};
// Forward declare the generic java reference template class.
template<typename T> class JavaRef;
// Template specialization of JavaRef, which acts as the base class for all
// other JavaRef<> template types. This allows you to e.g. pass
// ScopedJavaLocalRef<jstring> into a function taking const JavaRef<jobject>&
template<>
class BASE_EXPORT JavaRef<jobject> {
public:
// Initializes a null reference. Don't add anything else here; it's inlined.
constexpr JavaRef() : obj_(nullptr) {}
// Allow nullptr to be converted to JavaRef. This avoids having to declare an
// empty JavaRef just to pass null to a function, and makes C++ "nullptr" and
// Java "null" equivalent.
constexpr JavaRef(std::nullptr_t) : JavaRef() {}
// Public to allow destruction of null JavaRef objects.
// Don't add anything else here; it's inlined.
~JavaRef() {}
jobject obj() const { return obj_; }
bool is_null() const { return obj_ == nullptr; }
protected:
// Takes ownership of the |obj| reference passed; requires it to be a local
// reference type.
#if DCHECK_IS_ON()
// Implementation contains a DCHECK; implement out-of-line when DCHECK_IS_ON.
JavaRef(JNIEnv* env, jobject obj);
#else
// Don't add anything else here; it's inlined.
JavaRef(JNIEnv* env, jobject obj) : obj_(obj) {}
#endif
void swap(JavaRef& other) { std::swap(obj_, other.obj_); }
// The following are implementation detail convenience methods, for
// use by the sub-classes.
JNIEnv* SetNewLocalRef(JNIEnv* env, jobject obj);
void SetNewGlobalRef(JNIEnv* env, jobject obj);
void ResetLocalRef(JNIEnv* env);
void ResetGlobalRef();
jobject ReleaseInternal();
private:
jobject obj_;
DISALLOW_COPY_AND_ASSIGN(JavaRef);
};
// Generic base class for ScopedJavaLocalRef and ScopedJavaGlobalRef. Useful
// for allowing functions to accept a reference without having to mandate
// whether it is a local or global type.
template<typename T>
class JavaRef : public JavaRef<jobject> {
public:
JavaRef() {}
JavaRef(std::nullptr_t) : JavaRef<jobject>(nullptr) {}
~JavaRef() {}
T obj() const { return static_cast<T>(JavaRef<jobject>::obj()); }
protected:
JavaRef(JNIEnv* env, T obj) : JavaRef<jobject>(env, obj) {}
private:
DISALLOW_COPY_AND_ASSIGN(JavaRef);
};
// Holds a local reference to a JNI method parameter.
// Method parameters should not be deleted, and so this class exists purely to
// wrap them as a JavaRef<T> in the JNI binding generator. Do not create
// instances manually.
template<typename T>
class JavaParamRef : public JavaRef<T> {
public:
// Assumes that |obj| is a parameter passed to a JNI method from Java.
// Does not assume ownership as parameters should not be deleted.
JavaParamRef(JNIEnv* env, T obj) : JavaRef<T>(env, obj) {}
// Allow nullptr to be converted to JavaParamRef. Some unit tests call JNI
// methods directly from C++ and pass null for objects which are not actually
// used by the implementation (e.g. the caller object); allow this to keep
// working.
JavaParamRef(std::nullptr_t) : JavaRef<T>(nullptr) {}
~JavaParamRef() {}
// TODO(torne): remove this cast once we're using JavaRef consistently.
// http://crbug.com/506850
operator T() const { return JavaRef<T>::obj(); }
private:
DISALLOW_COPY_AND_ASSIGN(JavaParamRef);
};
// Holds a local reference to a Java object. The local reference is scoped
// to the lifetime of this object.
// Instances of this class may hold onto any JNIEnv passed into it until
// destroyed. Therefore, since a JNIEnv is only suitable for use on a single
// thread, objects of this class must be created, used, and destroyed, on a
// single thread.
// Therefore, this class should only be used as a stack-based object and from a
// single thread. If you wish to have the reference outlive the current
// callstack (e.g. as a class member) or you wish to pass it across threads,
// use a ScopedJavaGlobalRef instead.
template<typename T>
class ScopedJavaLocalRef : public JavaRef<T> {
public:
constexpr ScopedJavaLocalRef() : env_(nullptr) {}
constexpr ScopedJavaLocalRef(std::nullptr_t) : env_(nullptr) {}
// Non-explicit copy constructor, to allow ScopedJavaLocalRef to be returned
// by value as this is the normal usage pattern.
ScopedJavaLocalRef(const ScopedJavaLocalRef<T>& other)
: env_(other.env_) {
this->SetNewLocalRef(env_, other.obj());
}
ScopedJavaLocalRef(ScopedJavaLocalRef<T>&& other) : env_(other.env_) {
this->swap(other);
}
explicit ScopedJavaLocalRef(const JavaRef<T>& other) : env_(nullptr) {
this->Reset(other);
}
// Assumes that |obj| is a local reference to a Java object and takes
// ownership of this local reference.
// TODO(torne): this shouldn't be used outside of JNI helper functions but
// there are currently some cases where there aren't helpers for things.
ScopedJavaLocalRef(JNIEnv* env, T obj) : JavaRef<T>(env, obj), env_(env) {}
~ScopedJavaLocalRef() {
this->Reset();
}
// Overloaded assignment operator defined for consistency with the implicit
// copy constructor.
void operator=(const ScopedJavaLocalRef<T>& other) {
this->Reset(other);
}
void operator=(ScopedJavaLocalRef<T>&& other) {
env_ = other.env_;
this->swap(other);
}
void Reset() {
this->ResetLocalRef(env_);
}
void Reset(const ScopedJavaLocalRef<T>& other) {
// We can copy over env_ here as |other| instance must be from the same
// thread as |this| local ref. (See class comment for multi-threading
// limitations, and alternatives).
this->Reset(other.env_, other.obj());
}
void Reset(const JavaRef<T>& other) {
// If |env_| was not yet set (is still null) it will be attached to the
// current thread in SetNewLocalRef().
this->Reset(env_, other.obj());
}
// Creates a new local reference to the Java object, unlike the constructor
// with the same parameters that takes ownership of the existing reference.
// TODO(torne): these should match as this is confusing.
void Reset(JNIEnv* env, T obj) { env_ = this->SetNewLocalRef(env, obj); }
// Releases the local reference to the caller. The caller *must* delete the
// local reference when it is done with it. Note that calling a Java method
// is *not* a transfer of ownership and Release() should not be used.
T Release() {
return static_cast<T>(this->ReleaseInternal());
}
private:
// This class is only good for use on the thread it was created on so
// it's safe to cache the non-threadsafe JNIEnv* inside this object.
JNIEnv* env_;
// Prevent ScopedJavaLocalRef(JNIEnv*, T obj) from being used to take
// ownership of a JavaParamRef's underlying object - parameters are not
// allowed to be deleted and so should not be owned by ScopedJavaLocalRef.
// TODO(torne): this can be removed once JavaParamRef no longer has an
// implicit conversion back to T.
ScopedJavaLocalRef(JNIEnv* env, const JavaParamRef<T>& other);
};
// Holds a global reference to a Java object. The global reference is scoped
// to the lifetime of this object. This class does not hold onto any JNIEnv*
// passed to it, hence it is safe to use across threads (within the constraints
// imposed by the underlying Java object that it references).
template<typename T>
class ScopedJavaGlobalRef : public JavaRef<T> {
public:
constexpr ScopedJavaGlobalRef() {}
constexpr ScopedJavaGlobalRef(std::nullptr_t) {}
ScopedJavaGlobalRef(const ScopedJavaGlobalRef<T>& other) {
this->Reset(other);
}
ScopedJavaGlobalRef(ScopedJavaGlobalRef<T>&& other) { this->swap(other); }
ScopedJavaGlobalRef(JNIEnv* env, T obj) { this->Reset(env, obj); }
explicit ScopedJavaGlobalRef(const JavaRef<T>& other) { this->Reset(other); }
~ScopedJavaGlobalRef() {
this->Reset();
}
// Overloaded assignment operator defined for consistency with the implicit
// copy constructor.
void operator=(const ScopedJavaGlobalRef<T>& other) {
this->Reset(other);
}
void operator=(ScopedJavaGlobalRef<T>&& other) { this->swap(other); }
void Reset() {
this->ResetGlobalRef();
}
void Reset(const JavaRef<T>& other) { this->Reset(nullptr, other.obj()); }
void Reset(JNIEnv* env, const JavaParamRef<T>& other) {
this->Reset(env, other.obj());
}
void Reset(JNIEnv* env, T obj) { this->SetNewGlobalRef(env, obj); }
// Releases the global reference to the caller. The caller *must* delete the
// global reference when it is done with it. Note that calling a Java method
// is *not* a transfer of ownership and Release() should not be used.
T Release() {
return static_cast<T>(this->ReleaseInternal());
}
};
} // namespace android
} // namespace base
#endif // BASE_ANDROID_SCOPED_JAVA_REF_H_