blob: e37a992445d801d5a32913e9ce1b5727697ab616 [file] [log] [blame]
/*
* Copyright 2017 The WebRTC project authors. All Rights Reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
// Originally these classes are from Chromium.
// https://cs.chromium.org/chromium/src/base/android/scoped_java_ref.h.
#ifndef SDK_ANDROID_NATIVE_API_JNI_SCOPED_JAVA_REF_H_
#define SDK_ANDROID_NATIVE_API_JNI_SCOPED_JAVA_REF_H_
#include <jni.h>
#include <utility>
#include "rtc_base/constructor_magic.h"
#include "sdk/android/native_api/jni/jvm.h"
namespace webrtc {
// 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;
// Template specialization of JavaRef, which acts as the base class for all
// other JavaRef<> template types. This allows you to e.g. pass JavaRef<jstring>
// into a function taking const JavaRef<jobject>&.
template <>
class JavaRef<jobject> {
public:
jobject obj() const { return obj_; }
bool is_null() const {
// This is not valid for weak references. For weak references you need to
// use env->IsSameObject(objc_, nullptr), but that should be avoided anyway
// since it does not prevent the object from being freed immediately
// thereafter. Consequently, programmers should not use this check on weak
// references anyway and should first make a ScopedJavaLocalRef or
// ScopedJavaGlobalRef before checking if it is null.
return obj_ == nullptr;
}
protected:
constexpr JavaRef() : obj_(nullptr) {}
explicit JavaRef(jobject obj) : obj_(obj) {}
jobject obj_;
private:
RTC_DISALLOW_COPY_AND_ASSIGN(JavaRef);
};
template <typename T>
class JavaRef : public JavaRef<jobject> {
public:
T obj() const { return static_cast<T>(obj_); }
protected:
JavaRef() : JavaRef<jobject>(nullptr) {}
explicit JavaRef(T obj) : JavaRef<jobject>(obj) {}
private:
RTC_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.
explicit JavaParamRef(T obj) : JavaRef<T>(obj) {}
JavaParamRef(JNIEnv*, T obj) : JavaRef<T>(obj) {}
private:
RTC_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:
ScopedJavaLocalRef() = default;
ScopedJavaLocalRef(std::nullptr_t) {} // NOLINT(runtime/explicit)
ScopedJavaLocalRef(JNIEnv* env, const JavaRef<T>& other) : env_(env) {
Reset(other.obj(), OwnershipPolicy::RETAIN);
}
// Allow constructing e.g. ScopedJavaLocalRef<jobject> from
// ScopedJavaLocalRef<jstring>.
template <typename G>
ScopedJavaLocalRef(ScopedJavaLocalRef<G>&& other) : env_(other.env()) {
Reset(other.Release(), OwnershipPolicy::ADOPT);
}
ScopedJavaLocalRef(const ScopedJavaLocalRef& other) : env_(other.env_) {
Reset(other.obj(), OwnershipPolicy::RETAIN);
}
// Assumes that |obj| is a reference to a Java object and takes
// ownership of this reference. This should preferably not be used
// outside of JNI helper functions.
ScopedJavaLocalRef(JNIEnv* env, T obj) : JavaRef<T>(obj), env_(env) {}
~ScopedJavaLocalRef() {
if (obj_ != nullptr)
env_->DeleteLocalRef(obj_);
}
void operator=(const ScopedJavaLocalRef& other) {
Reset(other.obj(), OwnershipPolicy::RETAIN);
}
void operator=(ScopedJavaLocalRef&& other) {
Reset(other.Release(), OwnershipPolicy::ADOPT);
}
// Releases the reference to the caller. The caller *must* delete the
// 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() {
T obj = static_cast<T>(obj_);
obj_ = nullptr;
return obj;
}
JNIEnv* env() const { return env_; }
private:
using JavaRef<T>::obj_;
enum OwnershipPolicy {
// The scoped object takes ownership of an object by taking over an existing
// ownership claim.
ADOPT,
// The scoped object will retain the the object and any initial ownership is
// not changed.
RETAIN
};
void Reset(T obj, OwnershipPolicy policy) {
if (obj_ != nullptr)
env_->DeleteLocalRef(obj_);
obj_ = (obj != nullptr && policy == OwnershipPolicy::RETAIN)
? env_->NewLocalRef(obj)
: obj;
}
JNIEnv* const env_ = AttachCurrentThreadIfNeeded();
};
// 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:
using JavaRef<T>::obj_;
explicit constexpr ScopedJavaGlobalRef(std::nullptr_t) {}
ScopedJavaGlobalRef(JNIEnv* env, const JavaRef<T>& other)
: JavaRef<T>(static_cast<T>(env->NewGlobalRef(other.obj()))) {}
explicit ScopedJavaGlobalRef(const ScopedJavaLocalRef<T>& other)
: ScopedJavaGlobalRef(other.env(), other) {}
ScopedJavaGlobalRef(ScopedJavaGlobalRef&& other)
: JavaRef<T>(other.Release()) {}
~ScopedJavaGlobalRef() {
if (obj_ != nullptr)
AttachCurrentThreadIfNeeded()->DeleteGlobalRef(obj_);
}
// Releases the reference to the caller. The caller *must* delete the
// 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() {
T obj = static_cast<T>(obj_);
obj_ = nullptr;
return obj;
}
private:
RTC_DISALLOW_COPY_AND_ASSIGN(ScopedJavaGlobalRef);
};
template <typename T>
inline ScopedJavaLocalRef<T> static_java_ref_cast(JNIEnv* env,
JavaRef<jobject> const& ref) {
ScopedJavaLocalRef<jobject> owned_ref(env, ref);
return ScopedJavaLocalRef<T>(env, static_cast<T>(owned_ref.Release()));
}
} // namespace webrtc
#endif // SDK_ANDROID_NATIVE_API_JNI_SCOPED_JAVA_REF_H_