1 /*
2  * Copyright (C) 2010 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 #ifndef LIBNATIVEHELPER_HEADER_ONLY_INCLUDE_NATIVEHELPER_SCOPED_LOCAL_REF_H_
18 #define LIBNATIVEHELPER_HEADER_ONLY_INCLUDE_NATIVEHELPER_SCOPED_LOCAL_REF_H_
19 
20 #include <cstddef>
21 
22 #include "jni.h"
23 #include "nativehelper_utils.h"
24 
25 // A smart pointer that deletes a JNI local reference when it goes out of scope.
26 template<typename T>
27 class ScopedLocalRef {
28 public:
29     ScopedLocalRef(JNIEnv* env, T localRef) : mEnv(env), mLocalRef(localRef) {
30     }
31 
32     ScopedLocalRef(ScopedLocalRef&& s) noexcept : mEnv(s.mEnv), mLocalRef(s.release()) {
33     }
34 
35     explicit ScopedLocalRef(JNIEnv* env) : mEnv(env), mLocalRef(nullptr) {
36     }
37 
38     ~ScopedLocalRef() {
39         reset();
40     }
41 
42     void reset(T ptr = NULL) {
43         if (ptr != mLocalRef) {
44             if (mLocalRef != NULL) {
45                 mEnv->DeleteLocalRef(mLocalRef);
46             }
47             mLocalRef = ptr;
48         }
49     }
50 
51     T release() __attribute__((warn_unused_result)) {
52         T localRef = mLocalRef;
53         mLocalRef = NULL;
54         return localRef;
55     }
56 
57     T get() const {
58         return mLocalRef;
59     }
60 
61 
62     // We do not expose an empty constructor as it can easily lead to errors
63     // using common idioms, e.g.:
64     //   ScopedLocalRef<...> ref;
65     //   ref.reset(...);
66 
67     // Move assignment operator.
68     ScopedLocalRef& operator=(ScopedLocalRef&& s) noexcept {
69         reset(s.release());
70         mEnv = s.mEnv;
71         return *this;
72     }
73 
74     // Allows "if (scoped_ref == nullptr)"
75     bool operator==(std::nullptr_t) const {
76         return mLocalRef == nullptr;
77     }
78 
79     // Allows "if (scoped_ref != nullptr)"
80     bool operator!=(std::nullptr_t) const {
81         return mLocalRef != nullptr;
82     }
83 
84 private:
85     JNIEnv* mEnv;
86     T mLocalRef;
87 
88     DISALLOW_COPY_AND_ASSIGN(ScopedLocalRef);
89 };
90 
91 #endif  // LIBNATIVEHELPER_HEADER_ONLY_INCLUDE_NATIVEHELPER_SCOPED_LOCAL_REF_H_
92