1 // Copyright 2014 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef BASE_ANDROID_JNI_INT_WRAPPER_H_ 6 #define BASE_ANDROID_JNI_INT_WRAPPER_H_ 7 8 // Wrapper used to receive int when calling Java from native. 9 // The wrapper disallows automatic conversion of long to int. 10 // This is to avoid a common anti-pattern where a Java int is used 11 // to receive a native pointer. Please use a Java long to receive 12 // native pointers, so that the code works on both 32-bit and 64-bit 13 // platforms. Note the wrapper allows other lossy conversions into 14 // jint that could be consider anti-patterns, such as from size_t. 15 16 // Checking is only done in debugging builds. 17 18 #ifdef NDEBUG 19 20 typedef jint JniIntWrapper; 21 22 // This inline is sufficiently trivial that it does not change the 23 // final code generated by g++. 24 inline jint as_jint(JniIntWrapper wrapper) { 25 return wrapper; 26 } 27 28 #else 29 30 class JniIntWrapper { 31 public: 32 JniIntWrapper() : i_(0) {} 33 JniIntWrapper(int i) : i_(i) {} 34 JniIntWrapper(const JniIntWrapper& ji) : i_(ji.i_) {} 35 template <class T> JniIntWrapper(const T& t) : i_(t) {} 36 jint as_jint() const { return i_; } 37 private: 38 // If you get an "is private" error at the line below it is because you used 39 // an implicit conversion to convert a long to an int when calling Java. 40 // We disallow this, as a common anti-pattern allows converting a native 41 // pointer (intptr_t) to a Java int. Please use a Java long to represent 42 // a native pointer. If you want a lossy conversion, please use an 43 // explicit conversion in your C++ code. Note an error is only seen when 44 // compiling on a 64-bit platform, as intptr_t is indistinguishable from 45 // int on 32-bit platforms. 46 JniIntWrapper(long); 47 jint i_; 48 }; 49 50 inline jint as_jint(const JniIntWrapper& wrapper) { 51 return wrapper.as_jint(); 52 } 53 54 #endif // NDEBUG 55 56 #endif // BASE_ANDROID_JNI_INT_WRAPPER_H_ 57
