1# NativeBuffer开发指导 (C/C++) 2 3## 场景介绍 4 5NativeBuffer是提供**共享内存**的模块。开发者可以通过`NativeBuffer`接口实现共享内存的申请、使用、属性查询、释放等操作。 6针对NativeBuffer,常见的开发场景如下: 7 8* 通过`NativeBuffer`提供的Native API接口申请`OH_NativeBuffer`实例,获取内存的属性信息,把对应的ION内存映射到进程空间。 9 10## 接口说明 11 12| 接口名 | 描述 | 13| -------- | -------- | 14| OH_NativeBuffer_Alloc (const OH_NativeBuffer_Config \*config) | 通过OH_NativeBuffer_Config创建OH_NativeBuffer实例,每次调用都会产生一个新的OH_NativeBuffer实例。本接口需要与OH_NativeBuffer_Unreference接口配合使用,否则会存在内存泄露。 | 15| OH_NativeBuffer_Reference (OH_NativeBuffer \*buffer) | 将OH_NativeBuffer对象的引用计数增加1。 | 16| OH_NativeBuffer_Unreference (OH_NativeBuffer \*buffer) | 将OH_NativeBuffer对象的引用计数减1,当引用计数为0的时候,该NativeBuffer对象会被析构掉。 | 17| OH_NativeBuffer_GetConfig (OH_NativeBuffer \*buffer, OH_NativeBuffer_Config \*config) | 用于获取OH_NativeBuffer的属性。 | 18| OH_NativeBuffer_Map (OH_NativeBuffer \*buffer, void \*\*virAddr) | 将OH_NativeBuffer对应的ION内存映射到进程空间。 | 19| OH_NativeBuffer_Unmap (OH_NativeBuffer \*buffer) | 将OH_NativeBuffer对应的ION内存从进程空间移除。 | 20| OH_NativeBuffer_GetSeqNum (OH_NativeBuffer \*buffer) | 获取OH_NativeBuffer的序列号。 | 21 22详细的接口说明请参考[native_buffer](../reference/apis-arkgraphics2d/_o_h___native_buffer.md)。 23 24## 开发步骤 25 26以下步骤描述了如何使用`NativeBuffer`提供的Native API接口,创建`OH_NativeBuffer`实例获取内存的属性信息,并把对应的ION内存映射到进程空间。 27 28**添加动态链接库** 29 30CMakeLists.txt中添加以下lib。 31```txt 32libnative_buffer.so 33``` 34 35**头文件** 36```c++ 37#include <native_buffer/native_buffer.h> 38``` 39 401. **创建OH_NativeBuffer实例**。 41 ```c++ 42 #include <iostream> 43 44 OH_NativeBuffer_Config config { 45 .width = 0x100, 46 .height = 0x100, 47 }; 48 OH_NativeBuffer* buffer = OH_NativeBuffer_Alloc(&config); 49 if (buffer == nullptr) { 50 std::cout << "OH_NativeBuffer_Alloc Failed" << std::endl; 51 } 52 ``` 53 542. **将OH_NativeBuffer对应的ION内存映射到进程空间**。 55 应用如需要访问这块buffer的内存空间,需要通过OH_NativeBuffer_Map接口将buffer对应的ION内存映射到进程空间。 56 ```c++ 57 // 将ION内存映射到进程空间 58 void* virAddr = nullptr; 59 int32_t ret = OH_NativeBuffer_Map(buffer, &virAddr); // 映射后通过第二个参数virAddr返回内存的首地址 60 if (ret != 0) { 61 std::cout << "OH_NativeBuffer_Map Failed" << std::endl; 62 } 63 64 // 使用后请及时将OH_NativeBuffer对应的ION内存从进程空间移除 65 ret = OH_NativeBuffer_Unmap(buffer); 66 if (ret != 0) { 67 std::cout << "OH_NativeBuffer_Unmap Failed" << std::endl; 68 } 69 ``` 70 713. **获取内存的属性信息**。 72 ```c++ 73 // 获取OH_NativeBuffer的属性 74 OH_NativeBuffer_Config config2 = {}; 75 OH_NativeBuffer_GetConfig(buffer, &config2); 76 // 获取OH_NativeBuffer的序列号 77 uint32_t hwBufferID = OH_NativeBuffer_GetSeqNum(buffer); 78 ``` 79 804. **销毁OH_NativeBuffer**。 81 ```c++ 82 // 调用OH_NativeBuffer_Unreference引用计数减1,之后buffer的引用计数为0,buffer会销毁 83 ret = OH_NativeBuffer_Unreference(buffer); 84 if (ret != 0) { 85 std::cout << "OH_NativeBuffer_Unreference Failed" << std::endl; 86 } 87 ```