harmony 鸿蒙NativeBuffer开发指导

2023-10-30
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NativeBuffer开发指导

场景介绍

NativeBuffer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。针对NativeBuffer，常见的开发场景如下：

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。

接口说明

接口名	描述
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。
OH_NativeBuffer_Reference (OH_NativeBuffer *buffer)	将OH_NativeBuffer对象的引用计数加1。
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。
OH_NativeBuffer_GetConfig (OH_NativeBuffer buffer, OH_NativeBuffer_Config config)	用于获取OH_NativeBuffer的属性。
OH_NativeBuffer_Map (OH_NativeBuffer buffer, void *virAddr)	将OH_NativeBuffer对应的ION内存映射到进程空间。
OH_NativeBuffer_Unmap (OH_NativeBuffer *buffer)	将OH_NativeBuffer对应的ION内存从进程空间移除。
OH_NativeBuffer_GetSeqNum (OH_NativeBuffer *buffer)	获取OH_NativeBuffer的序列号。

详细的接口说明请参考native_buffer。

开发步骤

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。

添加动态链接库

CMakeLists.txt中添加以下lib。

libnative_buffer.so

头文件

#include <native_buffer/native_buffer.h>

创建OH_NativeBuffer实例。

#include <iostream>


OH_NativeBuffer_Config config {
    .width = 0x100,
    .height = 0x100,
};
OH_NativeBuffer* buffer = OH_NativeBuffer_Alloc(&config);
if (buffer == nullptr) {
    std::cout << "OH_NativeBuffer_Alloc Failed" << std::endl;
}

将OH_NativeBuffer对应的ION内存映射到进程空间。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

// 将ION内存映射到进程空间
void* virAddr = nullptr;
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
if (ret != 0) {
    std::cout << "OH_NativeBuffer_Map Failed" << std::endl;
}


// 使用后请及时将OH_NativeBuffer对应的ION内存从进程空间移除
ret = OH_NativeBuffer_Unmap(buffer);
if (ret != 0) {
    std::cout << "OH_NativeBuffer_Unmap Failed" << std::endl;
}

获取内存的属性信息。

// 获取OH_NativeBuffer的属性
OH_NativeBuffer_Config config2 = {};
OH_NativeBuffer_GetConfig(buffer, &config2);
// 获取OH_NativeBuffer的序列号
 uint32_t hwBufferID = OH_NativeBuffer_GetSeqNum(buffer);

销毁OH_NativeBuffer。

// 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
ret = OH_NativeBuffer_Unreference(buffer);
if (ret != 0) {
    std::cout << "OH_NativeBuffer_Unreference Failed" << std::endl;
}