android sharedmemory 怎样读写数据

Android SharedMemory 是一种进程间通信（IPC）机制，它允许不同进程访问同一块内存区域。在 Android 中，可以使用 Binder 框架来实现 SharedMemory。以下是如何在 Android 中使用 SharedMemory 读写数据的步骤：

1. 创建 SharedMemory 对象：

#include <
    android/binder_interface_utils.h>
    
#include <
    android/log.h>
    
#include <
    binder/IServiceManager.h>
    
#include <
    binder/MemoryBase.h>
    
#include <
    binder/MemoryHeapBase.h>
    

using namespace android;
    

status_t createSharedMemory(size_t size, sp<
    IMemory>
 *memory) {
    
    sp<
    IServiceManager>
     sm = defaultServiceManager();
    
    const String16 name("MySharedMemory");
    
    return sm->
    addService(String16(name.string()), new SharedMemoryService(size), true);

}

1. 实现 SharedMemoryService 类：

class SharedMemoryService : public BnMemory {

public:
    SharedMemoryService(size_t size) : mSize(size) {
    
        mHeap = new MemoryHeapBase(mSize);

    }
    

    virtual status_t onTransact(uint32_t code, const Parcel &
data, Parcel *reply, uint32_t flags = 0) {

        switch (code) {

            case GET_SIZE: {
    
                reply->
    writeInt32(mSize);
    
                return NO_ERROR;

            }

            case READ_DATA: {
    
                void *buffer = nullptr;
    
                status_t status = mHeap->
    lock(0, mSize, &
    buffer, false);

                if (status == NO_ERROR) {
    
                    memcpy(buffer, mData.get(), mSize);
    
                    mHeap->
    unlock(buffer);
    
                    reply->
    writeInt32(mSize);

                }
 else {
    
                    reply->
    writeInt32(0);

                }
    
                return status;

            }

            case WRITE_DATA: {
    
                void *buffer = nullptr;
    
                status_t status = mHeap->
    lock(0, mSize, &
    buffer, true);

                if (status == NO_ERROR) {
    
                    memcpy(buffer, data.data(), data.size());
    
                    mHeap->
    unlock(buffer);
    
                    reply->
    writeInt32(data.size());

                }
 else {
    
                    reply->
    writeInt32(0);

                }
    
                return status;

            }
    
            default:
                return BBinder::onTransact(code, data, reply, flags);

        }

    }
    

private:
    size_t mSize;
    
    sp<
    MemoryHeapBase>
     mHeap;
    
    Vector<
    uint8_t>
     mData;

}
    ;
    

1. 在客户端进程中读写 SharedMemory 数据：

#include <
    android/binder_interface_utils.h>
    
#include <
    android/log.h>
    
#include <
    binder/IServiceManager.h>
    
#include <
    binder/MemoryBase.h>
    
#include <
    binder/MemoryHeapBase.h>
    

using namespace android;
    

status_t createSharedMemory(size_t size, sp<
    IMemory>
 *memory) {
    
    sp<
    IServiceManager>
     sm = defaultServiceManager();
    
    const String16 name("MySharedMemory");
    
    return sm->
    addService(String16(name.string()), new SharedMemoryService(size), true);

}
    

void readSharedMemoryData(sp<
    IMemory>
 memory) {
    
    void *buffer = nullptr;
    
    status_t status = memory->
    lock(0, memory->
    getSize(), &
    buffer, false);

    if (status == NO_ERROR) {
    
        size_t size = memory->
    getSize();
    
        memcpy(buffer, mData.get(), size);
    
        memory->
    unlock(buffer);

    }

}
    

void writeSharedMemoryData(sp<
    IMemory>
 memory, const uint8_t *data, size_t size) {
    
    void *buffer = nullptr;
    
    status_t status = memory->
    lock(0, memory->
    getSize(), &
    buffer, true);

    if (status == NO_ERROR) {
    
        memcpy(buffer, data, size);
    
        memory->
    unlock(buffer);

    }

}
    

注意：这里的示例代码仅供参考，实际使用时需要根据具体需求进行调整。在实际开发中，还需要考虑内存管理、错误处理等方面的问题。

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