android sharedmemory 怎样读写数据 - 问答

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：

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);
}

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;
};

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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