OpenHarmony轻量系统服务管理samgr-feature赏析及实现

本文主要针对feature部分进行分析，这部分代码的分析囊括了interfaces\kits\samgr\feature.h、samgr\source\feature_impl.h和samgr\source\feature.c。

在feature.h中定义了feature的基类，分析如下：

struct Feature {
    const char *(*GetName)(Feature *feature);//获取feature名
    //@feature指向当前特性
    //@parent指向特性所属的服务
    //@identity系统调度特性的标识
    //特性初始化，Samgr将任务分派给服务后，该服务在其自己的任务中调用此函数
    void (*OnInitialize)(Feature *feature, Service *parent, Identity identity);
    //停止一个特性
    void (*OnStop)(Feature *feature, Identity identity);
    //处理特性消息，用于处理调用者通过IUnknown发送的请求
    BOOL (*OnMessage)(Feature *feature, Request *request);
};

在feature_impl.h中声明了feature的一些方法，分析如下：

//包含feature和iUnknown的结构体FeatureImpl
struct FeatureImpl {
    Feature *feature;
    IUnknown *iUnknown;
};
//inline--内联函数，在函数调用处展开，可以减少函数调用的开销
//判断指定的Feature是否有效
inline static BOOL IsInvalidFeature(Feature *feature)
{
    return (feature == NULL || feature->GetName == NULL || feature->OnInitialize == NULL ||
            feature->OnMessage == NULL || feature->OnStop == NULL);
}
//判断指定的IUnknown是否有效
inline static BOOL IsInvalidIUnknown(IUnknown *iUnknown)
{
    return (iUnknown == NULL || iUnknown->QueryInterface == NULL || iUnknown->AddRef == NULL ||
            iUnknown->Release == NULL);
}
//添加接口
BOOL SAMGR_AddInterface(FeatureImpl *featureImpl, IUnknown *iUnknown);
//删除接口
IUnknown *SAMGR_DelInterface(FeatureImpl *featureImpl);
//获取接口
IUnknown *SAMGR_GetInterface(FeatureImpl *featureImpl);
//判断featureImpl的接口是否为NULL
BOOL SAMGR_IsNoInterface(FeatureImpl *featureImpl);
//创建FeatureImpl对象
FeatureImpl *FEATURE_CreateInstance(Feature *feature);

在feature.c中对方法进行了实现，分析如下： 添加接口操作

/*
    函数功能：为featureImpl添加接口
    函数返回：添加成功返回true，添加失败返回false
*/
BOOL SAMGR_AddInterface(FeatureImpl *featureImpl, IUnknown *iUnknown)
{
    //参数检查
    if (featureImpl == NULL || iUnknown == NULL || featureImpl->iUnknown != NULL) {
        return FALSE;
    }
    //将iUnknown添加到featureImpl中
    featureImpl->iUnknown = iUnknown;
    return TRUE;
}

删除接口

/*
    函数功能：删除featureImpl的接口
    函数返回：删除成功返回被删除的对象IUnknown，删除失败返回NULL
    函数描述：删除指定featureImpl的接口，将featureImpl的iUnknown成员赋值为NULL，并返回iUnknown
*/
IUnknown *SAMGR_DelInterface(FeatureImpl *featureImpl)
{
    //参数检查
    if (featureImpl == NULL) {
        return NULL;
    }
    //保存将被删除的iUnknown接口
    IUnknown *iUnknown = featureImpl->iUnknown;
    //置为NULL，删除的作用
    featureImpl->iUnknown = NULL;
    //返回被删除的接口对象
    return iUnknown;
}

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获取接口

//返回指定featureImpl的成员iUnknown
IUnknown *SAMGR_GetInterface(FeatureImpl *featureImpl)
{
    //参数检查
    if (featureImpl == NULL) {
        return NULL;
    }
    //返回featureImpl的接口
    return featureImpl->iUnknown;
}

判断接口是否存在

//判断featureImpl的接口是否为NULL，返回true or false
BOOL SAMGR_IsNoInterface(FeatureImpl *featureImpl)
{
    return (BOOL)(featureImpl == NULL || featureImpl->iUnknown == NULL);
}

创建featureimpl实例

//为指定的feature创建一个FeatureImpl实例
FeatureImpl *FEATURE_CreateInstance(Feature *feature)
{
    if (feature == NULL) {
        return NULL;
    }
    //分配内存
    FeatureImpl *featureImpl = (FeatureImpl *)SAMGR_Malloc(sizeof(FeatureImpl));
    if (featureImpl == NULL) {
        //内存分配失败
        return NULL;
    }
    //赋值，默认iUnknown为NULL
    featureImpl->feature = feature;
    featureImpl->iUnknown = NULL;
    return featureImpl;
}