鸿蒙开发实战：【系统服务管理部件】

简介

samgr组件是OpenHarmony的核心组件，提供OpenHarmony系统服务启动、注册、查询等功能。

系统架构

图 1 系统服务管理系统架构图

说明

1. samgr服务接收到sa框架层发送的注册消息，会在本地缓存中存入系统服务相关信息。

   int32_t SystemAbilityManager::AddSystemAbility(int32_t systemAbilityId, const sptr<IRemoteObject>& ability,
       const SAExtraProp& extraProp)
   {
       if (!CheckInputSysAbilityId(systemAbilityId) || ability == nullptr) {
           HILOGE("AddSystemAbilityExtra input params is invalid.");
           return ERR_INVALID_VALUE;
       }
       {
           unique_lock<shared_mutex> writeLock(abilityMapLock_);
           auto saSize = abilityMap_.size();
           if (saSize >= MAX_SERVICES) {
               HILOGE("map size error, (Has been greater than %zu)", saSize);
               return ERR_INVALID_VALUE;
           }
           SAInfo saInfo;
           saInfo.remoteObj = ability;
           saInfo.isDistributed = extraProp.isDistributed;
           saInfo.capability = extraProp.capability;
           saInfo.permission = Str16ToStr8(extraProp.permission);
           abilityMap_[systemAbilityId] = std::move(saInfo);
           HILOGI("insert %{public}d. size : %{public}zu", systemAbilityId, abilityMap_.size());
       }
       RemoveCheckLoadedMsg(systemAbilityId);
       if (abilityDeath_ != nullptr) {
           ability->AddDeathRecipient(abilityDeath_);
       }
   
       u16string strName = Str8ToStr16(to_string(systemAbilityId));
       if (extraProp.isDistributed && dBinderService_ != nullptr) {
           dBinderService_->RegisterRemoteProxy(strName, systemAbilityId);
           HILOGD("AddSystemAbility RegisterRemoteProxy, serviceId is %{public}d", systemAbilityId);
       }
       if (systemAbilityId == SOFTBUS_SERVER_SA_ID && !isDbinderStart_) {
           if (dBinderService_ != nullptr && rpcCallbackImp_ != nullptr) {
               bool ret = dBinderService_->StartDBinderService(rpcCallbackImp_);
               HILOGI("start result is %{public}s", ret ? "succeed" : "fail");
               isDbinderStart_ = true;
           }
       }
       SendSystemAbilityAddedMsg(systemAbilityId, ability);
       return ERR_OK;
   }

2. 对于本地服务而言，samgr服务接收到sa框架层发送的获取消息，会通过服务id，查找到对应服务的代理对象，然后返回给sa框架。

   sptr<IRemoteObject> SystemAbilityManager::CheckSystemAbility(int32_t systemAbilityId)
   {
       if (!CheckInputSysAbilityId(systemAbilityId)) {
           HILOGW("CheckSystemAbility CheckSystemAbility invalid!");
           return nullptr;
       }
   
       shared_lock<shared_mutex> readLock(abilityMapLock_);
       auto iter = abilityMap_.find(systemAbilityId);
       if (iter != abilityMap_.end()) {
           HILOGI("found service : %{public}d.", systemAbilityId);
           return iter->second.remoteObj;
       }
       HILOGI("NOT found service : %{public}d", systemAbilityId);
       return nullptr;
   }

3. 动态加载系统服务进程及SystemAbility, 系统进程无需开机启动，而是在SystemAbility被访问的时候按需拉起，并加载指定SystemAbility。
   3.1 继承SystemAbilityLoadCallbackStub类，并覆写OnLoadSystemAbilitySuccess(int32_t systemAbilityId, const sptr& remoteObject)、OnLoadSystemAbilityFail(int32_t systemAbilityId)方法。

   class OnDemandLoadCallback : public SystemAbilityLoadCallbackStub {
   public:
       void OnLoadSystemAbilitySuccess(int32_t systemAbilityId, const sptr<IRemoteObject>& remoteObject) override;
       void OnLoadSystemAbilityFail(int32_t systemAbilityId) override;
   };
   
   void OnDemandLoadCallback::OnLoadSystemAbilitySuccess(int32_t systemAbilityId,
       const sptr<IRemoteObject>& remoteObject) // systemAbilityId为指定加载的SAID，remoteObject为指定systemAbility的代理对象
   {
       cout << "OnLoadSystemAbilitySuccess systemAbilityId:" << systemAbilityId << " IRemoteObject result:" <<
           ((remoteObject != nullptr) ? "succeed" : "failed") << endl;
   }
   
   void OnDemandLoadCallback::OnLoadSystemAbilityFail(int32_t systemAbilityId) // systemAbilityId为指定加载的SAID
   {
       cout << "OnLoadSystemAbilityFail systemAbilityId:" << systemAbilityId << endl;
   }

   3.2 调用samgr提供的动态加载接口LoadSystemAbility(int32_t systemAbilityId, const sptr& callback)。

   // 构造步骤1的SystemAbilityLoadCallbackStub子类的实例
   sptr<OnDemandLoadCallback> loadCallback_ = new OnDemandLoadCallback();
   // 调用LoadSystemAbility方法
   sptr<ISystemAbilityManager> sm = SystemAbilityManagerClient::GetInstance().GetSystemAbilityManager();
   if (sm == nullptr) {
       cout << "GetSystemAbilityManager samgr object null!" << endl;
       return;
   }
   int32_t result = sm->LoadSystemAbility(systemAbilityId, loadCallback_);
   if (result != ERR_OK) {
       cout << "systemAbilityId:" << systemAbilityId << " load failed, result code:" << result << endl;
       return;
   }

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说明：
1.LoadSystemAbility方法调用成功后，指定SystemAbility加载成功后会触发回调OnLoadSystemAbilitySuccess，加载失败触发回调OnLoadSystemAbilityFail。
2.动态加载的进程cfg文件不能配置为开机启动，需指定"ondemand" : true, 示例如下:

{
  "services" : [{
          "name" : "listen_test",
          "path" : ["/system/bin/sa_main", "/system/profile/listen_test.json"],
          "ondemand" : true,
          "uid" : "system",
          "gid" : ["system", "shell"]
      }   
  ]
}

3.LoadSystemAbility方法适用于动态加载场景，其他获取SystemAbility场景建议使用CheckSystemAbility方法。
4.cfg里进程名称需要与SA的配置json文件里进程名保持一致