远端状态订阅开发实例

IPC/RPC提供对远端Stub对象状态的订阅机制，在远端Stub对象消亡时，可触发消亡通知告诉本地Proxy对象。这种状态通知订阅需要调用特定接口完成，当不再需要订阅时也需要调用特定接口取消。使用这种订阅机制的用户，需要实现消亡通知接口DeathRecipient并实现onRemoteDied方法清理资源。该方法会在远端Stub对象所在进程消亡或所在设备离开组网时被回调。值得注意的是，调用这些接口有一定的顺序。首先，需要Proxy订阅Stub消亡通知，若在订阅期间Stub状态正常，则在不再需要时取消订阅；若在订阅期间Stub所在进程退出或者所在设备退出组网，则会自动触发Proxy自定义的后续操作。

使用场景

这种订阅机制适用于本地Proxy对象需要感知远端Stub对象所在进程消亡，或所在设备离开组网的场景。当Proxy感知到Stub端消亡后，可适当清理本地资源。此外，RPC目前不提供匿名Stub对象的消亡通知，即只有向SAMgr注册过的服务才能被订阅消亡通知，IPC则支持匿名对象的消亡通知。

Native侧接口

参考代码

#include "iremote_broker.h"
#include "iremote_stub.h"

//定义消息码
enum {
    TRANS_ID_PING_ABILITY = 5,
    TRANS_ID_REVERSED_MONITOR
};

const std::string DESCRIPTOR = "test.ITestAbility";

class ITestService : public IRemoteBroker {
public:
    // DECLARE_INTERFACE_DESCRIPTOR是必需的，入参需使用std::u16string；
    DECLARE_INTERFACE_DESCRIPTOR(to_utf16(DESCRIPTOR));
    virtual int TestPingAbility(const std::u16string &dummy) = 0; // 定义业务函数
};

class TestServiceProxy : public IRemoteProxy<ITestAbility> {
public:
    explicit TestAbilityProxy(const sptr<IRemoteObject> &impl);
    virtual int TestPingAbility(const std::u16string &dummy) override;
    int TestAnonymousStub();
private:
    static inline BrokerDelegator<TestAbilityProxy> delegator_; // 方便后续使用iface_cast宏
};

TestServiceProxy::TestServiceProxy(const sptr<IRemoteObject> &impl)
    : IRemoteProxy<ITestAbility>(impl)
{
}

int TestServiceProxy::TestPingAbility(const std::u16string &dummy){
    MessageOption option;
    MessageParcel dataParcel, replyParcel;
    dataParcel.WriteString16(dummy);
    int error = PeerHolder::Remote()->SendRequest(TRANS_ID_PING_ABILITY, dataParcel, replyParcel, option);
    int result = (error == ERR_NONE) ? replyParcel.ReadInt32() : -1;
    return result;
}

#include "iremote_object.h"

class TestDeathRecipient : public IRemoteObject::DeathRecipient {
public:
    virtual void OnRemoteDied(const wptr<IRemoteObject>& remoteObject);
}

void TestDeathRecipient::OnRemoteDied(const wptr<IRemoteObject>& remoteObject)
{
}

sptr<IPCObjectProxy> object = new IPCObjectProxy(1, to_utf16(DESCRIPTOR));
sptr<IRemoteObject::DeathRecipient> deathRecipient (new TestDeathRecipient()); // 构造一个消亡通知对象
bool result = object->AddDeathRecipient(deathRecipient); // 注册消亡通知
result = object->RemoveDeathRecipient(deathRecipient); // 移除消亡通知

JS侧接口

获取context

Stage模型在连接服务前需要先获取context

import UIAbility from '@ohos.app.ability.UIAbility';
import Want from '@ohos.app.ability.Want';
import AbilityConstant from '@ohos.app.ability.AbilityConstant';
import window from '@ohos.window';

export default class MainAbility extends UIAbility {
    onCreate(want: Want, launchParam: AbilityConstant.LaunchParam) {
        console.log("[Demo] MainAbility onCreate");
        let context = this.context;
    }
    onDestroy() {
        console.log("[Demo] MainAbility onDestroy");
    }
    onWindowStageCreate(windowStage: window.WindowStage) {
        // Main window is created, set main page for this ability
        console.log("[Demo] MainAbility onWindowStageCreate");
    }
    onWindowStageDestroy() {
        // Main window is destroyed, release UI related resources
        console.log("[Demo] MainAbility onWindowStageDestroy");
    }
    onForeground() {
        // Ability has brought to foreground
        console.log("[Demo] MainAbility onForeground");
    }
    onBackground() {
        // Ability has back to background
        console.log("[Demo] MainAbility onBackground");
    }
}

参考代码

// 仅FA模型需要导入@ohos.ability.featureAbility
// import FA from "@ohos.ability.featureAbility";
import Want from '@ohos.app.ability.Want';
import common from '@ohos.app.ability.common';
import rpc from '@ohos.rpc';

let proxy: rpc.IRemoteObject|undefined = undefined;
let connect: common.ConnectOptions = {
  onConnect: (elementName, remoteProxy) => {
    console.log("RpcClient: js onConnect called.");
    proxy = remoteProxy;
  },
  onDisconnect: (elementName) => {
    console.log("RpcClient: onDisconnect");
  },
  onFailed: () => {
    console.log("RpcClient: onFailed");
  }
};
let want: Want = {
  bundleName: "com.ohos.server",
  abilityName: "com.ohos.server.EntryAbility",
};
// FA模型通过此方法连接服务
// FA.connectAbility(want, connect);

this.context.connectServiceExtensionAbility(want, connect);

上述onConnect回调函数中的proxy对象需要等ability异步连接成功后才会被赋值，然后才可调用proxy对象的unregisterDeathRecipient接口方法注销死亡回调

import Want from '@ohos.app.ability.Want';
import common from '@ohos.app.ability.common';
import rpc from '@ohos.rpc';
class MyDeathRecipient implements rpc.DeathRecipient{
    onRemoteDied() {
        console.log("server died");
    }
}
let deathRecipient = new MyDeathRecipient();
let proxy: rpc.IRemoteObject|undefined = undefined;
proxy.registerDeathRecipient(deathRecipient, 0);
proxy.unregisterDeathRecipient(deathRecipient, 0);

Stub感知Proxy消亡（匿名Stub的使用）

正向的消亡通知是Proxy感知Stub的状态，若想达到反向的死消亡通知，即Stub感知Proxy的状态，可以巧妙的利用正向消亡通知。如两个进程A（原Stub所在进程）和B（原Proxy所在进程），进程B在获取到进程A的Proxy对象后，在B进程新建一个匿名Stub对象（匿名指未向SAMgr注册），可称之为回调Stub，再通过SendRequest接口将回调Stub传给进程A的原Stub。这样一来，进程A便获取到了进程B的回调Proxy。当进程B消亡或B所在设备离开组网时，回调Stub会消亡，回调Proxy会感知，进而通知给原Stub，便实现了反向消亡通知。

注意：

反向死亡通知仅限设备内跨进程通信使用，不可用于跨设备。

当匿名Stub对象没有被任何一个Proxy指向的时候，内核会自动回收。

参考代码

// Proxy
int TestAbilityProxy::TestAnonymousStub()
{
    MessageOption option;
    MessageParcel dataParcel, replyParcel;
    dataParcel.UpdateDataVersion(Remote());
    dataParcel.WriteRemoteObject(new TestAbilityStub());
    int error = Remote()->SendRequest(TRANS_ID_REVERSED_MONITOR,dataParcel, replyParcel, option);
    int result = (error == ERR_NONE) ? replyParcel.ReadInt32() : -1;
    return result;
}

// Stub

int TestAbilityStub::OnRemoteRequest(uint32_t code, MessageParcel &data, MessageParcel &reply, MessageOption &option)
{
    switch (code) {
        case TRANS_ID_REVERSED_MONITOR: {
            sptr<IRemoteObject> obj = data.ReadRemoteObject();
            if (obj == nullptr) {
                reply.WriteInt32(ERR_NULL_OBJECT);
                return ERR_NULL_OBJECT;
            }
            bool result = obj->AddDeathRecipient(new TestDeathRecipient());
            result ? reply.WriteInt32(ERR_NONE) : reply.WriteInt32(-1);
            break;
        }
        default:
            break;
    }
    return ERR_NONE;
}

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