README.md · OH_IPC/distributedschedule_samgr_lite

# samgr\_lite<a name="EN-US_TOPIC_0000001081604584"></a>

-   [Introduction](#section11660541593)
-   [Directory Structure](#section1464106163817)
-   [Constraints](#section1718733212019)
-   [Developing a Service](#section159991817144514)
-   [Developing a Feature of a Service](#section11510542164514)
-   [Developing an External API for Intra-Process Communication](#section1685211117463)
-   [Invoking a Service in the Same Process](#section3690162916462)
-   [Developing an External API for IPC](#section9220246194615)
-   [Invoking a Service in Another Process](#section114372711475)
-   [Developing a Client Proxy for Inter-Process Service Invocation](#section09341923114710)
-   [Repositories Involved](#section10365113863719)

## Introduction<a name="section11660541593"></a>

Due to limited platform resources, a unified system ability \(SA\) framework is provided to harmonize differences of hardware architectures \(for example, RISC-V, Cortex-M, and Cortex-A\), resources, and running modes. Two types of hardware platforms \(M- and A-core\) are defined.

-   M-core: hardware platforms with Cortex-M or equivalent processing capabilities. The system memory is generally less than 512 KB. There is only a lightweight file system that can be used in limited scenarios, or no file system at all. M-core platforms comply with the Cortex Microcontroller Software Interface Standard \(CMSIS\).
-   A-core: hardware platforms with Cortex-A or equivalent processing capabilities. The system memory is greater than 512 KB. There is a comprehensive file system for storing a large amount of data. A-core platforms comply with the Portable Operating System Interface \(POSIX\) specifications.

This service-oriented SA framework enables you to develop services, features, and external APIs, and implement multi-service process sharing and service invoking for inter-process communication \(IPC\). Wherein:

-   M core provides services, features, external APIs, and multi-service process sharing development.
-   In addition to the capabilities provided by M-core, A-core provides capabilities such as IPC service invoking, permission control for IPC service invoking, and IPC service API development.

Service-oriented architecture

![](figures/en-us_image_0000001128146921.png)

-   Provider: a service provider that provides capabilities \(external APIs\) for the system
-   Consumer: a service consumer that invokes the features \(external APIs\) provided by the service
-   Samgr: an agency that manages capabilities provided by providers and helps consumers discover providers' capabilities

Main objects of the SA framework:

![](figures/en-us_image_0000001081285004.png)

-   SamgrLite: provides service registration and discovery.
-   Service: implements lifecycle APIs of the service during service development.
-   Feature: implements lifecycle APIs of the feature during feature development.
-   IUnknown: implements external APIs for services or features based on  **IUnknown**.
-   IClientProxy: implements the consumer's proxy to send messages during IPC invoking.
-   IServerProxy: implements the provider's proxy during IPC invoking, which needs to be implemented by developers.

## Directory Structure<a name="section1464106163817"></a>

**Table  1**  Structure of the source code directory of the SA framework

<a name="table2977131081412"></a>
<table><thead align="left"><tr id="row7977610131417"><th class="cellrowborder" valign="top" width="31.3%" id="mcps1.2.3.1.1"><a name="p18792459121314"></a><a name="p18792459121314"></a>Directory
</th>
<th class="cellrowborder" valign="top" width="68.7%" id="mcps1.2.3.1.2"><a name="p77921459191317"></a><a name="p77921459191317"></a>Description
</th>
</tr>
</thead>
<tbody><tr id="row17977171010144"><td class="cellrowborder" valign="top" width="31.3%" headers="mcps1.2.3.1.1 "><a name="p2793159171311"></a><a name="p2793159171311"></a>interfaces/kits/samgr_lite/samgr
</td>
<td class="cellrowborder" valign="top" width="68.7%" headers="mcps1.2.3.1.2 "><a name="p879375920132"></a><a name="p879375920132"></a>External APIs of the M- and A-core SA frameworks
</td>
</tr>
<tr id="row6978161091412"><td class="cellrowborder" valign="top" width="31.3%" headers="mcps1.2.3.1.1 "><a name="p37931659101311"></a><a name="p37931659101311"></a>interfaces/kits/samgr_lite/registry
</td>
<td class="cellrowborder" valign="top" width="68.7%" headers="mcps1.2.3.1.2 "><a name="p6793059171318"></a><a name="p6793059171318"></a>External APIs for service invocation between A-core processes
</td>
</tr>
<tr id="row6978201031415"><td class="cellrowborder" valign="top" width="31.3%" headers="mcps1.2.3.1.1 "><a name="p117935599130"></a><a name="p117935599130"></a>interfaces/kits/samgr_lite/communication/broadcast
</td>
<td class="cellrowborder" valign="top" width="68.7%" headers="mcps1.2.3.1.2 "><a name="p0793185971316"></a><a name="p0793185971316"></a>External APIs of the event broadcast service within M- and A-core processes
</td>
</tr>
<tr id="row124243183397"><td class="cellrowborder" valign="top" width="31.3%" headers="mcps1.2.3.1.1 "><a name="p104249183396"></a><a name="p104249183396"></a>services/samgr_lite/samgr/adapter
</td>
<td class="cellrowborder" valign="top" width="68.7%" headers="mcps1.2.3.1.2 "><a name="p2424318203914"></a><a name="p2424318203914"></a>POSIX and CMSIS interface adaptation layer, which is used to harmonize the differences between the APIs of M- and A-core
</td>
</tr>
<tr id="row1634915717405"><td class="cellrowborder" valign="top" width="31.3%" headers="mcps1.2.3.1.1 "><a name="p193493571406"></a><a name="p193493571406"></a>services/samgr_lite/samgr/registry
</td>
<td class="cellrowborder" valign="top" width="68.7%" headers="mcps1.2.3.1.2 "><a name="p14349257184012"></a><a name="p14349257184012"></a>Stub functions for M-core service registration and discovery
</td>
</tr>
<tr id="row1385432741312"><td class="cellrowborder" valign="top" width="31.3%" headers="mcps1.2.3.1.1 "><a name="p1485582714135"></a><a name="p1485582714135"></a>services/samgr_lite/samgr/source
</td>
<td class="cellrowborder" valign="top" width="68.7%" headers="mcps1.2.3.1.2 "><a name="p085522751319"></a><a name="p085522751319"></a>Basic code for the M- and A-core SA frameworks
</td>
</tr>
<tr id="row7968155877"><td class="cellrowborder" valign="top" width="31.3%" headers="mcps1.2.3.1.1 "><a name="p89681851717"></a><a name="p89681851717"></a>services/samgr_lite/samgr_client
</td>
<td class="cellrowborder" valign="top" width="68.7%" headers="mcps1.2.3.1.2 "><a name="p169681051873"></a><a name="p169681051873"></a>Registration and discovery for service invocation between A-core processes
</td>
</tr>
<tr id="row18291912179"><td class="cellrowborder" valign="top" width="31.3%" headers="mcps1.2.3.1.1 "><a name="p1729111214715"></a><a name="p1729111214715"></a>services/samgr_lite/samgr_server
</td>
<td class="cellrowborder" valign="top" width="68.7%" headers="mcps1.2.3.1.2 "><a name="p7839893352"></a><a name="p7839893352"></a>IPC address management and access control for service invocation between A-core processes
</td>
</tr>
<tr id="row6971514279"><td class="cellrowborder" valign="top" width="31.3%" headers="mcps1.2.3.1.1 "><a name="p1797118141671"></a><a name="p1797118141671"></a>services/samgr_lite/samgr_endpoint
</td>
<td class="cellrowborder" valign="top" width="68.7%" headers="mcps1.2.3.1.2 "><a name="p597119145716"></a><a name="p597119145716"></a>Packet RX/TX management for A-core IPC
</td>
</tr>
<tr id="row33121991272"><td class="cellrowborder" valign="top" width="31.3%" headers="mcps1.2.3.1.1 "><a name="p143121991875"></a><a name="p143121991875"></a>services/samgr_lite/communication/broadcast
</td>
<td class="cellrowborder" valign="top" width="68.7%" headers="mcps1.2.3.1.2 "><a name="p16312169179"></a><a name="p16312169179"></a>Event broadcast service for M- and A-core processes
</td>
</tr>
</tbody>
</table>

## Constraints<a name="section1718733212019"></a>

-   The SA framework is developed using the C programming language.
-   Services in the same process use  **IUnknown**  for invoking. Messages are passed to the service through  **IUnknown**.
-   The service name and feature name must be constant character strings and the length must be less than 16 bytes.
-   More-core depends on the Bootstrap service and calls the  **OHOS\_SystemInit\(\)**  function in the system startup function.
-   A-core depends on the Samgr library and calls the  **SAMGR\_Bootstrap\(\)**  function in the  **main**  function.

## Developing a Service<a name="section159991817144514"></a>

-   Inherit and redefine a service.

```
    typedef struct ExampleService {
        INHERIT_SERVICE;
        INHERIT_IUNKNOWNENTRY(DefaultFeatureApi);
        Identity identity;
    } ExampleService;
    ```

-   Implement the lifecycle function of the service.

```
    static const char *GetName(Service *service)
    {
        return EXAMPLE_SERVICE;
    }
    
    static BOOL Initialize(Service *service, Identity identity)
    {
        ExampleService *example = (ExampleService *)service;
        // Save the unique ID of the service, which is used when IUnknown is used to send messages to the service.
        example->identity = identity;
        return TRUE;
    }
    static BOOL MessageHandle(Service *service, Request *msg)
    {
        ExampleService *example = (ExampleService *)service;
        switch (msg->msgId) {
            case MSG_SYNC:
                // Process the service.
                break;
            default:break;
        }
        return FALSE;
    }
    static TaskConfig GetTaskConfig(Service *service)
    {
        TaskConfig config = {LEVEL_HIGH, PRI_BELOW_NORMAL,
                             0x800, 20, SHARED_TASK};
        return config;
    }
    ```

-   Create a service object.

```
    static ExampleService g_example = {
        .GetName = GetName,
        .Initialize = Initialize,
        .MessageHandle = MessageHandle,
        .GetTaskConfig = GetTaskConfig,
        SERVER_IPROXY_IMPL_BEGIN,
            .Invoke = NULL,
            .SyncCall = SyncCall,
        IPROXY_END,
    };
    ```

-   Register the service and API with Samgr.

```
    static void Init(void)
    {
        SAMGR_GetInstance()->RegisterService((Service *)&g_example);
        SAMGR_GetInstance()->RegisterDefaultFeatureApi(EXAMPLE_SERVICE, GET_IUNKNOWN(g_example));
    }
    ```

-   Define the initializer of the service.

```
    SYSEX_SERVICE_INIT(Init);
    
    ```

## Developing a Feature of a Service<a name="section11510542164514"></a>

-   Inherit and redefine a feature.

```
    typedef struct DemoFeature {
        INHERIT_FEATURE;
        INHERIT_IUNKNOWNENTRY(DemoApi);
        Identity identity;
        Service *parent;
    } DemoFeature;
    ```

-   Implement the lifecycle function of the feature.

```
    static const char *FEATURE_GetName(Feature *feature)
    {
        return EXAMPLE_FEATURE;
    }
    
    static void FEATURE_OnInitialize(Feature *feature, Service *parent, Identity identity)
    {
        DemoFeature *demoFeature = (DemoFeature *)feature;
        demoFeature->identity = identity;
        demoFeature->parent = parent;
    }
    
    static void FEATURE_OnStop(Feature *feature, Identity identity)
    {
        g_example.identity.queueId = NULL;
        g_example.identity.featureId = -1;
        g_example.identity.serviceId = -1;
    }
    
    static BOOL FEATURE_OnMessage(Feature *feature, Request *request)
    {
        if (request->msgId == MSG_PROC) {
            Response response = {.data = "Yes, you did!", .len = 0};
            SAMGR_SendResponse(request, &response);
            return TRUE;
        } else {
            if (request->msgId == MSG_TIME_PROC) {
                LOS_Msleep(WAIT_FEATURE_PROC * 10);
                if (request->msgValue) {
                    SAMGR_PrintServices();
                } else {
                    SAMGR_PrintOperations();
                }
                AsyncTimeCall(GET_IUNKNOWN(g_example));
                return FALSE;
            }
        }
        return FALSE;
    }
    ```

-   Create a feature object.

```
    static DemoFeature g_example = {
        .GetName = FEATURE_GetName,
        .OnInitialize = FEATURE_OnInitialize,
        .OnStop = FEATURE_OnStop,
        .OnMessage = FEATURE_OnMessage,
        DEFAULT_IUNKNOWN_ENTRY_BEGIN,
            .AsyncCall = AsyncCall,
            .AsyncTimeCall = AsyncTimeCall,
            .SyncCall = SyncCall,
            .AsyncCallBack = AsyncCallBack,
        DEFAULT_IUNKNOWN_ENTRY_END,
        .identity = {-1, -1, NULL},
    };
    ```

-   Register the feature and API with Samgr.

```
    static void Init(void){
        SAMGR_GetInstance()->RegisterFeature(EXAMPLE_SERVICE, (Feature *)&g_example);
        SAMGR_GetInstance()->RegisterFeatureApi(EXAMPLE_SERVICE, EXAMPLE_FEATURE, GET_IUNKNOWN(g_example));
    }
    ```

-   Define the initializer of the feature.

```
    SYSEX_FEATURE_INIT(Init);
    
    ```

## Developing an External API for Intra-Process Communication<a name="section1685211117463"></a>

-   Define the  **IUnknown**  API.

```
    typedef struct DemoApi {
        INHERIT_IUNKNOWN;
        BOOL (*AsyncCall)(IUnknown *iUnknown, const char *buff);
        BOOL (*AsyncTimeCall)(IUnknown *iUnknown);
        BOOL (*SyncCall)(IUnknown *iUnknown, struct Payload *payload);
        BOOL (*AsyncCallBack)(IUnknown *iUnknown, const char *buff, Handler handler);
    } DemoApi;
    ```

-   Define the reference object of  **IUnknown**.

```
    typedef struct DemoRefApi {
        INHERIT_IUNKNOWNENTRY(DemoApi);
    } DemoRefApi;
    ```

-   Initialize the object of  **IUnknown**.

```
    static DemoRefApi api = {
        DEFAULT_IUNKNOWN_ENTRY_BEGIN,
            .AsyncCall = AsyncCall,
            .AsyncTimeCall = AsyncTimeCall,
            .SyncCall = SyncCall,
            .AsyncCallBack = AsyncCallBack,
        DEFAULT_IUNKNOWN_ENTRY_END,
    };
    ```

-   Register the feature API.

```
    SAMGR_GetInstance()->RegisterFeatureApi(EXAMPLE_SERVICE, EXAMPLE_FEATURE, GET_IUNKNOWN(api));
    
    ```

## Invoking a Service in the Same Process<a name="section3690162916462"></a>

-   Obtain the external API of the service.

```
    DemoApi *demoApi = NULL;
    IUnknown *iUnknown = SAMGR_GetInstance()->GetFeatureApi(EXAMPLE_SERVICE, EXAMPLE_FEATURE);
    if (iUnknown == NULL) {
        return NULL;
    }
    int result = iUnknown->QueryInterface(iUnknown, DEFAULT_VERSION, (void **)&demoApi);
    if (result != 0 || demoApi == NULL) {
        return NULL;
    }
    ```

-   Call the API.

```
    if (demoApi->AsyncCallBack == NULL) {
        return NULL;
    }
    demoApi->AsyncCallBack((IUnknown *)demoApi, "I wanna async call callback good result!", AsyncHandler);
    ```

-   Release the API.

```
    int32 ref = demoApi->Release((IUnknown *)demoApi);
    
    ```

## Developing an External API for IPC<a name="section9220246194615"></a>

-   Inherit  **IServerProxy**  to replace  **IUnknown**: INHERIT\_SERVER\_IPROXY

```
    typedef struct DemoFeatureApi {
        INHERIT_SERVER_IPROXY;
        BOOL (*AsyncCall)(IUnknown *iUnknown, const char *buff);
        BOOL (*AsyncTimeCall)(IUnknown *iUnknown);
        BOOL (*SyncCall)(IUnknown *iUnknown, struct Payload *payload);
        BOOL (*AsyncCallBack)(IUnknown *iUnknown, const char *buff, IOwner notify, INotifyFunc handler);
    } DemoFeatureApi;
    ```

-   Initialize the  **IServerProxy**  object.

```
    static DemoFeature g_example = {
        SERVER_IPROXY_IMPL_BEGIN,
        .Invoke = Invoke,
        .AsyncCall = AsyncCall,
        .AsyncTimeCall = AsyncTimeCall,
        .SyncCall = SyncCall,
        .AsyncCallBack = AsyncCallBack,
        IPROXY_END,
    };
    ```

-   Implement the  **Invoke**  function to process IPC messages.

```
    static int32 Invoke(IServerProxy *iProxy, int funcId, void *origin, IpcIo *req, IpcIo *reply)
    {
        DemoFeatureApi *api = (DemoFeatureApi *)iProxy;
        BOOL ret;
        size_t len = 0;
        switch (funcId) {
            case ID_ASYNCALL:
                ret = api->AsyncCall((IUnknown *)iProxy, (char *)IpcIoPopString(req, &len));
                IpcIoPushBool(reply, ret);
                break;
            case ID_ASYNTIMECALL:
                ret = api->AsyncTimeCall((IUnknown *)iProxy);
                IpcIoPushBool(reply, ret);
                break;
            case ID_SYNCCALL: {
                struct Payload payload;
                payload.id = IpcIoPopInt32(req);
                payload.value = IpcIoPopInt32(req);
                payload.name = (char *)IpcIoPopString(req, &len);
                ret = api->SyncCall((IUnknown *)iProxy, &payload);
                IpcIoPushString(reply, ret ? "TRUE" : "FALSE");
            }
                break;
            case ID_ASYNCCALLBACK: { // convert to sync proxy
                IpcIoPushString(reply, "Yes, you did!");
                IpcIoPushBool(reply, TRUE);
            }
                break;
            default:
                IpcIoPushBool(reply, FALSE);
                break;
        }
        return EC_SUCCESS;
    }
    ```

-   Register the API. This step is same as the API registration for intra-process communication.

```
    SAMGR_GetInstance()->RegisterFeatureApi(EXAMPLE_SERVICE, EXAMPLE_FEATURE, GET_IUNKNOWN(g_example));
    
    ```

## Invoking a Service in Another Process<a name="section114372711475"></a>

-   Obtain the external API of the service in another process.

```
    IClientProxy *demoApi = NULL;
    IUnknown *iUnknown = SAMGR_GetInstance()->GetFeatureApi(EXAMPLE_SERVICE, EXAMPLE_FEATURE);
    if (iUnknown == NULL) {
        return NULL;
    }
    int result = iUnknown->QueryInterface(iUnknown, CLIENT_PROXY_VER, (void **)&demoApi);
    if (result != 0 || demoApi == NULL) {
        return NULL;
    }
    ```

-   Invoke the API for sending IPC messages.

```
    IpcIo request;char data[250];
    IpcIoInit(&request, data, sizeof(data), 0);
    demoApi->Invoke(demoApi, 0, &request, NULL, NULL);
    ```

-   Release the API.

```
    int32 ref = demoApi->Release((IUnknown *)demoApi);
    
    ```

## Developing a Client Proxy for Inter-Process Service Invocation<a name="section09341923114710"></a>

-   Define a client proxy for the IPC API.

```
    typedef struct DemoClientProxy {
        INHERIT_CLIENT_IPROXY;
        BOOL (*AsyncCall)(IUnknown *iUnknown, const char *buff);
        BOOL (*AsyncTimeCall)(IUnknown *iUnknown);
        BOOL (*SyncCall)(IUnknown *iUnknown, struct Payload *payload);
        BOOL (*AsyncCallBack)(IUnknown *iUnknown, const char *buff, IOwner notify, INotifyFunc handler);
    } DemoClientProxy;
    typedef struct DemoClientEntry {
        INHERIT_IUNKNOWNENTRY(DemoClientProxy);
    } DemoClientEntry;
    ```

-   Enable the client proxy to encapsulate the IPC message API.

```
    static BOOL AsyncCall(IUnknown *iUnknown, const char *buff)
    {
        DemoClientProxy *proxy = (DemoClientProxy *)iUnknown;
        IpcIo request;
        char data[MAX_DATA_LEN];
        IpcIoInit(&request, data, MAX_DATA_LEN, 0);
        IpcIoPushString(&request, buff);
        int ret = proxy->Invoke((IClientProxy *)proxy, ID_ASYNCALL, &request, NULL, NULL);
        return ret == EC_SUCCESS;
    }
    
    static BOOL AsyncTimeCall(IUnknown *iUnknown)
    {
        DemoClientProxy *proxy = (DemoClientProxy *)iUnknown;
        IpcIo request;
        char data[MAX_DATA_LEN];
        IpcIoInit(&request, data, MAX_DATA_LEN, 0);
        int ret = proxy->Invoke((IClientProxy *)proxy, ID_ASYNTIMECALL, &request, NULL, NULL);
        return ret == EC_SUCCESS;
    }
    
    static int Callback(IOwner owner, int code, IpcIo *reply)
    {
        size_t len = 0;
        return strcpy_s(owner, MAX_DATA_LEN, (char *)IpcIoPopString(reply, &len));
    }
    
    static BOOL SyncCall(IUnknown *iUnknown, struct Payload *payload)
    {
        DemoClientProxy *proxy = (DemoClientProxy *)iUnknown;
        IpcIo request;
        char data[MAX_DATA_LEN];
        IpcIoInit(&request, data, MAX_DATA_LEN, 0);
        IpcIoPushInt32(&request, payload->id);
        IpcIoPushInt32(&request, payload->value);
        IpcIoPushString(&request, payload->name);
        int ret = proxy->Invoke((IClientProxy *)proxy, ID_SYNCCALL, &request, data, Callback);
        data[MAX_DATA_LEN - 1] = 0;
        HILOG_INFO(HILOG_MODULE_APP, "[TID:0x%lx]Remote response is %s!", pthread_self(), data);
        return ret == EC_SUCCESS;
    }
    
    struct CurrentNotify {
        IOwner notify;
        INotifyFunc handler;
    };
    
    static int CurrentCallback(IOwner owner, int code, IpcIo *reply)
    {
        struct CurrentNotify *notify = (struct CurrentNotify *)owner;
        size_t len = 0;
        char *response = (char *)IpcIoPopString(reply, &len);
        HILOG_INFO(HILOG_MODULE_APP, "[TID:0x%lx]Notify Remote response is %s!", pthread_self(), response);
        notify->handler(notify->notify, response);
        return EC_SUCCESS;
    }
    
    static BOOL AsyncCallBack(IUnknown *iUnknown, const char *buff, IOwner notify, INotifyFunc handler)
    {
        struct CurrentNotify owner = {notify, handler};
        DemoClientProxy *proxy = (DemoClientProxy *)iUnknown;
        IpcIo request;
        char data[MAX_DATA_LEN];
        IpcIoInit(&request, data, MAX_DATA_LEN, 0);
        IpcIoPushString(&request, buff);
        int ret = proxy->Invoke((IClientProxy *)proxy, ID_ASYNCCALLBACK, &request, &owner, CurrentCallback);
        return ret == EC_SUCCESS;
    }
    ```

-   Implement the factory method for creating the client proxy.

```
    void *DEMO_CreatClient(const char *service, const char *feature, uint32 size)
    {
        (void)service;
        (void)feature;
        uint32 len = size + sizeof(DemoClientEntry);
        uint8 *client = malloc(len);
        (void)memset_s(client, len, 0, len);
        DemoClientEntry *entry = (DemoClientEntry *)&client[size];
        entry->ver = ((uint16)CLIENT_PROXY_VER | (uint16)DEFAULT_VERSION);
        entry->ref = 1;
        entry->iUnknown.QueryInterface = IUNKNOWN_QueryInterface;
        entry->iUnknown.AddRef = IUNKNOWN_AddRef;
        entry->iUnknown.Release = IUNKNOWN_Release;
        entry->iUnknown.Invoke = NULL;
        entry->iUnknown.AsyncCall = AsyncCall;
        entry->iUnknown.AsyncTimeCall = AsyncTimeCall;
        entry->iUnknown.SyncCall = SyncCall;
        entry->iUnknown.AsyncCallBack = AsyncCallBack;
        return client;
    }
    void DEMO_DestroyClient(const char *service, const char *feature, void *iproxy)
    {
        free(iproxy);
    }
    ```

-   Register the factory method of the client proxy with Samgr.

```
    SAMGR_RegisterFactory(EXAMPLE_SERVICE, EXAMPLE_FEATURE, DEMO_CreatClient, DEMO_DestroyClient);
    ```

-   Obtain the external API of the service in another process.

```
    DemoClientProxy *demoApi = NULL;
    IUnknown *iUnknown = SAMGR_GetInstance()->GetFeatureApi(EXAMPLE_SERVICE, EXAMPLE_FEATURE);
    if (iUnknown == NULL) {
        return NULL;
    }
    int result = iUnknown->QueryInterface(iUnknown, DEFAULT_VERSION, (void **)&demoApi);
    if (result != 0 || demoApi == NULL) {
        return NULL;
    }
    ```

-   Invoke the client proxy API of the service in another process.

```
    if (demoApi->AsyncCallBack == NULL) {
        return NULL;
    }
    demoApi->AsyncCallBack((IUnknown *)demoApi,
                           "I wanna async call callback good result!", NULL, AsyncHandler);
    ```

-   Release the API.

```
    int32 ref = demoApi->Release((IUnknown *)demoApi);
    ```

## Repositories Involved<a name="section10365113863719"></a>

Distributed Scheduler subsystem

**samgr\_lite**

OH_IPC/distributedschedule_samgr_lite

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简介

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