Transient Task (C/C++)

When to Use

An application is suspended after it runs in the background for a short period of time. If the application needs to execute a short-time task in the background, for example, saving the status, it can request a transient task to extend the running time in the background.

Available APIs

The following table lists the common APIs.

How to Develop

Encapsulating the Functions and Registering Modules in the napi_init.cpp File

1. Encapsulate the functions.

   #include "napi/native_api.h"
   #include "transient_task/transient_task_api.h"

   TransientTask_DelaySuspendInfo delaySuspendInfo;

   static void callback(void)
   {
      // The transient task is about to end. The service cancels the transient task here.
      OH_BackgroundTaskManager_CancelSuspendDelay(delaySuspendInfo.requestId);
   }

   // Request a transient task.
   static napi_value RequestSuspendDelay(napi_env env, napi_callback_info info)
   {
         napi_value result;
         int32_t res = OH_BackgroundTaskManager_RequestSuspendDelay("test", callback, &delaySuspendInfo);
         if (res == 0) {
            napi_create_int32(env, delaySuspendInfo.requestId, &result);
         } else {
            napi_create_int32(env, -1, &result);
         }
         return result;
   }

   // Obtain the remaining time.
   static napi_value GetRemainingDelayTime(napi_env env, napi_callback_info info)
   {
         napi_value result;
         int32_t delayTime = 0;
         int32_t res = OH_BackgroundTaskManager_GetRemainingDelayTime(delaySuspendInfo.requestId, &delayTime);
         if (res == 0) {
            napi_create_int32(env, delayTime, &result);
         } else {
            napi_create_int32(env, -1, &result);
         }
         return result;
   }

   // Cancel the transient task.
   static napi_value CancelSuspendDelay(napi_env env, napi_callback_info info)
   {
         napi_value result;
         int32_t res = OH_BackgroundTaskManager_CancelSuspendDelay(delaySuspendInfo.requestId);
         napi_create_int32(env, res, &result);
         return result;
   }

1. Register the functions.

   EXTERN_C_START
   static napi_value Init(napi_env env, napi_value exports)
   {
       napi_property_descriptor desc[] = {
           {"RequestSuspendDelay", nullptr, RequestSuspendDelay, nullptr, nullptr, nullptr, napi_default, nullptr},
           {"GetRemainingDelayTime", nullptr, GetRemainingDelayTime, nullptr, nullptr, nullptr, napi_default, nullptr},
           {"CancelSuspendDelay", nullptr, CancelSuspendDelay, nullptr, nullptr, nullptr, napi_default, nullptr},
       };
       napi_define_properties(env, exports, sizeof(desc) / sizeof(desc[0]), desc);
       return exports;
   }
   EXTERN_C_END

1. Register the module.

   static napi_module demoModule = {
       .nm_version = 1,
       .nm_flags = 0,
       .nm_filename = nullptr,
       .nm_register_func = Init,
       .nm_modname = "entry",
       .nm_priv = ((void*)0),
       .reserved = { 0 },
   };

   extern "C" __attribute__((constructor)) void RegisterEntryModule(void)
   {
       napi_module_register(&demoModule);
   }

Declaring the Functions in the index.d.ts File

   export const RequestSuspendDelay: () => number;
   export const GetRemainingDelayTime: () => number;
   export const CancelSuspendDelay: () => number;

Calling the Functions in the index.ets File

   import testTransientTask from 'libentry.so';

   @Entry
   @Component
   struct Index {
     @State message: string = '';

     build() {
       Row() {
         Column() {
           Text(this.message)
             .fontSize(50)
             .fontWeight(FontWeight.Bold)
           Button('Request transient task').onClick(event => {
             this.RequestSuspendDelay();
           })
           Button('Obtain remaining time').onClick(event =>{
             this.GetRemainingDelayTime();
           })
           Button('Cancel transient task').onClick(event =>{
             this.CancelSuspendDelay();
           })
         }
         .width('100%')
        }
       .height('100%')
     }

     RequestSuspendDelay() {
       let requestId = testTransientTask.RequestSuspendDelay();
       console.log("The return requestId is " + requestId);
     }

     GetRemainingDelayTime() {
       let time = testTransientTask.GetRemainingDelayTime();
       console.log("The time is " + time);
     }

     CancelSuspendDelay() {
       let ret = testTransientTask.CancelSuspendDelay();
       console.log("The ret is " + ret);
     }
   }

Configuring the Library Dependency

Configure the CMakeLists.txt file. Add the required shared library, that is, libtransient_task.so, to target_link_libraries in the CMakeLists.txt file automatically generated by the project.

   target_link_libraries(entry PUBLIC libace_napi.z.so libtransient_task.so)

How to Test

1. Connect to the device and run the program.

2. Touch the Request transient task button. The console prints a log. The following is an example:

   The return requestId is 1

1. Touch the Obtain remaining time button. The console prints a log. The following is an example:

   The return requestId is 18000

1. Touch the Cancel transient task button. The console prints a log. The following is an example:

   The ret is 0

NOTE

If the Request transient task button is touched for more than three consecutive times, an error is reported. For more constraints, see Transient Task (ArkTS).

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