# Subscribing to Resource Leak Events (ArkTS)

## Available APIs

For details about how to use the APIs (such as parameter usage constraints and value ranges), see [Application Event Logging](../reference/apis-performance-analysis-kit/js-apis-hiviewdfx-hiappevent.md).

| API                                             | Description                                        |
| --------------------------------------------------- | -------------------------------------------- |
| addWatcher(watcher: Watcher): AppEventPackageHolder | Adds a watcher to listen for application events.|
| removeWatcher(watcher: Watcher): void               | Removes a watcher to unsubscribe from application events.|

## How to Develop

The following describes how to subscribe to a memory leak event.

1. Create an ArkTS application project. In the **entry/src/main/ets/entryability/EntryAbility.ets** file, import the dependent modules.

   ```ts
   import { hiAppEvent, hilog, hidebug } from '@kit.PerformanceAnalysisKit';
   ```

2. In the **entry/src/main/ets/entryability/EntryAbility.ets** file, add a watcher in **onCreate()** to subscribe to system events. The sample code is as follows:

   ```ts
    hiAppEvent.addWatcher({
      // Set the watcher name. The system identifies different watchers based on their names.
      name: "watcher",
      // Add the system events to watch, for example, the resource leak event.
      appEventFilters: [
        {
          domain: hiAppEvent.domain.OS,
          names: [hiAppEvent.event.RESOURCE_OVERLIMIT]
        }
      ],
      // Implement a callback for the registered system event so that you can apply custom processing to the event data obtained.
      onReceive: (domain: string, appEventGroups: Array<hiAppEvent.AppEventGroup>) => {
        hilog.info(0x0000, 'testTag', `HiAppEvent onReceive: domain=${domain}`);
        for (const eventGroup of appEventGroups) {
          // The event name uniquely identifies a system event.
          hilog.info(0x0000, 'testTag', `HiAppEvent eventName=${eventGroup.name}`);
          for (const eventInfo of eventGroup.appEventInfos) {
            // You can obtain the memory information when the resource leak event occurs.
            hilog.info(0x0000, 'testTag', `HiAppEvent eventInfo.params.memory=${JSON.stringify(eventInfo)}`);
          }
        }
      }
    });
   ```

3. In the **entry/src/main/ets/pages/index.ets** file, add the **memoryleak** button and construct a scenario for triggering a resource leak event in **onClick()**.
   In this case, use [hidebug.setAppResourceLimit](../reference/apis-performance-analysis-kit/js-apis-hidebug.md#hidebugsetappresourcelimit12) to set the memory limit to trigger a memory leak event, and enable **System resource leak log** in **Developer options**. The sample code is as follows:

   ```ts
    import hidebug from "@ohos.hidebug";

    @Entry
    @Component
    struct Index {
    @State leakedArray: string[][] = [];

    build() {
      Column() {
        Row() {
          Column() {
            Button("pss leak")
              .onClick(() => {
                hidebug.setAppResourceLimit("pss_memory", 1024, true);
                for (let i = 0; i < 20 * 1024; i++) {
                  this.leakedArray.push(new Array(1).fill("leak"));
                }
              })
          }
        }
        .height('100%')
        .width('100%')
      }
    }
   ```

4. Click the **Run** button in DevEco Studio to run the project, and then a memory leak event will be reported after 15 to 30 minutes.
   For the same application, the memory leak event can be reported at most once within 24 hours. If the memory leak needs to be reported again within a shorter time, restart the device.

5. After a memory leak event is reported, the system calls **onReceive()**. You can view the following event information in the **Log** window.

   ```text
   HiAppEvent onReceive: domain=OS
   HiAppEvent eventName=RESOURCE_OVERLIMIT
   HiAppEvent eventInfo={"domain":"OS","name":"RESOURCE_OVERLIMIT","eventType":1,"params":{"bundle_name":"com.example.myapplication","bundle_version":"1.0.0","memory":{"pss":2100257,"rss":1352644,"sys_avail_mem":250272,"sys_free_mem":60004,"sys_total_mem":1992340,"vss":2462936},"pid":20731,"resource_type":"pss_memory","time":1502348798106,"uid":20010044,"external_log": ["/data/storage/el2/log/resourcelimit/RESOURCE_OVERLIMIT_1725614572401_6808.log", "/data/storage/el2/log/resourcelimit/RESOURCE_OVERLIMIT_1725614572412_6808.log"], "log_over_limit": false}}
   ```