# Subscribing to Freeze Events (C/C++) ## Available APIs For details about how to use the APIs (such as parameter usage restrictions and value ranges), see [HiAppEvent](../reference/apis-performance-analysis-kit/_hi_app_event.md#hiappevent). **Subscription APIs** | API | Description | | ------------------------------------------------------------ | -------------------------------------------- | | int OH_HiAppEvent_AddWatcher (HiAppEvent_Watcher \*watcher) | Adds a watcher to listen for application events.| | int OH_HiAppEvent_RemoveWatcher (HiAppEvent_Watcher *watcher) | Removes a watcher to unsubscribe from application events.| ## How to Develop The following describes how to subscribe to the freeze event triggered by a button click. 1. Create a native C++ project and import the **jsoncpp** file to the project. The directory structure is as follows: ```yml entry: src: main: cpp: - json: - json.h - json-forwards.h - types: libentry: - index.d.ts - CMakeLists.txt - napi_init.cpp - jsoncpp.cpp ets: - entryability: - EntryAbility.ets - pages: - Index.ets ``` 2. In the **CMakeLists.txt** file, add the source file and dynamic libraries. ```cmake # Add the jsoncpp.cpp file, which is used to parse the JSON strings in the subscription events. add_library(entry SHARED napi_init.cpp jsoncpp.cpp) # Add libhiappevent_ndk.z.so and libhilog_ndk.z.so (log output). target_link_libraries(entry PUBLIC libace_napi.z.so libhilog_ndk.z.so libhiappevent_ndk.z.so) ``` 3. Import the dependency files to the **napi_init.cpp** file, and define **LOG_TAG**. ```c++ #include "napi/native_api.h" #include "json/json.h" #include "hilog/log.h" #include "hiappevent/hiappevent.h" #undef LOG_TAG #define LOG_TAG "testTag" ``` 4. Subscribe to system events. - Watcher of the onReceive type: In the **napi_init.cpp** file, define the methods related to the watcher of the onReceive type. ```c++ // Define a variable to cache the pointer to the created watcher. static HiAppEvent_Watcher *systemEventWatcher; static void OnReceive(const char *domain, const struct HiAppEvent_AppEventGroup *appEventGroups, uint32_t groupLen) { for (int i = 0; i < groupLen; ++i) { for (int j = 0; j < appEventGroups[i].infoLen; ++j) { OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.domain=%{public}s", appEventGroups[i].appEventInfos[j].domain); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.name=%{public}s", appEventGroups[i].appEventInfos[j].name); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.eventType=%{public}d", appEventGroups[i].appEventInfos[j].type); if (strcmp(appEventGroups[i].appEventInfos[j].domain, DOMAIN_OS) == 0 && strcmp(appEventGroups[i].appEventInfos[j].name, EVENT_APP_FREEZE) == 0) { Json::Value params; Json::Reader reader(Json::Features::strictMode()); Json::FastWriter writer; if (reader.parse(appEventGroups[i].appEventInfos[j].params, params)) { auto time = params["time"].asInt64(); auto foreground = params["foreground"].asBool(); auto bundleVersion = params["bundle_version"].asString(); auto bundleName = params["bundle_name"].asString(); auto processName = params["process_name"].asString(); auto pid = params["pid"].asInt(); auto uid = params["uid"].asInt(); auto uuid = params["uuid"].asString(); auto exception = writer.write(params["exception"]); auto hilogSize = params["hilog"].size(); auto handleSize = params["event_handler"].size(); auto handleSize3s = params["event_handler_size_3s"].asString(); auto handleSize6s = params["event_handler_size_6s"].asString(); auto peerBindSize = params["peer_binder"].size(); auto threadSize = params["threads"].size(); auto memory = writer.write(params["memory"]); auto externalLog = writer.write(params["external_log"]); auto logOverLimit = params["log_over_limit"].asBool(); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.time=%{public}lld", time); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.foreground=%{public}d", foreground); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.bundle_version=%{public}s", bundleVersion.c_str()); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.bundle_name=%{public}s", bundleName.c_str()); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.process_name=%{public}s", processName.c_str()); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.pid=%{public}d", pid); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.uid=%{public}d", uid); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.uuid=%{public}s", uuid.c_str()); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.exception=%{public}s", exception.c_str()); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.hilog.size=%{public}d", hilogSize); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.event_handler.size=%{public}d", handleSize); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.event_handler_3s.size=%{public}s", handleSize3s.c_str()); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.event_handler_6s.size=%{public}s", handleSize6s.c_str()); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.peer_binder.size=%{public}d", peerBindSize); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.threads.size=%{public}d", threadSize); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.memory=%{public}s", memory.c_str()); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.external_log=%{public}s", externalLog.c_str()); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.log_over_limit=%{public}d", logOverLimit); } } } } } static napi_value RegisterWatcher(napi_env env, napi_callback_info info) { // Set the watcher name. The system identifies different watchers based on their names. systemEventWatcher = OH_HiAppEvent_CreateWatcher("onReceiverWatcher"); // Set the event to watch to EVENT_APP_FREEZE. const char *names[] = {EVENT_APP_FREEZE}; // Add the events to watch, for example, system events. OH_HiAppEvent_SetAppEventFilter(systemEventWatcher, DOMAIN_OS, 0, names, 1); // Set the implemented callback. After receiving the event, the watcher immediately triggers the OnReceive callback. OH_HiAppEvent_SetWatcherOnReceive(systemEventWatcher, OnReceive); // Add a watcher to listen for the specified event. OH_HiAppEvent_AddWatcher(systemEventWatcher); return {}; } ``` - Watcher of the onTrigger type: In the **napi_init.cpp** file, define the methods related to the watcher of the OnTrigger type. ```c++ // Define a variable to cache the pointer to the created watcher. static HiAppEvent_Watcher *systemEventWatcher; // Implement the callback function used to return the listened events. The content pointed to by the events pointer is valid only in this function. static void OnTake(const char *const *events, uint32_t eventLen) { Json::Reader reader(Json::Features::strictMode()); Json::FastWriter writer; for (int i = 0; i < eventLen; ++i) { Json::Value eventInfo; if (reader.parse(events[i], eventInfo)) { auto domain = eventInfo["domain_"].asString(); auto name = eventInfo["name_"].asString(); auto type = eventInfo["type_"].asInt(); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.domain=%{public}s", domain.c_str()); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.name=%{public}s", name.c_str()); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.eventType=%{public}d", type); if (domain == DOMAIN_OS && name == EVENT_APP_FREEZE) { auto time = eventInfo["time"].asInt64(); auto foreground = eventInfo["foreground"].asBool(); auto bundleVersion = eventInfo["bundle_version"].asString(); auto bundleName = eventInfo["bundle_name"].asString(); auto processName = eventInfo["process_name"].asString(); auto pid = eventInfo["pid"].asInt(); auto uid = eventInfo["uid"].asInt(); auto uuid = eventInfo["uuid"].asString(); auto exception = writer.write(eventInfo["exception"]); auto hilogSize = eventInfo["hilog"].size(); auto handleSize = eventInfo["event_handler"].size(); auto handleSize3s = eventInfo["event_handler_size_3s"].asString(); auto handleSize6s = eventInfo["event_handler_size_6s"].asString(); auto peerBindSize = eventInfo["peer_binder"].size(); auto threadSize = eventInfo["threads"].size(); auto memory = writer.write(eventInfo["memory"]); auto externalLog = writer.write(eventInfo["external_log"]); auto logOverLimit = eventInfo["log_over_limit"].asBool(); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.time=%{public}lld", time); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.foreground=%{public}d", foreground); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.bundle_version=%{public}s", bundleVersion.c_str()); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.bundle_name=%{public}s", bundleName.c_str()); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.process_name=%{public}s", processName.c_str()); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.pid=%{public}d", pid); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.uid=%{public}d", uid); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.uuid=%{public}s", uuid.c_str()); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.exception=%{public}s", exception.c_str()); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.hilog.size=%{public}d", hilogSize); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.event_handler.size=%{public}d", handleSize); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.event_handler_3s.size=%{public}s", handleSize3s.c_str()); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.event_handler_6s.size=%{public}s", handleSize6s.c_str()); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.peer_binder.size=%{public}d", peerBindSize); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.threads.size=%{public}d", threadSize); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.memory=%{public}s", memory.c_str()); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.external_log=%{public}s", externalLog.c_str()); OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.log_over_limit=%{public}d", logOverLimit); } } } } // Implement the subscription callback function to apply custom processing to the obtained event logging data. static void OnTrigger(int row, int size) { // After the callback is received, obtain the specified number of received events. OH_HiAppEvent_TakeWatcherData(systemEventWatcher, row, OnTake); } static napi_value RegisterWatcher(napi_env env, napi_callback_info info) { // Set the watcher name. The system identifies different watchers based on their names. systemEventWatcher = OH_HiAppEvent_CreateWatcher("onTriggerWatcher"); // Set the event to watch to EVENT_APP_FREEZE. const char *names[] = {EVENT_APP_FREEZE}; // Add the events to watch, for example, system events. OH_HiAppEvent_SetAppEventFilter(systemEventWatcher, DOMAIN_OS, 0, names, 1); // Set the implemented callback function. The callback function will be triggered when the conditions set by OH_HiAppEvent_SetTriggerCondition are met. OH_HiAppEvent_SetWatcherOnTrigger(systemEventWatcher, OnTrigger); // Set the conditions for triggering the subscription callback. For example, trigger this onTrigger callback when the number of new event logs is 1. OH_HiAppEvent_SetTriggerCondition(systemEventWatcher, 1, 0, 0); // Add a watcher to listen for the specified event. OH_HiAppEvent_AddWatcher(systemEventWatcher); return {}; } ``` 5. Register **RegisterWatcher** as an ArkTS API. In the **napi_init.cpp** file, register **RegisterWatcher** as an ArkTS API. ```c++ static napi_value Init(napi_env env, napi_value exports) { napi_property_descriptor desc[] = { { "registerWatcher", nullptr, RegisterWatcher, nullptr, nullptr, nullptr, napi_default, nullptr } }; napi_define_properties(env, exports, sizeof(desc) / sizeof(desc[0]), desc); return exports; } ``` In the **index.d.ts** file, define the ArkTS API. ```typescript export const registerWatcher: () => void; ``` 6. In the **EntryAbility.ets** file, add the following interface invocation to **onCreate()**. ```typescript // Import the dependent module. import testNapi from 'libentry.so' // Add the interface invocation to onCreate(). // Register the system event watcher at startup. testNapi.registerWatcher(); ``` 7. In the **Index.ets** file, add a button to trigger the freeze event. ```typescript Button("appFreeze").onClick(() => { setTimeout(()=>{ while(true) {} }, 1000) }) ``` 8. In DevEco Studio, click the **Run** button to run the project. Then, click the **appfreeze** button to trigger a freeze event. 9. The application crashes. After restarting the application, you can view the following event information in the **Log** window. ```text HiAppEvent eventInfo.domain=OS HiAppEvent eventInfo.name=APP_FREEZE HiAppEvent eventInfo.eventType=1 HiAppEvent eventInfo.params.time=1502049167732 HiAppEvent eventInfo.params.foreground=1 HiAppEvent eventInfo.params.bundle_version=1.0.0 HiAppEvent eventInfo.params.bundle_name=com.example.myapplication HiAppEvent eventInfo.params.process_name=com.example.myapplication HiAppEvent eventInfo.params.pid=1587 HiAppEvent eventInfo.params.uid=20010043 HiAppEvent eventInfo.params.uuid=a78a23b20f3dd9730f18a5cfa2304deac1104ac4086755c4a59cf7c72d414e2e HiAppEvent eventInfo.params.exception={"message":"App main thread is not response!","name":"THREAD_BLOCK_6S"} HiAppEvent eventInfo.params.hilog.size=6 HiAppEvent eventInfo.params.event_handler.size=16 HiAppEvent eventInfo.params.event_handler_3s.size=15 HiAppEvent eventInfo.params.event_handler_6s.size=16 HiAppEvent eventInfo.params.peer_binder.size=0 HiAppEvent eventInfo.params.threads.size=28 HiAppEvent eventInfo.params.memory={"pss":0,"rss":0,"sys_avail_mem":1326520,"sys_free_mem":940588,"sys_total_mem":1992340,"vss":0} HiAppEvent eventInfo.params.external_log=["/data/storage/el2/log/hiappevent/APP_FREEZE_1502049185239_1587.log"] HiAppEvent eventInfo.params.log_over_limit=0 ``` 10. Remove the event watcher. ```c++ static napi_value RemoveWatcher(napi_env env, napi_callback_info info) { // Remove the watcher. OH_HiAppEvent_RemoveWatcher(systemEventWatcher); return {}; } ``` 11. Destroy the event watcher. ```c++ static napi_value DestroyWatcher(napi_env env, napi_callback_info info) { // Destroy the created watcher and set systemEventWatcher to nullptr. OH_HiAppEvent_DestroyWatcher(systemEventWatcher); systemEventWatcher = nullptr; return {}; } ```