# Development of Distributed Call Chain Tracing ## Introduction hiTraceChain is a lightweight implementation of the cloud-based distributed call chain tracing. It allows applications to trace cross-thread, cross-process, and cross-device service calls. The hiTraceChain module generates a unique **chainId** for a service process and passes it to various information (including application events, system time, and logs) specific to the service process. During debugging and fault locating, you can use the unique **chainId** to quickly correlate various information related to the service process. The hiTraceChain module provides APIs to implement call chain tracing throughout a service process. This can help you quickly obtain the run log for the call chain of a specified service process and locate faults in inter-device, inter-process, or inter-thread communications. ## Basic Concepts - **chainId** Distributed call chain tracing ID, which is a part of **HiTraceId** and is used to identify the service process being traced. ## Available APIs The APIs for distributed call chain tracing are provided by the **hiTraceChain** module. For details, see [API Reference](../reference/apis/js-apis-hitracechain.md). **APIs for distributed call chain tracing** | API | Return Value | Description | | ------------------------------------------------------------------------------------------------------------------- | -------------- | ------------ | | hiTraceChain.begin(name: string, flags: number = HiTraceFlag.DEFAULT) | HiTraceId | Starts call chain tracing. | | hiTraceChain.end(id: HiTraceId) | void | Stops call chain tracing. | ## How to Develop The following example illustrates how to simulate one-time [system event logging](../reference/apis/js-apis-hisysevent.md) to implement cross-thread distributed call chain tracing in a single HAP service. 1. Create an eTS application project. In the displayed **Project** window, choose **entry** > **src** > **main** > **ets** > **pages** > **index.ets**, and double-click **index.ets**. Then, add a button to trigger system event logging. ```ts import hiTraceChain from '@ohos.hiTraceChain'; import hiSysEvent from '@ohos.hiSysEvent'; @Entry @Component struct Index { @State message: string = 'Start writing system event'; build() { Row() { Column() { Button(this.message) .fontSize(20) .margin(5) .width(350) .height(60) .fontWeight(FontWeight.Bold) .onClick(() => { try { // Enable distributed call chain tracing before the service starts. let traceId = hiTraceChain.begin("Write a new system event", hiTraceChain.HiTraceFlag.INCLUDE_ASYNC); // Implement one-time system event logging when the service starts. hiSysEvent.write({ domain: "RELIABILITY", name: "STACK", eventType: hiSysEvent.EventType.FAULT, params: { PID: 1, UID: 1, PACKAGE_NAME: "com.demo.hitracechain", PROCESS_NAME: "hitracechaindemo", MSG: "no msg." } }).then((val) => { console.info(`write result is ${val}`); // Disable distributed call chain tracing when the service ends. hiTraceChain.end(traceId); }).catch((err) => { console.error(`error message is ${err.message}`); }); } catch (err) { console.error(`error message is ${err.message}`); } }) } .width('100%') } .height('100%') } } ``` 2. Touch the run button on the IDE to run the project. Then, touch the **Start writing system event** button on the application UI to trigger system event logging. 3. View the information printed in the **Log** window. You can use **.*: \[([0-9a-zA-Z]{15}),.*].*** to access distributed call chain tracing information specific to the HAP service. The process ID of the HAP service is **8801**. Two threads, whose IDs are **8801** and **8819**, are involved in the system event logging. Based on the chain ID **edcfa53017a88e3**, you can then effectively trace the log information of the two threads. ```text 07-05 19:50:47.690 8801-8801/com.demo.hitracechain I C02d03/HiTraceC: [edcfa53017a88e3, 0, 0] HiTraceBegin name:Write a new system event flags:0x01. 07-05 19:50:47.690 8801-8801/com.demo.hitracechain D C02d03/HITRACE_UTIL_NAPI: [edcfa53017a88e3, 0, 0] Native2Js: chainId is edcfa53017a88e3. 07-05 19:50:47.690 8801-8801/com.demo.hitracechain D C02d03/HITRACE_UTIL_NAPI: [edcfa53017a88e3, 0, 0] Native2Js: spanId is 0. 07-05 19:50:47.690 8801-8801/com.demo.hitracechain D C02d03/HITRACE_UTIL_NAPI: [edcfa53017a88e3, 0, 0] Native2Js: parentSpanId is 0. 07-05 19:50:47.690 8801-8801/com.demo.hitracechain D C02d03/HITRACE_UTIL_NAPI: [edcfa53017a88e3, 0, 0] Native2Js: flags is 1. 07-05 19:50:47.690 8801-8801/com.demo.hitracechain D C02d08/NAPI_HISYSEVENT_UTIL: [edcfa53017a88e3, 0, 0] domain is RELIABILITY. 07-05 19:50:47.690 8801-8801/com.demo.hitracechain D C02d08/NAPI_HISYSEVENT_UTIL: [edcfa53017a88e3, 0, 0] name is STACK. 07-05 19:50:47.690 8801-8801/com.demo.hitracechain D C02d08/NAPI_HISYSEVENT_UTIL: [edcfa53017a88e3, 0, 0] eventType is 1. 07-05 19:50:47.690 8801-8801/com.demo.hitracechain E C02d08/NAPI_HISYSEVENT_UTIL: [edcfa53017a88e3, 0, 0] napi value type not match: valueType=3, typeName=6. 07-05 19:50:47.690 8801-8801/com.demo.hitracechain E C02d08/NAPI_HISYSEVENT_UTIL: [edcfa53017a88e3, 0, 0] napi value type not match: valueType=3, typeName=6. 07-05 19:50:47.690 8801-8801/com.demo.hitracechain E C02d08/NAPI_HISYSEVENT_UTIL: [edcfa53017a88e3, 0, 0] napi value type not match: valueType=4, typeName=6. 07-05 19:50:47.690 8801-8801/com.demo.hitracechain E C02d08/NAPI_HISYSEVENT_UTIL: [edcfa53017a88e3, 0, 0] napi value type not match: valueType=4, typeName=6. 07-05 19:50:47.690 8801-8801/com.demo.hitracechain E C02d08/NAPI_HISYSEVENT_UTIL: [edcfa53017a88e3, 0, 0] napi value type not match: valueType=4, typeName=6. 07-05 19:50:47.690 8801-8801/com.demo.hitracechain D C02d08/NAPI_HISYSEVENT_UTIL: [edcfa53017a88e3, 0, 0] create napi value of string type, value is JSHiSysEventWrite. 07-05 19:50:47.690 8801-8801/com.demo.hitracechain I C03900/Ace: [edcfa53017a88e3, 0, 0] [flutter_ace_view.cpp(operator())-(0)] Mark 0 id Touch Event Processed 07-05 19:50:47.690 8801-8801/com.demo.hitracechain D C02800/ClientMsgHandler: [edcfa53017a88e3, 0, 0] in OnDispatchEventProcessed, enter 07-05 19:50:47.690 8801-8801/com.demo.hitracechain D C02800/ANRHandler: [edcfa53017a88e3, 0, 0] in SetLastProcessedEventId, enter 07-05 19:50:47.690 8801-8819/com.demo.hitracechain D C02d08/HISYSEVENT: [edcfa53017a88e3, 0, 0] size=312, sysevent={"domain_":"RELIABILITY","name_":"STACK","type_":1,"time_":47591447690,"tz_":"+0000","pid_":8801,"tid_":8819,"uid_":20010045,"traceid_":"edcfa53017a88e3","spanid_":"0","pspanid_":"0","trace_flag_":1,"UID":1,"PID":1,"MSG":"no msg.","PROCESS_NAME":"hitracechaindemo","PACKAGE_NAME":"com.demo.hitracechain"} 07-05 19:50:47.690 8801-8801/com.demo.hitracechain D C02800/ANRHandler: [edcfa53017a88e3, 0, 0] in SetLastProcessedEventId, Processed event type:0, id:831, actionTime:6694499314, currentTime:6694501330, timeoutTime:4997984 07-05 19:50:47.691 8801-8801/com.demo.hitracechain D C02800/ANRHandler: [edcfa53017a88e3, 0, 0] in SetLastProcessedEventId, leave 07-05 19:50:47.691 8801-8801/com.demo.hitracechain D C02800/ClientMsgHandler: [edcfa53017a88e3, 0, 0] in OnDispatchEventProcessed, leave 07-05 19:50:47.691 8801-8819/com.demo.hitracechain D C02d08/HISYSEVENT: [edcfa53017a88e3, 0, 0] reset send buffer size old=245760, new=524288 07-05 19:50:47.691 8801-8819/com.demo.hitracechain D C02d08/HISYSEVENT: [edcfa53017a88e3, 0, 0] HiSysEvent send data successful 07-05 19:50:47.691 8801-8801/com.demo.hitracechain D C02d08/NAPI_HISYSEVENT_UTIL: [edcfa53017a88e3, 0, 0] create napi value of int32 type, value is 0. 07-05 19:50:47.691 8801-8801/com.demo.hitracechain E A0fefe/JsApp: [edcfa53017a88e3, 399db38, 0] write result is 0 07-05 19:50:47.691 8801-8801/com.demo.hitracechain D C02d03/HITRACE_UTIL_NAPI: [edcfa53017a88e3, 399db38, 0] Js2Native: chainId is edcfa53017a88e3. 07-05 19:50:47.691 8801-8801/com.demo.hitracechain D C02d03/HITRACE_UTIL_NAPI: [edcfa53017a88e3, 399db38, 0] Js2Native: spanId is 0. 07-05 19:50:47.691 8801-8801/com.demo.hitracechain D C02d03/HITRACE_UTIL_NAPI: [edcfa53017a88e3, 399db38, 0] Js2Native: parentSpanId is 0. 07-05 19:50:47.691 8801-8801/com.demo.hitracechain D C02d03/HITRACE_UTIL_NAPI: [edcfa53017a88e3, 399db38, 0] Js2Native: flags is 1. 07-05 19:50:47.691 8801-8801/com.demo.hitracechain I C02d03/HiTraceC: [edcfa53017a88e3, 399db38, 0] HiTraceEnd. ``` ## About Cross-Process/Cross-Device Distributed Call Chain Tracing Cross-process/cross-device distributed call chain tracing depends on the NAPI implementation of the corresponding service APIs of each OpenHarmony module. For details, see the [HiTraceChain Development](../../device-dev/subsystems/subsys-dfx-hitracechain.md).