# Development of Performance Tracing (Native)

## Overview

hiTraceMeter provides APIs for system performance tracing. You can call the APIs provided by the hiTraceMeter module in your own service logic to effectively track service processes and check the system performance.
> **NOTE**
>
> - This development guide is applicable only when you use Native APIs for application development. For details about APIs, see [API Reference](../reference/native-apis/_hitrace.md).
> - For details about how to use ArkTS APIs for application development, see [Development Guidelines](hitracemeter-guidelines.md) and [API Reference](../reference/apis/js-apis-hitracemeter.md).

## Available APIs

| API| Description|
| -------- | -------- |
| void OH_HiTrace_StartTrace(const char* name) | Starts a synchronous time slice trace.|
| void OH_HiTrace_FinishTrace() | Ends a synchronous time slice trace.|
| void OH_HiTrace_StartAsyncTrace(const char* name, int32_t taskId) | Starts an asynchronous time slice trace.|
| void OH_HiTrace_FinishAsyncTrace(const char* name, int32_t taskId) | Ends an asynchronous time slice trace.|
| void OH_HiTrace_CountTrace(const char* name, int64_t count) | Performs an integer trace.|

**Parameter Description**

| Name| Type| Mandatory| Description                                                        |
| ------ | ------ | ---- | ------------------------------------------------------------ |
| name   | string | Yes  | Name of the variable.|
| taskId | number | Yes  | ID used to indicate the association of APIs in a trace. If multiple traces with the same name need to be performed at the same time or a trace needs to be performed multiple times concurrently, different task IDs must be specified in **startTrace**.|
| count  | number | Yes  | Value of the variable. |

## Development Example

1. Add the link of **libhitrace_ndk.z.so** to **CMakeLists.txt**.

    ```
    target_link_libraries(entry PUBLIC libhitrace_ndk.z.so)
    ```

2. Reference the **hitrace** header file in the source file.

    ```c++
    #include "hitrace/trace.h"
    ```

3. Perform a performance trace. The following uses an asynchronous trace as an example. (The sample code is a part of the default **hello.cpp** file. You only need to put related APIs at the required positions according to the usage instruction.)
    
    ```c++
    #include "napi/native_api.h"
    #include "hitrace/trace.h"
    static napi_value Add(napi_env env, napi_callback_info info)
    {
        // Start of an asynchronous time slice trace
        OH_HiTrace_StartAsyncTrace("hitraceTest", 123);
        // End of the asynchronous time slice trace (The start and end points are for reference only. Change them as needed during practice.)
        OH_HiTrace_FinishAsyncTrace("hitraceTest", 123);
        size_t requireArgc = 2;
        size_t argc = 2;
        napi_value args[2] = {nullptr};

        napi_get_cb_info(env, info, &argc, args , nullptr, nullptr);

        napi_valuetype valuetype0;
        napi_typeof(env, args[0], &valuetype0);

        napi_valuetype valuetype1;
        napi_typeof(env, args[1], &valuetype1);

        double value0;
        napi_get_value_double(env, args[0], &value0);

        double value1;
        napi_get_value_double(env, args[1], &value1);

        napi_value sum;
        napi_create_double(env, value0 + value1, &sum);

        return sum;

    }
    ```

4. Push the compiled HAP to the device for installation. In the **cmd** window, run **hdc shell** to connect to the device, and run **hitrace --trace_begin app** to start trace.
    
    ```shell
    capturing trace...
    ```

5. Click the newly installed HAP several times on the device, and then run **hitrace --trace_dump | grep hitraceTest** in the **shell** window to view the trace result.
    
    ```shell
    <...>-2477    (-------) [001] ....   396.427165: tracing_mark_write: S|2477|H:hitraceTest 123
    <...>-2477    (-------) [001] ....   396.427196: tracing_mark_write: F|2477|H:hitraceTest 123
    ```