# I/O密集型任务开发指导 (TaskPool)
<!--Kit: ArkTS-->
<!--Subsystem: CommonLibrary-->
<!--Owner: @lijiamin2025-->
<!--Designer: @weng-changcheng-->
<!--Tester: @kirl75; @zsw_zhushiwei-->
<!--Adviser: @ge-yafang-->


使用异步并发可以解决单次I/O任务阻塞的问题。对于I/O密集型任务，若线程中的其他任务仍可能被阻塞，建议采用多线程并发来处理。


I/O密集型任务的性能关键在于I/O操作的速度和效率，而非CPU的处理能力。这类任务需要频繁进行磁盘读写和网络通信。此处通过频繁读写系统文件来模拟I/O密集型并发任务的处理。


1. 定义并发函数，内部密集调用I/O能力。
    ```ts
    // write.ets
    import { fileIo } from '@kit.CoreFileKit';

    // 定义并发函数，内部频繁调用I/O能力
    // 写入文件的实现
    export async function write(data: string, filePath: string): Promise<void> {
      let file: fileIo.File = await fileIo.open(filePath, fileIo.OpenMode.READ_WRITE | fileIo.OpenMode.CREATE);
      await fileIo.write(file.fd, data);
      fileIo.close(file);
    }
    ```
    <!-- @[define_concurrent_function](https://gitcode.com/openharmony/applications_app_samples/blob/master/code/DocsSample/ArkTS/ArkTsConcurrent/ApplicationMultithreadingDevelopment/ApplicationMultithreading/entry/src/main/ets/managers/write.ets) -->

	```ts
    // Index.ets
    import { write } from './write';
    import { BusinessError } from '@kit.BasicServicesKit';
    import { taskpool } from '@kit.ArkTS';
    import { common } from '@kit.AbilityKit';

    @Concurrent
    async function concurrentTest(context: common.UIAbilityContext): Promise<void> {
      // 应用文件路径
      let filePath1: string = context.filesDir + "/path1.txt";
      let filePath2: string = context.filesDir + "/path2.txt";
      // 循环写文件操作
      let fileList: Array<string> = [];
      fileList.push(filePath1);
      fileList.push(filePath2);
      for (let i: number = 0; i < fileList.length; i++) {
        write('Hello World!', fileList[i]).then(() => {
          console.info(`Succeeded in writing the file. FileList: ${fileList[i]}`);
        }).catch((err: BusinessError) => {
          console.error(`Failed to write the file. Code is ${err.code}, message is ${err.message}`);
        })
      }
      return;
    }
	```
  <!-- @[define_concurrent_function](https://gitcode.com/openharmony/applications_app_samples/blob/master/code/DocsSample/ArkTS/ArkTsConcurrent/ApplicationMultithreadingDevelopment/ApplicationMultithreading/entry/src/main/ets/managers/IoIntensiveTaskDevelopment.ets) -->

2. 使用TaskPool执行包含密集I/O的并发函数，通过调用[execute()](../reference/apis-arkts/js-apis-taskpool.md#taskpoolexecute)方法执行任务，并在回调中处理调度结果。示例中获取filePath1和filePath2的方式请参见[获取应用文件路径](../application-models/application-context-stage.md#获取应用文件路径)。在TaskPool中使用context时，需先在并发函数外部准备好，并通过参数传递给并发函数。

    ```ts
    // Index.ets
    @Entry
    @Component
    struct Index {
      @State message: string = 'Hello World';
      build() {
        Row() {
          Column() {
            Text(this.message)
              .fontSize(50)
              .fontWeight(FontWeight.Bold)
              .onClick(() => {
                let context = this.getUIContext().getHostContext() as common.UIAbilityContext;
    
                // 使用TaskPool执行包含密集I/O的并发函数
                // 数组较大时，I/O密集型任务分发也会抢占UI主线程，需要使用多线程能力
                taskpool.execute(concurrentTest, context).then(() => {
                  // 调度结果处理
                  console.info("taskpool: execute success");
                })
              })
          }
          .width('100%')
        }
        .height('100%')
      }
    }
    ```
    <!-- @[taskpool_execute_concurrent_function](https://gitcode.com/openharmony/applications_app_samples/blob/master/code/DocsSample/ArkTS/ArkTsConcurrent/ApplicationMultithreadingDevelopment/ApplicationMultithreading/entry/src/main/ets/managers/IoIntensiveTaskDevelopment.ets) -->