I/O Intensive Task Development (TaskPool)

I/O intensive tasks are tasks that require frequent I/O operations such as disk read/write and network communication. While asynchronous concurrency can address the thread blocking issue for single I/O tasks, it falls short in the case of I/O intensive tasks. This is where multithread concurrency comes into play.

The performance focus of I/O intensive tasks is not the CPU processing capability, but the speed and efficiency of I/O operations, since such a task usually requires frequent operations such as disk read/write and network communication. The following uses frequent read/write operations on a system file to simulate concurrency processing of I/O intensive tasks.

1. Define a concurrency function that internally calls I/O capabilities intensively.

   // a.ts
   import fs from '@ohos.file.fs';
   
   // Define a concurrency function that internally calls I/O capabilities intensively.
   // Write data to the file.
   export async function write(data: string, filePath: string): Promise<void> {
     let file: fs.File = await fs.open(filePath, fs.OpenMode.READ_WRITE);
     await fs.write(file.fd, data);
     fs.close(file);
   }
   

   import { write } from './a'
   import { BusinessError } from '@ohos.base';
   
   @Concurrent
   async function concurrentTest(fileList: string[]): Promise<boolean> {
     // Write data to the file cyclically.
     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 false;
       })
     }
     return true;
   }
   

2. Use TaskPool to execute the concurrency function that contains the intensive I/O operations. Specifically, call execute() to execute the tasks and process the scheduling result in a callback. For details about how to obtain filePath1 and filePath2 in the example, see Obtaining Application File Paths.

   import taskpool from '@ohos.taskpool';
   
   let filePath1: string = "path1"; // Application file path.
   let filePath2: string = "path2";
   
   // Use TaskPool to execute the concurrency function that contains the intensive I/O operations.
   // In the case of a large array, the distribution of I/O intensive tasks also preempts the main thread. Therefore, multiple threads are required.
   taskpool.execute(concurrentTest, [filePath1, filePath2]).then(() => {
     // Process the scheduling result.
   })