Question

我正在尝试为与串行端口接口的Promise添加一个timout。将超时应用于承诺的脚手架基于Italo Nascimento's blog article（请参见代码段中的promiseTimeout函数）。

由于node-serialport不提供Promise接口，因此我在stream interface周围写了一个小的包装程序（请参见函数dummyDetectPort），该包装程序可以正常工作。但是，当将此承诺传递给promiseTimeout以便使承诺访问串行端口超时时，该承诺既不会得到解决也不会被拒绝。因此，无论给定的超时时间为ms，“限制”承诺都是超时承诺。

我在哪里不明白这一点？为什么在与timeout承诺竞争时，序列承诺会按预期工作，但没有得到解决或拒绝？

'use strict';
const SerialPort = require('serialport');
const Readline = require('@serialport/parser-readline');


// https://italonascimento.github.io/applying-a-timeout-to-your-promises/
const promiseTimeout = (ms, promise) => {
  // Create a promise that rejects in <ms> milliseconds
  let timeout = new Promise((resolve, reject) => {
    let id = setTimeout(() => {
      clearTimeout(id);
      reject(`Timed out in ${ms} ms.`);
    }, ms)
  })
  // Returns a race between our timeout and the passed in promise
  return Promise.race([
    timeout,
    promise,
  ])

}


const dummyDetectPort = (portName) => {
  console.log(`Promise created (${portName}).`);

  return new Promise( (reject, resolve) => {
    const port = new SerialPort(portName);
    const parser = port.pipe(new Readline());

    port.write(`${portName}\n`);
    parser.on('data', (data) => {
      console.log(`Received data on ${portName}: ${data}`);
      port.close( (err) => reject(err) );
      console.log(data == portName);
      if (data == portName)
      {
        const msg = `Promise resolved (${portName}).`;
        return resolve(msg);
      }
      else
      {
        const msg = `Promise rejected (${portName}).`;
        return reject(msg);
      }
    })

  })

}


const main = (portName) => {
    promiseTimeout(60000, dummyDetectPort(portName))
    // dummyDetectPort(portName)
      .then(result => console.log(result))
      .catch(err => console.log(err))
}


main('/dev/tty.usbserial-FTG7L3FX');

承诺超时既不会解决也不会拒绝包装的承诺

0 个答案: