Question

我正在使用jsmodbus（https://github.com/Cloud-Automation/node-modbus）模块在modbus项目中工作，这样我就可以使用readHoldingRegister函数了：

var modbus = require('jsmodbus');

function read(station, callback){
var client = modbus.client.tcp.complete({ 
            'host'              : station.ipAdress, 
            'port'              : station.port, //502
            'autoReconnect'     : true,
            'reconnectTimeout'  : 1000,
            'timeout'           : 5000,
            'unitId'            : 0
        });

client.connect();
    client.on('connect', function () {
        client.readHoldingRegisters(startReg, endReg).then(function (resp) {
            return callback(resp); 
        }).fail(console.log);
    });
    client.on('error', function (err) {
        retrun callback(null);
    });
}

我需要为我拥有多少IP而执行此操作并推送每个IP＆＃34; resp＆＃34;得到一个数组＆＃34; allResults＆＃34;然后返回它，但是当我把上面的代码放在for循环中时，我没有得到结果async.each。

readAll(ip_adresses, (allResults) => {
     doSomethingWith(allResults);
});

这样做的正确方法是什么？

Answer 1

尝试以下

var async = require('async');
...
function read(station, callback) {
    ...
}

async.map(ips, read, function(err, results) {
    if (err)
        return console.log(err);
    ...
    // Process results
})

Answer 2

在承诺中阅读

function read(station) {
  return new Promise((resolve, reject) => {
     ...
     client.readHoldingRegisters(startReg, endReg).then(function (resp) {
        // here is the point
        // in every promise, after resolve, the result will transform to `then` function
        // and you will get the result via `read(station).then(result)`
        return resolve(resp); 
     }).fail(console.log)
  });
}

function readAll(stations) {
  // the stations contain multiple ip, such as [ip1, ip2, ip3...]
  // the map function transform every ip to a promise
  // use Promise.all to run every promise
  // and then, get the results
  var readTasks = stations.map(read);
  Promise.all(readTask)
    .then(allResults => {
      doSomethingWith(allResults);
    });
}

NodeJS Modbus Master从多个IP地址读取

2 个答案: