Question

我真的被困在这里了。根据定义，承诺只返回一次。但是，我需要找到一种方法来获得使用cron模块的promise。以下是我尝试做的缩短版本。一切都在第一次执行得很好但在此之后承诺永远不会解决。

不幸的是，我很难使用承诺来自的节点池模块。与HANA数据库建立连接池需要此模块。

谢谢！

var pool = require('generic-pool');
var servers = require('../config/servers');
var CronJob = require('cron').CronJob;
var hdb = require('hdb'); // database driver
var factories = {};
var pools = {};

for (let i = 0; i < servers.length; i++) {

    factories[servers[i].name] = {

        create: function(){
             return new Promise(function(resolve, reject){
                var client = hdb.createClient({
                    host: servers[i].host,
                    port: servers[i].port,
                    user: servers[i].user,
                    password: servers[i].password
                });

                resolve(client);

            });
        },
        destroy: function(client){
            if (!client.hadError && client.readyState !== 'closed') {
                client.end();
            }
        }

    };

    pools[servers[i].name] = pool.createPool(factories[servers[i].name]);

}


var job = new CronJob({

    cronTime: '0 * * * *',
    onTick: () => {

        async.waterfall([

            (callbackWF) => {

                var resourcePromise = pools[name].acquire();

                console.log(moment().format('YYYY-MM-DD HH:mm:ss.SS - ') + 'Attempting to resolve promise for Name: ' + name + ' Table: ' + table);

                resourcePromise.then( (client) => {

                    console.log(moment().format('YYYY-MM-DD HH:mm:ss.SS - ') + 'Got promise for Name: ' + name + ' Table: ' + table);

                    if (client.readyState != 'connected') {

                        client.connect( (err) => {

                            if (err) {

                                console.log(moment().format('YYYY-MM-DD HH:mm:ss.SS - ') + 'Error while connecting to client. Name: ' + name + ' Host: ' + host + ' Port: ' + port + ' User: ' + user + ' Error: ' + JSON.stringify(err));

                                return callbackWF('error', client);

                            } 

                            callbackWF(null, client);

                        });

                    } else {

                        callbackWF(null, client);

                    }

                }).catch( (err) => {

                    if (err) {

                        console.log(moment().format('YYYY-MM-DD HH:mm:ss.SS - ') + 'Error getting promise for connection pool. Name: ' + name + ' Host: ' + host + ' Port: ' + port + ' User: ' + user + ' Error: ' + JSON.stringify(err));
                        callbackWF('error');

                    }

                    console.log(moment().format('YYYY-MM-DD HH:mm:ss.SS - ') + 'Caught promise');

                });


            },

            // Get data for table.
            (client, callbackWF) => {

                client.exec(select, {rowsAsArray: true}, (err, rows) => {

                    if (err) {

                        console.log(moment().format('YYYY-MM-DD HH:mm:ss.SS - ') + 'Error while getting data from ' + name +  " table: " + table + ". " + err + select);
                        return callbackWF(err, client);

                    }

                    callbackWF(null, client);

                });

            }

        ], (err, client) => {

            if (typeof client != 'undefined') {

                console.log(moment().format('YYYY-MM-DD HH:mm:ss.SS - ') + 'Releasing pool for Name: ' + name + ' Table: ' + table);

                pools[name].release(client);

            }

        });

    },
    start: true,
    timeZone: 'UTC'
});

Answer 1

我没有看到任何错误。承诺可能只返回一次，但您可以根据需要多次调用then()。

在cron里面的承诺只执行一次

1 个答案: