连接完成后承诺不解决

Question

我有一个猫鼬连接功能，如果第一次尝试失败，我会尝试等待重新连接：

async connect() {
    const options = {...}
    try {
        console.log("starting")
        await this._connectWithRetry(options)
        console.log("finished")
    } catch (err) {
        winston.error(`Could not connect to Mongo with error: ${err}`)
    }
}

private async _connectWithRetry(options) {
    return new Promise( async (resolve, reject) => {
        try {
            winston.info("Connecting to mongo...")
            await mongoose.connect(this.dbURI, options)
            winston.info("Connection successful.")
            resolve()
        } catch (err) {
            winston.info("Failed to connect to mongo. Retrying in 5 seconds...")
            setTimeout( async () => {
                await this._connectWithRetry(options)
            }, 5000)
        }
    })
}

它成功地等待我连接。但是一旦我连接，第二条控制台线就不会被击中（“完成”）。所以我认为我的承诺解决方案是错误的。我做错了什么？

Answer 1

如果第一次建立与数据库的连接，您的代码“有效”。

如果使用重试机制，你会看到你描述的错误。

第一次调用mongoDBConnect 实例化的Promise 在重试执行路径中永远不会被解析。

这是因为mongoDBConnect 的后续调用是在事件循环的未来滴答声中完全独立的执行上下文中进行的，由setTimeout 控制 - 并且每次调用都会实例化一个新的Promise 与您的@ 完全断开连接987654326@函数。

这种重构应该可以解决问题：

const delay = (interval) => new Promise(resolve => setTimeout(resolve, interval))

async connect() {
    const options = {...}
    try {
        console.log("starting")
        await this._connectWithRetry(options)
        console.log("finished")
    } catch (err) {
        winston.error(`Could not connect to Mongo with error: ${err}`)
    }
}

private async _connectWithRetry(options) {
    try {
        winston.info("Connecting to mongo...")
        await mongoose.connect(this.dbURI, options)
        winston.info("Connection successful.")
    } catch (err) {
        winston.info("Failed to connect to mongo. Retrying in 5 seconds...")
        await delay(5000)
        await this._connectWithRetry(options)
    }
}

测试工具：

let retryCount = 0

const mongoose = {
    connect: ()=>retryCount++ === 2 ? Promise.resolve() : Promise.reject('fake error')
}

async function connect() {
    try {
        console.log("starting")
        await connectWithRetry()
        console.log("finished")
    } catch (err) {
        console.error(`connect error`, err)
    }
}

async function connectWithRetry() {
    try {
        console.log("Connecting to mongo...")
        await mongoose.connect()
        console.log("Connection successful.")
    } catch (err) {
        console.log("Retrying in 1 second...", err)
        await delay(1000)
        await connectWithRetry()
    }
}

const delay = (interval) => new Promise(resolve => setTimeout(resolve, interval))

connect()