javascript - 即使在添加 catch block 之后，nodejs 中的 "UnhandledPromiseRejectionWarning"

Question

我正在为 postgres 数据库编写一个 api 服务器，并且正在测试一些压力情况。我正在使用模块 node-postgres 中的池，遇到了这个问题。

在启动服务器之前，我首先耗尽了所有的 postgers 连接。然后我尝试通过池运行查询。

我尝试在 promise 周围添加 try catch block 。在 promise 内(在 catch block 内)，没有任何帮助。

以下是我重现错误的一些测试代码。

var pg = require('./node_modules/pg')

var pool = new pg.Pool(
    {
        user: "test",
        password: "pass134",
        host: "localhost",
        database: "testdb",
        port: 5432,
        max: 32,
        min: 16,
        idleTimeoutMillis: 60000,
        connectionTimeoutMillis: 10000
    }
);

pool.on("error", function(err){

    console.log("Error1: " + String(err));

});

pool.query("SELECT COUNT(*) FROM acal_cust", [])
.then(function(err, results){

    console.log(err);
    console.log(results);

}).catch(function(err){

    console.log("Error2:" + String(err));

    pool.end();

});

这是我运行代码时得到的结果。

Error2: error: sorry, too many clients already
(node:10422) UnhandledPromiseRejectionWarning: error: sorry, too many clients already
    at Connection.parseE (/ext/node_modules/pg/lib/connection.js:554:11)
    at Connection.parseMessage (/ext/node_modules/pg/lib/connection.js:381:17)
    at Socket.<anonymous> (/ext/node_modules/pg/lib/connection.js:117:22)
    at emitOne (events.js:116:13)
    at Socket.emit (events.js:211:7)
    at addChunk (_stream_readable.js:263:12)
    at readableAddChunk (_stream_readable.js:250:11)
    at Socket.Readable.push (_stream_readable.js:208:10)
    at TCP.onread (net.js:597:20)
(node:10422) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:10422) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

我想知道如何正确处理错误。这样它就不会被抛出。

Answer 1

catch Undled拒绝

process.on('unhandledRejection', error => {
  // Will print "unhandledRejection err is not defined"
  console.log('unhandledRejection', error.message);
});

catch block 用于 promises 而不是异步代码的回调版本。因此，如果抛出任何错误，它将被 if(err) {//do whatever} 捕获或

pool.query("SELECT COUNT(*) FROM acal_cust", []).then((results) => {

    console.log(results);

}).catch(function(err){

    console.log("Error:" + String(err));

});

并在完成查询或出现任何错误时关闭池。