node.js - _read()的 Node 可读流什么时候调用

Question

我创建自己的阅读流。但我想知道_read()什么时候被调用？如果我不添加on('data')监听器，_read()就不会被调用，为什么？

var data = [{"id":0,"name":"object 0","value":3}],
    Readable = require('stream').Readable,
    util = require('util');

var ReadStream = function() {
    Readable.call(this, {objectMode: true});
    this.data = data;
    this.curIndex = 0;
};
util.inherits(ReadStream, Readable);

ReadStream.prototype._read = function() {
    if (this.curIndex === this.data.length)
        return this.push(null);

    var data = this.data[this.curIndex++];
    //console.log('read: ' + JSON.stringify(data));
    this.push(data);
};


var stream = new ReadStream();
stream.on('data', function(record) {
    console.log('received: ' + JSON.stringify(record));
});

stream.on('end', function() {
    console.log('done111');
});

Answer 1

If I don't add on('data'） listerner, the _read() will not be called. Why?

流已暂停。假设您使用的是最新版本的 Node 。

https://nodejs.org/api/stream.html#stream_two_modes

All Readable streams begin in paused mode but can be switched to flowing mode in one of the following ways:

Adding a 'data' event handler.

Calling the stream.resume() method.

Calling the stream.pipe() method to send the data to a Writable.

顺便说一句，要创建可读的，请检查 noms或mississippi.from