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http: added scheduling option to http agent
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In some cases, it is preferable to use a lifo scheduling strategy
for the free sockets instead of default one, which is fifo.
This commit introduces a scheduling option to add the ability
to choose which strategy best fits your needs.

PR-URL: #33278
Reviewed-By: Robert Nagy <ronagy@icloud.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
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delvedor authored and mcollina committed May 20, 2020
1 parent a82001a commit daa65fb
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Showing 3 changed files with 174 additions and 1 deletion.
17 changes: 17 additions & 0 deletions doc/api/http.md
Expand Up @@ -110,6 +110,11 @@ http.get({
### `new Agent([options])`
<!-- YAML
added: v0.3.4
changes:
- version: REPLACEME
pr-url: https://github.com/nodejs/node/pull/33278
description: Add `scheduling` option to specify the free socket
scheduling strategy.
-->

* `options` {Object} Set of configurable options to set on the agent.
Expand All @@ -132,6 +137,18 @@ added: v0.3.4
* `maxFreeSockets` {number} Maximum number of sockets to leave open
in a free state. Only relevant if `keepAlive` is set to `true`.
**Default:** `256`.
* `scheduling` {string} Scheduling strategy to apply when picking
the next free socket to use. It can be `'fifo'` or `'lifo'`.
The main difference between the two scheduling strategies is that `'lifo'`
selects the most recently used socket, while `'fifo'` selects
the least recently used socket.
In case of a low rate of request per second, the `'lifo'` scheduling
will lower the risk of picking a socket that might have been closed
by the server due to inactivity.
In case of a high rate of request per second,
the `'fifo'` scheduling will maximize the number of open sockets,
while the `'lifo'` scheduling will keep it as low as possible.
**Default:** `'fifo'`.
* `timeout` {number} Socket timeout in milliseconds.
This will set the timeout when the socket is created.

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10 changes: 9 additions & 1 deletion lib/_http_agent.js
Expand Up @@ -35,6 +35,7 @@ const { async_id_symbol } = require('internal/async_hooks').symbols;
const {
codes: {
ERR_INVALID_ARG_TYPE,
ERR_INVALID_OPT_VALUE,
},
} = require('internal/errors');
const { once } = require('internal/util');
Expand Down Expand Up @@ -86,6 +87,11 @@ function Agent(options) {
this.keepAlive = this.options.keepAlive || false;
this.maxSockets = this.options.maxSockets || Agent.defaultMaxSockets;
this.maxFreeSockets = this.options.maxFreeSockets || 256;
this.scheduling = this.options.scheduling || 'fifo';

if (this.scheduling !== 'fifo' && this.scheduling !== 'lifo') {
throw new ERR_INVALID_OPT_VALUE('scheduling', this.scheduling);
}

this.on('free', (socket, options) => {
const name = this.getName(options);
Expand Down Expand Up @@ -219,7 +225,9 @@ Agent.prototype.addRequest = function addRequest(req, options, port/* legacy */,
while (freeSockets.length && freeSockets[0].destroyed) {
freeSockets.shift();
}
socket = freeSockets.shift();
socket = this.scheduling === 'fifo' ?
freeSockets.shift() :
freeSockets.pop();
if (!freeSockets.length)
delete this.freeSockets[name];
}
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148 changes: 148 additions & 0 deletions test/parallel/test-http-agent-scheduling.js
@@ -0,0 +1,148 @@
'use strict';

const common = require('../common');
const assert = require('assert');
const http = require('http');

function createServer(count) {
return http.createServer(common.mustCallAtLeast((req, res) => {
// Return the remote port number used for this connection.
res.end(req.socket.remotePort.toString(10));
}), count);
}

function makeRequest(url, agent, callback) {
http
.request(url, { agent }, (res) => {
let data = '';
res.setEncoding('ascii');
res.on('data', (c) => {
data += c;
});
res.on('end', () => {
process.nextTick(callback, data);
});
})
.end();
}

function bulkRequest(url, agent, done) {
const ports = [];
let count = agent.maxSockets;

for (let i = 0; i < agent.maxSockets; i++) {
makeRequest(url, agent, callback);
}

function callback(port) {
count -= 1;
ports.push(port);
if (count === 0) {
done(ports);
}
}
}

function defaultTest() {
const server = createServer(8);
server.listen(0, onListen);

function onListen() {
const url = `http://localhost:${server.address().port}`;
const agent = new http.Agent({
keepAlive: true,
maxSockets: 5
});

bulkRequest(url, agent, (ports) => {
makeRequest(url, agent, (port) => {
assert.strictEqual(ports[0], port);
makeRequest(url, agent, (port) => {
assert.strictEqual(ports[1], port);
makeRequest(url, agent, (port) => {
assert.strictEqual(ports[2], port);
server.close();
agent.destroy();
});
});
});
});
}
}

function fifoTest() {
const server = createServer(8);
server.listen(0, onListen);

function onListen() {
const url = `http://localhost:${server.address().port}`;
const agent = new http.Agent({
keepAlive: true,
maxSockets: 5,
scheduling: 'fifo'
});

bulkRequest(url, agent, (ports) => {
makeRequest(url, agent, (port) => {
assert.strictEqual(ports[0], port);
makeRequest(url, agent, (port) => {
assert.strictEqual(ports[1], port);
makeRequest(url, agent, (port) => {
assert.strictEqual(ports[2], port);
server.close();
agent.destroy();
});
});
});
});
}
}

function lifoTest() {
const server = createServer(8);
server.listen(0, onListen);

function onListen() {
const url = `http://localhost:${server.address().port}`;
const agent = new http.Agent({
keepAlive: true,
maxSockets: 5,
scheduling: 'lifo'
});

bulkRequest(url, agent, (ports) => {
makeRequest(url, agent, (port) => {
assert.strictEqual(ports[ports.length - 1], port);
makeRequest(url, agent, (port) => {
assert.strictEqual(ports[ports.length - 1], port);
makeRequest(url, agent, (port) => {
assert.strictEqual(ports[ports.length - 1], port);
server.close();
agent.destroy();
});
});
});
});
}
}

function badSchedulingOptionTest() {
try {
new http.Agent({
keepAlive: true,
maxSockets: 5,
scheduling: 'filo'
});
} catch (err) {
assert.strictEqual(err.code, 'ERR_INVALID_OPT_VALUE');
assert.strictEqual(
err.message,
'The value "filo" is invalid for option "scheduling"'
);
}
}

defaultTest();
fifoTest();
lifoTest();
badSchedulingOptionTest();

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