科学·技术
干电池（碱性锌锰电池、锌锰电池、碳锌电池等，...
生活·娱乐
不推荐将任何东西塞进癫痫发作者口内的，当然也...
人文·社科
大部分人生年不满百，说大，看不清银河系的样子...
自然·生态
在河北农业大学进行的一项实验中发现，振动频率...
文史·观点
他们懂得如何做闲人
兼谈故事创作的一些原则
文艺·腔调
龙潭镇的祠堂及书院
偶像AKB48专题
图不太好看预警。
还记得去年5月去兰屿旅行，在春天柔和的海风中...
居然被人偷走啦！
竟然还有切前任？？
(C)2017果壳网&&&&京ICP证100430号&&&&京网文[-239号&&&&新出发京零字东150005号&&&&
违法和不良信息举报邮箱：&&&&举报电话：Node.js v9.8.0 Documentation
Table of Contents
- StableA single instance of Node.js runs in a single thread. To take advantage of
multi-core systems, the user will sometimes want to launch a cluster of Node.js
processes to handle the load.
The cluster module allows easy creation of child processes that all share
server ports.
const cluster = require('cluster');
const http = require('http');
const numCPUs = require('os').cpus().
if (cluster.isMaster) {
console.log(`Master ${process.pid} is running`);
// Fork workers.
for (let i = 0; i & numCPUs; i++) {
cluster.fork();
cluster.on('exit', (worker, code, signal) =& {
console.log(`worker ${worker.process.pid} died`);
// Workers can share any TCP connection
// In this case it is an HTTP server
http.createServer((req, res) =& {
res.writeHead(200);
res.end('hello world\n');
}).listen(8000);
console.log(`Worker ${process.pid} started`);
Running Node.js will now share port 8000 between the workers:
$ node server.js
Master 3596 is running
Worker 4324 started
Worker 4520 started
Worker 6056 started
Worker 5644 started
Please note that on Windows, it is not yet possible to set up a named pipe
server in a worker.
How It Works
The worker processes are spawned using the
so that they can communicate with the parent via IPC and pass server
handles back and forth.
The cluster module supports two methods of distributing incoming
connections.
The first one (and the default one on all platforms except Windows),
is the round-robin approach, where the master process listens on a
port, accepts new connections and distributes them across the workers
in a round-robin fashion, with some built-in smarts to avoid
overloading a worker process.
The second approach is where the master process creates the listen
socket and sends it to interested workers. The workers then accept
incoming connections directly.
The second approach should, in theory, give the best performance.
In practice however, distribution tends to be very unbalanced due
to operating system scheduler vagaries. Loads have been observed
where over 70% of all connections ended up in just two processes,
out of a total of eight.
Because server.listen() hands off most of the work to the master
process, there are three cases where the behavior between a normal
Node.js process and a cluster worker differs:
server.listen({fd: 7}) Because the message is passed to the master,
file descriptor 7 in the parent will be listened on, and the
handle passed to the worker, rather than listening to the worker's
idea of what the number 7 file descriptor references.
server.listen(handle) Listening on handles explicitly will cause
the worker to use the supplied handle, rather than talk to the master
server.listen(0) Normally, this will cause servers to listen on a
random port.
However, in a cluster, each worker will receive the
same &random& port each time they do listen(0).
In essence, the
port is random the first time, but predictable thereafter. To listen
on a unique port, generate a port number based on the cluster worker ID.
Note: Node.js does not provide routing logic. It is, therefore important to
design an application such that it does not rely too heavily on in-memory data
objects for things like sessions and login.
Because workers are all separate processes, they can be killed or
re-spawned depending on a program's needs, without affecting other
As long as there are some workers still alive, the server will
continue to accept connections.
If no workers are alive, existing connections
will be dropped and new connections will be refused. Node.js does not
automatically manage the number of workers, however. It is the application's
responsibility to manage the worker pool based on its own needs.
Although a primary use case for the cluster module is networking, it can
also be used for other use cases requiring worker processes.
Class: Worker
Added in: v0.7.0
A Worker object contains all public information and method about a worker.
In the master it can be obtained using cluster.workers. In a worker
it can be obtained using cluster.worker.
Event: 'disconnect'
Added in: v0.7.7
Similar to the cluster.on('disconnect') event, but specific to this worker.
cluster.fork().on('disconnect', () =& {
// Worker has disconnected
Event: 'error'
Added in: v0.7.3
This event is the same as the one provided by .
Within a worker, process.on('error') may also be used.
Event: 'exit'
Added in: v0.11.2
The exit code, if it exited normally.
The name of the signal (e.g. 'SIGHUP') that caused
the process to be killed.
Similar to the cluster.on('exit') event, but specific to this worker.
const worker = cluster.fork();
worker.on('exit', (code, signal) =& {
if (signal) {
console.log(`worker was killed by signal: ${signal}`);
} else if (code !== 0) {
console.log(`worker exited with error code: ${code}`);
console.log('worker success!');
Event: 'listening'
Added in: v0.7.0
Similar to the cluster.on('listening') event, but specific to this worker.
cluster.fork().on('listening', (address) =& {
// Worker is listening
It is not emitted in the worker.
Event: 'message'
Added in: v0.7.0
Similar to the cluster.on('message') event, but specific to this worker.
Within a worker, process.on('message') may also be used.
As an example, here is a cluster that keeps count of the number of requests
in the master process using the message system:
const cluster = require('cluster');
const http = require('http');
if (cluster.isMaster) {
// Keep track of http requests
let numReqs = 0;
setInterval(() =& {
console.log(`numReqs = ${numReqs}`);
// Count requests
function messageHandler(msg) {
if (msg.cmd && msg.cmd === 'notifyRequest') {
numReqs += 1;
// Start workers and listen for messages containing notifyRequest
const numCPUs = require('os').cpus().
for (let i = 0; i & numCPUs; i++) {
cluster.fork();
for (const id in cluster.workers) {
cluster.workers[id].on('message', messageHandler);
// Worker processes have a http server.
http.Server((req, res) =& {
res.writeHead(200);
res.end('hello world\n');
// notify master about the request
process.send({ cmd: 'notifyRequest' });
}).listen(8000);
Event: 'online'
Added in: v0.7.0
Similar to the cluster.on('online') event, but specific to this worker.
cluster.fork().on('online', () =& {
// Worker is online
It is not emitted in the worker.
worker.disconnect()
VersionChanges
This method now returns a reference to worker.
Added in: v0.7.7
A reference to worker.
In a worker, this function will close all servers, wait for the 'close' event on
those servers, and then disconnect the IPC channel.
In the master, an internal message is sent to the worker causing it to call
.disconnect() on itself.
Causes .exitedAfterDisconnect to be set.
Note that after a server is closed, it will no longer accept new connections,
but connections may be accepted by any other listening worker. Existing
connections will be allowed to close as usual. When no more connections exist,
see , the IPC channel to the worker will close allowing it to
die gracefully.
The above applies only to server connections, client connections are not
automatically closed by workers, and disconnect does not wait for them to close
before exiting.
Note that in a worker, process.disconnect exists, but it is not this function,
Because long living server connections may block workers from disconnecting, it
may be useful to send a message, so application specific actions may be taken to
close them. It also may be useful to implement a timeout, killing a worker if
the 'disconnect' event has not been emitted after some time.
if (cluster.isMaster) {
const worker = cluster.fork();
worker.on('listening', (address) =& {
worker.send('shutdown');
worker.disconnect();
timeout = setTimeout(() =& {
worker.kill();
worker.on('disconnect', () =& {
clearTimeout(timeout);
} else if (cluster.isWorker) {
const net = require('net');
const server = net.createServer((socket) =& {
// connections never end
server.listen(8000);
process.on('message', (msg) =& {
if (msg === 'shutdown') {
// initiate graceful close of any connections to server
worker.exitedAfterDisconnect
Added in: v6.0.0
Set by calling .kill() or .disconnect(). Until then, it is undefined.
The boolean
allows distinguishing between
voluntary and accidental exit, the master may choose not to respawn a worker
based on this value.
cluster.on('exit', (worker, code, signal) =& {
if (worker.exitedAfterDisconnect === true) {
console.log('Oh, it was just voluntary – no need to worry');
// kill worker
worker.kill();
Added in: v0.8.0
Each new worker is given its own unique id, this id is stored in the
While a worker is alive, this is the key that indexes it in
cluster.workers
worker.isConnected()
Added in: v0.11.14
This function returns true if the worker is connected to its master via its
IPC channel, false otherwise. A worker is connected to its master after it
has been created. It is disconnected after the 'disconnect' event is emitted.
worker.isDead()
Added in: v0.11.14
This function returns true if the worker's process has terminated (either
because of exiting or being signaled). Otherwise, it returns false.
worker.kill([signal='SIGTERM'])
Added in: v0.9.12
Name of the kill signal to send to the worker
This function will kill the worker. In the master, it does this by disconnecting
the worker.process, and once disconnected, killing with signal. In the
worker, it does it by disconnecting the channel, and then exiting with code 0.
Causes .exitedAfterDisconnect to be set.
This method is aliased as worker.destroy() for backwards compatibility.
Note that in a worker, process.kill() exists, but it is not this function,
worker.process
Added in: v0.7.0
All workers are created using , the returned object
from this function is stored as .process. In a worker, the global process
is stored.
Note that workers will call process.exit(0) if the 'disconnect' event occurs
on process and .exitedAfterDisconnect is not true. This protects against
accidental disconnection.
worker.send(message[, sendHandle][, callback])
VersionChanges
The callback parameter is supported now.
Added in: v0.7.0
sendHandle
Send a message to a worker or master, optionally with a handle.
In the master this sends a message to a specific worker. It is identical to
In a worker this sends a message to the master. It is identical to
process.send().
This example will echo back all messages from the master:
if (cluster.isMaster) {
const worker = cluster.fork();
worker.send('hi there');
} else if (cluster.isWorker) {
process.on('message', (msg) =& {
process.send(msg);
Event: 'disconnect'
Added in: v0.7.9
Emitted after the worker IPC channel has disconnected. This can occur when a
worker exits gracefully, is killed, or is disconnected manually (such as with
worker.disconnect()).
There may be a delay between the 'disconnect' and 'exit' events.
These events
can be used to detect if the process is stuck in a cleanup or if there are
long-living connections.
cluster.on('disconnect', (worker) =& {
console.log(`The worker #${worker.id} has disconnected`);
Event: 'exit'
Added in: v0.7.9
The exit code, if it exited normally.
The name of the signal (e.g. 'SIGHUP') that caused
the process to be killed.
When any of the workers die the cluster module will emit the 'exit' event.
This can be used to restart the worker by calling .fork() again.
cluster.on('exit', (worker, code, signal) =& {
console.log('worker %d died (%s). restarting...',
worker.process.pid, signal || code);
cluster.fork();
Event: 'fork'
Added in: v0.7.0
When a new worker is forked the cluster module will emit a 'fork' event.
This can be used to log worker activity, and create a custom timeout.
const timeouts = [];
function errorMsg() {
console.error('Something must be wrong with the connection ...');
cluster.on('fork', (worker) =& {
timeouts[worker.id] = setTimeout(errorMsg, 2000);
cluster.on('listening', (worker, address) =& {
clearTimeout(timeouts[worker.id]);
cluster.on('exit', (worker, code, signal) =& {
clearTimeout(timeouts[worker.id]);
errorMsg();
Event: 'listening'
Added in: v0.7.0
After calling listen() from a worker, when the 'listening' event is emitted
on the server a 'listening' event will also be emitted on cluster in the
The event handler is executed with two arguments, the worker contains the
worker object and the address object contains the following connection
properties: address, port and addressType. This is very useful if the
worker is listening on more than one address.
cluster.on('listening', (worker, address) =& {
console.log(
`A worker is now connected to ${address.address}:${address.port}`);
The addressType is one of:
-1 (unix domain socket)
&udp4& or &udp6& (UDP v4 or v6)
Event: 'message'
VersionChanges
The worker par see below for details.
Added in: v2.5.0
Emitted when the cluster master receives a message from any worker.
Before Node.js v6.0, this event emitted only the message and the handle,
but not the worker object, contrary to what the documentation stated.
If support for older versions is required but a worker object is not
required, it is possible to work around the discrepancy by checking the
number of arguments:
cluster.on('message', (worker, message, handle) =& {
if (arguments.length === 2) {
Event: 'online'
Added in: v0.7.0
After forking a new worker, the worker should respond with an online message.
When the master receives an online message it will emit this event.
The difference between 'fork' and 'online' is that fork is emitted when the
master forks a worker, and 'online' is emitted when the worker is running.
cluster.on('online', (worker) =& {
console.log('Yay, the worker responded after it was forked');
Event: 'setup'
Added in: v0.7.1
Emitted every time .setupMaster() is called.
The settings object is the cluster.settings object at the time
.setupMaster() was called and is advisory only, since multiple calls to
.setupMaster() can be made in a single tick.
If accuracy is important, use cluster.settings.
cluster.disconnect([callback])
Added in: v0.7.7
Called when all workers are disconnected and handles are
Calls .disconnect() on each worker in cluster.workers.
When they are disconnected all internal handles will be closed, allowing the
master process to die gracefully if no other event is waiting.
The method takes an optional callback argument which will be called when finished.
This can only be called from the master process.
cluster.fork([env])
Added in: v0.6.0
Key/value pairs to add to worker process environment.
Spawn a new worker process.
This can only be called from the master process.
cluster.isMaster
Added in: v0.8.1
True if the process is a master. This is determined
by the process.env.NODE_UNIQUE_ID. If process.env.NODE_UNIQUE_ID is
undefined, then isMaster is true.
cluster.isWorker
Added in: v0.6.0
True if the process is not a master (it is the negation of cluster.isMaster).
cluster.schedulingPolicy
Added in: v0.11.2
The scheduling policy, either cluster.SCHED_RR for round-robin or
cluster.SCHED_NONE to leave it to the operating system. This is a
global setting and effectively frozen once either the first worker is spawned,
or cluster.setupMaster() is called, whichever comes first.
SCHED_RR is the default on all operating systems except Windows.
Windows will change to SCHED_RR once libuv is able to effectively
distribute IOCP handles without incurring a large performance hit.
cluster.schedulingPolicy can also be set through the
NODE_CLUSTER_SCHED_POLICY environment variable. Valid
values are &rr& and &none&.
cluster.settings
VersionChanges
The inspectPort option is supported now.
The stdio option is supported now.
Added in: v0.7.1
List of string arguments passed to the Node.js
executable. Default: process.execArgv
File path to worker file. Default: process.argv[1]
String arguments passed to worker.
Default: process.argv.slice(2)
Current working directory of the worker process. Default:
undefined (inherits from parent process)
Whether or not to send output to parent's stdio.
Default: false
Configures the stdio of forked processes. Because the
cluster module relies on IPC to function, this configuration must contain an
'ipc' entry. When this option is provided, it overrides silent.
Sets the user identity of the process. (See .)
Sets the group identity of the process. (See .)
inspectPort
Sets inspector port of worker.
This can be a number, or a function that takes no arguments and returns a
number. By default each worker gets its own port, incremented from the
master's process.debugPort.
windowsHide
Hide the forked processes console window that would
normally be created on Windows systems. Default: false
After calling .setupMaster() (or .fork()) this settings object will contain
the settings, including the default values.
This object is not intended to be changed or set manually.
cluster.setupMaster([settings])
VersionChanges
The stdio option is supported now.
Added in: v0.7.1
setupMaster is used to change the default 'fork' behavior. Once called,
the settings will be present in cluster.settings.
Note that:
Any settings changes only affect future calls to .fork() and have no
effect on workers that are already running.
The only attribute of a worker that cannot be set via .setupMaster() is
the env passed to .fork().
The defaults above apply to the first call only, the defaults for later
calls is the current value at the time of cluster.setupMaster() is called.
const cluster = require('cluster');
cluster.setupMaster({
exec: 'worker.js',
args: ['--use', 'https'],
silent: true
cluster.fork(); // https worker
cluster.setupMaster({
exec: 'worker.js',
args: ['--use', 'http']
cluster.fork(); // http worker
This can only be called from the master process.
cluster.worker
Added in: v0.7.0
A reference to the current worker object. Not available in the master process.
const cluster = require('cluster');
if (cluster.isMaster) {
console.log('I am master');
cluster.fork();
cluster.fork();
} else if (cluster.isWorker) {
console.log(`I am worker #${cluster.worker.id}`);
cluster.workers
Added in: v0.7.0
A hash that stores the active worker objects, keyed by id field. Makes it
easy to loop through all the workers. It is only available in the master
A worker is removed from cluster.workers after the worker has disconnected and
exited. The order between these two events cannot be determined in advance.
However, it is guaranteed that the removal from the cluster.workers list happens
before last 'disconnect' or 'exit' event is emitted.
// Go through all workers
function eachWorker(callback) {
for (const id in cluster.workers) {
callback(cluster.workers[id]);
eachWorker((worker) =& {
worker.send('big announcement to all workers');
Using the worker's unique id is the easiest way to locate the worker.
socket.on('data', (id) =& {
const worker = cluster.workers[id];