socket_listen()

(PHP 4 >= 4.1.0, PHP 5, PHP 7)

Listens for a connection on a socket

说明

socket_listen(resource $socket[,int $backlog= 0]): bool

After the socket$sockethas been created using socket_create() and bound to a name with socket_bind(), it may be told to listen for incoming connections on$socket.

socket_listen() is applicable only to sockets of type SOCK_STREAM or SOCK_SEQPACKET.

参数

$socket: A valid socket resource created with socket_create() or socket_addrinfo_bind()
$backlog: A maximum of$backlogincoming connections will be queued for processing. If a connection request arrives with the queue full the client may receive an error with an indication ofECONNREFUSED, or, if the underlying protocol supports retransmission, the request may be ignored so that retries may succeed.
Note:
The maximum number passed to the$backlogparameter highly depends on the underlying platform. On Linux, it is silently truncated to SOMAXCONN. On win32, if passed SOMAXCONN, the underlying service provider responsible for the socket will set the backlog to a maximumreasonablevalue. There is no standard provision to find out the actual backlog value on this platform.

返回值

成功时返回TRUE，或者在失败时返回FALSE。 The error code can be retrieved with socket_last_error(). This code may be passed to socket_strerror() to get a textual explanation of the error.

参见

socket_accept()Accepts a connection on a socket
socket_bind()给套接字绑定名字
socket_connect()开启一个套接字连接
socket_create()创建一个套接字（通讯节点）
socket_strerror()Return a string describing a socket error
socket_addrinfo_bind()Create and bind to a socket from a given addrinfo

<?php
// create for tcp
$sock = socket_create(AF_INET, SOCK_STREAM, getprotobyname('tcp'));
socket_bind($sock, '127.0.0.1',5000);
socket_listen($sock,1);
sleep(20);
?>
<fruit>
netstat -ntpl
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address      Foreign Address     State    PID/Program name
tcp    0   0 127.0.0.1:5000     0.0.0.0:*        LISTEN   1839/php

To change the maximum allowed backlog by your system (*nix machines only), first you need to find the variable for this limit:
sudo sysctl -a | grep somaxconn
On ubuntu boxes, it returns net.core.somaxconn (you need to look for the 'somaxconn' variable, the full name will vary across different systems).
Update this to a large number as follows:
sudo sysctl -w net.core.somaxconn=1024
This will work straight away. no restart required.