socket_set_option

To expand a bit more on what "tim at e2-media dot co dot nz" started.
SO_SNDTIMEO is one of the many constants you can use with socket_set_option.
See http://ca.php.net/manual/en/ref.sockets.php for the available Predefind Constants and visit http://man.he.net/man2/setsockopt for the meaning of the ones relevant.
Tim's example might seem at first a bit non-intuitive since he is using the SO_SNDTIMEO constant. Which means, if the socket has to send out data, it must do it within the limit specified - in his case 10 seconds. Usually you won't set a timeout for sending out data. Nevertheless, the example is valid, and there are situations where you need to do so.
A more intuitive use of socket_set_option would be to set a time out for a blocking socket (a socket that waits for data to be receive when read from). You would do this like so:
socket_set_option($socket,SOL_SOCKET, SO_RCVTIMEO, array("sec"=>0, "usec"=>100));
Notice that sec= 0 and usec= 100; Depending on how long you want your program to wait to recieve data, you might want to change these values.
Regards,
 drenintell

Lingering will sometimes not work when you're working with non-blocking sockets. Even if the socket is set to linger and you keep tying to close until the socket doesn't return an error and the resource is no longer identifiable as type 'Socket', the socket may STILL close without sending everything.
Therefore, in the event that you are using non-blocking sockets (which is preferable if you care at all about signaling), you should set the socket as blocking (socket_set_block()) before calling to close it. This will allow everything to flush before it returns.
Dustin Oprea

To set a socket timeout value (assuming you've set it blocking) use:
socket_set_option(
 $socket,
 SOL_SOCKET, // socket level
 SO_SNDTIMEO, // timeout option
 array(
 "sec"=>10, // Timeout in seconds
 "usec"=>0 // I assume timeout in microseconds
 )
 );

PLEASE NOTE
PHP 7.3.6, and probably many previous versions, automatically sets SO_REUSEADDR when you use stream_socket_server().
php_network_bind_socket_to_local_addr() is called at https://github.com/php/php-src/blob/623911f993f39ebbe75abe2771fc89faf6b15b9b/main/streams/xp_socket.c#L675 and defined at https://github.com/php/php-src/blob/61a6a6ec51297506c54f3c6e60ace9b892d0a3e4/main/network.c#L401 and if you take a look you'll see
#ifdef SO_REUSEADDR
 setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (char*)&sockoptval, sizeof(sockoptval));
#endif
I initially thought I'd need to play with context options to turn this on, but no, the simplest single-arg call with no error checking and just an address, works for me.
strace your PHP binary to be 100% sure:
...
setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
...
The chances are you ARE using SO_REUSEADDR unless you're using a 100-year old UNIX clone in a month with a Z in it.

<question>
 Why is the size of the buffer 2 times that set by me?
<?php
//Before setting the cache area
$sock = socket_create(AF_INET, SOCK_STREAM, getprotobyname('tcp'));
socket_bind($sock, '127.0.0.1',5000);
socket_listen($sock,1024);
$sndbuf = socket_get_option($sock,SOL_SOCKET,SO_SNDBUF);
$rcvbuf = socket_get_option($sock,SOL_SOCKET,SO_RCVBUF);
printf("send buffer size(写缓存区大小):%sm \n",$sndbuf/1024);
printf("receive buffer(读缓存区大小)%sm \n",$rcvbuf/1024);
//After setting the cache area
$snd_buf = 1024*3;
$rcv_buf = 1024*3;
socket_set_option($sock,SOL_SOCKET,SO_SNDBUF, $snd_buf);
socket_set_option($sock,SOL_SOCKET,SO_RCVBUF, $rcv_buf);
$sndbuf = socket_get_option($sock,SOL_SOCKET,SO_SNDBUF);
$rcvbuf = socket_get_option($sock,SOL_SOCKET,SO_RCVBUF);
printf("send buffer size(写缓存区大小):%sm \n",$sndbuf/1024);
printf("receive buffer size(读缓存区大小)%sm \n",$rcvbuf/1024);
?>

I would like to comment on the previous note regarding blocking sockets.
There is more to blocking sockets than waiting for data to be received when trying to be read upon, just to make example, a listening blocking socket will wait for a client to try to connect before it returns when you socket_accept() it.

Setting the socket timeout microseconds ('usec') does not work under Windows, at least under PHP/5.2.9:
<?php
 $timeout = array('sec'=>1,'usec'=>500000);
 socket_set_option($socket,SOL_SOCKET,SO_RCVTIMEO,$timeout);
 var_dump(socket_set_option($socket,SOL_SOCKET,SO_RCVTIMEO));
?>

Output on Windows box:
array(2) {
 ["sec"]=>
 int(1)
 ["usec"]=>
 int(0)
}
Output on Linux box:
array(2) {
 ["sec"]=>
 int(1)
 ["usec"]=>
 int(500000)
}

It appears that Winsock does not acknowledge timeout (send and receive) on Windows.