PHP不一定要以http方式调用。PHP与其它应用的接口叫做SAPI，选用不同的SAPI决定了调用PHP的方式。例如Apache的mod_php就是一个SAPI的实现，用于Apache与PHP交互，同样，CGI和FastCGI(如fpm)的SAPI实现也是用于以HTTP方式调用PHP解释器。除此之外，还有很多SAPI，如CLI的SAPI可以支持命令行方式运行PHP脚本，运用php的pcntl_fork函数可以用与C类似的方式(两次fork)创建deamon进程，这样PHP脚本就可以当做服务使用了。至于服务与其它进程的交互，php支持socket。我写过一个小的Demo，展示了如何用PHP写Server，你可以看一下：

//Accpet the http client request and generate response content.

//As a demo, this function just send "PHP HTTP Server" to client.

function handle_http_request($address, $port)

{

$max_backlog = 16;

$res_content = "HTTP/1.1 200 OK\nContent-Length: 15\nContent-Type: text/plain; charset=UTF-8\n\nPHP HTTP Server

";

$res_len = strlen($res_content);

//Create, bind and listen to socket: 127.0.0.1:8888

if(($socket = socket_create(AF_INET, SOCK_STREAM, SOL_TCP)) === FALSE)

{

echo "Create socket failed!\n";

exit;

}

if((socket_bind($socket, $address, $port)) === FALSE)

{

echo "Bind socket failed!\n";

exit;

}

if((socket_listen($socket, $max_backlog)) === FALSE)

{

echo "Listen to socket failed!\n";

exit;

}

//Loop

while(TRUE)

{

if(($accept_socket = socket_accept($socket)) === FALSE)

{

continue;

}

else

{

socket_write($accept_socket, $res_content, $res_len);

socket_close($accept_socket);

}

}

}

//Run as deamon process.

function run()

{

if(($pid1 = pcntl_fork()) === 0)

//First child process

{

posix_setsid(); //Set first child process as the session leader.

if(($pid2 = pcntl_fork()) === 0)

//Second child process, which run as deamon.

{

handle_http_request('www.codinglabs.org', 9999); //Replaced by your own domain or address.

}

else

{

//Second child process exit;

exit;

}

}

else

{

//First child process exit;

pcntl_wait($status);

}

}

//Entry point.

run();