php中的socket_select方法

Question

任何人都可以帮助我理解以下有关在PHP套接字编程中处理多个连接的示例。

我只需要向我解释这些步骤

  if(socket_select($read , $write , $except , null) === false)
            {
                $errorcode = socket_last_error();
                $errormsg = socket_strerror($errorcode);

                die("Could not listen on socket : [$errorcode] $errormsg \n");
            }

            //if ready contains the master socket, then a new connection has come in
            if (in_array($sock, $read)) 
            {
            }

我真的无法理解这些步骤会发生什么。

这是完整的例子：

        error_reporting(~E_NOTICE);
        set_time_limit (0);

        $address = "0.0.0.0";
        $port = 6000;
        $max_clients = 10;

        if(!($sock = socket_create(AF_INET, SOCK_STREAM, 0)))
        {
            $errorcode = socket_last_error();
            $errormsg = socket_strerror($errorcode);

            die("Couldn't create socket: [$errorcode] $errormsg \n");
        }

        echo "Socket created \n";

        // Bind the source address
        if( !socket_bind($sock, $address , 5000) )
        {
            $errorcode = socket_last_error();
            $errormsg = socket_strerror($errorcode);

            die("Could not bind socket : [$errorcode] $errormsg \n");
        }

        echo "Socket bind OK \n";

        if(!socket_listen ($sock , 10))
        {
            $errorcode = socket_last_error();
            $errormsg = socket_strerror($errorcode);

            die("Could not listen on socket : [$errorcode] $errormsg \n");
        }

        echo "Socket listen OK \n";

        echo "Waiting for incoming connections... \n";
        //array of client sockets
        $client_socks = array();

        //array of sockets to read
        $read = array();

        //start loop to listen for incoming connections and process existing connections
        while (true) 
        {

            //prepare array of readable client sockets
            $read = array();

            //first socket is the master socket
            $read[0] = $sock;

            //now add the existing client sockets
            for ($i = 0; $i < $max_clients; $i++)
            {
                if($client_socks[$i] != null)
                {
                    $read[$i+1] = $client_socks[$i];
                }
            }
            //now call select - blocking call
            if(socket_select($read , $write , $except , null) === false)
            {
                $errorcode = socket_last_error();
                $errormsg = socket_strerror($errorcode);

                die("Could not listen on socket : [$errorcode] $errormsg \n");
            }

            //if ready contains the master socket, then a new connection has come in
            if (in_array($sock, $read)) 
            {
                for ($i = 0; $i < $max_clients; $i++)
                {
                    if ($client_socks[$i] == null) 
                    {
                        $client_socks[$i] = socket_accept($sock);

                        //display information about the client who is connected
                        if(socket_getpeername($client_socks[$i], $address, $port))
                        {
                            echo "Client $address : $port is now connected to us. \n";
                        }

                        //Send Welcome message to client
                        $message = "Welcome to php socket server version 1.0 \n";
                        $message .= "Enter a message and press enter, and i shall reply back \n";

                        socket_write($client_socks[$i] , $message);

                        break;
                    }
                }
            }

            //check each client if they send any data
            for ($i = 0; $i < $max_clients; $i++)
            {
                if (in_array($client_socks[$i] , $read))
                {
                    $input = socket_read($client_socks[$i] , 1024);

                    if ($input == null) 
                    {
                        //zero length string meaning disconnected, remove and close the socket
                        unset($client_socks[$i]);
                        socket_close($client_socks[$i]);
                    }

                    $n = trim($input);

                    $output = "OK ... $input";

                    echo "Sending output to client \n";

                    //send response to client
                    socket_write($client_socks[$i] , $output." welcome any time");
                }
            }
        }