执行php swoole的echo.php 样例

报WARNING swSocket_bind (ERROR 502): bind(0.0.0.0:9501) failed. Error: Address already in use [98]

PHP Fatal error:  Uncaught Swoole\Exception: failed to listen server port[0.0.0.0:9501]. Error: Address already in use[98]. in /usr/local/src/swoole/examples/server/echo.php:2

Stack trace:

#0 /usr/local/src/swoole/examples/server/echo.php(2): Swoole\Server->__construct('0.0.0.0', 9501)

#1 {main}

  thrown in /usr/local/src/swoole/examples/server/echo.php on line 2

Fatal error: Uncaught Swoole\Exception: failed to listen server port[0.0.0.0:9501]. Error: Address already in use[98]. in /usr/local/src/swoole/examples/server/echo.php:2

Stack trace:

#0 /usr/local/src/swoole/examples/server/echo.php(2): Swoole\Server->__construct('0.0.0.0', 9501)

#1 {main}

  thrown in /usr/local/src/swoole/examples/server/echo.php on line 2

vim  echo.php 

<?php

$serv = new swoole_server("0.0.0.0", 9501);

//$serv->on('connect', function ($serv, $fd, $reactor_id){

//      echo "[#".posix_getpid()."]\tClient@[$fd:$reactor_id]: Connect.\n";

//});

$serv->set(array(

    'worker_num' => 1,

));

$serv->on('receive', function (swoole_server $serv, $fd, $reactor_id, $data) {

        echo "[#".$serv->worker_id."]\tClient[$fd] receive data: $data\n";

    if ($serv->send($fd, "hello {$data}\n") == false)

    {

        echo "error\n";

    }

});