message: Use free port.
diff: @@ -7,13 +7,13 @@ swoole_coroutine: complete test server&&client&&timeout(millisecond)
  require_once __DIR__ . '/../include/bootstrap.php';
  require_once __DIR__ . '/../include/swoole.inc';
  $pm = new ProcessManager;
  -
  -$pm->parentFunc = function ($pid) use ($pm) {
  +$port = get_one_free_port();
  +$pm->parentFunc = function ($pid) use ($pm, $port) {
  $socket = new Swoole\Coroutine\Socket(AF_INET, SOCK_STREAM, 0);
  assert($socket instanceof Swoole\Coroutine\Socket);
  assert($socket->errCode === 0);
  - go(function () use ($socket) {
  - assert($socket->connect('localhost', 9501));
  + go(function () use ($socket, $port) {
  + assert($socket->connect('localhost', $port));
  $i = 0.000;
  while (true) {
  $socket->send("hello");
  @@ -31,9 +31,9 @@ $pm->parentFunc = function ($pid) use ($pm) {
  swoole_event_wait();
  };
  -$pm->childFunc = function () use ($pm) {
  +$pm->childFunc = function () use ($pm, $port) {
  $socket = new Swoole\Coroutine\Socket(AF_INET, SOCK_STREAM, 0);
  - assert($socket->bind('127.0.0.1', 9501));
  + assert($socket->bind('127.0.0.1', $port));
  assert($socket->listen(128));
  go(function () use ($socket, $pm) {
  $client = $socket->accept();
  