PHP flock() - 幕后是什么？

在与 PHP 源码搏斗了半个小时后，我放弃了。 :P 问题是 - 在 Gentoo Linux 系统上，PHP freeze() 函数调用归结为什么系统调用？我遇到了一些问题（比如每 20 次循环迭代中阻塞 30 秒类问题），我想知道为什么会这样。

// example: $stream = fopen(FILE, 'rb') or die('???');
$md = stream_get_meta_data($stream);
echo $md['wrapper_type'];

flock($stream);

if this prints plainfile then the call to the php function flock() is handled by php_stdiop_set_option(...) which calls flock(). Depending on whether PHP was compiled with HAVE_FLOCK or not this may be the system call flock() http://www.kernel.org/doc/man-pages/online/pages/man2/flock.2.html or a function defined in flock_compat.c which utilizes fcntl() http://www.kernel.org/doc/man-pages/online/pages/man2/fcntl.2.html. On my gentoo system PHP was compiled with HAVE_FLOCK.

main/streams/plain_wrapper.c @ static int php_stdiop_set_option(...):

       case PHP_STREAM_OPTION_LOCKING:
            if (fd == -1) {
                return -1;
            }

            if ((zend_uintptr_t) ptrparam == PHP_STREAM_LOCK_SUPPORTED) {
                return 0;
            }

            if (!flock(fd, value)) {
                data->lock_flag = value;
                return 0;
            } else {
                return -1;
            }
            break;