( resource stream, int mode )
If mode is 0, the given stream
will be switched to non-blocking mode, and if 1, it
will be switched to blocking mode. This affects calls like
fgets() and fread()
that read from the stream. In non-blocking mode an
fgets() call will always return right away
while in blocking mode it will wait for data to become available
on the stream.
如果成功则返回 TRUE，失败则返回 FALSE。
This function was previously called as
set_socket_blocking() and later
socket_set_blocking() but this usage is deprecated.
Prior to PHP 4.3, this function only worked on socket based streams.
Since PHP 4.3, this function works for any stream that supports
non-blocking mode (currently, regular files and socket streams).