If mode is FALSE, the given stream will be switched to non-blocking mode, and if TRUE, 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.
注: 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).
See also stream_select().