The timeout is an upper bound on the amount of time elapsed before stream_select() returns. tv_sec may be zero, causing stream_select() to return immediately.
The tv_sec and tv_usec together form the timeout parameter. The timeout is an upper bound on the amount of time elapsed before stream_select() returns. tv_sec may be zero, causing stream_select() to return immediately. This is useful for polling. If tv_sec is NULL (no timeout), stream_select() can block indefinitely.