closing a socket while another thread is in an IO.select() call on it

Hello Rubyists,

I have a program that opens a TCPSocket, connects it to a server, and
then creates a thread which loops until the socket closes, reading from
the socket and processing the data read. It calls IO.select() to wait
until there is data available to read. Meanwhile, another thread can
close the socket in certain circumstances. If the first thread is in
IO.select() when the socket is closed, the result is unpredictable -
sometimes the select() returns and sometimes it blocks. I'm not sure of
the circumstances that cause it to block or not - it seems random.

So, is there some way to make it reliably unblock? Or is there something
that the second thread can do to cause the select() to return (set a
flag on the socket before closing it, or something)?

This is with Ruby 2.0.0 p247 on Centos 5 Linux if that's significant.

Thanks in advance for any suggestions.
    Graham