sysread blocking writer thread?

Hi All.

I have a program where two threads are handling one socket. One thread is
reading and the other is writing to the socket.
(using ActiveState Perl 5.8.8_822 on WinXP)
However, the writer thread sometimes blocks for no apperent reason. I saw
that the reader thead is using sysread, and got a suspicion that this
sysread is blocking the writer thread from writing.

Is it possible?

Thanks,
Shmuel.