fifo doesn't work

Thanks Marc. It turned out that the problem is not the bufferring, but something wrong inside the fifo file.
I tried the pair of command

cat <fifo1 &
echo "111" >fifo1

for several times, and it stopped to work at about the 4th time I tried. Even "unbuffer" could not change anything.
Furthermore, writing to the fifo (without any reader) wouldn't block the command(echo >fifo1). Sometime later, it suddenly began to work, but writing without any reader still didn't block the command.

Later I removed this fifo and created a new one, and now everything works fine. BTW, I put this fifo inside a Ubuntu One folder, so it's automatically synchronized to the server, and I'm not sure whether it's the cause.

Thanks again.