Re: [9fans] trying to understand how fork/pipe a filtering program

[rog@vitanuova.com]

> I'm just trying to understand what goes on -
> is this the way to do this? if not, what am I missing?

ahh, having thought about the original question, i finally understand what was going on.
readimage doesn't need EOF, since it knows exactly how many bytes it needs to read.
hence axel's original program could work without a zero-length write.
however the reason he needed the sleep was that without it,
both processes were reading the original image's bytes from the pipe at the same time,
which (depending on scheduling) would result in too little data (and a hangup) or
a corrupt image message, or both.

if you were guaranteed that the image data would fit into the pipe without
blocking, then you could wait for the process to exit before reading,
but the two pipe solution is preferable.