From: Scott Rubin <srubin@...>
Date: 2004-08-26T06:50:44+09:00
Subject: Open Fifo for Writing

Ok, this problem I'm having is a little bit strange. I have two seperate 
processes running as part of this application. One process is written in 
C and the other process is written in Ruby.  To communicate between the 
two processes I have two fifos in the file system.  One fifo sends ASCII 
strings in one direction, and the other fifo goes in the other direction.

Now, the problem is that pipes need to be opened on the reading end 
first. So I have it coded like this.

# open the incoming fifo
infifo = File.open( "infifo", IO::NONBLOCK | IO::RDONLY )
	
# launch the C process
pid = fork do exec( "cprocess" ) end

# open the outfifo
outfifo = File.open( "outfifo", "w" )

There is an obvious problem here. The problem is that at some point the 
cprocess opens the outfifo on the other end. And the ruby program cannot 
open the outfifo for writing before the cprocess opens it for reading. I 
tried to place the outfifo = File.open call inside a while outfifo == 
nil.  But that didn't work either.  Is there a way in ruby to detect 
when the outfifo has been opened for reading on the other end?  One way 
I thought of was for the C process to send a message up the incoming 
fifo to the ruby process to tell it when the outfifo is ready for 
opening. But I just want to make sure there isn't an easier and slicker 
way to do it with ruby.

-Scott