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From: z93john@mtek.chalmers.se (John I Quist)
Subject: Opening a fifo hangs
Date: 1999/02/18
Message-ID: <7agtmi$8a$1@nyheter.chalmers.se>#1/1
X-Deja-AN: 445659971
Organization: School of Mechanical Engineering,
 Chalmers University of Technology
Newsgroups: comp.lang.ada
Date: 1999-02-18T00:00:00+00:00
List-Id: <comp.lang.ada>

Hi!

I'm tring to establish communication between two processes on the same 
Sun machine. (SunOS 5.6; running GNAT 3.05)

I have created two named pipes, and if I open two terminals, I can do
the following, without a problem:

In /dev/pts/3 (e.g.)
cat > mypipe
typetypetype
^D

In /dev/pts/4
cat mypipe

As expected, the text typed into the pipe on "pts/3" arrives neatly
on "pts/4"... 

BUT, if I make a small Ada hack to open the pipes and read/write to them,
one program reads and the other writes, the program hangs.
The lines where execution halts are:

--- Write side ---
open(IN_F, IN_FILE, "/users/ztek/z93john/.comm_pipe");
------------------

--- Read side ---
open(OUT_F, OUT_FILE, "/users/ztek/z93john/.comm_pipe");
-----------------

(Both programs use TEXT_IO)


If I run "truss" to get the system calls, I find that both programs do
open("/users/ztek/z93john/.comm_pipe", O_RDONLY) (sleeping...)

BUT; if I kill the "writer" and do a 
cat > .comm_pipe [Return]
the "reader" opens the fifo!

Why doesn't the writer open the pipe? 
I have read the GNAT reference, and I didn't get much wiser...
- Is Ada doing something weird here, or is it me? 

(As I understand it, the programs are supposed to block until both 
ends of the pipe are open, but that's what I'm doing, isn't it?
Open for write on one end, read on the other...)


I would really appreciate an email copy of your replies.

Thank you!
/John.