waltbrad wrote:
> I'm proceeding slowly though the Lutz book "Programming Python". I'm
> in the section on named pipes. The script he uses has two functions:
> one for the child the other for the parent. You start the parent then
> the child:
>
> python pipefifo.py #starts the parent
>
> file /tmp/pipefifo # shows that the file is a named pipe
You appear to be using something Unix-like.
> python pipefifo.py -child # starts a child process and writes to the
> pipe.
>
> This is done between two command windows - the first for the parent
> and the second for the child.
>
> Now, the child's write loop is infinite. So, I used Ctrl-C and stopped
> the process. But the parent's read loop is also infinite and without
> and exception, so it keeps reading from the pipe after the child is
> shutdown even though the lines are empty. So, I had to shut that down
> also.
>
> I then wanted to start the child process first and see what happened
> when I ran the parent. Well that works but the reads come out in
> random order. This got me wondering about the pipe file itself. So I
> tried to open it with leafpad and found that I couldn't. I guess
> these files can only be opened by processes?
>
> Okay. But exactly when does the system brand this file as a named pipe
> and how?
A Unix fifo is only nominally a file. It's really just a convenient way
of referring to an in-memory object.
mkfifo f
some_prog > f &
cat f
Is semantically equivalent to:
some_prog | cat
If you want to peruse the data in your editor, use a regular file, not a
fifo. Have the writer (producer, "child" in your example) open it in
append mode.
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