Re: named pipe and "Text file busy"

in reply to named pipe and "Text file busy"

There is a contract for the use of a named pipe. I will suppose un*xlike and to simplify I will not talk about non-blocking. For pipes the default is blocking.

You need a reader and usually the reader is a long-running process.

The reader will block on read as soon as it opens. If there is no reader any writer will block.

Remember it *is* a pipe so what gets in must get out... If you write more than a certain maximum number of bytes input is likely to be intermixed between the writers. If the reader does not process the input quickly enough then eventually a writer will be blocked and then all the other writers, so you need some flow analysis or special janitor processes.

So do you have a permanent reader? If you have a read-once reader the behavior you seem to be experiencing is *normal*. Can it be somehow that the pipe is opened by the two threads? Can you check with lsof or similar the processes that maintain a descriptor opened to the named pipe. If you had posted some code we might have been able to help better.

% steph@ape (/home/stephan) %
% cat reader.sh 
#!/bin/ksh
trap 'exit 0' INT
pipe=named_pipe outfile=out
[[ -p $pipe ]] || mkfifo $pipe

exec 0<$pipe
while dd if=$pipe bs=64 count=1 >> $outfile
do
    print .processing
    sleep 2
done

% steph@ape (/home/stephan) %
% jobs
[1] +  Running                 ./reader.sh &
[download]

cheers --stephan

In Section Seekers of Perl Wisdom