Pipes and non blocking writing

[Sébastien Cottalorda]

Hi all,

Several programs need to write in a pipe (created with "mknod /tmp/pipe.tub
p").
My problem is the following :
If no program read the other side of the pipe, all writing operations are
blocked.
I don't care if I lost information, but I'd like programs to try to write to
the pipe and return doing what they are programmed to.

Here is my program:

#====================================================================
#!/usr/bin/perl -w

use strict;
use Fcntl;
my $named_pipe='/tmp/pipe.tub';
unless (-e $named_pipe){
die "No way" if (system("/bin/mknod $named_pipe p"));
}
unless (sysopen(PIPE, $named_pipe, O_WRONLY|O_NONBLOCK)){
die "Can\'t open $named_pipe : $!";
}
while(1){
print "Trying to write in the pipe ...";
print PIPE "Heelo World\n";
print "Done\n";
sleep 3;
}
close(PIPE);
exit;
#=====================================================================

When I run that program, I get:
Can`t open pipe: Device not configured at line 10

What's wrong ????
My OS: Mandrake 7.1 (kernel 2.2.15-4mdk)
My Perl: perl 5.6.0

Thanks in advance for any kind of help.

Sébastien

 

[Anno Siegel]

Hi all,

Several programs need to write in a pipe (created with "mknod /tmp/pipe.tub
p").
My problem is the following :
If no program read the other side of the pipe, all writing operations are
blocked.
I don't care if I lost information, but I'd like programs to try to write to
the pipe and return doing what they are programmed to.

Here is my program:

#====================================================================
#!/usr/bin/perl -w

use strict;
use Fcntl;
my $named_pipe='/tmp/pipe.tub';
unless (-e $named_pipe){
die "No way" if (system("/bin/mknod $named_pipe p"));
}
unless (sysopen(PIPE, $named_pipe, O_WRONLY|O_NONBLOCK)){
die "Can\'t open $named_pipe : $!";
}
while(1){
print "Trying to write in the pipe ...";
print PIPE "Heelo World\n";
print "Done\n";
sleep 3;
}
close(PIPE);
exit;
#=====================================================================

When I run that program, I get:
Can`t open pipe: Device not configured at line 10

What's wrong ????
My OS: Mandrake 7.1 (kernel 2.2.15-4mdk)
My Perl: perl 5.6.0

Nothing is wrong, it's working to specification. A pipe can't be opened
for writing when there's no reader at the other end.

The solution is not to die when open() fails (why sysopen, btw?), but
do other things an try again later. It would also be a good idea to
install a SIGPIPE handler in case the reader disappears while you're
writing.

Anno

 

[Sébastien Cottalorda]

Nothing is wrong, it's working to specification. A pipe can't be opened
for writing when there's no reader at the other end.

The solution is not to die when open() fails (why sysopen, btw?), but
do other things an try again later. It would also be a good idea to
install a SIGPIPE handler in case the reader disappears while you're
writing.

Anno

Hi,

Thanks Ano,

that's helps me to solve my problem:
* intercepting SIGPIPE,
* bypassing open error,
* re-try to open again the pipe,
allow me to manage correctly my pipe.

thanks again.

Sébastien