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Get status of pipe-process

Posted on 2003-10-28
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Last Modified: 2010-05-18
Hi!

I want to use a perl-program to check, whether a program, that feeds a pipe (endless loop) is running or not:
I would use something like:
------------
die "FIFO is no pipe\n" unless (-p "fifo.txt");
$SIG{ALRM} = sub {
  print "Process does NOT feed the pipe!!!\n";
  open(WRITER,">fifo.txt");#make the program end properly -> write to pipe myself <- this does not work?????
  print WRITER "ALARM!\n";
  close(WRITER);
};
alarm(3);
open(READER,"fifo.txt");
while (<READER>){
}
close(READER);
alarm(0);
--------
why does this not work???

another idea:
--------
die "FIFO is no pipe\n" unless (-p "fifo.txt");
if ($pid = fork()) {
  sleep 3;
  kill($pid); #kill child
}else{
  open(FIFO,"fifo.txt");
  while (<FIFO>){
  }
  close FIFO;
  print "PIPE is OK!\n";
  exit;
}
-------
but killing the child would only make the parent exit, but if the pipe is fed afterwards, the child would say "OK"!

any idea how to make this?

thx
michi
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Question by:witty
3 Comments
 
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Accepted Solution

by:
witty earned 0 total points
ID: 9638341
I found the answer myself:

die "FIFO is no pipe\n" unless (-p "fifo.txt");

my $pipeok=1;

$SIG{ALRM} = sub {
  if ($pid=fork()){
    `echo XXX > fifo.txt`;
    exit(0);
  }
  $pipeok=0;
};

alarm(3);
open(READER,"fifo.txt");
while (<READER>){}
close(READER);
alarm(0);
if ($pipeok){
  print "PIPE OK!\n";
}else{
  print "PIPE NOT OK!\n";
}
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Expert Comment

by:jmcg
ID: 9638427
If you want to drop a note in Community Support saying you'd like this question closed, you can ask for your points to be refunded. I suggest you ask that the question be PAQed, so it will remain searchable if someone has a question like this in the future.
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