sthoenna at efn
May 22, 2008, 11:18 PM
Post #3 of 3
(176 views)
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Re: [perl #54644] Perl script hang at while statement
[In reply to]
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On Thu, May 22, 2008 6:11 am, Chaitanya Vutukuru wrote:
> And also please let me know, if these is not the correct correct/proper
> channel for support.
This is the proper place for perl bug reports, but not general support
of perl. For help with perl programming, try http://perlmonks.org.
> Here is the brief explanation of the perl script and the problem
> we are facing:
> In the script we create pipe like:
> pipe(FROMDBREAD,FROMDBWRITE);
>
> we dup STDOUT and STDERR, to FROMDBWRITE pipe descriptor like:
> open(STDOUT,">&FROMDBWRITE") || die "$ME (child): can't redirect STDOUT\n";
> open(STDERR,">&STDOUT") || die "$ME (child): can't redirect STDERR\n";
>
> Then we will wait for the pipe descriptor in the while loop:
> while(<FROMDBREAD>) {
> ..
> ..
> }
>
> We know that few messages are loggedin STDOUT and STDERR, but we see
> that the script is hanging in the above while statement.
> We are telling it as a hang because its not coming out of that
> while(for false) or even not running the statements under that while
> (for true), it is just waiting at "while(<FROMDBREAD>)", which is
> leading to the whole script hanging.
> We and customer facing this issue in one particular scenario
> and in some machines.
I believe you are not understanding how pipes work; you may want to
unless you are in non-blocking mode, reading on a pipe will wait for
something to be written if there are any open write filehandles on
the pipe.
See http://www.opengroup.org/onlinepubs/009695399/functions/read.html
and/or try the following:
#!/usr/bin/perl
use strict;
use warnings;
my $ME = "me";
open OUT, ">&STDOUT" or die "couldn't dup\n";
pipe(FROMDBREAD,FROMDBWRITE);
#we dup STDOUT and STDERR, to FROMDBWRITE pipe descriptor like:
open(STDOUT,">&FROMDBWRITE") || die "$ME (child): can't redirect STDOUT\n";
open(STDERR,">&STDOUT") || die "$ME (child): can't redirect STDERR\n";
print OUT "warning foo\n";
warn "foo";
print OUT "warned foo\n";
$SIG{ALRM} = sub { close FROMDBWRITE; close STDOUT; close STDERR; print
OUT "closed\n" };
alarm 5;
#Then we will wait for the pipe descriptor in the while loop:
while(<FROMDBREAD>) {
print OUT "got :$_:\n";
}
print OUT "done\n";
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bugrep0954564
