From @eserte

The following script goes into an endless loop for all modern perl versions (5.8.9 .. 5.21.7, seen on FreeBSD and Linux)​:

#!/usr/bin/perl

my $extra_len = shift || 1022; # may be somewhat smaller, down to 970 or so
binmode \*STDERR, "​:encoding(US-ASCII)";
my $foo = "\x{dc}" . "x" x $extra_len;
alarm 3;
warn "$foo\n";

__END__

My guess​: the inEncodeCall hack in PerlIO/encoding.xs was triggered, and maybe some file pointer was not advanced.

Regards,
  Slaven

From @jkeenan

On Tue Dec 23 14​:23​:50 2014, slaven@​rezic.de wrote​:

The following script goes into an endless loop for all modern perl
versions (5.8.9 .. 5.21.7, seen on FreeBSD and Linux)​:

#!/usr/bin/perl

my $extra_len = shift || 1022; # may be somewhat smaller, down to 970
or so
binmode \*STDERR, "​:encoding(US-ASCII)";
my $foo = "\x{dc}" . "x" x $extra_len;
alarm 3;
warn "$foo\n";

__END__

My guess​: the inEncodeCall hack in PerlIO/encoding.xs was triggered,
and maybe some file pointer was not advanced.

Regards,
Slaven

On Linux/amd64 (Ubuntu 14.04 LTS), find that if I run the code above I get the alarm after 3 seconds.

#####
$ perl 123489-loop.pl
Alarm clock
#####

However, when I edit the file to insert a print to STDERR statement after the assignment to $foo, I get the endless loop.

#####
$ cat 123489-loop.pl
my $extra_len = shift || 1022; # may be somewhat smaller, down to 970 or so
binmode \*STDERR, "​:encoding(US-ASCII)";
my $foo = "\x{dc}" . "x" x $extra_len;
print STDERR "$foo\n";
alarm 3;
warn "$foo\n";
#####
$ perl 123489-loop.pl
^C
#####

If, however, I print that line to STDOUT, I get the line, then the alarm in a few seconds.

Thank you very much.

--
James E Keenan (jkeenan@​cpan.org)

The RT System itself - Status changed from 'new' to 'open'

From @eserte

Dana Uto 23. Pro 2014, 14​:50​:28, jkeenan reče​:

On Tue Dec 23 14​:23​:50 2014, slaven@​rezic.de wrote​:

The following script goes into an endless loop for all modern perl
versions (5.8.9 .. 5.21.7, seen on FreeBSD and Linux)​:

#!/usr/bin/perl

my $extra_len = shift || 1022; # may be somewhat smaller, down to 970
or so
binmode \*STDERR, "​:encoding(US-ASCII)";
my $foo = "\x{dc}" . "x" x $extra_len;
alarm 3;
warn "$foo\n";

__END__

My guess​: the inEncodeCall hack in PerlIO/encoding.xs was triggered,
and maybe some file pointer was not advanced.

Regards,
Slaven

On Linux/amd64 (Ubuntu 14.04 LTS), find that if I run the code above I
get the alarm after 3 seconds.

This is already the bug reproduced, unless you have a very (!) slow CPU which needs longer than three seconds for one warn() statement :-). The alarm clock is just there in case somebody wants to turn this into a test script which must not hang.

From @Leont

On Tue, Dec 23, 2014 at 11​:23 PM, slaven@​rezic.de <perlbug-followup@​perl.org

wrote​:

The following script goes into an endless loop for all modern perl
versions (5.8.9 .. 5.21.7, seen on FreeBSD and Linux)​:

#!/usr/bin/perl

my $extra_len = shift || 1022; # may be somewhat smaller, down to 970 or so
binmode \*STDERR, "​:encoding(US-ASCII)";
my $foo = "\x{dc}" . "x" x $extra_len;
alarm 3;
warn "$foo\n";

__END__

My guess​: the inEncodeCall hack in PerlIO/encoding.xs was triggered, and
maybe some file pointer was not advanced.

This sounds like a duplicate of #117537

Leon

From @eserte

Dana Tue, 23 Dec 2014 14​:23​:50 -0800, slaven@​rezic.de reče​:

The following script goes into an endless loop for all modern perl
versions (5.8.9 .. 5.21.7, seen on FreeBSD and Linux)​:

#!/usr/bin/perl

my $extra_len = shift || 1022; # may be somewhat smaller, down to 970
or so
binmode \*STDERR, "​:encoding(US-ASCII)";
my $foo = "\x{dc}" . "x" x $extra_len;
alarm 3;
warn "$foo\n";

__END__

My guess​: the inEncodeCall hack in PerlIO/encoding.xs was triggered,
and maybe some file pointer was not advanced.

Good news​: starting with perl 5.29.9 the script does not hang anymore (checked on various FreeBSD and Linux systems).