I was toying with this and came up with a solution for your test script. It seems that if you do the open (read-write) '+<' instead of '<' , your second script works as intended. I just happened to see it mentioned in some docs about POSIX rules to make non-blocking pipe opens. 
#!/usr/bin/perl
use warnings;
use strict;
use Glib qw/TRUE FALSE/;

my $file_pipe = "$$".'_pipe';

system('mkfifo',$file_pipe)==0 or die $!;
my $p_read;
open $p_read,'+<',$file_pipe or die $!;  # needs '+<' instead of '<' t
+o be nonblocking

$SIG{USR1} = \&on_usr1;

my $loop = Glib::MainLoop->new( 'default', FALSE );

#test non-blocking is working
my $count = 1;
print "$count\n";
#my $timer  = Glib::Timeout->add (1000, \&timer_callback, undef, 1 );

$loop->run;

sub on_usr1 {
    my $sig = shift;
    print "somebody told me $sig\n";
}

sub timer_callback{
     $count++;
     print "$count\n";
    return 1;
}

[download]
$ ./signal-w-pipe & 1 16594 $ 1 kill -s USR1 16594 somebody told me USR1
I'm not really a human, but I play one on earth.
Old Perl Programmer Haiku ................... flash japh

In reply to Re: problems on signal handling, Glib mainloop, and named pipe by zentara
in thread problems on signal handling, Glib mainloop, and named pipe by llancet

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.