If you try running your test program via the Linux strace command, i.e.:

strace perl iosrv.pl
[download]

Thank you.

First, I constructed a smallest possible failing code:

#!/usr/local/bin/perl8

use 5.006001;
use strict;
use warnings;

use IO::Socket;

my $sock = undef;

eval {
    while (1) {
        outsend(scalar(localtime()) . "\n");
        sleep 5;
    }
}; if (my $e = $@) {
    die "Exception: $e";
}

sub outsend {
    my $data = shift;

    $sock ||= IO::Socket::INET->new(
        PeerAddr => '127.0.0.1',
        PeerPort => 5555,
        Proto    => 'tcp',
        ) || die $!;
    my $lw = syswrite($sock, $data);
    die $! unless defined $lw and $lw == length($data);
}
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So, here's the strace:

nanosleep({5, 0}, {5, 0})               = 0
time([1122281453])                      = 1122281453
time([1122281453])                      = 1122281453
write(3, "Mon Jul 25 10:50:53 2005\n", 25) = 25
time([1122281453])                      = 1122281453
rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0
rt_sigaction(SIGCHLD, NULL, {SIG_DFL}, 8) = 0
rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
nanosleep({5, 0}, {5, 0})               = 0
time([1122281458])                      = 1122281458
time([1122281458])                      = 1122281458
write(3, "Mon Jul 25 10:50:58 2005\n", 25) = -1 EPIPE (Broken pipe)
--- SIGPIPE (Broken pipe) ---
+++ killed by SIGPIPE +++
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A SIGPIPE? What? I'm not quite sure, but I would not expect to have to handle that myself on a TCP connection. Or on any IO operation, I'd say.

Ok, now the question is---what do I put into the %SIG-handler?

---

_Search, Ask, ^Know

Ok, now the question is---what do I put into the %SIG-handler?

For SIGPIPE, perhaps the most common technique (in both Perl and C) is to ignore it and then test the return code of the write, for example:

use Errno ':POSIX';
$SIG{PIPE} = 'IGNORE';
for (1 .. 3) {
    unless (print SOMEPIPE "blah") {
        last if $! == EPIPE;   # terminate the loop if reader goes awa
+y
        die "I/O error: $!";   # this is more serious, so die
    }
}
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If you use 4 arg select (or IO::Select) before you write to your socket then you can avoid getting SIGPIPE for a relatively unsurprising condition like "the reading end is dead".

Firstly, whether to handle the signal as a warning or an error. For example, you could assign $SIG{ PIPE } to a handler that treats it as a warning, e.g.

$SIG{ PIPE } = sub { warn "Broken pipe trap, traceback follows:\n" . T
+race::trace(); }
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I'd like the syswrite() to simply return undef, nothing more. My existing code then will throw away the socket and try to (re-)connect to any available server.

    TRY: for (1 .. $maxretries) {
        eval {
            $sock ||= outconnect() || die $diag=$!;
            my $lw = syswrite($sock, $$data);
            die $! unless defined $lw and $lw == length($$data);
            $$data = '';
        }; if (my $e = $@) {
            $diag ||= $e;
            $sock = undef;
            next TRY;
[download]

PS: Setting it to 'IGNORE' works just fine: Exception: Broken pipe at /root/iotest.pl line 31.

---

_Search, Ask, ^Know

You are of course right, that it can be made to be ignored. I forgot that because I am used to project standards that require all fatal conditions to at the least be written to a log file for review by production support personnel, even though this often leads to huge logfiles that need to be regularly archived off!

One world, one people