Perl 5.10 - POSIX Signals ignored unless received during sleep() call? - perl

Question

I'm running into a bit of an issue when it comes to how Perl handles POSIX signals. Namely, Perl seems to ignore the signals unless they're received during a call to sleep().
For example, the following code works fine:
#/usr/bin/perl
$SIG{PIPE} = sub { print STDERR "WARNING: Received SIGPIPE"; exit(1); };
while (1) { print "Waiting on signal...\n"; sleep(10); }
When using the above SIGPIPE handler in another script which reads from an Oracle database, the subroutine never seems to get called.
#/usr/bin/perl
use DBI;
$SIG{PIPE} = sub { print STDERR "WARNING: Received SIGPIPE"; exit(1); };
my $db = "redacted";
my $user = "redacted";
my $pass = "redacted";
my $table = "redacted";
my $ora = DBI->connect("dbi:Oracle:" . $db, $user, $pass);
my $sql = "SELECT * FROM " . $table;
my $query = $ora->prepare($sql);
$query->execute();
while (my #row = $query->fetchrow_array()) {
print(join('|', #row) . "\n");
}
if ( $DBI::err ) { print STDERR "ERROR: Unload terminated due to error"; }
I'm sending the SIGPIPE signal to both scripts in the same manner (kill -sPIPE pid), but only the first script responds to it. The second script simply carries on. No message, no exit, nothing.
How can I rectify this situation?

Answer 1

Setting up the signal handler before the DBI calls somehow leads it to being ignored after some of the DBI methods are called. The solution was to move the signal handler subroutine to just before the processing loop, but after the call to execute:
#/usr/bin/perl
use DBI;
# SIGPIPE handler used to be here
my $db = "redacted";
my $user = "redacted";
my $pass = "redacted";
my $table = "redacted";
my $ora = DBI->connect("dbi:Oracle:" . $db, $user, $pass);
my $sql = "SELECT * FROM " . $table;
my $query = $ora->prepare($sql);
$query->execute();
$SIG{PIPE} = sub { print STDERR "WARNING: Received SIGPIPE"; exit(1); };
while (my #row = $query->fetchrow_array()) {
print(join('|', #row) . "\n");
}
if ( $DBI::err ) { print STDERR "ERROR: Unload terminated due to error"; }
I'm not exactly sure why it fixes the issue, but it does.

Answer 2

It is likely that the DBI driver being used to communicate with the database is written in XS code. XS code that is going to block for a long time has to be carefully written to cope with signals and perl's "safe signals" delivery system. It is possible that the DB driver you are using doesn't take account of this, and therefore won't work.