geoff at modperlcookbook
Oct 17, 2007, 8:30 AM
Post #1 of 5
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[Fwd: [rt.cpan.org #30061] $r->pnotes stores aliases not copies so is subject to action at a distance]
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heh, didn't this just come up?
:)
gozer: I did find the documentation, and I posted it to the rt ticket.
I guess we don't have a historical way of managing rt tickets, but I'm
tempted to resolve this one as "rejected" (though the thought of
rejecting tim isn't a pleasant one ;)
--Geoff
-------- Original Message --------
Subject: [rt.cpan.org #30061] $r->pnotes stores aliases not copies so is
subject to action at a distance
Date: Wed, 17 Oct 2007 10:58:22 -0400
From: Tim_Bunce via RT <bug-mod_perl [at] rt>
Reply-To: bug-mod_perl [at] rt
To: undisclosed-recipients:;
References: <RT-Ticket-30061 [at] rt>
Wed Oct 17 10:57:58 2007: Request 30061 was acted upon.
Transaction: Ticket created by TIMB
Queue: mod_perl
Subject: $r->pnotes stores aliases not copies so is subject to
action at a
distance
Broken in: (no value)
Severity: Important
Owner: Nobody
Requestors: TIMB [at] cpan
Status: new
Ticket <URL: http://rt.cpan.org/Ticket/Display.html?id=30061 >
This code:
$x = 42;
$r->pnotes( 'foo', $x );
++$x;
warn $r->pnotes( 'foo', $x );
should print the value that was stored, 42, but it actually prints 43!
The value stored has been modified by action at a distance. *Not good*
This can cause some very hard to debug problems, where values stored in
pnotes change for
no readily apparent reason. I know, I've spent way too long doing just
that before I identified
this as the cause.
A workaround for affected code is to assign to a temporary variable so
the alias taken by
pnotes isn't an alias for the orginal value:
$r->pnotes( 'foo', my $tmp = $x )
The minimal fix is to change:
hv_store(cfg->pnotes, key, len, SvREFCNT_inc(val), FALSE);
in pnotes in src/modules/perl/Apache.xs to something more like
SV **svp = hv_fetch(cfg->pnotes, key, len, TRUE);
sv_setsv(*svp, val);
with a little more work you could eliminate the earlier hv_exists and
hv_fetch by doing
SV **svp = hv_fetch(cfg->pnotes, key, len, (val) ? TRUE : FALSE);
and working with svp.
Tim Bunce.
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