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[Bug translator/2056] avoid locking within foreach iteration for maps & pmaps
- From: "hunt at redhat dot com" <sourceware-bugzilla at sourceware dot org>
- To: systemtap at sources dot redhat dot com
- Date: 5 Jan 2006 06:08:44 -0000
- Subject: [Bug translator/2056] avoid locking within foreach iteration for maps & pmaps
- References: <20051214214948.2056.hunt@redhat.com>
- Reply-to: sourceware-bugzilla at sourceware dot org
------- Additional Comments From hunt at redhat dot com 2006-01-05 06:08 -------
(In reply to comment #3)
> Regarding the pmap deadlock, one possible fix is to have foreach() iterating
> over a pmap hold an exclusive lock around the whole loop, and the @extraction
> operators to hold none, when they're nested within foreach(). In fact, ordinary
> array reads enclosed within foreach() don't need to be locked either. Let's
> transmute this bugzilla entry to track this bug.
Maybe I'm missing something, but the problem is the writelock. Why does the
generated code take a writelock on the pmap when it is reading stats?
I suspect the reason is confusion over reading from a map and a pmap. You need
a writelock when doing _stp_pmap_agg() or _stp_pmap_get(). However,
_stp_pmap_agg() creates a normal map and you only want to readlock it when reading.
Until this gets fixed, pmaps of stats are broken because we cannot print without
using foreach.
--
http://sourceware.org/bugzilla/show_bug.cgi?id=2056
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