| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Andres Freund <andres(at)2ndquadrant(dot)com> |
| Cc: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: dynamic shared memory and locks |
| Date: | 2014-01-06 14:59:49 |
| Message-ID: | 2790.1389020389@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Andres Freund <andres(at)2ndquadrant(dot)com> writes:
> On 2014-01-06 10:35:59 +0200, Heikki Linnakangas wrote:
>> That assumes that you never hold more than one spinlock at a time, otherwise
>> you can get deadlocks. I think that assumptions holds currently, because
>> acquiring two spinlocks at a time would be bad on performance grounds
>> anyway.
> I think that's a pretty dangerous assumption
I think it's a fine assumption. Code that could possibly do that should
never get within hailing distance of being committed, because you are only
supposed to have short straight-line bits of code under a spinlock.
Taking another spinlock breaks both the "straight line code" and the "no
loops" aspects of that coding rule.
regards, tom lane
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