Re: Buggy SELEC ... FROM UPDATE ?

From: Helge Bahmann <bahmann(at)math(dot)tu-freiberg(dot)de>
To: Patrice Espié <patrice(dot)espie(at)univ-lyon2(dot)fr>
Cc: pgsql-novice(at)postgresql(dot)org
Subject: Re: Buggy SELEC ... FROM UPDATE ?
Date: 2001-04-10 14:39:01
Message-ID: Pine.LNX.4.21.0104101635010.13043-100000@lothlorien.stunet2.tu-freiberg.de
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All locks are released when you commit your transaction.

> boolean Got = false
> while Got == false
> Start transaction
> SELECT * FROM syslock WHERE id=%d AND used='f' FOR UPDATE
the row is locked here ...
> if SELECT returns a row
> then
> UPDATE syslock SET used='t' WHERE id=%d
> Commit transaction
... and released again here; probably not what you want
> Got = true
> else
> Rollback transaction
> continue // yes, active wait ... I'm testing !
> end if
> end while
> Trace "I get the syslock number %d !!"
> Do something with the syslock %d which is now reserved
> UPDATE syslock SET used='f' WHERE id=%d
should move your "commit transaction" here

have fun
helge

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