Thread

1. nonblocking lock?

   Pablo Funes <pablo@cs.brandeis.edu> — 1999-05-27T22:42:11Z

   Is it possible to do a nonblocking lock? That is, 
   I want several clients to execute,
   
       begin
       if table A is locked
       then
           go around doing stuff on other tables
       else
           lock A and do stuff on A
       endif
   
   the problem is, if I use normal lock, then 
   after one client has locked and is doing stuff on A
   the other one will block and thus it won't be able
   to go around doing stuff on other tables. Is it
   possible to do a nonblocking lock that will just
   fail if the table is locked already? 
   
   
   NOTE: I tried using PQrequestCancel but it won't
   cancel the request. It still blocks for as long
   as the lock lasts. The only way around I've found so 
   far is to use PQreset. That's crude but works. But 
   it leaves a dangling postmaster process that lives
   until the orignal lock is freed. Any other ideas? 
   
   Thanks a lot 
   
   Pablo Funes
   Brandeis University
   pablo@cs.brandeis.edu
   
   

2. Re: [HACKERS] nonblocking lock?

   Massimo Dal Zotto <dz@cs.unitn.it> — 1999-06-02T10:23:47Z

   > Is it possible to do a nonblocking lock? That is, 
   > I want several clients to execute,
   > 
   >     begin
   >     if table A is locked
   >     then
   >         go around doing stuff on other tables
   >     else
   >         lock A and do stuff on A
   >     endif
   > 
   > the problem is, if I use normal lock, then 
   > after one client has locked and is doing stuff on A
   > the other one will block and thus it won't be able
   > to go around doing stuff on other tables. Is it
   > possible to do a nonblocking lock that will just
   > fail if the table is locked already? 
   
   Try with user locks. You can find the code in contrib/userlocks.
   
   -- 
   Massimo Dal Zotto
   
   +----------------------------------------------------------------------+
   |  Massimo Dal Zotto               email: dz@cs.unitn.it               |
   |  Via Marconi, 141                phone: ++39-0461534251              |
   |  38057 Pergine Valsugana (TN)      www: http://www.cs.unitn.it/~dz/  |
   |  Italy                             pgp: finger dz@tango.cs.unitn.it  |
   +----------------------------------------------------------------------+
   
   

3. Re: [HACKERS] nonblocking lock?

   Bruce Momjian <maillist@candle.pha.pa.us> — 1999-06-02T15:33:23Z

   > > Is it possible to do a nonblocking lock? That is, 
   > > I want several clients to execute,
   > > 
   > >     begin
   > >     if table A is locked
   > >     then
   > >         go around doing stuff on other tables
   > >     else
   > >         lock A and do stuff on A
   > >     endif
   > > 
   > > the problem is, if I use normal lock, then 
   > > after one client has locked and is doing stuff on A
   > > the other one will block and thus it won't be able
   > > to go around doing stuff on other tables. Is it
   > > possible to do a nonblocking lock that will just
   > > fail if the table is locked already? 
   > 
   > Try with user locks. You can find the code in contrib/userlocks.
   
   Yes, this is the proper PostgreSQL solution.
   
   -- 
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     maillist@candle.pha.pa.us            |  (610) 853-3000
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