Re: Non-reentrant plperlu function & concurrent access

On Tue, Aug 17, 2010 at 4:15 AM, Philippe Lang
<philippe.lang@attiksystem.ch> wrote:
>> Hi,
>>
>> I have a non-reentrant plperlu function, which does no database
>> modification. It basically stores input data into a file, calls a unix
>> shell command, and reads the result back from another file.
>>
>> I don't really care about database isolation here, phantom reads and
>> such. It is not likely to be a problem. What could be a problem, is if
>> another call to this function is fired while another one is running.
>>
>> In this specific case, I could solve the problem by generating random
>> input and ouput filenames, but I would prefer a more general solution,
>> like using some sort of mutex for the function. What is the best way to
>> do that under Postgresql? Although not designed for this (if I
>> understand correctly), would a "serializable" isolation level help
>> here?
>
> I answer to my own post, sorry...
>
> Maybe Postgresql functions "pg_try_advisory_lock_shared" and "pg_advisory_unlock_shared" are the solution?
>

There is perl self locking mechanism using flock on __DATA__ .  Have
you tried that?   google is your friend.