[Pljava-dev] doubtful PL/Java's activity

Hi,

Thank you, everyone.
Excuse me my poor explanation.
So, I made a figure.
Look attachment.
Red arrow in this fig. is unlikely ?

> You may, of course, have multiple Java threads in the JVM that resides in the PostgreSQL session. But any interaction with the session is serialized, so this isn?t a problem at all.

I worry about interaction between PostgreSQL and JVM library functions rather than interaction with the session.

> PL/Java goes to some length in protecting the single threaded PostgreSQL kernel. All accesses to it must be made from the caller thread. Multiple threads > can be used for background tasks but such threads will be completely blocked from accessing the PostgreSQL functions.
>
> It works like this:
> A call is made from PostgreSQL. This call grabs a mutex.
> During PL/Java execution, only the thread that owns the mutex can call PostgreSQL.
> When the call eventually returns, the mutex is released.

If I'm correct, PL/Java is also a single thread library ?
If so, it would not be a problem.

> Java maintenance (garbage collection for instance) will still run in separate threads. If someone should write a finalizer that actually tries to do database access (god forbid), then that finalizer would throw an exception.

Uh.. It may become a restriction of usage.
Probably, some restrictions else would exist, doesn't it?

Regards.

-----Original Message-----
From: pljava-dev-bounces at lists.pgfoundry.org [mailto:pljava-dev-bounces at lists.pgfoundry.org] On Behalf Of Thomas Hallgren
Sent: Thursday, December 12, 2013 5:16 PM
To: pljava-dev at lists.pgfoundry.org
Subject: Re: [Pljava-dev] doubtful PL/Java's activity

PL/Java goes to some length in protecting the single threaded PostgreSQL kernel. All accesses to it must be made from the caller thread. Multiple threads can be used for background tasks but such threads will be completely blocked from accessing the PostgreSQL functions.

It works like this:
A call is made from PostgreSQL. This call grabs a mutex.
During PL/Java execution, only the thread that owns the mutex can call PostgreSQL.
When the call eventually returns, the mutex is released.

Java maintenance (garbage collection for instance) will still run in separate threads. If someone should write a finalizer that actually tries to do database access (god forbid), then that finalizer would throw an exception.

- thomas

On 2013-12-09 12:16, Taniguchi, Yasunori wrote:
> Hi,
>
> I'm investigating PL/Java and find out a doubtful fact.
>
> Postgres is compiled as a single thread application and linked with
> JavaVM(.so/.dll) which is a multi thread library.
> Sp, I think PL/Java's activity may not be assured.
>
> Thread-unsafe functions and global variables used in single thread
> standard libraries may be inconsistent with multi thread libraries.
>
> Can anybody respond me ?
>
>
> Regards.
> -----
> Y.Taniguchi
>
>
> _______________________________________________
> Pljava-dev mailing list
> Pljava-dev at lists.pgfoundry.org
> http://lists.pgfoundry.org/mailman/listinfo/pljava-dev

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