Thread: Libpq and multithreading

Hello,

I am trying to use libpq in two threads, the issue is that I am getting access violation after several successful
connections.
Each thread connects to different db and disconnects immediately after making a conenction.

So my question is if this is supported by libpq? Is it possible to use it in more than one thread and make connections
atthe same time? 

Kind regards,
Joanna

On Fri, Jan 11, 2013 at 04:27:42PM +0100, Asia wrote:
> Hello,
>
> I am trying to use libpq in two threads, the issue is that I am getting access violation after several successful
connections.
> Each thread connects to different db and disconnects immediately after making a conenction.
>
> So my question is if this is supported by libpq? Is it possible to use it in more than one thread and make
connectionsat the same time? 

Each connection can be created and accessed from only one thread.

--
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + It's impossible for everything to be true. +

I am using 2 threads, each declares seperate PGconn conenction object.

It connects e.g. 60 times, one connection from one thread, the other connection from the other thread, usually one
aftereach other. 
And it fails at 61'st connection with access violation.

I already tried with PQconnect and PQsetdbLogin. I am using mututal SSL authentication with this connections, maybe
thisis the case? 

Kind regards,
Joanna

On Mon, Jan 14, 2013 at 8:28 AM, Alban Hertroys <haramrae@gmail.com> wrote:
> An access violation means that you're trying to access memory that doesn't
> belong to your process. I'm not sure where it's originating, that could be
> the server but I suspect the issue is at the client-side.
>
> You're probably just forgetting to free memory somewhere.

Or freeing the connection and then another thread attempts to use it.
This might even "work" a couple of times without crashing.

merlin

It is not possible because connection is local variable in both thread functions, no common variables are used.

I checked that it also crashes without SSL. Two threads connecting to the same server, different databases.

Joanna

On Mon, Jan 14, 2013 at 9:57 AM, Asia <asia123321@op.pl> wrote:
> It is not possible because connection is local variable in both thread functions, no common variables are used.
>
> I checked that it also crashes without SSL. Two threads connecting to the same server, different databases.

hm, where is your libpq coming from -- is it possible you are using
the non thread-safe variant?

are you 100% sure there is no thread interplay on the connection itself?

is it possible to get a backtrace for the access violation?

merlin

I am sure that I am using seperate threads with seperate connection objects and libpq is compiled to be threadsafe.
I get access violation both with ssl and without it (without ssl it seems to be more stable, however afer several
hundredconnects/disconnects it fails). 

J.