Re: help needed: hsqldb shutdown race condition, how to fix without deadlock

On Tue, Jun 09, 2015 at 03:05:57PM +0200, Michael Stahl wrote:
> On 09.06.2015 14:33, Lionel Elie Mamane wrote:
> > On Wed, Jun 03, 2015 at 11:08:36PM +0200, Michael Stahl wrote:
> > > On 03.06.2015 17:31, Lionel Elie Mamane wrote:
> > > > On Wed, Jun 03, 2015 at 03:01:39PM +0200, Michael Stahl wrote:
> > > > > On 03.06.2015 14:47, Lionel Elie Mamane wrote:
> >
> > > > > > Since the problem is essentially that the two threads take the same mutexes
> > > > > > in different order, here is a dirty hack that forces the hsqldb thread
> > > > > > to take the "affine bridge" mutex before taking the "HSQL driver"
> > > > > > mutex.
> >
> > > > > i'm not entirely sure this is sensible...
> >
> > > > Thinking the issue from yet another angle, if we go back to the
> > > > situation at the start of this thread (hsqldb is *not* affine). I
> > > > don't understand why the
> > > > connectivity::hsqldb::ODriverDelegator::disposing thread holds the
> > > > affine lock, and goes through the affine bridge:
> >
> > > > Why does the call from dbaccess::OConnection::disposing into
> > > > connectivity::hsqldb::ODriverDelegator::disposing go through the
> > > > affine bridge?
> >
> > > because OConnection is outside the affine environment, so it has to go
> > > through the bridge to call a component inside the affine environment.
> >
> > > however the ODriverDelegator isn't inside the affine environment, what
> > > happens is that while AffineBridge::v_callInto_v() waits for the call on
> > > the "inner" thread to return, it assigns the current (calling) thread as
> > > the "outer" thread and in AffineBridge::outerDispatch() it waits for
> > > outgoing calls from the "inner" thread.
> >
> > You discuss what happens when the call goes into the affine bridge. I
> > don't understand why it goes through the affine brige in the first
> > place.
>
> presumably because OConnection::disposing() is calling XConnection
> methods that are implemented by class java_sql_Connection in the JDBC
> driver.

Oh, you mean:

In thread 3, OConnection::disposing() is calling something that is
implemented by class java_sql_Connection in the JDBC driver. I'll
assume for that it is the "close" method.

java_sql_Connection::close is executed in another thread (e.g. thread
4) because JDBC declared thread affine, and in thread 4 calls
connectivity::hsqldb::ODriverDelegator::disposing. *That* call in
thread 4 is messaged to thread 3 to be executed in thread 3.

That's why the backtrace in thread 3 shows a call from
OConnection::disposing() to
connectivity::hsqldb::ODriverDelegator::disposing, but that actually
goes through java_sql_Connection::close (and
java_sql_Connection::dispose and java_sql_Connection::disposing) in
thread 4.

Did I understand correctly now?

-- 
Loinel