How it was was probably correct - intrusive_ptr can be confusing - what you may need to look at is constructor initialisation or use in-place initialisation elsewhere otherwise, the explicit in-place you're doing will leave memory leak.


On 15 Aug, 2013, at 7:23 am, Andrew McDonnell wrote:

> Summary of status:
> 
> I think we can close this and open a new one against the debug build.
> Maybe.
> 
> The raw segfault was caused by something using a thing called an
> 'intrusive_ptr' which is used to add reference counting.  However its
> copy cnstructor has odd sematics such that the assignment operator
> actually does a swap operation with the assignee(!), which means if the
> memory you are assigning to is uninitialised, you end up with junk in
> where you were copying from, which causes a crash when the assignee is
> destructed.
> 
> #3  <signal handler called>
> #4  0x000000000098f292 in oqgraph3::intrusive_ptr_release (ptr=0xa5a5a5a5a5a5a5a5) at /home/andrew/develop/maria/repo/oqgraph-varchar/storage/oqgraph/oqgraph_thunk.h:132
> #5  0x0000000000991e19 in boost::intrusive_ptr<oqgraph3::cursor>::~intrusive_ptr (this=0x7fe72e1f5ed0, __in_chrg=<optimized out>) at /usr/include/boost/smart_ptr/intrusive_ptr.hpp:101
> #6  0x0000000000991f1a in boost::intrusive_ptr<oqgraph3::cursor>::operator= (this=0x22bef68, rhs=...) at /usr/include/boost/smart_ptr/intrusive_ptr.hpp:133
> #7  0x000000000098f1a5 in oqgraph3::cursor_ptr::operator= (this=0x22bef68) at /home/andrew/develop/maria/repo/oqgraph-varchar/storage/oqgraph/oqgraph_thunk.h:58
> 
> The memory coming from the SQL core (the 'ref') via index_read is
> uninitalised when we first see it, but we seem to use it as a persistent
> storage area (I dont fully understand how all thatworks as yet, and
> ha_example.cc "explains" it but doesnt really...)
> 
> Thus, in-place should theoretically sort that one out:
> 
>     if (cursor)
>       cursor->current(ref);
>     else
> -      ref= reference();
> +      new (ref_ptr) reference(); 
> 
> This actually passes the regression test now in a normal build!
> In a debug build however, it is failing... tracing through with the debugger I worked out we can reset the contents of the ref via ha_oqgraph::index_read which seems to be called once at the start of the query:
> 
> {
>   DBUG_ASSERT(inited==INDEX);
> +  graph->row_ref((void*) ref);	// reset before we have a cursor, so the memory is inited, avoiding the sefgault in position() when select with order by (bug #1133093)
>   return index_read_idx(buf, active_index, key, key_len, find_flag);
> }
> 
> THIS now fixes the segfault, but causes an assertion indicating we
> havent properly closed something in my_isam; specifically, the
> edges->file table, we have missed a closing ha_index_end().  This is
> where I finally got stuck...
> 
> The 'normal' build still passes...
> 
> -- 
> You received this bug notification because you are a member of Open
> Query core, which is subscribed to OQGRAPH.
> https://bugs.launchpad.net/bugs/1133093
> 
> Title:
>  Crash on ORDER BY in OQGRAPH v3
> 
> Status in OQGraph Engine for MariaDB:
>  Triaged
> 
> Bug description:
>  SELECT * FROM graph WHERE latch=1 AND origid=1 AND destid=6;
>  works
> 
>  SELECT * FROM graph WHERE latch=1 AND origid=1 AND destid=6 ORDER BY seq;
>  segfaults.
> 
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/oqgraph/+bug/1133093/+subscriptions