[PATCH 05/12] alter: allocate triggers before the point of no return

[Vladimir Davydov]

On Mon, Apr 09, 2018 at 11:36:02PM +0300, Konstantin Osipov wrote:
> * Vladimir Davydov <vdavydov.dev at gmail.com> [18/04/09 10:33]:
> > Trigger allocation, as any other memory allocation, is allowed to fail.
> > If this happens in alter_space_do, the space will be left in an
> > inconsistent state. Let's move trigger allocation to the beginning of
> > alter_space_do and add a comment denoting the point of no return.
> 
> Previously we would reference the allocated trigger immediately 
> in txn_on_commit() /txn_on_rollback(), the changed code leaks
> memory in case of any exception between allocation and "point of no
> return".
> 
> Please add guards.

We don't need guards for the triggers, because they are allocated on
region - see txn_alter_trigger_new().

> 
> > ---
> >  src/box/alter.cc | 14 ++++++++++----
> >  1 file changed, 10 insertions(+), 4 deletions(-)
> > 
> > diff --git a/src/box/alter.cc b/src/box/alter.cc
> > index 36310f1c..9d0c4c23 100644
> > --- a/src/box/alter.cc
> > +++ b/src/box/alter.cc
> > @@ -803,6 +803,11 @@ alter_space_rollback(struct trigger *trigger, void * /* event */)
> >  static void
> >  alter_space_do(struct txn *txn, struct alter_space *alter)
> >  {
> > +	/* Prepare triggers while we may fail. */
> > +	struct trigger *on_commit, *on_rollback;
> > +	on_commit = txn_alter_trigger_new(alter_space_commit, alter);
> > +	on_rollback = txn_alter_trigger_new(alter_space_rollback, alter);
> > +
> >  	/* Create a definition of the new space. */
> >  	space_dump_def(alter->old_space, &alter->key_list);
> >  	class AlterSpaceOp *op;
> > @@ -853,6 +858,11 @@ alter_space_do(struct txn *txn, struct alter_space *alter)
> >  		throw;
> >  	}
> >  
> > +	/*
> > +	 * This function must not throw exceptions or yield after
> > +	 * this point.
> > +	 */
> > +
> >  	/* Rebuild index maps once for all indexes. */
> >  	space_fill_index_map(alter->old_space);
> >  	space_fill_index_map(alter->new_space);
> > @@ -873,11 +883,7 @@ alter_space_do(struct txn *txn, struct alter_space *alter)
> >  	 * finish or rollback the DDL depending on the results of
> >  	 * writing to WAL.
> >  	 */
> > -	struct trigger *on_commit =
> > -		txn_alter_trigger_new(alter_space_commit, alter);
> >  	txn_on_commit(txn, on_commit);
> > -	struct trigger *on_rollback =
> > -		txn_alter_trigger_new(alter_space_rollback, alter);
> >  	txn_on_rollback(txn, on_rollback);
> >  }