Re: execute_control_command may not remove its cleanups

[Andrew Cagney <cagney@gnu.org>]

Dave,

> Ok.  I see your point.  How about setting old_chain to cleanup_chain
> unconditionally at the beginning of the function and doing the cleanups
> unconditionally at the end?  That way, we're safe against both
> scenarios: against doing cleanups prematurely, but also safe against
> getting into the function with cleanup_chain null and then freeing
> something random at a later point.  

FYI, that is one of the ways recommended in the doco:

> The first style is try/finally.  Before it exits, your code-block calls
> @code{do_cleanups} with the old cleanup chain and thus ensures that your
> code-block's cleanups are always performed.  For instance, the following
> code-segment avoids a memory leak problem (even when @code{error} is
> called and a forced stack unwind occurs) by ensuring that the
> @code{xfree} will always be called:
> 
> @smallexample
> struct cleanup *old = make_cleanup (null_cleanup, 0);
> data = xmalloc (sizeof blah);
> make_cleanup (xfree, data);
> ... blah blah ...
> do_cleanups (old);
> @end smallexample

The main reason why the the code you're studying doesn't match the doco 
is because it pre-dates that said doco :-(

Andrew