Jonathon Mah <jmah@xxxxxx> writes:
> Just to note, the proposals so far don't prevent a "smart-ass"
> function from freeing the buffer when it's called underneath the
> use/release scope, as in:
>
> with_commit_buffer(commit); {
> fn1_needing_buffer(commit);
> walk_rev_tree_or_something();
> fn2_needing_buffer(commit);
> } done_with_commit_buffer(commit);
I think the goal of everybody discussing these ideas is to make sure
that all code follows the simple ownership policy proposed at the
beginning of this subthread: commit->buffer belongs to the revision
traversal machinery, and other users could borrow it when available.
Even though your sample code will break, from that point of view, I
do not think it is something worth worrying about. If the function
"walk_rev_tree_or_something()" discards commit->buffer, it by
definition must be a part of the revision traversal machinery, and
any code that calls it inside with_commit_buffer() or uses the field
after such a call without revalidating commit->buffer, is already in
violation. With or without such a macro, we would need to be
careful about enforcing the ownership rule, and I think a code
structure like the above example is easier to spot problems in
during the review than the current code.
Because retaining commit->buffer is done for the benefit of the
next/future users of the data, and not for the users that _are_
using them right now, I do not think the usual refcounting that
discards when nobody references the data is a good match to the
problem we are discussing.
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