Re: [PATCH v2] strbuf doc: reuse after strbuf_release is fine
From: Junio C Hamano <hidden>
Date: 2017-10-04 05:00:27
Jonathan Nieder [off-list ref] writes:
strbuf_release leaves the strbuf in a valid, initialized state, so there is no need to call strbuf_init after it. Moreover, this is not likely to change in the future: strbuf_release leaving the strbuf in a valid state has been easy to maintain and has been very helpful for Git's robustness and simplicity (e.g., preventing use-after-free vulnerabilities). Document the semantics so the next generation of Git developers can become familiar with them without reading the implementation. It is still not advisable to call strbuf_release too often because it is wasteful, so add a note pointing to strbuf_reset for that. The same semantics apply to strbuf_detach. Add a similar note to its docstring to make that clear. Improved-by: Jeff King [off-list ref] Signed-off-by: Jonathan Nieder <redacted> --- Jeff King wrote:quoted
I think it's actually OK to use the string buffer after this function. It's just an empty string. Perhaps we should be more explicit: this releases any resources and resets to a pristine, empty state. I suspect strbuf_detach() probably should make the same claim.Like this?
Looks good to me.
quoted hunk
Thanks, Jonathan strbuf.h | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-)diff --git a/strbuf.h b/strbuf.h index 7496cb8ec5..249df86711 100644 --- a/strbuf.h +++ b/strbuf.h@@ -82,8 +82,12 @@ extern char strbuf_slopbuf[]; extern void strbuf_init(struct strbuf *, size_t); /** - * Release a string buffer and the memory it used. You should not use the - * string buffer after using this function, unless you initialize it again. + * Release a string buffer and the memory it used. After this call, the + * strbuf points to an empty string that does not need to be free()ed, as + * if it had been set to `STRBUF_INIT` and never modified. + * + * To clear a strbuf in preparation for further use without the overhead + * of free()ing and malloc()ing again, use strbuf_reset() instead. */ extern void strbuf_release(struct strbuf *);@@ -91,6 +95,9 @@ extern void strbuf_release(struct strbuf *); * Detach the string from the strbuf and returns it; you now own the * storage the string occupies and it is your responsibility from then on * to release it with `free(3)` when you are done with it. + * + * The strbuf that previously held the string is reset to `STRBUF_INIT` so + * it can be reused after calling this function. */ extern char *strbuf_detach(struct strbuf *, size_t *);