reftable/stack: reuse buffers when reloading stack

In `reftable_stack_reload_once()` we iterate over all the tables added
to the stack in order to figure out whether any of the tables needs to
be reloaded. We use a set of buffers in this context to compute the
paths of these tables, but discard those buffers on every iteration.
This is quite wasteful given that we do not need to transfer ownership
of the allocated buffer outside of the loop.

Refactor the code to instead reuse the buffers to reduce the number of
allocations we need to do. Note that we do not have to manually reset
the buffer because `stack_filename()` does this for us already.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/reftable/stack.c b/reftable/stack.c
index f5d18a842a42f713b8b7b26ae03ea16d29dd471f..2dd23733606d734889c8455d0f2394300b5a0d44 100644 (file)
--- a/reftable/stack.c
+++ b/reftable/stack.c
@@ -204,6 +204,7 @@ static int reftable_stack_reload_once(struct reftable_stack *st, char **names,
                reftable_calloc(sizeof(struct reftable_table) * names_len);
        int new_readers_len = 0;
        struct reftable_merged_table *new_merged = NULL;
+       struct strbuf table_path = STRBUF_INIT;
        int i;
 
        while (*names) {
@@ -223,13 +224,10 @@ static int reftable_stack_reload_once(struct reftable_stack *st, char **names,
 
                if (!rd) {
                        struct reftable_block_source src = { NULL };
-                       struct strbuf table_path = STRBUF_INIT;
                        stack_filename(&table_path, st, name);
 
                        err = reftable_block_source_from_file(&src,
                                                              table_path.buf);
-                       strbuf_release(&table_path);
-
                        if (err < 0)
                                goto done;
 
@@ -267,16 +265,13 @@ static int reftable_stack_reload_once(struct reftable_stack *st, char **names,
        for (i = 0; i < cur_len; i++) {
                if (cur[i]) {
                        const char *name = reader_name(cur[i]);
-                       struct strbuf filename = STRBUF_INIT;
-                       stack_filename(&filename, st, name);
+                       stack_filename(&table_path, st, name);
 
                        reader_close(cur[i]);
                        reftable_reader_free(cur[i]);
 
                        /* On Windows, can only unlink after closing. */
-                       unlink(filename.buf);
-
-                       strbuf_release(&filename);
+                       unlink(table_path.buf);
                }
        }
 
@@ -288,6 +283,7 @@ done:
        reftable_free(new_readers);
        reftable_free(new_tables);
        reftable_free(cur);
+       strbuf_release(&table_path);
        return err;
 }