reftable/stack: simplify tracking of table locks

When compacting tables, we store the locks of all tables we are about to
compact in the `table_locks` array. As we currently only ever compact
all tables in the user-provided range or none, we simply track those
locks via the indices of the respective tables in the merged stack.

This is about to change though, as we will introduce a mode where auto
compaction gracefully handles the case of already-locked files. In this
case, it may happen that we only compact a subset of the user-supplied
range of tables. In this case, the indices will not necessarily match
the lock indices anymore.

Refactor the code such that we track the number of locks via a separate
variable. The resulting code is expected to perform the same, but will
make it easier to perform the described change.

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 e5959d2c765afe88fd88826bc1f03ff204806c24..07e7ffc6b97ef6f79f0e24a487e23481f9e03917 100644 (file)
--- a/reftable/stack.c
+++ b/reftable/stack.c
@@ -1016,7 +1016,7 @@ static int stack_compact_range(struct reftable_stack *st,
        struct lock_file *table_locks = NULL;
        struct tempfile *new_table = NULL;
        int is_empty_table = 0, err = 0;
-       size_t i;
+       size_t i, nlocks = 0;
 
        if (first > last || (!expiry && first == last)) {
                err = 0;
@@ -1051,7 +1051,7 @@ static int stack_compact_range(struct reftable_stack *st,
        for (i = first; i <= last; i++) {
                stack_filename(&table_name, st, reader_name(st->readers[i]));
 
-               err = hold_lock_file_for_update(&table_locks[i - first],
+               err = hold_lock_file_for_update(&table_locks[nlocks],
                                                table_name.buf, LOCK_NO_DEREF);
                if (err < 0) {
                        if (errno == EEXIST)
@@ -1066,7 +1066,7 @@ static int stack_compact_range(struct reftable_stack *st,
                 * run into file descriptor exhaustion when we compress a lot
                 * of tables.
                 */
-               err = close_lock_file_gently(&table_locks[i - first]);
+               err = close_lock_file_gently(&table_locks[nlocks++]);
                if (err < 0) {
                        err = REFTABLE_IO_ERROR;
                        goto done;
@@ -1183,8 +1183,8 @@ static int stack_compact_range(struct reftable_stack *st,
         * Delete the old tables. They may still be in use by concurrent
         * readers, so it is expected that unlinking tables may fail.
         */
-       for (i = first; i <= last; i++) {
-               struct lock_file *table_lock = &table_locks[i - first];
+       for (i = 0; i < nlocks; i++) {
+               struct lock_file *table_lock = &table_locks[i];
                char *table_path = get_locked_file_path(table_lock);
                unlink(table_path);
                free(table_path);
@@ -1192,8 +1192,8 @@ static int stack_compact_range(struct reftable_stack *st,
 
 done:
        rollback_lock_file(&tables_list_lock);
-       for (i = first; table_locks && i <= last; i++)
-               rollback_lock_file(&table_locks[i - first]);
+       for (i = 0; table_locks && i < nlocks; i++)
+               rollback_lock_file(&table_locks[i]);
        reftable_free(table_locks);
 
        delete_tempfile(&new_table);