bftw: Don't force buffering for parallel dfs

diff --git a/src/bftw.c b/src/bftw.c
index 6eec42c1f213488ae4ea57d7bfcf1e11a5380e59..c0bff75bb979b4096cc03c94a9bb75ef9e6aacf9 100644 (file)
--- a/src/bftw.c
+++ b/src/bftw.c
@@ -456,6 +456,33 @@ struct bftw_state {
        struct BFTW ftwbuf;
 };
 
+/** Check if we have to buffer files before visiting them. */
+static bool bftw_must_buffer(const struct bftw_state *state) {
+       if (state->flags & BFTW_SORT) {
+               // Have to buffer the files to sort them
+               return true;
+       }
+
+       if (state->strategy == BFTW_DFS && state->nthreads == 0) {
+               // Without buffering, we would get a not-quite-depth-first
+               // ordering:
+               //
+               //     a
+               //     b
+               //     a/c
+               //     a/c/d
+               //     b/e
+               //     b/e/f
+               //
+               // This is okay for iterative deepening, since the caller only
+               // sees files at the target depth.  We also deem it okay for
+               // parallel searches, since the order is unpredictable anyway.
+               return true;
+       }
+
+       return false;
+}
+
 /** Initialize the bftw() state. */
 static int bftw_state_init(struct bftw_state *state, const struct bftw_args *args) {
        state->paths = args->paths;
@@ -465,11 +492,6 @@ static int bftw_state_init(struct bftw_state *state, const struct bftw_args *arg
        state->flags = args->flags;
        state->strategy = args->strategy;
        state->mtab = args->mtab;
-
-       if ((state->flags & BFTW_SORT) || state->strategy == BFTW_DFS) {
-               state->flags |= BFTW_BUFFER;
-       }
-
        state->error = 0;
 
        if (args->nopenfd < 2) {
@@ -501,6 +523,9 @@ static int bftw_state_init(struct bftw_state *state, const struct bftw_args *arg
        }
        state->nthreads = nthreads;
 
+       if (bftw_must_buffer(state)) {
+               state->flags |= BFTW_BUFFER;
+       }
 
        SLIST_INIT(&state->dir_batch);
        SLIST_INIT(&state->to_open);