Hi,
On Sat, 7 Jun 2008, Geoffrey Irving wrote:
> Added cached-sha-map.[hc] implementing a persistent hash map from sha1 to sha1.
> The map is read with mmap, and completely rewritten if any entries change. It
> would be good to add incremental update to handle the usual case where only a
> few entries change.
Please keep your commit messages shorter than 77 columns/row, so that
output of "git log" is cutting lines.
> This structure is used by patch-ids.c to cache the mapping from commit
> to patch-id into $GIT_DIR/patch-id-cache. In the one case I've tested
> so far, this speeds up the second invocation of git-cherry by two orders
> of magnitude.
>
> Original code cannibalized from Johannes Schindelin's notes-index structure.
S-O-B?
> diff --git a/cached-sha1-map.c b/cached-sha1-map.c
> new file mode 100644
> index 0000000..e363745
> --- /dev/null
> +++ b/cached-sha1-map.c
>
> [...]
>
> +int get_cached_sha1_entry(struct cached_sha1_map *cache,
> + const unsigned char *key, unsigned char *value)
> +{
> + size_t i, mask;
> +
> + if (!cache->initialized)
> + init_cached_sha1_map(cache);
> +
> + mask = cache->size - 1;
> +
> + for (i = get_hash_index(key) & mask; ; i = (i+1) & mask) {
I think get_hash_index() should already return the correct index, IOW it
should take a pointer to cached_sha1_map() and "& (cache->size - 1)".
> + if (!hashcmp(key, cache->entries[i].key)) {
> + hashcpy(value, cache->entries[i].value);
> + return 0;
> + } else if (is_null_sha1(cache->entries[i].key))
> + return -1;
> + }
> +}
> +
> +void set_cached_sha1_entry(struct cached_sha1_map *cache,
> + const unsigned char *key, const unsigned char *value)
> +{
> + size_t i, mask;
> + struct cached_sha1_entry *entry;
> +
> + if (!cache->initialized)
> + init_cached_sha1_map(cache);
> +
> + if (4*cache->count >= 3*cache->size)
> + grow_map(cache);
IIRC the optimal size for a hash set was double the number of non-NULL
entries.
> + mask = cache->size - 1;
> +
> + for (i = get_hash_index(key) & mask; ; i = (i+1) & mask) {
> + entry = cache->entries+i;
> +
> + if (is_null_sha1(entry->key)) {
> + hashcpy(entry->key, key);
> + hashcpy(entry->value, value);
> + cache->count++;
> + cache->dirty = 1;
> + return;
> + } else if(!hashcmp(key, entry->key)) {
> + if (hashcmp(value, entry->value)) {
> + hashcpy(entry->value, value);
> + cache->dirty = 1;
> + }
> + return;
> + }
> + }
> +}
Would it not be better to avoid duplicating code here, by having a helper
that returns the index if the entry exists, and the negative index of the
next free entry otherwise?
> diff --git a/patch-ids.c b/patch-ids.c
> index 3be5d31..36332f3 100644
> --- a/patch-ids.c
> +++ b/patch-ids.c
> @@ -2,17 +2,31 @@
> #include "diff.h"
> #include "commit.h"
> #include "patch-ids.h"
> +#include "cached-sha1-map.h"
> +
> +struct cached_sha1_map patch_id_cache;
>
> static int commit_patch_id(struct commit *commit, struct diff_options *options,
> unsigned char *sha1)
> {
> + /* pull patch-id out of the cache if possible */
> + patch_id_cache.filename = "patch-id-cache";
> + if (!get_cached_sha1_entry(&patch_id_cache, commit->object.sha1, sha1))
> + return 0;
> +
> if (commit->parents)
> diff_tree_sha1(commit->parents->item->object.sha1,
> commit->object.sha1, "", options);
> else
> diff_root_tree_sha1(commit->object.sha1, "", options);
> diffcore_std(options);
> - return diff_flush_patch_id(options, sha1);
> + int ret = diff_flush_patch_id(options, sha1);
> + if (ret)
> + return ret;
> +
> + /* record commit, patch-id pair in cache */
> + set_cached_sha1_entry(&patch_id_cache, commit->object.sha1, sha1);
> + return 0;
> }
>
> static uint32_t take2(const unsigned char *id)
> @@ -136,6 +150,8 @@ int free_patch_ids(struct patch_ids *ids)
> next = patches->next;
> free(patches);
> }
> +
> + write_cached_sha1_map(&patch_id_cache);
> return 0;
Ah, so here you ignore the error when writing. Thank you. Maybe a
comment that we fail gracefully if the repository is write-protected?
Ciao,
Dscho
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