On 29.07.2014 16:43, Patrick Reynolds wrote:
> Remotes are stored as an array, so looking one up or adding one without
> duplication is an O(n) operation. Reading an entire config file full of
> remotes is O(n^2) in the number of remotes. For a repository with tens of
> thousands of remotes, the running time can hit multiple minutes.
>
> Hash tables are way faster. So we add a hashmap from remote name to
> struct remote and use it for all lookups. The time to add a new remote to
> a repo that already has 50,000 remotes drops from ~2 minutes to < 1
> second.
>
> We retain the old array of remotes so iterators proceed in config-file
> order.
>
> Signed-off-by: Patrick Reynolds <patrick.reyno...@github.com>
> ---
> mark function with no arguments as taking void
>
> remote.c | 63 ++++++++++++++++++++++++++++++++++++++++++++++-----------------
> remote.h | 3 +++
> 2 files changed, 49 insertions(+), 17 deletions(-)
>
> diff --git a/remote.c b/remote.c
> index a0701f6..52533e4 100644
> --- a/remote.c
> +++ b/remote.c
> @@ -42,6 +42,7 @@ struct rewrites {
> static struct remote **remotes;
> static int remotes_alloc;
> static int remotes_nr;
> +static struct hashmap remotes_hash;
>
> static struct branch **branches;
> static int branches_alloc;
> @@ -136,26 +137,51 @@ static void add_url_alias(struct remote *remote, const
> char *url)
> add_pushurl_alias(remote, url);
> }
>
> +struct remotes_hash_key {
> + const char *str;
> + int len;
> +};
> +
> +static int remotes_hash_cmp(const struct remote *a, const struct remote *b,
> const struct remotes_hash_key *key)
> +{
> + if (key)
> + return strncmp(a->name, key->str, key->len) ||
> a->name[key->len];
> + else
> + return strcmp(a->name, b->name);
> +}
> +
> +static inline void init_remotes_hash(void)
> +{
> + if (!remotes_hash.cmpfn)
> + hashmap_init(&remotes_hash, (hashmap_cmp_fn)remotes_hash_cmp,
> 0);
> +}
> +
> static struct remote *make_remote(const char *name, int len)
> {
> - struct remote *ret;
> - int i;
> + struct remote *ret, *replaced;
> + struct remotes_hash_key lookup;
> + struct hashmap_entry lookup_entry;
>
> - for (i = 0; i < remotes_nr; i++) {
> - if (len ? (!strncmp(name, remotes[i]->name, len) &&
> - !remotes[i]->name[len]) :
> - !strcmp(name, remotes[i]->name))
> - return remotes[i];
> - }
> + if (!len)
> + len = strlen(name);
> +
> + init_remotes_hash();
> + lookup.str = name;
> + lookup.len = len;
> + hashmap_entry_init(&lookup_entry, memhash(name, len));
> +
> + if ((ret = hashmap_get(&remotes_hash, &lookup_entry, &lookup)) != NULL)
> + return ret;
>
> ret = xcalloc(1, sizeof(struct remote));
> ret->prune = -1; /* unspecified */
> ALLOC_GROW(remotes, remotes_nr + 1, remotes_alloc);
> remotes[remotes_nr++] = ret;
> - if (len)
> - ret->name = xstrndup(name, len);
> - else
> - ret->name = xstrdup(name);
> + ret->name = xstrndup(name, len);
> +
> + hashmap_entry_init(ret, lookup_entry.hash);
> + replaced = hashmap_put(&remotes_hash, ret);
> + assert(replaced == NULL); /* no previous entry overwritten */
> return ret;
> }
>
> @@ -722,13 +748,16 @@ struct remote *pushremote_get(const char *name)
>
> int remote_is_configured(const char *name)
> {
> - int i;
> + struct remotes_hash_key lookup;
> + struct hashmap_entry lookup_entry;
> read_config();
>
> - for (i = 0; i < remotes_nr; i++)
> - if (!strcmp(name, remotes[i]->name))
> - return 1;
> - return 0;
> + init_remotes_hash();
> + lookup.str = name;
> + lookup.len = strlen(name);
> + hashmap_entry_init(&lookup_entry, memhash(name, lookup.len));
> +
> + return hashmap_get(&remotes_hash, &lookup_entry, &lookup) != NULL;
> }
>
> int for_each_remote(each_remote_fn fn, void *priv)
> diff --git a/remote.h b/remote.h
> index 917d383..81cb5ff 100644
> --- a/remote.h
> +++ b/remote.h
> @@ -1,6 +1,7 @@
> #ifndef REMOTE_H
> #define REMOTE_H
>
> +#include "hashmap.h"
> #include "parse-options.h"
>
> enum {
> @@ -10,6 +11,8 @@ enum {
> };
>
> struct remote {
> + struct hashmap_entry ent; /* must be first */
> +
I stumbled about this comment "/* must be first */"
when reading the changelog.
Why does it need to be first?
Is it a common reason I'm just not aware of,
or would it make sense to put the reason into the comment as well?
Thanks,
Stefan
> const char *name;
> int origin;
>
>
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